This is a very simple but useful LED tester that lets you test, compare and check the colour of just about any two pin LED.
To make it you will need the following:-
A PP3 battery connector.
A 470 ohm resistor.
A bit of heat-shrink sleeving to cover the resistor.
A two pin Molex style 0.1" (2.54mm) pitch miniature socket.
Two contacts for the socket.
A PP3 9V battery. Alkaline preferred.
And some LEDs to play with.
Step 1: The battery connector.
The main part of this instructable is a cheap and common PP3 battery connector used to connect to the small rectangular 9V batteries.
Step 2: Adding a resistor.
The tester needs a resistor to limit the current through the LED. I generally use a 470 ohm resistor which has the colour code:-
Yellow, Violet, Brown and gold. (For a standard four band resistor.)
To put the resistor in line the red lead is cut about 2" (50mm) from the end and the wire stripped, the resistor soldered in and a piece of heat-shrink tubing shrunk over the resistor and solder connections to protect them.
The three steps are shown in the image.
Step 3: The LED socket.
This project uses an ordinary two pin Molex style socket to connect to the LED. To use the socket you need to crimp or solder wires to the contacts before they are pressed into an empty socket shell. The crimping tool for these contacts is quite expensive, so you may find it cheaper to just solder the wires to the contacts as shown.
Since the red lead may be slightly longer with the inline resistor, it's may be a good idea to trim the red and black leads down to the same length.
The easiest way to solder these contacts is to tin both the contact and wire with a touch of solder and then touch them both together and reflow the solder with your soldering iron.
Step 4: Assembling the socket.
Once both the contacts have been soldered to the wires they are pushed into the housing so that their little latches click into place in the matching slots in the socket.
Step 5: The finishing touches.
To make polarity identification easier it's useful to use a red and black marker pen to mark the front of the socket as shown. Give the two wires a quick twist for neatness and snap your new tester onto a PP3 battery and you now have an LED tester that will test your LEDs with about 10 to 15mA when their leads are pushed into the socket.
Makes a useful little emergency flashlight too.