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Sensors

Mon, 11 Feb 2008 08:47:06 -0800

hI,
How can i make a sensor for checking moisture in soil and air humidity? ckts on the net not working! I am working on a control system which needs these parameters where can i get help on this?

Re: Sensors

Mon, 11 Feb 2008 10:52:41 -0800

kts on the net not working! I am working

you might be missing something... people in our field seldom upload their work unless tested.. give us the reference to your work...

Re: Sensors

Tue, 12 Feb 2008 08:37:28 -0800

Hi Shyam,
Finally my soil moisture sensor is working. I have not tested it fully. Will upload the ckt and resposnse voltage ranges for it. I need to make a humidity, temp and light sensor now and pH if possible. Temp is easy using LM35. Humidity is a problem. unable to get ICs here for it. Need todevise another way. Light can be done using LDR but i want a varying voltage or resistance response just as LM35 gives. Any suggestions? Pls help me out...

Re: Sensors

Tue, 12 Feb 2008 22:18:46 -0800

LDR is good for light sensing. or a photo transistor for a better voltage o/p

Re: Sensors

Tue, 12 Feb 2008 10:23:14 -0800

look here for humidity sesnsor: http://www.sumeetinstruments.com/sensors.htm

Re: Sensors

Wed, 13 Feb 2008 07:20:02 -0800

Shashi thanks for the link. I tried mailing them as no details are given on the site but the mail couldnt be sent, probably the company has shut down! Om Technologies is the only shop having a himdity sensor kit @750 Rs and he says he has not tested it. No one has any of the ICs i searched online and felt that it could be used! Does anyone have any suggestions?
Ajay I tried LDR but its respons is On-Off kind but i need a varying response. Atleast 4 levels(On Off givem me 2). Am trying using a opamps may work. not completed it at the lab. Photo transstors am unable to bias them right. need to get some ckt for it. (I got QT120 photo transistor)

Re: Sensors

Wed, 13 Feb 2008 21:00:42 -0800

Maybe I can help you with the humidity sensor, Amit, it is HIH3605 from Honeywell. Linear O/P 0.8-3.9V at 5V supply. Details at Honeywell site. Product is available in market, else try RS components. Thanks.

Re: Sensors

Wed, 13 Feb 2008 20:44:25 -0800

LDR is actually a variable resistor who's value changes according to intensity of light falls on it. Resistance of LDR is inversely proportional to light intensity.

you can connect LDR's o/p to ADC and get 256 levels more than what you wanted..

Re: Sensors

Thu, 14 Feb 2008 06:58:51 -0800

Hi ajay i know about the LDR but the problem is that the voltage across it switces instantly in a dark/light condition. so it effectively gives only 2 values. Have u tried it with the ADC directly and got 256 levels? I have managed to get 3 descrete levels out of it by sing the quad opamp LM324 and then to a summer today! Not yet soldered and tested properly.

Chiru, Thanks for the info. I found about the HIH series of Honeywell and i got circuits based on 3605 and 3610 also but in Bangalore I am unable to get a dealer! no shop on SP road has it! RS components only sells finished goods and i dont want a device that gives me the humidty readings on a display because i need to give that as an input to my microcontroller.

Can u name any dealers or any ither ideas for making the sensor?

Re: Sensors

Thu, 14 Feb 2008 08:42:44 -0800

hmmm il try that out... need to get to the lab for that. as of now the quad opamp gives me 3 leves. the reason i dint use the LDR as u mentioned is because i checked the voltage variations with multimeter under different lighting conditions, and the ldr just switched directly. il try this way u mentioned also tomorro.

can u pls help me on the humidity sensor! that is wats not happening now. temperature il be doing with LM35.

Re: Sensors

Thu, 14 Feb 2008 08:00:10 -0800

do not use opamp... try connecting LDR between ADC and VCC directly... something like this..
,,,,
VCC |----/\/\/\----> ADC PIN
LDR

make it work like a variable resistor, usually with opamp it act like a switching device

Re: Sensors

Sat, 16 Feb 2008 08:23:52 -0800

Hi Ajay,
I tried doing the light sensor the way u mentioned but i am not getting a varying voltage response! why is that? the voltage just switches from a low value to high and vice versa!! i used LM324 and summer to finnaly get 3 levels! a huge complicated setup!!!

Was having a quiery regarding LM35. Can i directly give its voltage o/p to the adc? i use resistance from 80k to 470k but my voltage readings dint cross 1V. Wont be too low as an i/p to adc? Pardon me forbeing so lame (I am yet to read the data sheets ) I am going bnkers now. been 2 weeks and just done 3 sensors, yet to test them properly and unable to get the IC for humidity sensor!

Re: Sensors

Sat, 16 Feb 2008 11:19:10 -0800

The LDR's resistance can reach 1M in dark conditions and 100 ohms or so in full brightness.So it naturally follows that you'll get an instantaneous swing between (almost) 0v and (near) Vcc under the dark\bright condition.
You may add a resistor in parallel to the LDR and another in series to limit the swing.
With the values shown and Vcc=12V you'll get ~4.85V if LDR=1K
~6.1V if LDR=2k
~7.7V if LDR=10K
~8.2V if LDR=1M
You may fine tune the resistor values to suit your needs.
Regarding LM35 you need to give it's output directly to the ADC;no resistors.It will output 1.5V at 150C.
As for the Honeywell humidity sensor,a friend had bought it from Emaar Impex for ~450 bucks.You may drop them a mail.....http://www.emaarindia.com/contact.html
(their website sucks)

Re: Sensors

Sat, 16 Feb 2008 20:38:58 -0800

thanks sashijoseph for this info i did not know this thing about LDR.

Re: Sensors

Sun, 17 Feb 2008 18:51:00 -0800

Hi shasi,
Thanks for the update! Il surely check it out today and let u know about the results Thanks for the link too. Il try getting the IC. Need it desperately.

Today have to start testing the bands and regions of operation after interfacing with the adc.

Il need all your help and Ajay and Shyam, yours too to code!!

Thanks again
Cya

Re: Sensors

Sun, 17 Feb 2008 21:19:55 -0800

To add some finer points for Amit with LDR and LM35

Most of the ADC chips works with 5V, so its better to power the LDR from 5V too. As for the circuit suggested by Sashi it is perfect, only change the 1K with 10K and remove the 2K2.

There should be small resistance like 1K at the OP of LM35 so as to prevent any short circuit conditions for the IC. You may also consider shunting the input of ADC with 0.1uf to bypass noise.

Re: Sensors

Sun, 17 Feb 2008 20:51:08 -0800

Yes Amit, contact Mr. Paresh 09967022244 02223869472 of Precious Electronics Corporation, he placed at Mumbai, tall him you got this information from me - Chiranjib from Kolkata, he will help you out with humidity sensors. If he cannot give sensors of honeywell ask for tech details of the same.

Re: Sensors

Mon, 18 Feb 2008 04:51:52 -0800

Shashi the ckt wrked like a charm! thanks a million. My board size has become 1/4th of wat i made!!!I am using it with 5V supply only.

Chiru, thanks for the details. I am trying through a person in Bangalore now, if its unavailable il surely use ur contact. And il surely make use of your tips in my project. I have already solderd the LM35 so cant make any changes to it. But most probably i will not be using the ckt because the HIH3605 humidity sensor needs a temperature sensor for temperature compensation in its calculation and a specific IC has been mentioned (DS2438) so i wil be probably using that only for my temperature readings.

Any more suggestions please do post it here. I shall try incorporating it.

Another problem i am facing now is that my faculty says that the project is too basic and that it is doing nothing great nor is it innovative!!! so i have to think of something more to add onto it!!! Pls help!!!!

