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Support Forum » Tempsensor tutorial

November 08, 2009
by zylphyr
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Hi,

Having set up the tempsensor project according to the tutorial (in the guide) everything seems to work fine expect that the ADCL/ADCH registers both return a value of zero. Does that mean that the LM34 chip is broken (assuming I have wired stuff up correctly, which I'm pretty sure I have) or is there something else that I should be checking?

thanks in advance!

Marcus

November 08, 2009
by mrobbins
(NerdKits Staff)

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Hi Marcus,

If you have a multimeter, then measure the voltage from ground to the LM34 output. This is supposed to be 10mV per degree F, so if it's 70 degrees Fahrenheit at your workspace, it should be about 0.70 volts at the output.

Without a multimeter, another good way to see whether the problem is on the sensor side or not is to do the following:

  1. Remove the LM34 chip from the breadboard.
  2. Put a wire from pin PC0 (this is microcontroller pin #23) to GND, and look at the ADC output (should be 0). Then move the wire from GND to VCC, and look at the output (should be 1023).
  3. Now remove that wire, and put one 100K resistor from PC0 to GND, and one 100K resistor from P0C0 to VCC. This makes a voltage divider and should put about 2.5V at that pin. Look at the output (should be about 512, but could be +/- a few percent -- the resistors have a 5% tolerance).

Finally, you can always e-mail us a photo of your breadboard (or you can upload it somewhere and link to it in a reply to this forum post) and we'll try to spot if there's anything out of place. Let us know what the result is!

Mike

November 09, 2009
by zylphyr
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Thanks Mike!

I'll test it tonight and let you know how it worked out.

:)

M.

November 09, 2009
by zylphyr
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turns out I had miswired (is that a word?) the GND...blush

thanks again though. I learned several new things :)

M.

November 09, 2009
by mrobbins
(NerdKits Staff)

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Hi Marcus,

Awesome, glad to hear that you got it working and learned something in the process!

Mike

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