Intro to electronics: Making a capacitor

Watching other people build cool stuff made me want to get into hardware hacking.

I was most inspired by the following YouTube channels, to which I link some videos:

  • AvE - opens up a diaphragm pump (a very robust kind of pump), and explains how it works
  • bigclivedotcom - review of a "suicide shower" (electrically heated shower head)
  • EEVBlog - teardown of cheap Chinese Apple chargers
  • Practical Engineering - this guy built an automated Arduino solution that waters his plants
  • How To Mechatronics - many more awesome Arduino contraptions and tutorials
  • ElectroBOOM - guy knows how to show you what not to do
My favorite idea right now is the automated plant watering. I want to replicate this, so stay tuned for more.

I ordered an Arduino-compatible board and some electronic components yesterday, I expect them to arrive tomorrow.


I had found and ordered a multimeter 3 days ago; it's a "UNI-T UT139C" on Vexio, and it seems good. It arrived today. I found this "Vexio" site on Price.ro.
It was 190 RON including delivery; which might be a bit expensive for a hobbyist just starting up.

You can get cheaper ones, but do check reviews of them and their certifications first.

Input protection

If they're not certified for at least 240V household current (at least CAT II), don't use them for household current, only for low power applications (like signals from an Arduino).

I even opened mine to see the circuits:
The thick white fuses burn out when there's too much current (Ampere) flowing through them. These are ceramic types (opaque), and they likely have sand inside them, that absorbs the heat and prevents an explosion. If they were just glass ones, they would explode and possibly burn the PCB or even the user.

The red, green and blue bubbly bits are for voltage protection.

Red rectangle: 103J 100V (a capacitor)
Blue bubbles: CNR 07D681K (a MOV or metal-oxide varistor; strongly resists current after heating up)
Green bubbles: WMZ12A (varistor; works similar to the MOV)

In case you want more details, here is a video from EEVblog about multimeter input protection.

Look for the CE mark - "Conformité Européenne". If such a mark is present on a device, it is either compliant with EU legislation, or the manufacturer is lying :)

Measuring stuff

I want to get used to my multimeter; so I measured stuff:
  • voltage of some batteries I had
  • the resistance of various materials (hint: metal conducts, and paper doesn't; who knew!)
  • the continuity beeper (of which the response time is quite important)
  • the temperature sensor (wow! I didn't know many multimeters have temperature sensors also).
  • a Non-Contact Voltage sensor (which can sense the changing electromagnetic field of AC wires, even through walls! useful when you're tearing walls down)
I think it works great so far, but I wanted to try out some more stuff. Say, measuring capacitance.
But I don't have any capacitors anywhere. So I decided to build one, for fun.

Building a capacitor

By sandwiching together aluminium foil and cling wrap, you get two large-area conductors (the foil) separated by a very thin non-conductor (the wrap).
If you build up electrical charge between the foils, positive on one and negative on the other, then the capacitor can stay that way - since opposite charges attract, and they like it really close together. 

However, they can't touch, because the cling wrap insulates them. Touching them would mean discharging the capacitor (and let the charges mingle back together and even out to zero).

This is the diagram from the side:

Wrapping the aluminum:

Rolling up the capacitor:
Note: When rolling up the capacitor, you should constantly test that the two foils are still isolated (very useful to have a multimeter with a beeping continuity test).
The first time I did this, I didn't check, and found out that a sharp corner where I bent foil cut through in a tiny spot, and then the foils touched (they can't hold a charge in that case).

Just in case it was statically charged from making it, I decide to short it out (so that it doesn't discharge into my multimeter instead):

I squish it together, tighten it with a wire, then measure the capacitance across the two leads:

Voilà! We have 37.08 nanoFarads! 

If we could somehow coerce the capacitor to output 5 volts, we could give out 189nAs, or 52.5 pAh out of it!

If your phone has a battery of 2000mAh, then we could charge it a whopping 0.000000002625%!

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