Re: Sensors

Mon, 18 Feb 2008 08:01:18 -0800

Hey,
It seems the 3605 and 3610 are outdated and now only the 4000 series are available @ Rs. 750+VAT!!! Also i am unable to find a circuit for it online. I think its not wise to but the IC without having a ckt that is sure to work.
Wat do i do??? Any ideas? Pls help!!!! I really need to find a solution to this problem!And i am yet to start coding for the damn project

Re: Sensors

Mon, 18 Feb 2008 21:06:16 -0800

Dear Amit, the HIH4000 is smiler to 3605, find the same in the pdf, download it with search for HIH4000 pdf .
As for temp compensation, i don't think its required given the recommended operating temperature zone, the shift in o/p voltage with temp and the application .
You may add in your code some indications for comfort limit like hot, dry, wet, comfortable, etc., depending on the data collected, to make the project interesting .

Re: Sensors

Tue, 19 Feb 2008 06:26:22 -0800

Hi Chiru,
Thanks for the info.I did go thro the datasheets earlier but...they dint make much sense to me
I am able to get the HIH4000 locally @ Rs 750 shall i buy it? I am attaching a pdf document in which i found a ckt for the HIH3605. (humsensor 3605IC.pdf)Pls do go through it and let me know of i can do it. I shal only then proceed with buying the ic.
Also i found an interesting ckt done by someone using an open cap in an Astable multivibrator to sense humidity. Il upload that too. (Humidity_opencap.pdf) Pls do have a look
Il surely incorporate ur ideas in the code. Any more h/w or sensors u suggest could be added to the system? I am also planning to make it an sms based system, but that is Stage 2. I need to get this done 1st and foremost. Stage 3 is to make a multiprocessor system where i can use a master controller to control other controllers which will be interfaced with the sensors and actuators.
Do u think it is viable?
humsensor_3605ic.pdf
humidity_opencap.pdf

Re: Sensors

Thu, 21 Feb 2008 07:15:13 -0800

Hi Chiru,
No issues with the late reply. My work's on hold anyway! I think i have developed RSI. Bad pain at the left back of my head, neck and shoulder.And was busy with seminar stuff.
But u have given me reasin to cheer I needed assurance on the ckt for the HIH4000 b4 buying it and now i can buy it in peace and try it out.
The ASD & ASC ics u mentioned also from honeywell?
And how do i use them for the overhead tank level gauge? that will be a good feature for the system. Pls do post the ckt for it if u have. els il google it
Wel my system aint critical at all... just need to show that something practical and usefull can be made

Re: Sensors

Tue, 19 Feb 2008 09:38:19 -0800

Hi...
with 3605 measuring humidity is a cinch.You don't need that exotic dallas chip.You can easily use LM35 for temperature compensation.
Just measure the 3605's output voltage with an ADC and the temperature with the LM and apply the fol. formulae for calculating RH

Sensor RH = (VOUT / VSUPPLY) – 0.16 /0.0062, typical at 25°C
To correct the calculation for temperature and compute true RH, use:
True RH = sensor RH / (1.0546 –0.00216 T)
where T is in °C

The open cap one could be used to detect changes in humidity,but to measure humidity you would need some kind of a relation between frequency(or capacitance) and humidity,which isn't provided.....so it's pretty useless.

Re: Sensors

Wed, 20 Feb 2008 06:28:12 -0800

Hey shashijoseph
Thanks for the post. Well the formulae for using with the 3605 is given in the document i had uploaded. But i am not getting the 3605 locally. The HIH4000 is available and much cheaper than the 3605 (from bombay) so i needed to know if i can use that instead of the 3605 in the same ckt.
That open cap thing seemed to be really useless to me too.
Pls let me know if i can use the 4000 in the same ckt?
Can i just read the voltage at pin2 of the HIH and keep my LM35 away from the ckt? and then do the necessary calculation in my code right?

Re: Sensors

Wed, 20 Feb 2008 20:41:59 -0800

Hi, sorry for being late to reply .
Sashi has already clarified something. But i think you can go straight and use HIH4000. No LM35. Just feed the pin 2 signal to ADC. The O/P voltage is proportional to RH (at reg 5V supply) and there is a little deviation with temp which may be overlooked for your kind of application .You may consult the data sheet for the same .
Want to add a barometer to your system , add one ASDX015D or ASCX15DN pressure sensor to your system (voltage o/p at 5V). You can also make overhead tank water level gauge etc. with this .
This sensors are from honeywell, and i am using one 1psi sensor for a critical medical equipment for a long time, and am more than happy (O/P directly connected to ADC).

Re: Sensors

Thu, 21 Feb 2008 21:05:54 -0800

Hi Amit get wel soon .
ASCX and ASDX series pressure sensors are from honeywell (formally Sensym). ASCX is temp compemsated but costly. Both ASCX and ASDX are amplified voltage o/p 5V sensors, unlike normal 4-20 mA or mV o/p types. You can also use a cheap 4-20 mA type (14PC series) with a series resistance connected at the ground end and read the voltage against that res. There are also some cheap sensors in the market with reasonable stability, but ask for pin out details.
I shall try and give you the idea for cct of a tank lavel gauge. Its basically a rigid tube with one open end and the other end connected to the sensor, the open end facing down is dipped into the water. Initial or null pressure is measured with no water in the tank and set with the o/p voltage as zero lavel. Similarly fill the tank and take reading/s for other level/s (water goes inside the tube and the positive pressure gives a corresponding higher voltage o/p)
So go ahead...

Re: Sensors

Fri, 22 Feb 2008 06:21:44 -0800

Hi Chiru,
Thanks a ton for the good wishes and ur prompt replies really boosts my morale!!! il surely try and add the sensor for the water level indicator. I had read of another kind of ckt for this sometime earlier it was based on some varying resistance. dont remember it though now
Started working on getting digital o/ps from the adc for my sensors and i hit a roadblock! I get crap o/ps!!! tried with all the ICs (0808) in my lab still no success! anything i should keep in mind while using an ADC? I have connected al the unused pins viz. In1 to In7, EOC, SOC, etc to +5v I tried connecting the pot to In7 and In3 (as mentioned in the datasheet) to use only 8 or 4 bit o/p but the result was the same. Am i missing out on something???
Also i think its high time i started coding... wat do u think should be my approach? I also intend to have a RTC in teh system and also include a manual over-ride incase of system failure!

Re: Sensors

Fri, 22 Feb 2008 20:37:12 -0800

Hi Amit, I think you are familiar with ADC conversion. If not, first try with 0804, try the "free running connection" in the Harris Semiconductor datasheet .
Conversion time is very important. Use adequate delay. The clock should be within recommended frequency range. I think all analog inputs are within 0 to 5V DC, with v ref set to 5V. Follow the "timing diagram" properly. Check power supply for noise, minimal wire length ( if unavoidable) at analog input .
These should solve your problem (provided the code is OK, chip is not fake).

Re: Sensors

Sat, 23 Feb 2008 06:25:00 -0800

Hi chiru, il look into the datasheet of 0804 as u mentioned. I used the NS 0808 with i/ps in the range 0 to 5V either from my sensors or variable supply (both yielded no o/p). infact i encountered a peculiar problem of changing digital o/p everytime i turned ON the trainer kit but eventhough i changed nothing! I am not using it with the uC so i had clocked the ALE. I shorted the SOC and EOC pins. and the ckt i tried was almost similar to that given in the datasheet of NS 0808!
Il try wat u have suggested. gotta check if i have 0804 in the lab though
Roadblock after roadblock

Re: Sensors

Mon, 25 Feb 2008 00:49:03 -0800

Hi Amit,
The LSB of the digital o/p may drift a bit even with a stable analog i/p
A steady clock is required at the CLK i/p for the functioning of the ADC itself, why should you clock the ALE
I didnt find any SOC pin of 0808 in the National ds, is it START is it supposed to be shorted to EOC
You may follow the typical application at p12 of National ds, also check figure5 at p7
There is no ROADBLOCK if you are open in your mind

Re: Sensors

Mon, 25 Feb 2008 08:01:54 -0800

Hi chiru,
Thanks for the info.

