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I have built a circuit that uses a MCP9700 to read the temperature as explained here.

This is the circuit schema:

circuit schema

I understand that C2 is used as a decoupling capacitor to clean up the noise (datasheet). However, I am not sure about C1. Is it a decoupling capacitor as well? I did the experiment without C1 and the temperature reading was not significantly affected.

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  • \$\begingroup\$ C1 could help the ADC inside the arduino produce a more stable reading. \$\endgroup\$
    – Andy aka
    Commented May 24, 2013 at 22:31
  • \$\begingroup\$ OK, so how can I be sure that it is it's purpose? And how would you calculate the actual value? I saw this diagram in a couple of tutorials but nobody ever explained what's C1 purpose. \$\endgroup\$
    – Flanfl
    Commented May 24, 2013 at 22:43
  • \$\begingroup\$ According to the datasheet, no additional parts are needed. C1 was added in for who knows what reason. Microchip doesn't recommend it. \$\endgroup\$
    – Passerby
    Commented May 24, 2013 at 23:03

2 Answers 2

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The answer is on the datasheet 1st page:

enter image description here

So in short it doesn't hurt and slows down the response to prevent overshoot, presumably upon power up or from Power supply ripples. The PSR is \$0.1 ^\circ C/V\$ which is not bad.

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  • \$\begingroup\$ Arf, I did not read carefully enough the datasheet and I missed this information. \$\endgroup\$
    – Flanfl
    Commented May 25, 2013 at 10:46
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The purpose of C1 is just to remove off the fluctuations in the analog output given by the sensor. It is basically acting as a noise filter making the output more and more stable even in the noisy environment.

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