please dont rip this site

Tom Hartman says:

...I developed a way to measure thermistor resistance without an ADC. This requires two bi-directional port pins a reference resistor and a capacitor. I think others have done this as well.
PIN1|---\/\/\/-----+
    |     R1       |  C1
PIN2|---\/\/\/-----+--)(--> (GND)
          T1

Create a reference measurement from precision resistor R1:

  1. Output 0 on pins 1,2 to discharge C.
  2. Make both pins inputs.
  3. Pulse PIN1 from input to high output back to input.
  4. Increment reference counter.
  5. While PIN1 input is low, go to 3.

Measure the thermistor:

  1. Output 0 on pins 1,2 to discharge C.
  2. Make both pins inputs.
  3. Pulse PIN2 from input to high output back to input.
  4. Increment themistor counter.
  5. While PIN1 input is low, go to 3.

Now (thermistor counter)/(reference counter) = T1/R1. C1 is cancelled. The same pin is used to detect the threshold for both resistors, so the pin threshold is also cancelled.

So T1 = R1 * (thermistor counter)/(reference counter).

There are lots of tricks you can do to simplify the math. Then use a lookup table to linearize the result.

Size C1 so the RC time constants are slow enough to be able to count with some precision.

Questions:

See also:


file: /Techref/io/sensor/thermist/capchrg.htm, 1KB, , updated: 2004/1/31 04:29, local time: 2017/11/22 04:48,
TOP NEW HELP FIND: 
54.198.2.110:LOG IN

 ©2017 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?
Please DO link to this page! Digg it! / MAKE! / 

<A HREF="http://techref.massmind.org/techref/io/sensor/thermist/capchrg.htm"> io sensor thermist capchrg</A>

After you find an appropriate page, you are invited to your to this massmind site! (posts will be visible only to you before review) Just type in the box and press the Post button. (HTML welcomed, but not the <A tag: Instead, use the link box to link to another page. A tutorial is available Members can login to post directly, become page editors, and be credited for their posts.


Link? Put it here: 
if you want a response, please enter your email address: 
Attn spammers: All posts are reviewed before being made visible to anyone other than the poster.
Did you find what you needed?

 

Welcome to massmind.org!

 

Welcome to techref.massmind.org!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  .