Sensors

Hi Chiru,
Thanks for the info.I did go thro the datasheets earlier but...they dint make much sense to me :mad
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?

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.

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?

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 !dance , 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). :bye

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

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... :bye

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!

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). :bye

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 :mad

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 :bye