Yes I did meant START (Pin6) by SOC. I had shorted it to EOC basically to use it free running mode (for continuous conversion just like how its done in 0804). I was trying to use the ckt mentioned in Fig. 9, Pg 9 of the NS datasheet. Il surely try out wat u have suggested tomorrow.

Oh and i forgot to mention...the ADCs in my lab were bad thats why i was not getting the o/p! I tried with the 0804 today and it worked so i have purchased 0809 (as 0808 was not available) and i shall try it out tomorrow. Could u pls tel me the diff b/w 0808 & 0809 i really couldnt figure it out from the ds!

I am facing another problem now i hope ul be able to give me a solution to it. In the ckt i uploaded for the HIH3605 in the 1st post of teh pg, they have used 2 diodes - BAT54S. It is not available here, i spent an hr today at the shops but couldn trace it! could u suggest an alternative. I shall look into its ds and try to find something.

And yes...as u truly mentioned ... "There is no ROADBLOCK if you are open in your mind ".

Thanks bye for now

Re: Sensors

Mon, 25 Feb 2008 11:12:13 -0800

Hi amit, you can take some info from tutorial section if you want.. and keep working for learning you are doing a good job.

Re: Sensors

Mon, 25 Feb 2008 19:03:20 -0800

Thanks Ajay il surely look into the tutorials. i hav exceeded my bandwidth for this month so wil do it on 1st march only. u guys are really helpful and motivating ... thanks a lot!!! hope il gain some knowledge n wil be help some more noobs lik me sometime in the near future bye for now

Re: Sensors

Tue, 26 Feb 2008 19:28:34 -0800

You don't need those Schottky diodes.They are used for supplying voltage from the 1-wire interface.You wouldn't be using that Dallas chip(in the attached pdf) would you?
Simply provide 5v regulated voltage to the HS and monitor it's output voltage.

Re: Sensors

Tue, 26 Feb 2008 08:24:43 -0800

Hi Ajay and Chiru,

Pls read the 1st post on this pg.

Tried with the 0808 today as u mentioned, but i used it in free running mode and not with uC. so i had to separately connect ALE (tried it both ways i.e. toggle and also permanently high) and as i had seen on another site online i had shorted START and EOC. Clock = 400kHz - 700kHz (mostly 650kHz).

I did get desired o/p ... but not always. infact below 1V i dint get a correct o/p. Above that it was not consistantly correct o/p. sometimes i would not get it. and generally i was getting double than wat i was supposed to get (i.e if my i/p was 1V the digital o/p was 2v).

Can u pls tel me wats wrong! this is getting really frustratimg. Cant move ahead!!! unless i am sure it works only then i can test it with my sensors and get the operating bands and only then can i start the biggest part of the proj - the coding!

Also am unable to get BAT54S for my humidty sensr and the ds shows it as a 3 terminal device (iv not studied it properly) but in the ckt dia its been shown as 2 terminal only...

Pls help asap!!! :'(

Re: Sensors

Tue, 26 Feb 2008 19:04:14 -0800

Hi Amit,
ADC0808 has max error of +/- 1/2% against 1% of 0809, it is a superior converter
BAT54S is dual Schottky SMD diode, you may use two BAT42 or BAT85, they are available
I am confused with what you mentioned in your last post, will work on it and let you know shortly.

Re: Sensors

Wed, 27 Feb 2008 08:17:58 -0800

Thanks Chiru and Shashi,

I dunno wats wrong, the ADC doesnt seem to be consistant at all! Behaves wierd!!! Today i tried it agin. Started with 1.5V (increased till 4.5V ) and got near perfect o/p but i tried for 0.5V and got garbage. after that i dint get a single correct o/p even for the same i/ps i tried before!!! did i spoil the IC? i dont think i did. I faced this same peculiar problem yesterday also but today i used the same IC and got correct o/p initially!

I will not be using the Dallas chip in the humidity sensor ckt. Should i use an LM35 or il just stop at the o/p of the HIH4000? eliminating the RC ckt also? So in that case i needednt use the BAT54S diode? or can i replace it with a zener?

Re: Sensors

Wed, 27 Feb 2008 18:13:36 -0800

Maybe a noise issue for the ADC.......have you used long wires at the i\p?Have you used a regulated power supply and proper bypass caps at the ADC Vcc pin?

As for the HS you may use LM35 for temp correction(if you want greater precision) and no need for the diodes.Just use a regulated ps.

Re: Sensors

Wed, 27 Feb 2008 21:24:57 -0800

Hi Amit, i don't know if the 0808 is bad , but in case you plan to buy a new one, shift to serial ADC (saves space) and buy MCP3208 . It is 8 ch serial 12 bit ADC from Microchip.
Enclosing a 8051 code for the same to scan the 8th channel whenever the ADC is CALLed (i use it with a 2051 ), the result is stored in R2 for MSB and R3 for LSB. It is a guideline for you and modify it for other channels .

CODE:

;TEST ROUTINE FOR MCP3208 WITH 8051
 
CS      .EQU    P1.4
CK      .EQU    P1.3
DIO     .EQU    P1.2

; -:IN  CS:---<---:P1.4   :
;  :   CLK:---<---:P1.3   :
;  :  DOUT:--->---:P1.2   :
; -:IN DIN:---<-I :       :
;  MCP3208          8051

ADC:
        MOV     A,#0FFH         ;DIN word for MCP3208
        SETB    CS              ;Make sure /CS is high
        CLR     CS              ;/CS goes low
        MOV     R4,#05          ;Load counter
LOOP1:  RLC     A               ;Rotate DIN bit into Carry
        CLR     CK              ;SCLK goes low
        MOV     DIO,C           ;Output DIN bit to LTC1298
        SETB    CK              ;SCLK goes high
        DJNZ    R4,LOOP1        ;Next bit
        MOV     P1,#04          ;Bit 2 becomes an input
        CLR     CK              ;SCLK goes low
        MOV     R4,#09          ;Load counter
LOOP2:  MOV     C,DIO           ;Read data bit into Carry
        RLC     A               ;Rotate data bit into Acc.
        SETB    CK              ;SCLK goes high
        CLR     CK              ;SCLK goes low
        DJNZ    R4,LOOP2        ;Next bit
        MOV     R2,A            ;Store MSBs in R2
        CLR     A               ;Clear Acc.
        MOV     R4,#04          ;Load counter
LOOP3:  MOV     C,DIO           ;Read data bit into Carry
        RLC     A               ;Rotate data bit into Acc.
        SETB    CK              ;SCLK goes high
        CLR     CK              ;SCLK goes low
        DJNZ    R4,LOOP3        ;next bit
        MOV     R4,#04          ;Load counter
LOOP4:  RRC     A               ;Rotate right into Acc.
        DJNZ    R4,LOOP4        ;Next Rotate
        MOV     R3,A            ;Store LSBs in R3
        SETB    CS              ;/CS goes high
        RET  
 

Re: Sensors

Thu, 28 Feb 2008 00:17:49 -0800

Hi Chiru....how much does it cost buddy?

Re: Sensors

Thu, 28 Feb 2008 00:30:28 -0800

What cost, Sashi

Re: Sensors

Fri, 29 Feb 2008 04:33:35 -0800

OMG!!! Well the cost of my proj is going up!!! Well, today i tried again with the 0809 and guess wat at IN7 i got precise digital o/p!!! exactly the same as expected. even for 0.2V. And then comes the bad news... it dint happen for any other i/p lines! we are not going wrong wit the address lines am sure of that. now i dunno wats wrong!

