Kit Review – Seeedstudio Capacitance Meter

[Updated 17/01/2013]

This is the first of many (hopefully) reviews of electronics kits. In the past I have often wondered what a kit would be like, as they aren’t something you can look at in a store, apart from a box of components or a magazine review. Especially products that need to be imported from abroad. So now I’m going to do some legwork for you! Let’s begin…

Recently several retailers had been offering a capacitance meter kit which seemed too cheap, however looking at the specifications it was too good to pass up.

But on with the review. From placing the order on the web (paying with Paypal) to receiving the package took eleven working days. It was sent via registered airmail. Your time will vary wildly, depending on the time of year. For example, during Chinese New Year, nothing happens! Another benefit of using local retailers, no delay. Anyhow, thankfully the kit was packaged well with bubble wrap in a sturdy cardboard box.

After opening the box and attacking the bubble wrap I opened the package to check the parts against the list, and they were all there. The kit I received was a version 2.0, which would explain the part outlines and holes on the PCB but not in the list. There are also pads for external leads, and and holes for header pins if you wish to reprogram the microcontroller (but the pins were not included). The resistors were metal film 1% values, and the board was silk-screened and solder masked. However, an IC socket was not included… I feel this should have been – for the price this kit will attract many beginners who may overheat the microcontroller IC.

Also note that there is a plastic layer over the LED display, this took me by surprise as have not seen this happen on other displays in the past.

So it was time to get started. Being colourblind I measure all the resistors and place them in numerical order (from R1…Rx) on a breadboard to avoid mistakes. Then before soldering the overhead light, fume extractor and helping hands are moved into place to make life healthier and easier.

And using a magnifying glass is also very useful in spotting soldering mistakes and generally helping poor eyesight…

The layout of the components is screened on top of the PCB, so you can merrily go forth and solder. However, the polarity of the electrolytic capacitors is not shown clearly or mentioned in the instructions. After some detective work it turns out the positive pin of the electrolytics goes into the square pad. First I soldered in the hardware (switch, push button, DC socket), then the resistors, then the capacitors…

Then the crystal. semiconductors, ending with the microcontoller. As mentioned earlier, an IC socket should have been included to save a lot of people a lot of worry. Not everyone has steady hands or a good sense of timing! The extra ten cents wouldn’t have hurt the retail price. Anyhow…

I plug in my 9V DC plugpack, turn it on … and it worked first time! Woohoo. Note that due to the use of an LM78L05 voltage regulator, the meter runs on around 8 to 16 volts DC, using less than 100mA current. Watching the display was almost mesmerising, there’s nothing like that feeling of assembling something and seeing it work.

But did it really work? Let’s see… where are my capacitors?

The specifications state it can measure between 1 picofarad and 500 microfarads. The manual states that for better accuracy with measuring small values to enclose the meter in a metal box and attached the ground to the box. No time for that! Made do with four 20mm spacers to raise it from the desk. The specs state it is accurate to less than 2%. The user also needs to take note that the capacitor tolerance levels can vary, especially with electrolytics. Always try and check the manufacturer’s data sheet if possible. Supplier websites such as element14, Digikey and Mouser can be useful for that purpose.

So, first of all I tried a 0.1uF greencap, and it measured 99.3 nanofarads. Not a bad start. Always remember to press the ‘zero’ button before each measurement.

Next a 0.01 uF greencap, returning 10.2~10.3 nF. Fair enough.

Then a 330 picofarad ceramic. Just to note at this point, one should clean the component leads before measuring, dirty leads will affect the value measured. Furthermore, short the capactor by crossing the leads over to discharge it completely. Anyway, that 330 pF returned 319 pF

How low can we go? Let’s try a 1.5 pF…

At this level, the metal shielding would be a good idea. The meter returned a floating reading 1.4~2.1 pF. Finally, an electrolytic. 330 uF.

Which returned 343 uF. Not bad considering the tolerance of electrolytics can vary, at the minimum they can be +/-10%.

Now let’s see it action! The first capacitor tested is a 4.7uF electrolytic, the second a 1.5 pF ceramic. There is no audio in this clip.

So there you have it. For less than twenty US dollars you can have a decent capacitor meter that is easy to construct, quite sturdy, and very useful for the electronics enthusiast. This kit is available from Seeedstudio, Sparkfun and others.

[Note - this kit was purchased by myself personally and reviewed without notifying the manufacturer or retailer]

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