using the prop chip to measure capacitors

mikediv

Guys I tried to search for this I remember a while back some had built a circuit using a prop chip to measure capacitors? I bought a bag of misc capacitors 500 to be exact they are all disk caps of different values I do not have a capacitor meter but was hoping
a simple circuit using the prop chip was available. I found "PE Kit Tools - Measure Resistance and Capacitance v0.92" But its not quite what I had in mind. I was hoping a simple meter could be built out of the prop and a serial LCD display
if anyone remembers where that project was or if you have something similar you can share please let me know Thank you.

localroger

It should be straightforward; basically you use an output ground the cap long enough to ensure it's discharged, then charge it through a resistor until the voltage reaches the 1.6V threshold of another input pin, measuring the time it takes with WAITPEQ. Basic RC formula then gives you C. But the R you use depends on C, and Spin might not be fast enough for very small caps. If you have some known caps to use for comparison, you can get the basic scale established by trial and error even if you're not sure of the unknowns.

Beau Schwabe

Here is a balance detection method that's a derivitive of a wheatstone bridge circuit. It works best when the input 'excite' signal is a sine wave, but it will also work when it is a square wave, triangle wave, etc.

You could setup a similar circuit using two RCTIME circuits and comparing the returned value to a known capacitor verses an unknown capacitor, however the advantage of the circuit below compared to an RCTIME circuit is that the value of the resistors used aren't as critical as the ratio of the resistors used, making a digital POT an ideal candidate.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Leon

Another technique that is often used is to measure the frequency of an LC oscillator built with known values of L and C, place the DUT in parallel with the LC circuit and measure the change in frequency. The value of the DUT can then be calculated. This LC meter (rejoicing in the name of ELSIE) uses this method:

www.amqrp.org/kits/elsie/

I designed a PCB for it and built my own version.

A Propeller could be substituted for the AVR, of course.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Carl Hayes

They aren't marked? Unusual.

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· -- Carl, nn5i@arrl.net

agfa

Thanks for that link Leon.· I had never·heard of·a "Manhattan-style" circuit board before.

agfa

Leon

Radio amateurs have been using them for over 30 years. I prefer to make a PCB, or I use something called "ugly" construction with the chips and other parts mounted directly on a piece of PCB material.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

mikediv

Great stuff guys thank you .. Beau funny you mentioned the digital pot I was trying to put somehting together with the AD5220 10K chip . The prop PE Tool Kit has a real good program but you have to build the circuit every time you want to figure out a cap value I wanted to try and streamline it so you could just connect the unknown cap to 2 leads like on a regular meter so while I Was looking at the circuit I Was thinking I could use the digital pot . my programing skills are very weak but I am learning.