Is it possible that i have spoilt bot my ICs? Well i had 1st tried them using IN0 and IN3 only and the o/p data lines to the LEDs on my college IC trainer kit. Is it possible that they tried to draw more current and in an attempt to drive them my IC got spoilt? But i always checked the IC from time to time nad it never heated up!

Wat is wrong? Tomorro i have planned to put it onto a pcb rather than get stuck with the bread board or trainer kit. that way can avaoid unnecessary noise also.

Well i am not a photography lover. Few of my friends are and i was just a volunteer helping to organise the event. I do love scenic and macro photography but... have never tried though. Will surely add u on gmail

Pls tel me wat do i do about the ADC!!! Cya for now

Re: Sensors

Thu, 28 Feb 2008 06:22:36 -0800

Hi shashi n chiru,

Well i am using a IC trainer kit in my college lab and using the power supply n gnd from that only. i have not added any bypass capacitors. Yes the clock was not a clean square wave it had a bit of distortion at the +ve edge. could that be the problem? Il try using a capacitor for that tomorrow.

Yes how much would that ADC cost? I have just spent Rs 150 on 2 new 0809s. I dont think i can buy another expensive IC

Are you sure about not using any diodes? The IC is very expensive @ Rs 750 + VAT. I have not yet bought it.

No improvement in the project still. Had a photo exhibition so was busy with that past 2 days. will get back to work tomorro onwars ... but i dunno wat to do. just sitting and there is no +ve result!

Re: Sensors

Thu, 28 Feb 2008 22:02:22 -0800

Yes Amit, all serial ADC's are dear. A 2ch will be around 120/- and 8ch as high as 400/- in Kolkata .
Give me some time, i shall get back to you with a working ckt of 0808 .
Diodes are not required, stick to the simple ckt in the DS. Supply should be neat and not exceeding 5V DC .

You love photography? i do. For that we can talk elsewhere, maybe. My id is ckarmakarams@gmail.com

Re: Sensors

Fri, 29 Feb 2008 21:29:06 -0800

Well Amit, since one of the i/p is working, the ADC is not bad .
You say the address is ok, still once more check it as, for ch7 it should be #7 (all high), ch6 = #6 (high high low), etc. Remember for each analog ch to be scanned, there should a complete cycle to get a valid o/p .
If it still doesn't work, then the input logic or the mux is spoiled somehow .

And never mind about the photography thing.

Re: Sensors

Sat, 01 Mar 2008 06:27:51 -0800

Hmmm, i did give it enough time for the conversion and yes, i did follow the addresses correctly. will try it out again els i have got a new 0809, wil try with that.
N u must check out the link http://www.flickr.com/photos/shakirfm/
Its my friends. hes an amazing photographer. got interested in it cos of him. hes a macro guy too. Cya for now. do let me know wat do i do to troubleshoot the damn thing

Re: Sensors

Sun, 02 Mar 2008 20:31:00 -0800

Take it cool, start it afresh

Checked flickr, excellent, thanks and regards to your friend.

Re: Sensors

Mon, 03 Mar 2008 06:48:37 -0800

Tried afresh with the new adc but the same prob :'(

But found something interesting... the IN7 works even in the new IC. also the junk o/p is the same in all the 3 ADCs. is it possible that i am making a mistake? i have checked and rechecked the address lines and also tried al kinds of permutations and combinations but to no avail

Dunno wat to do now. planning to interface it to the 8051 and try directly wat happens. probably am making a mistake while using it in a stand alone mode.

Any idea on AVRs? i heard that the ATmega has built in adc. but how about programming it? i have no skills in embedded C and had planned to code the 8051 in assembly only since i have learnt it.

Wat do i do now?

Help Help!!!!

Re: Sensors

Mon, 03 Mar 2008 11:44:12 -0800

Take the plunge buddy.For now stick to the 8051 since you learnt 8051 programming.Try out a few projects with ADCs,I2C,SPI,LCD etc etc and then you can migrate to any other platform.The transition won't be too difficult.

Re: Sensors

Mon, 03 Mar 2008 21:34:02 -0800

Hi Amit, follow Sashi's suggestion In case you need to change, shift to PIC, start with 12F675 There are lots of circuits and projects available on the net, moreover Microchip gives good application support for its chips.

Re: Sensors

Tue, 04 Mar 2008 10:51:53 -0800

that opamp is for calibrating the LM35 to obtain precise results.If one ortwo degree error will do for your application,then you don't need it.

Re: Sensors

Tue, 04 Mar 2008 08:56:22 -0800

Thanks Shashi and Chiru,

Il keep that in mind. I did start reading on the PIC 16F74. But there are no good books on them infact few ppl i asked said that u can only learn bout pics from their datasheets! is that true? Pls do suggect books, if any for them.

Yeah and another good news! The adc finally worked! All i did was to clock the ALE also with the same signal given to CLOCK of ADC. and it works. perfect o/p at 6 channels and a slight 1 t0 2 bit error at 2 channels. will check it for lower values also tomorrow.

While using the LM35 with ADC should i use an opamp? I think you told me not to. I had already put it on the board but. So should i pull it out now? But in this link http://www.freewebs.com/maheshwankhede/sensors.html (pls check it out.) he mentions that an opamp is required? Wat do u suggest?

Re: Sensors

Tue, 04 Mar 2008 12:59:56 -0800

yes opmp is needed to fulfill the "signal conditioning"
you can also use a divider network for this.
but as sashi said , you can connect lm35 directly with adc

Re: Sensors

Wed, 05 Mar 2008 06:22:02 -0800

Thanks a lot. il keep that in mind. wil be caliberating my sensors tomorrow for use wit the adc. and the next step is the programming.

I wanted to know. do i need to provide the OE, START, ALE signals from the uC or can i do them as i did in the stand alone mode and only supply the addresses A, B , C by the uC and read the data thro it? after reading the data from the ADC i plan to cyclicly display them onto the display or to use buttons for each sensor so that when u press a button, that sensors reading is shown in the display. Also an actuating mechanism wil be controlled by the uC for each sensor such as artificial lights, motors, pumps etc.

Re: Sensors

Wed, 05 Mar 2008 20:43:46 -0800

Hi Amit, to start with PIC, download the book "PIC in Practice A Project based Approach 2nd Ed." Its available for download in this site itself (in fact there are others too)
Do not jump to 16F74, start with simpler ones like 12F675, 16F88 16F818 etc (they all have build in ADC) .

If you are using a uC, why to feed control signals manually of course you can have switches for data out.

Re: Sensors

Wed, 05 Mar 2008 20:51:37 -0800

Yup Chiru is right......with a uc there's no point doing it manually and moreover in free running mode how will you decide exactly when to read in the data?So do it the right way and believe me it's very simple too.

Re: Sensors

Thu, 06 Mar 2008 08:49:32 -0800

Hmmm oki. Il keep that in mind. the basic reason i thought of not giving al signals to the uC was to save the i/o pins as il be needing quite a few. I was thinking of only controlling the address lines by the uC and obviously data lines also wil go to it. Since my ALE is connected to CLOCK in the free running mode i thought of keeping it that way only. Do u think its not right? can u pls tel me the basic part of the code... (dont get me wrong) i just mean the sequence of the control signals. Or can i use the same as mentioned by Mazzidi in his book?

Also i felt that since OE and START can be always connected to +5V and i can just read the o/p as and when i need by changing the Address lines. But then wont my EOC always be low and trigger my uC interrupt!

