Capacitor Measurement

[ronsimpson]

I have old Capacitor substitution boxes dating back 50 years. (20 years for the Heathkit boxes) Large capacitors 2 to 470 uf do not last many years. I replaces all the large capacitors in my HeathKit radio 10 years ago. I have some capacitor boxes where one decade failed because of a bad switch. “Anything below 100 pf returns 0, even with a 10meg discharge resistor.“

I think you should go to the store [DigiKey] and get some capacitors you know are good

[ronsimpson]

1)
I have used a NE555 IC + R + unknown Capacitor. The 555’s time is dependent on capacitor. The PIC measures time and drives a LCD display. A one-shot [multivibrator] converts capacitance to time. [74LS221]
2)
I built a C & L meter based off a kit. I measure well under 0.1pf.
http://my.integritynet.com.au/purdic...er-project.htm
It uses an oscillator and reference coil and two reference capacitors.
The oscillator oscillates at C1= 680pf and L1= 68uH or .01uf and 68uH.
An unknown capacitor is placed across the reference capacitor. If the unknown cap is 1pF then the frequency changes by square root (681/680). If the unknown cap is 1000pf then the new frequency is a product of 1680pf and 68uH.

The math is hell.
I measure the inductance of inches of wire or tiny ‘gimmick’ capacitors (1pf).

[Acetronics2]

http://www.electronics-diy.com/lc_meter.php

here ... soft available !!!

Alain