does heat effect rctime?

Tobias

I am noticing that when my project gets warm the rctime values jump up and down about 10% I am using it to read the voltage, would an ad converter solve this problem?

different question
convertion
I have 9 identical projects with rctime circuits and none read the same when I get my first board two read a psi of ten when it actually is ten and then plug in a different project it will not be the same. will an ad converter solve the problem?
Thankx
Toby

Mike Green

Many capacitors are temperature sensitive and the 10% you're seeing is typical. Some capacitors are made so they're less sensitive to temperature.

An external ADC would work better. They usually use methods that are not affected by the ambient temperature.

You could also calibrate your circuit, possibly by having an RC circuit that measures a known voltage (like the +5V supply). That would give you a value that you could use to correct the other RC circuits. You'd use the same capacitor for all of them.

Tracy Allen

Hi Tobias,

There is an article on error sources in RCTIME posted here: www.emesystems.com/BS2rct.htm#drift: There are errors due to thermal drift in both the capacitor and the Stamp threshold, and noise effects. The Stamp threshold varies from part to part and also with temperature. And I agree with Mike, and ADC will be more accurate. Consider a 12 bit serial ADC.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com