Am also confused with the algorithm for my code. need to code it properly as i need to store each data for each sensor in one shot to stack and then display onto the LCD. Then check for the thresholds and perform control operations!

Lots of questions sorry... my 1st proj on a uC. I thought i was good at this and now am busted!

K then waiting for u guys' expert advice... thanks a ton guys!!!! cya

Re: Sensors

Thu, 06 Mar 2008 22:30:40 -0800

You can follow Mazidi for programming the ADC.
And for starters you may follow these steps......
while(1)
{
get_adc(temp) x 10 => T //get 10 samples for temp and store the average in T
get_adc(hum) x 10 => H
get_adc(ldr) x 10 => L

Display(T)
Display(H)
Display(L)

if(T>Tthresh) do .....
if(H>Hthresh) do ....
if(L>Lthresh) do .....

some_delay()
}

Re: Sensors

Fri, 07 Mar 2008 06:18:00 -0800

Hi shashi thanks for the idea. this was basically wat i had in my mind. but i had not thought of having the avg of 10 values. as i thought il keep displaying the variations on a real time basis. I am basically foxed on the reading the data and storing into stak part. and another prob! i have not got a hold on programming the uC in C so i am stil stuck to assembly level programming only

Also i was having another doubt. how do i provide a clock to the ADC? i had thought of 2 inverters with an RC this was generating a 850kHz clock but wil i be able to synchronise the ADC with the 8051? I wil be using a 11.0592 crystal for it. In Mazidi he shows a diagram where the same crystal is tapped and a propagation delay is introduced by means of cascaded d flip flops. can i stick to the inverter buffer or the Mazidi way or do u suggest something else?

Re: Sensors

Fri, 07 Mar 2008 11:35:06 -0800

and another prob! i have not got a hold on programming the uC in C so i am stil stuck to assembly level programming only

You call it a problem?Many would love to be burdened with such a problem(asm skill)
As for the clock you can directly feed it from the 8051 using timer interrupt.

Re: Sensors

Fri, 07 Mar 2008 21:16:35 -0800

well thats the reason my preference for newbies is to use assembly first rather to go for C. C makes you lazy and you find things very very hard if you have to write a code in asm.

Re: Sensors

Sat, 08 Mar 2008 06:01:28 -0800

Wel my skills in assembly are nothing great either... but farely decent.
Regarding the clock, using timer is a very good idea as there wil be no synchronisation problemms and ul get a clean pulse but my problem is that i am trying to reduce the no of pins of the uC. This is mainly because i am having an ADC, LCD (probably buttons for it...which i most probably will have to eliminate and use a time varying display) and also mtors, relays etc to my uC. so i need to be careful with the no of pins i use for everything.

Also later i plan to make it an sms based system so that wil again need the serial commn pins! And my stage 3 is to make it a multi processor system (hope i can achieve that b4 the deadline).

Another embarrasing problem that has tied me down is that i am stuck with making my power supply. got the +5V but in an attempt to get -5V i blew the thing up (dint refer datasheets of 7905!!!) and all subsequent boards were al screwed up (pardon the language) i need to redo it carefully now!!!!

And i am yet to start coding :'(

Re: Sensors

Sat, 08 Mar 2008 10:11:52 -0800

Don't worry ...... we all make mistakes.I remember wiring a 78L05 like a 7805 without caring to read the datasheet and then ending up with a lighter pocket.

So make an estimate of exactly what all stuff you would be hooking up in ver1 of your project.Then calculate the total pin requirement and if it crosses whatever is available then you can start using alternate tricks to reduce pin count.

Re: Sensors

Sun, 09 Mar 2008 03:32:39 -0700

Hmmm il surely keep that in mind. Its been a real learning though slow experience for me. hope i can get this power supply sorted out tomorrow. I have started working on how i want the entire setup to look and work like. just been too lazy over the week end.

Also on the ADC and uC part i had a doubt, do u think there wil be synchronisation problems if i do not use a clock sourced by the crystal or the timer feature as u mentioned? also wil noise be a problem if i use a slightly longer wire for connecting the clock of the ADC from the uC?

Regarding the conncetions of sensors to the ADC. do i need to use any resistors b/w them to limit the current? My biggest concern is that the data sheet of the humidity sensor HIH4000 (my most expensive component- it costs as much as the rest of my h/w!) datasheet mentions the max i/p current as 500uA and the ideal operating current is 200uA. They would sertainly have ensured it does not draw more current than that unless at the o/p we happen to draw more current. so will the ADC cause trouble?

Re: Sensors

Mon, 10 Mar 2008 07:23:59 -0700

sure start a new one.. coz it will be easy to have a follow-up then

Re: Sensors

Fri, 28 Mar 2008 09:04:59 -0700

Okay! Now I am thoroughly confused!!!
I tried making a look up table for the LM35. But i realised I need to have 2 separate LUTs, one for the ten's place n the other for unit's place (Pls tell me if it needent be done that way) and I am unable to figure out how do u access the tables then?

Firstly I must mention I have connected the LM35 to a uA741 with a gain of 4.8 which is connected to the ADC. So at 25 deg C the o/p of my ckt will be 1.2V. The output of the ADC will be 3Dh ie 61d. How do i convert this to ASCII and display it now!

I initially though that its wiser to calculate the corresponding ASCII value and store it in a LUT n access it... but now i feel its far too complicated.

But i need to use a LUT because the formula for the Humidity sensor is far to complicated to be done in the uC so i have to manually calculate it for the range of voltages and store the corresponding value in a LUT.

Pls help

Also. How do i display degree symbol. The ASCII codes table in Mazidi doesnot list it...

Re: Sensors

Mon, 10 Mar 2008 07:05:30 -0700

Hey. Hows everyone? looks like its been a busy monday for all

Mine too. I finally hav my power supply up and i am getting +5 & -5V!! Hurrah!!!

And that leads me to my next hurdle. Programming the uC. I made a small code to try testing the LCD. And also another for the ADC. and then thought il integrate them to c how it works... and to my despair i am unable to proceed beyong the build option. I somehow managed to change somesettings and generated the hex file also. but beyond that i see no option o program. how do i procced? pls help asap.

also pls go thro my previous post and let me know about that current and synchronisation doubts i had..

BTW since my doubts on the sensors have been cleared for now and i am stuck in programming part etc, should i start a new thread for that or shall i continue here??

Cya for now

Re: Sensors

Mon, 10 Mar 2008 21:46:14 -0700

Hi Amit, couldn't keep in touch, was busy at Mumbai

Give the blue print of your project, we shall try to help u with the code

Re: Sensors

Tue, 11 Mar 2008 12:38:18 -0700

nice to see more helping people around
good work Chiru and Shashi...

Re: Sensors

Sat, 22 Mar 2008 06:12:59 -0700

Hey am so sorry for not posting for over a week. My connection was down. Thanks to BSNL!!!! Wel it was finally set right today. Besides that i was stuck up at college too due to some accreditation work and also had to do my 1st project seminar. Which by the way was a hit. The idea was appreciated alot and the presentation too impressed the evaluators. Also i have my internal assesment tests on monday n tuesday so il be stuck til tuesday due to that.
After doing some realistic work, it feels sick to go to books!

Coming back to the project. I have made my ADC board. I used a Schmitt triggered NAND gate (4093 if am not mistaken) to generate about 700khz clock. I need to make the uC board now n tehn try the code on it.

About the blue print, I have not yet drawn the ckt, but i have it on paper. N yeah another prob is that i was planning to use the ADCs EOC as INT0 of uC but i think that cant be done right.

