MCU Based Capacitance Meter Project

[MCU88]

I am interested in doing an MCU Based Capacitance Meter Project...

Requirements:

• Measures capacitors from 1pF to 10,000uF (accuracy +/- 1pF)
• Implements an cheap 8-bit PIC micro (Mikro C Firmware)
• Readout on 4-digit 7-segment LED displays multiplexed

Have you done an similar project, and / or what are your suggestions of an tangible schema?

 

[JimB]

While not completely meeting your requirements, this may give you a good start:

https://www.romanblack.com/onesec/CapMeter.htm

JimB

 

[ronsimpson]

What JimB said. and this topic comes up often.
Search the forum there are many threads on this subject.

 

[blueroomelectronics]

Take a look at the MK168 component tester. They sell for under $20 online.

 

[alec_t]

Do you really need ±1pF accuracy when measuring 10,000uF? That's not going to happen, IMO. Besides, electrolytic caps of that capacity have huge tolerances and their capacitance varies with time and temperature.

 

[Nigel Goodwin]

Do you really need ±1pF accuracy when measuring 10,000uF? That's not going to happen, IMO.

That's not an 'opinion', it's a statement of fact

The reading down to 1pF at all is a bit unlikely (and pretty pointless) as well.

 

[KeepItSimpleStupid]

Note that 1 pf +-1 pf really isn't "accurate" to 1 pf.

 

[MCU88]

While not completely meeting your requirements, this may give you a good start:

https://www.romanblack.com/onesec/CapMeter.htm

JimB

That's an excellent read mate. I notice that in the pF range accuracy is stipulated as being +/- 0.02pF

 

[MCU88]

Do you really need ±1pF accuracy when measuring 10,000uF? That's not going to happen, IMO. Besides, electrolytic caps of that capacity have huge tolerances and their capacitance varies with time and temperature.

Not 1pF accuracy in the uF range measuring 10,000uF. There would obviously be an range switch or auto ranging in the firmware to flick between pF, nF and uF.

 

[dr pepper]

I built this one, its excellent and only uses a pic and a few passives:

https://sites.google.com/site/vk3bhr/home/index2-html

It'll read down to 0.1pf, no idea on the accuracy, mines made from junk parts and is still wya more accurate than I need.

 

[MCU88]

I built this one, its excellent and only uses a pic and a few passives:

https://sites.google.com/site/vk3bhr/home/index2-html

It'll read down to 0.1pf, no idea on the accuracy, mines made from junk parts and is still wya more accurate than I need.

Yeah real nice top stuff. I have noticed that most of them don't do the high value electrolytic caps though. A few 100uF seems to be the upper limit. Inclined to engineer something that measures all the way up to 9,999uF... Don't think I'll be bothered posting it on the Internet though. There are so many of them. Like every man and his dog with PIC skills has done an capacitance meter or two. Perhaps I'll keep the design to myself and sell kits in an 'real world' hobby electronics shop... Interested in making money. The thrill of attention and compliments from posting stuff on the Internet has worn off. If I can do an kit that retails for $39.95 and I make 30-dollars profit then this will satisfy me more.

Easy greasy.

 

[dr pepper]

I've never asked him, but I dont think my dog has built a capacitance meter.

 

[BobW]

I built this one, its excellent and only uses a pic and a few passives:
https://sites.google.com/site/vk3bhr/home/index2-html
It'll read down to 0.1pf, no idea on the accuracy, mines made from junk parts and is still wya more accurate than I need.

I built that one as well, and I concur that it works very well. As MCU88 mentioned, this one doesn't do the high value capacitors though. It's really intended for the range of component values used in RF circuits which is the reason why I built one. Its real claim to fame is that it's the best inductance meter you'll get for the cost. For measuring high value capacitors, I use the capacitance range on my multimeter. It would be nice to have everything in one meter though.

 

[ronsimpson]

The method for measuring 1pF is different than measuring 1000uF. (at least in my head)
The very small capacitors are measured by making a oscillator and measuring the frequency.
Above 100pF you can use a current source and measure the time for the cap to charge from 0 to 1 volt. Using a very small amount of current at 100pF and a large amount of current at 1000uF.
The big ele. caps. have leakage so the oscillator will not work and the current source needs to be large to fight against the leakage current.

 

[Nigel Goodwin]

Its real claim to fame is that it's the best inductance meter you'll get for the cost.

How about this one - which I bought!

**broken link removed**

Supposedly very accurate, and an incredibly large range.

 

[BobW]

My cost was about $10 for all the parts (labour was free). So, I'll stand by my claim.
Seriously though, the Banggood one looks pretty good.

 

[Nigel Goodwin]

My cost was about $10 for all the parts (labour was free). So, I'll stand by my claim.
Seriously though, the Banggood one looks pretty good.

I didn't even want one - but it was too good to pass up

 

[blueroomelectronics]

It's a great little device and kit from Banggood.

 

[MCU88]

The method for measuring 1pF is different than measuring 1000uF. (at least in my head)
The very small capacitors are measured by making a oscillator and measuring the frequency.
Above 100pF you can use a current source and measure the time for the cap to charge from 0 to 1 volt. Using a very small amount of current at 100pF and a large amount of current at 1000uF.
The big ele. caps. have leakage so the oscillator will not work and the current source needs to be large to fight against the leakage current.

I built a rather large capacitance meter KIT using discrete components back in the 90s. It used the very hard to get now 74HC945 display driver to drive 4 digits (7-segment displays) It used an NE555 for the oscillator (it was a matter of converting frequency into capacitance) -- it had 3 ranges. pF. nF & uF selectable using an rotary switch. It measured from 1pF to 9,999uF. It served me well for years. I used to be KIT cRaZy I built hundreds of KITs back in the 90s.

 

[MCU88]

I've never asked him, but I dont think my dog has built a capacitance meter.

Australian saying.