Sensors

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.

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! :mad

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)

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

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

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. :bye

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. :-)

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!!!! :mad

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 :mad :-s

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 :bye .