The following is my flow for the prog on which i have started coding:
1.Switch on
2.Display initialisation msg
3.Initialise ADC
4.Read sensor1 from ADC
5.Store in uC buffer memory
6.Read sensor2 from ADC
7.Store in uC buffer memory
8.Read sensor3 from ADC
9.Store in uC buffer memory
10.Read sensor4 from ADC
11.Store in uC buffer memory
12.Initialise LCD
13.Display al sensor data from buffer
14.Check sensor1 data wrt threshold
15.Switch on/off actuator
16.store status in buffer for actuator1
17.Check sensor2 data wrt threshold
18.Switch on/off actuator
19.Store status in buffer for actuator2
20.Check sensor3 data wrt threshold
21.Switch on/off actuator
22.Store status in buffer for actuator3
23.Check sensor4 data wrt threshold
24.Switch on/off actuator
25.Store status in buffer for actuator4
26.Go to step 2.

Also the LCD will be used with a switch. In the normal condition it will display the readings of the sensors. When the button is pressed it should display the condition of the actuators(which will be stored in the actuator buffer). When the switch is turned off it must go to step 2 and start reading the sensors again. To achieve this i think i must connect the switch to INT0 or INT1 right.

Also the ADCs EOC cannot be connectd to INT0 for the flow i have mentioned and only polling method can be used right? Else while its waiting for the 1st sensors conversion to finish i wil be latching the 2nd sensors address to teh ADC.

Pin details
P0 LCD data
P2.7 RS
2.6 R/W
2.5 E
l
P1 ADC data
P3.0 OE
P3.1 Start
P3.2 EOC
P3.3 SWITCH FOR TOGGLING LCD DISPLAY
P3.4 ADD A
P3.5 ADD B
P3.6 ADD C
P3.7 ALE

am i on the right track now?

Re: Sensors

Mon, 24 Mar 2008 04:51:13 -0700

Reply pls am waiting..

Re: Sensors

Mon, 24 Mar 2008 10:54:01 -0700

Step12 "initialise LCD' should be before step2.
Polling the EOC would be better and simpler since you have to wait for the adc data before moving forward.So no point using an interrupt.
For the ADC values it would be better if you took ~10 samples for each sensor and used the average value.You may use the bucket(or was it barrel?) shifting algo posted somewhere by Shyam,for averaging.This way you minimise the chance of your actuators swinging wildly with each value.

Re: Sensors

Tue, 25 Mar 2008 07:06:18 -0700

Soory about Step12!! that was foolish of me!
Could u pls tel me the link or the thread where that algorithm is by shyam?
Thanks a ton

Re: Sensors

Tue, 25 Mar 2008 12:50:59 -0700

This is the thread.....
http://www.8051projects.net/plugins/forum/forum_viewtopic.php?5070.40#post_7316

Re: Sensors

Wed, 26 Mar 2008 08:33:05 -0700

Hey Shashijoseph,
I am unable to follow that algorithm. N my C skills for 8051 are pathetic so understanding that code is impossible for me!

Pls could u elaborate on that?

Sorry for being dumb

Re: Sensors

Wed, 26 Mar 2008 10:10:57 -0700

There is nothing difficult in it..
its same like taking average of 10 values..
you add all 10 values and divide it by 10, so you get average.

Now when next time you take average, you have to consider the 10 samples taken before too..

i explain like this..
data1, data2, data3, data4, data5, data6, data7, data8, data9, data10 => avg1
data2, data3, data4, data5, data6, data7, data8, data9, data10, data11 => avg2
data3, data4, data5, data6, data7, data8, data9, data10, data11, data12 => avg3
data4, data5, data6, data7, data8, data9, data10, data11, data12, data13 => avg4

so while taking average you are considering all samples taken before too..
so only first time you are waiting for 10 samples, after that you are just waiting for one sample and then keep taking averages..

I hope you now understand the algorithm.

Re: Sensors

Wed, 26 Mar 2008 10:16:48 -0700

oh oki got it now! i am such a dumb***
I thought it was wat u mentioned but was not sure. I am presently coding for the system using 1 sensor only. Once its done and working right, ill add the code for other sensors also. Am stuck at that LCD initialisation part also and displaying on the LCD! its very complicated. I have not completed the code yet thats y i have not yet posted it. Can i post an incoplete code for ur scrutiny?

Re: Sensors

Wed, 26 Mar 2008 10:27:17 -0700

if you feel any problem using LCD, you take a look at LCD tutorial..

why would i need the code?

Re: Sensors

Wed, 26 Mar 2008 10:34:33 -0700

Wel i did go through it. So quite a few of my doubts have been cleared am not sure on how to make those custom characters. I need to display % symbol.
Was having another doubt. Is it possible to store strings in the RAM of the 8051? i want do it to display the actuator status. els il have to store a 0 or 1 in RAM locations amd correspondingly pick up "On" or "Off" from the ROM (After putting it there ofcourse!)

I wanted u to see my code to tell me if i was on the right track.

For that ADC barrel algo, il need to use an array right? And how do i perform the averaging? And then shift all the data. Dont u think it will slow down the performance of the system because i need to read 4 sensors, display their data and then check the threshold for each n then turn on/off actuators and then display it!

Re: Sensors

Wed, 26 Mar 2008 11:29:02 -0700

'%' symbol is there in
LCD isn't it? try..

CODE:

 unsigned char string1[] = "this stored in ram";
unsigned char code string2[] = "this stored in rom";
 

averaging wont take much time.. yes you need array..

Amit Radha wrote ...

And how do i perform the averaging? And then shift all the data

see shyam's code.. he did exactly what you are looking.

Re: Sensors

Wed, 26 Mar 2008 11:32:37 -0700

Ajay i really dont follow the c codes! pls help me in assembly (if its not too much of a trouble)...

Re: Sensors

Wed, 26 Mar 2008 12:13:15 -0700

well its same as you do in C..
lets say adc_read is your routine for ADC then

CODE:

;for first time
acall adc_read
mov adc1, A
acall adc_read
mov adc2, A
;and so on...
acall adc_read
mov adc10, A
;adc1 to adc10 are location in RAM

;Now is mmm.. average..
;confusing :-p
 

Re: Sensors

Wed, 26 Mar 2008 22:51:44 -0700

hi amit...

forget abt the barrel shifter code a the moment...

there are several other DSP algorithms that can be used...

today i m gonna start a new thread regarding it...
wait for it to come... and afterwards u shud not have any problem regarding it..!!

Re: Sensors

Thu, 27 Mar 2008 06:44:18 -0700

Hi ajay, sorry i went offline suddenly! Had a power cut due t heavy rain I suppose!

Hey Shyam thanks a million! il have a look at that thread... hope its out.. pls do it soon! I really need it. I understood the algorithm, but coding the whole thing in assembly is very tedious! I am unable to do it I admit

First of all cant use an array like in C and then averaging it is another task! Also then performing the shift! How do u do that!!!

I am having another doubt regarding the ADC. Now the o/p of ADC is not hex right, its BCD so i need to do a BCD to HEX conversion and then store it in my buffer tehn do a HEX to ASCII to display it on the LCD? I need the HEX equivalent cos i need to perform the check for threshold.

Another doubt regarding the LCD. A pot is needed b/w Vcc, Vee & Vss for controlling the contrast. But what are the 2 pins +LED and -LED for on the LCD? (ie. pin 15 and 16) is it for the backlight? so do i connect it to +Vcc & GND respectively? was making my uC board today and got stuck here. The data sheet of HD44780 dint mention anything about it...

Re: Sensors

Thu, 27 Mar 2008 10:44:58 -0700

regarding LCD ..

yes Amit u r right +led =>vcc -led =>gnd and they r for backlight...

