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High Res Cap MeterAuthor
Ron P
January 8, 2012

The Project

Roman Black has described an easy to build Pic based high resolution capacitance meter on his web site. In need of a way to measure my junk box cap collection, I quickly saw the advantage of his design and built a copy.

 
 


DMM's are out

When using a DMM cap tester it is soon apparent that they work well on the larger caps, which is not really that helpful as the large caps are usually well marked. Small caps, in the pf and nano range, are a different story, tiny cryptic markings, if at all, and inconsistent, non-repeatable readings on the DMM.

What a treat then to use Roman's 0 to 50 MFD cap tester and be able to read down to several pf, with rock steady, repeatable results.

Easy to build

Simplicity itself, six caps, six resistors, a Pic 16f628 and a 2 x 16 LCD...

 
Original schematic, I used a 16f628A		 




Download file
The HEX file for the 16F628



Options

Roman suggests that for battery use a low quiescent current, 5 volt regulator be used. I didn't bother with this as I wanted to use the back light so used a regular LM 7805 (see Mods)and a wall wart for power.

The circuit is simple enough to be built on a vero board, if you wish. I like Target 3001 (free version) and so made a small PCB, using the blue film technique, shown here tin plated. A couple of foobah's but usable. When the unit is first powered up it reads the internal capacitor. The 270 pf that I had selected with the DMM was only 210 pf, so used the partially built unit to find a better fit cap. I found one that read 274 pf after settling, so used that. However, once in the box it now reads over 280 pf. I am not sure how or if this affects the accuracy so haven't worried about it!

PCB drilled, ready to populate It works! fist run


I am well pleased with the results. I used a 1% resistor for the 10K but the 1k5's were just 5%. For greater precision either the 10K or the 1k5 between RA3 and RA2 can be trimmed with trim pots. The "as built" accuracy of my unit is more than adequate for my needs.

In use

At first I was a bit concerned with accuracy, as most of my 1 uF caps measured low. But as I tested more caps my confidence rose. Mylar caps were best for being nearly right on the label value, electrolytic's the worst. A lot to do with manufacturing to the low tolerance, so that was why many of my 1 uF caps measured 965 nano F.

Here is a short video...



Mods

I am using a wall wart that is rated 9 volts @ 200 mA. This was fine to run the project minus the back light, However I found that the 12 volt open circuit voltage dropped to only six volts when the back light was connected. My next in line wall wart was rated at 9 volts 400 mA but the open circuit voltage was 18 volts! Didn't want to risk that so used the 200 mA one and put a 12 ohm resistor in the back light circuit. This brought the voltage down to 8.9 V so felt comfortable with that. However the regulator was starting to just get warm so took the regulator off the board, cut a window in the end of the box, with an aluminum plate over and bolted the regulator to that. Now any heat is dissipated outside of the box, much better.

 
 


With thanks

Kudos to Mr R B for this Pic based high resolution Capacitance meter and for sharing the details and the Hex code with us.
Simply an outstanding project

   Continue reading. Click here to view the presentation.


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  • At 8 October 2014, 7:19:15 user Kevin Mc Donald wrote:   [reply @ Kevin Mc Donald]
      • Hi Paul,
      what is the chance that you can send me the PCB layout you used... Will save me a lot of work... :)

      Have looked around and found a sweet double sided board, but my meager workshop does not cater for that...

      Nice job and hope to see some new goodies from you soon...

  • At 3 July 2013, 1:51:42 user Ron P wrote:   [reply @ Ron P]
      • Paul,

      Giorgos has done a fantastic tutorial on the PIC, well worth a read

      Failing that a google search on "pic16f628 configuration settings" will bring all you need.

      Ron P

  • At 1 July 2013, 18:19:49 user Paul wrote:   [reply @ Paul]
      • Hi Ron
      i was making this up on a mikroelektronika EasyPic4 Board..
      i have PicKit 3 if you think this is better..
      i am in need of configuration settings for the pic16f628 chip for programming..
      thank you for your time and patience
      much appreciated

  • At 1 July 2013, 15:22:12 user Ron P wrote:   [reply @ Ron P]
      • Hi Paul,

      I used the PICkit 2, v2.61 to program, (using a clone board)

      Hope this helps

      Ron

  • At 29 June 2013, 20:42:00 user Paul wrote:   [reply @ Paul]
      • i have made this up and i am having problems finding settings for programming options, i to am using pic16f628a version, i understand it's low voltage programming option with this..
      please let me know your programming settings, i really would like to finish this project..
      many thanks

  • At 11 October 2012, 8:53:17 user Zhong wrote:   [reply @ Zhong]
      • Hi Ron, I did try but zero cal button does not work ?

  • At 1 October 2012, 21:25:12 user steve wrote:   [reply @ steve]
      • What hardware did you use to program the chip? Ive tried a pic kit 2 and 3 and I'm not having any success :(

  • At 6 March 2012, 7:52:39 user Goce wrote:   [reply @ Goce]
      • I can check 10.000uf whit this esr meter? Thanks for the project :)

  • At 6 February 2012, 0:53:32 user Orides wrote:   [reply @ Orides]
      • Nice work!
      Can we use a 16F628A instead of the older 16F628?

  • At 24 January 2012, 15:01:29 user andee wrote:   [reply @ andee]
      • hex - http://www.romanblack.com/onesec/CapMeter.htm

  • At 23 January 2012, 18:47:14 user Pedro José wrote:   [reply @ Pedro José]
      • Hi, thank you for the project. Where are the hex files? I don't find it.

  • At 17 January 2012, 11:30:58 user Panagiotis wrote:   [reply @ Panagiotis]
      • Nice work Ron!!!! Thanks for sharing your project.Also nice work with the pcb exposure and the box you drilled...

  • At 15 January 2012, 8:51:17 user Kammenos wrote:   [reply @ Kammenos]
      • In your video, you measure 2 twisted wires. Those two twisted wires gave me a headache some time ago when i was experimenting with the capacitance touch buttons. I was using a 2-side PCB for sensor connected on the breadboard with 2 twisted wires... According to my calculations, the capacitance had to be very small, but in fact the PIC had a different opinion and measured almost double the expected capacitance. It was the stray capacitance of the 2 twisted wires :)



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