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need help in temperature sensor circuit!!

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compass1982

New Member
hi there, this is te 1st time i post in this forum.:)

i have a question here, i am doing a temperature sensor circuit. i am trying to convert the output voltage of the temperature sensor(LM335) to binary code, can i know is there any 8bit ADC converter (which is cheap and easy to find)available? i will be using it to show the temperature reading through seven segment display as well as controlling the fan and air conditioner operation with the use of PIC16F877A. can anyone pls give me some suggestions?


thanks in advance
 

Nigel Goodwin

Super Moderator
Most Helpful Member
The 16F877 already has analogue inputs, ten bit ones, you can read the analogue output directly using that - but you may need an opamp to amplify it?.

If you don't know how?, check my tutorials!.
 

Sebi

Active Member
When You thinking about PIC, i recommend DS1820 from Dallas Semi. This sensor give temp data via 1-wire bus. (no need work and time for calibration)
 

hgmjr

New Member
I recently played with the DS18B20 connected to a ATMEGA16 and it worked great. I even put it at the end of a 50 foot cable and it still worked just fine.

I really like the fact that all I had to do is connect it directly up to a digital IO port (with a pullup resistor) without the need for an opamp or an A-to-D converter and I was immediately in business.

Word of caution. You will need access to an oscilloscope to make sure that the timing of the various signals is spot on.

hgmjr
 
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ericgibbs

Well-Known Member
Most Helpful Member
hi compass,
Unless you have already purchased a LM335 have a look at the LM35.
The LM35 has a working range of +2 thru +150 Cdeg, also with
10mVolt/Cdeg, but without the offset the LM335 has, being a Kelvin abs device. If you are controlling air cond/temp, using the LM35 directly connected into the ADC of the 16F877, with +Vref at +5v, you will get an output resolution of 0.5Cdeg , after you have done the maths.

EricG
 

Mike - K8LH

Well-Known Member
hgmjr said:
I recently played with the DS18B20 connected to a ATMEGA16 and it worked great. I even put it at the end of a 50 foot cable and it still worked just fine.

I really like the fact that all I had to do is connect it directly up to a digital IO port (with a pullup resistor) without the need for an opamp or an A-to-D converter and I was immediately in business.

Word of caution. You will need access to an oscilloscope to make sure that the timing of the various signals is spot on.

hgmjr
The Dallas DS18B20 temperature sensor is great but I dissagree that you need an oscilloscope to make it work.

I fabricated a couple different boards to test the DS18B20 and the "one-wire" routines in the Dallas PIC application note and I didn't have any problems 'talking' to the DS18B20. Simply modify the routines as appropriate for your PIC oscillator frequency to maintain the recommended timing.

If anyone's interested, one of my test boards and software is available in the following Forum.Microchip thread;

DS18B20 Temperature Readings?

Good luck with your project.

Regards, Mike
 
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