Re: Sensors

Thu, 27 Mar 2008 11:01:44 -0700

The o/p of the ADC is definitely binary(hex).
For eg. if the input to the ADC(configured with 0-5v full scale) is 2.5v,the output of the ADC will be 128(decimal) or 80h.This is what will be stored in your buffer....so no need to convert BCD to hex.You can use this value directly for your threshold comparison.
For displaying,you'll have to multiply this hex value with the step size and then convert he result to ASCII.
For eg. step size with a 8-bit ADC configured 0-5v full scale is 5/256=19.53mV(say 20mV)
Now suppose you get a hex value 80h from the ADC.The value to be displayed is 80hx14h=A00h.Now convert this hex value to ASCII for displaying on the LCD.

The LED+/- are for the backlight.You may leave it unconnected or connect it through a 10ohms series resistor to vcc and ground.

Re: Sensors

Thu, 27 Mar 2008 11:47:01 -0700

Hey thanks a lot!!!
That gives me some work to do for tomorrow! mu uC board was on hold cos of that +/- LED doubt of mine. My code (for 1 sensor) is almost done. il complete it tomorrow and post it pls do let me know how to improve it or incase i have made any mistakes...
Cyas for now.. gnit

Re: Sensors

Thu, 27 Mar 2008 11:49:20 -0700

Well, i forgot to ask. is there any way i can improve the sensitiviy of the temp sensor? I mean in the present set up i cannot show decimal values, right? So can that be incorporated. its not very necessary though, but it certainly will improve the set up a bit i feel..

Re: Sensors

Thu, 27 Mar 2008 22:05:16 -0700

which temperature sensor you are using?
when taking average values.. you can get decimal values too..

Re: Sensors

Sat, 29 Mar 2008 07:10:38 -0700

Hi Shashijoseph and Chiru, thanks a ton for the repeated support and prompt solutions

I checked the o/p of my bridge rectifier, was getting nearly 7.5V (was reducing a bit though at times) So i got a 9V 2A tranformer. Not tested it yet. Will do it on monday.

sashijoseph wrote ...

Will using 2A tranformer damage the system by any chance? I will be using this to power my ADC, 4 sensors, uC, LCD, and a buzzer also. So i thought ite better to be on the safer side by sing 9V 2A.
I am using a heatsink on the 7805(used a mica sheet and heatsink paste also). But the 7905 has a complete plastic casing so i did not put a heatsink to it. Also,the regulators are followed by a 10uF and 1uF cap each.

sashijoseph wrote ...

As for the switch,why do you want it to reset the system...coz even after reset it will give you the same sensor readings as before reset(provided conditions don't change during reset).So for eg. if without reset(and the switch back from acuator mode to sensor mode) the temp display was 25deg,then even after reset it will display 25deg,provided temp. doesn't change to some other value during reset.

Wel i wanted to reset the system because the original mode of the LCD is to display the sensor data. Now, cosider a situation where the user presses the switch to see the actuator status, the interrupt occurs and the ISR changes the display, I include a delay in it so that the screen is on for say 5sec. After that on execution of RETI, the LCD must display the previous mode, ie. sensor status screen. for that it must restart from the beginning but RETI will cause it to continue where it was interrupted and there will be a delay till the uC completes what it may be doing at that time and then reach the part of the code to display the sensor status.

I thought of using the watchdog timer (using the AT89S52) which supposedly resets the system when it overflows. so I can give it a count upto 5sec and then it will overflow and consequently reset the system. But that as u mentioned and few others also should not be done. So pls tel me if its a healthy practice to reset the system like this.

Also one more doubt, to trigger INT0, i am using a push to on switch similar to the one which is used for the reset switch of the uC. now, one end is connected to the uC and the other to +5 or GND? and should i use an RC ckt also. I am thoroughly confused with wt to do about that! I hope u got my question. I have thoroughly confued my team also!!!

I have asked Lots of questions. Want to program my uC and test the system by monday! Hope i have not started bugging u guys... Thanks a lot once again! bye for now.

Re: Sensors

Sun, 30 Mar 2008 09:56:09 -0700

remember that the transformer current rating is the maximum capacity which it can sorce and not the actual current it is sourcing

Re: Sensors

Fri, 28 Mar 2008 05:25:25 -0700

Hi Ajay,
I am using an LM35. But not connecting it directly op the ADC, I am using an opamp as Shashi (or Chiru. dont remember) told me it wil help to smoothen and caliberate the o/p. How can i get the decimal values using it?
As Shashi mention 2 days back,

sashijoseph wrote ...

Now i am having a doubt regarding this. I thought instead of making the uC do the calculationsm i can create a look up table such that for a particular hex o/p of the ADC it picks up the corresponding ASCII value and stores in a buffer for display. Can this be done?
My code (for the temp sensor only is ready except for this part.)

Also i am facing a peculiar problem with my power supply circuit!
Its o/p voltage starts dropping as i start increasing the devices drawing supply from it! I am using a 6V 1A tranformer followed by a bridge rectifier then and LM7805 and LM7905 regulators (for +/-5V)

Re: Sensors

Fri, 28 Mar 2008 12:46:21 -0700

The LM7805 needs atleast 2V for dropout,ie ~7V at it's input.A 9v xformer would be better.

Re: Sensors

Fri, 28 Mar 2008 20:03:51 -0700

Hey thanks a lot. Yup no problem take ur time... ur doing us noobs a big favor by helping out on the forum i admit.
Regarding the supply, I was told to take a higher current rating transformer (2 or prefferably 3A, 5A tranformer wil become too huge). Also i bought a 6-0-6 tranfirmer and was using onle 6-0 terminals. Itseems that could also be a reason (i mean the center tap) so using a 0-6 transformer would be better.
So to solve the problem il use a 0-9, 3A tranformer. Hope that wont bee too much for the system right?

Regaring the Look up table, i think i have thought of a solution, il try coding it and if it solves the prob then il post it here.

I am facing another design issue now. I need to know in wat all ways can the uC be RESET, besides that reset momentary push button as mentioned in Mazidi.
I need this because as mentioned in my design, i show the actuator status only when a button is pressed. This i am doing by connecting teh switch to INT0, but when the switch is turned back to original position, I need to again reset the system so that it starts rading the sensors afresh and then displays the sensor data. I cant just use a RETI at the end of my ISR as that will take the IP to where it was before, but my display will not change instantaneously, right?

Re: Sensors

Fri, 28 Mar 2008 20:10:01 -0700

A 6V AC will give over 8V DC if not heavily loaded and should work fine with 7805, still its better to use a 9V one as Sashi suggested. Moreover there should be a good heatshink on the reg so as to prevent thermal shut down (current reduced and voltage against load)

Re: Sensors

Fri, 28 Mar 2008 20:28:42 -0700

Thanks...Anyway, I find this model, dunno can be used or not. It is from nemoto japan, http://www.nemoto.co.jp/en/products/sensor/manual/nhs-20.html or mec HCZ-H or HCZ-J series. May I know it can be used?

Thanks so much

Re: Sensors

Fri, 28 Mar 2008 21:06:09 -0700

3A for an embedded system is OVERKILL big time.With a cap(~1000uF) on the bridge,a 6v trans. should supply ~8.4v,but if it goes below 7v under load then regulation will suffer.So use a 9v,1A transformer and you'll be fine.Also use a 10\100 uF cap on the output pin of the 7805.
As for the switch,why do you want it to reset the system...coz even after reset it will give you the same sensor readings as before reset(provided conditions don't change during reset).So for eg. if without reset(and the switch back from acuator mode to sensor mode) the temp display was 25deg,then even after reset it will display 25deg,provided temp. doesn't change to some other value during reset.

Re: Sensors

Fri, 28 Mar 2008 21:15:00 -0700

Amit, employ a proper adc loop rather than reset

Re: Sensors

Sun, 30 Mar 2008 07:15:27 -0700

Hi shashijoseph,
Thanks a ton
Il include those 4.7k resistors b/w the port and Vcc.
I had got thoroughly confused with the switch! thanks for clearing that out too! Now in my code i make INT0 an endge trig. int. should i do it or leave it as level trig? i feel it should be edge trig. right?

