Logic probe

We have self-constructed a logic probe using:
1x Red L.E.D
1xGREEN L.E.D
1x Black wire(2 meters in length)
1x Red wire(2 meters in length)
2x 1K resistors
1x Red alligator clip
1x Black alligator clip
1x 100mm plastic 7mm diameter
Shrink tubing
1x Black 2.4mm diameter 300mm long
1x Red 6.4mm diameter 175mm long
1x Black 12.7mm diameter 125mm long
1x Brass rod 150mm long

Construction:
1st we soldered the 1K resistors and wires together then we soldered the L.E.D's to the resistors of the positive and earth wires respectively.
Next we put the heat shrink over both the wires up to the L.E.D's and proceeded to use the heat gun to shrink the material around the wires.
Next we have to solder the L.E.D's to the brass rod, then we machine the end of the brass rod to a pen like tip.
After that we put heat shrinks over both ends of the brass rod leaving the pen like tip exposed and L.E.D's visible and apply the heat gun.
next we cut a groove out of the plastoc tube approx 5-10mm long and then we put the plastic tube over both wires and position it just behind the L.E.D's then put a large heat shrink over the plastic tube and then apply the heat gun proceed to do the same to the other end still leaving the pen like tip exposed.
Next we solder the alligator clips to the respective wires for positive and earth wires.

To Test:
Attach to a power supply no more than 24v DC
Then touch against positive and negative terminal, the red L.E.D should light up on the positive terminal and the green L.E.D should light up on the earth wire.

The Logic Probe uses a series circuit with 2 one way diodes one allowing flow to the positive and the other allowing flow to the earth