# Cap Meter Schemas For Front End

Discussion in 'The Projects Forum' started by MCU88, Mar 16, 2015.

1. ### MCU88 Thread Starter Member

Mar 12, 2015
360
35
If you were going to do an capacitance meter project based around an MCU, would you do either a, b or c for the front end?

Schemas:

a. RC time constant
b. Constant current source
c. 555 timer to feed an square wave to the MCU

What do you think?

2. ### Dodgydave AAC Fanatic!

Jun 22, 2012
5,134
767
Constant current and measure the time it takes to charge,

555 feeds an AC signal, measure the frequency,

both are ok

3. ### MCU88 Thread Starter Member

Mar 12, 2015
360
35
Pulsating DC actually. Not AC. To be classed as AC the wave must swing below the zero volt line.

4. ### wayneh Expert

Sep 9, 2010
12,368
3,224
Here we go again!

5. ### MCU88 Thread Starter Member

Mar 12, 2015
360
35
Too many cap meter projects already? Too boring?

Give me some ideas for some projects to submit to the site then

6. ### wayneh Expert

Sep 9, 2010
12,368
3,224
This isn't really an answer to your question, but that's how I do it. Charge up the cap, apply voltmeter probes, and measure the time it takes to go from one voltage to another. It's workable for large electrolytic caps but falls apart when the time you have to measure drops below 5 seconds or so. A human can't do that very well. A machine could.

It's the equivalent of the chemical engineer's tried-and-true method for flow measurement - a bucket and a stopwatch.

7. ### wayneh Expert

Sep 9, 2010
12,368
3,224
No, no not at all. I was joking about the distinction made by MCU88 between AC and DC. I can't tell you how many discussions and differences of opinion we've seen here on that topic.

8. ### MCU88 Thread Starter Member

Mar 12, 2015
360
35
Yes this is interesting. The project would have to measure say from down to 1pF to 9,999uF though. Will be using an 4-digit LED display for the readout.

9. ### MCU88 Thread Starter Member

Mar 12, 2015
360
35
Class of 1997 I come from and my teacher told us that it is not AC unless it swings below the zero volt rail. Textbooks tell it too. No big on theory to be honest. I am more of an get in and just get the job done person. I am very impatient to basically just see the final product powered up. Looks neat and works easy greasy...