U dint tell me if its safe to use the 0-9V 2A transformer? I have explained my ckt in the post just after chiru's reply.

Regarding the RESET of the system. I tried to include a proper loop as u and Chiru suggested but i have come across a peculiar situation. Hope i can explain it properly-
cosider that the uC is initialising the LCD for displaying sensor data rom the buffer or that it is displaying the sensor data from the buffer. At that instant user presses the button for viewing actuator status. this triggers the interrupt and in the ISR, the LCD is re initialised and sensor status is displayed. after 5sec delay, RETI instrn executes and uC starts from where it was interrupted ie : halfway initialising the LCD or halfway thrugh displaying the sensor data.

In both these cases, the display will now probably be garbled or only partly correct data will be displayed right?

What do i do now?

Re: Sensors

Sat, 29 Mar 2008 11:23:26 -0700

Just saw this in a thread "ABOUT MICROCONTROLLERS" by TPS:-

۞ TPS ۞ wrote ...

ABOUT THE Microcontrollers

A: Port 0 has open drain outputs. Ports 1, 2, and 3 have internal
pullups. What does this mean? See the next question and answer.

Q: Port 0 has open drain outputs. Ports 1, 2, and 3 have internal
pullups. What does this mean, and why should I care?

A: When used as outputs, all port pins will drive the state to which
the associated SFR latch bit has been set. Except for port 0,
which will only drive low (not high). When a 0 is written to a
bit in port 0, the pin is pulled low (0). But, when a 1 is
written to a bit in port 0, the pin goes into a high impedance
state - or in other words, "disconnected", no value. To be able
to get a 1 as output, you need an external pullup resistor to
pull up the port (to 1) when the port is in its high impedence
state. Typical values for pullups might be 470 ohm to drive a
LED, and 4.7K or higher to drive logic circuits.

C: Any port pin may be used as a general purpose input simply by
writing a 1 into the associated SFR latch bit. Since ports 1, 2,
and 3 have internal pull-up devices they will pull high and will
source current when pulled low. When a port 0 bit is programmed
for input (set to 1) it will go to a high impedance state.

I am using P0 of the uC to DB0 to DB7 of LCD. Does that mean i need to add 4.7k Resistors between the uC amd the LCD pins???

Re: Sensors

Sat, 29 Mar 2008 23:54:22 -0700

Nope......between Port and Vcc (pullup).

Re: Sensors

Sun, 30 Mar 2008 00:33:24 -0700

Also one more doubt, to trigger INT0, i am using a push to on switch similar to the one which is used for the reset switch of the uC. now, one end is connected to the uC and the other to +5 or GND? and should i use an RC ckt also. I am thoroughly confused with wt to do about that! I hope u got my question. I have thoroughly confued my team also!!!

The switch should be connected to the port pin and Gnd.....never to Vcc(atleast not directly without a resistor).
I think switch debouncing isn't necessary in your application since you'll be returning from the interrupt(5 sec delay like you said) long after the switch would have settled. So no chance of 'misfiring'.You would need to debounce if your ISR were to complete in say 5ms.

Re: Sensors

Sun, 30 Mar 2008 11:08:15 -0700

Hey i got a solution to the problem. Just tell me if my logic is not faulty!!!
In the ISR, After displaying the actuator status, there is a 5sec delay (so that user can see the status on the LCD for 5sec.) then instead of RETI il again display the sensor data from the buffer and then RETI.
This will send back the control to where the uC was interrupted. So even if it was displaying sensor data and was interrupted midway, it will just redisplay it in the same locations on the LCD but the LCD wont be garbled right?
And yes, i will remove the repeated initialisation of the LCD from the code.
Pls do tell me incase of any more mistakes in my code...

Thanks

Re: Sensors

Sun, 30 Mar 2008 11:21:49 -0700

Had a brief look at your code.Like Ajay said you should initialise the LCD only once whereas you've done it 3 times.
This is how it should be:
1- initialise LCD
2- display welcome msg
3- Read ADC
4- Convert
5- Data Display
6- Threshold check
7- Back to step 3

You needn't re-initialise the LCD in steps 2,5 or the ISR.

As for the ISR doubt.....this is what you can try.Use a flag,say 'Act'.Inside the ISR you do 2 things.First set the Act flag ie. Act=1.Then display a msg "Hang on,gathering Actuator data....." or sth similar.Then a RETI.
Now in the data display routine(step 5) this is what you do.....
1 check Act bit.
2 If Act=1
(-IE=0 ;disable interrupts
-Display Actuator Data.
-Wait 5 sec.
-Make Act=0
-Display Sensor data
-IE = 81h ;re-enable interrupts
-Ret
)
Else (-Display sensor data
-Ret
)

Re: Sensors

Sun, 30 Mar 2008 09:04:30 -0700

why are you initializing lcd again and again? I mean just use lcd clear command to clear lcd instead of re-initializing. Init part should be just once at the starting of program.

Re: Sensors

Sun, 30 Mar 2008 09:10:01 -0700

have read all the details of your project. Am confused about your power supply part. I havealready used all the components you are using and in fact had used multiplexed 0.5" LED displays instead of LCD. but never did i find a need for a supply current exceeding 500mA. The only current consuming part in your ckt is the backlight which itself takes upto 100mA. Do connect the 10 ohms resistor in series as it will limit the current to the led.
check your sensor ciruit (analog input section) as it may be draining most of the current.
the 7805 cannot source more than 1A current and will shut down if excess current is drawn.
As for the ADC resolution part, I have a novel way to interface ICL7135 to the 8051 by using only 4 i/o pins. and will post it shortly. The 7135 can give a resolution of upto +/-20,000 counts i.e. more than 14 bit resolution and is as cheap or even cheaper than ADC0808. check out its datasheet.

Re: Sensors

Sun, 30 Mar 2008 09:15:38 -0700

ajay is right . Why reset the whole uC when you can just refresh the data??

Re: Sensors

Sun, 30 Mar 2008 09:34:47 -0700

Ok i am terribly confused now :'( i dunno wat to do.
I hope u understod my concern regarding the display. Il upload my code pls do go thro it and suggest changes. (It is not yet complete and it is for the LM35 only not done for other sensors.)
Regarding the supply, i interfaced my boards and sensors to a 9v transformer (dunno the current rating) in my lab and dint face any loading problem. I purchased a 2A one to be on the safer side.l Dint know the 7805 cant handle higer current

Pls do check my code and tel me wat to do. Also do i need to include any file in the beginning? i will be using keil uVision 2

Re: Sensors

Mon, 31 Mar 2008 10:04:07 -0700

Hmmm thanks alot, il incorporate all the changes into the code and the hardware.
Am facing a peculiar problem regarding the power supply. I am unable to make a common groung from the 7805 & 7905. When i tried the 1000uF cap swole up and the rectifier heated up. So i changed the cap and inverted it (as i had made that mistake) now it is exactly same as the dual power suppy in the datasheet but that still doesnt allow me to have a common ground as shown in that. The rectifier still heats up when i short the 2 grounds.
Does anyone have a tested circuit for +-5V?

Pls post it here. It will be a huge help. I dunnot want to buy a ready supply, even though i have spent ~150 bucks already on it and it is still not working!

Re: Sensors

Sun, 30 Mar 2008 09:53:06 -0700

it doesnot matter if u use a higher current txformer as long as ur curcuit does not sink more than 1amp current, go ahead and use it

Re: Sensors

Sun, 30 Mar 2008 10:08:54 -0700

where is the code?