This Instructable will show you how to make your very own short circuit tester, of course you can just use your own multimeter but, sometimes they're just too cumbersome to get into small solder joints.
Its small and is perfect for you electronics kit!
It uses a npn transistor with a 1 mega ohm resistor to allow current to flow from the coin cell to the led. This setup means you can use it in most electronics projects.
When electricity flows from the front two ports, it allows the higher voltage and current to flow from the CR2032 to the led of your choice.
Step 1: Materials
You will need:
An led (colour of your choice):
Npn transistor (I used the 2222a):
Cr2032 coin cell battery holder:
1 mega ohm resistor:
Wire port holder:
Step 2: Circuit Diagrams
As explained before, The Npn transistor allows no current to pass through unless a small current is passed through the base of the transistor.
As always the best way to start is by prototyping on a breadboard, it took me a while to get the position of the transistor right and to have the emitter and base and collector on the right polarity.
The base should connected to positive, the emitter to negative and the collector to positive.
Step 3: Assembling the Tester
First put the coin cell holder on the pcb. Then place a wire from the positive side, to the center of the board.
Put the transistor with the semi circle facing out wards next to the wire. solder them in place, then place an led, with the positive side facing the transistor solder the positive lead to the transistor and the negative side to the batter holder.
Then solder one lead of the 1 mega ohm resistor to the positive side of the battery holder, place the wire holder ontop of the other lead of the resistor. Solder them in place.
Bend the base lead of the transistor to the open pin on the wire holder, And solder in place.
And that's it!
Step 4: Finishing
Yours should be looking a bit like this when your done. I made two, the second one looks a bit neater then the first in my opinon, as I used less wire.
I trimmed the edges a bit, but I still mean to sand them down. My soldering was quite shabby but it held up well enough.
If you want you could surround the whole of the circuit in heat shrink tubing, but I didn't have any big enough.
Hope you liked my instructable!