One of the many workshop tasks that I cover with my students at Unitec during their Electrics course is to make their own Logic Probe. Sure, many already have test lights which, as many of you know, can be used to perform many initial diagnostic tests on a vehicle's electrical system. A Logic Probe is, I suppose, the next step & is extremely useful, and as it uses LED lights it's amperage draw is very very low making it ideal for testing ignition and fuel injection circuits.
Their construction is simple enough as there are few components, though it's easy to make mistakes on the assembly. This video covers the complete process of making your own Logic Probe, from the components needed, step by step construction, helpful hints along the way and of course, the testing and operation of the finished probe.
The cost of the making the tool is very low and all of the components are readily available from your local electronics store. The extra benefit of making your own is that, if it stops working you'll know exactly how to fix it too!
So, all you'll need to make this Logic Probe is:
A Brass rod 2.4mm diameter (approx) 150mm long
Red LED
Green LED
Length of BLACK and RED wire - min 1 meter but 2 meters is better
2x 1,000 ohm resistors
Red & Black alligator clips (insulated type is best)
Plastic tube with 7mm I.D.
Shrink tubing 2.4mm diameter - 300mm long
Shrink tubing 6.4mm diameter -175mm long
Shrink tubing 12.7mm diameter - 125mm long
Solder - flux core type
Emery cloth or sand paper
You'll also need a few standard workshop tools for the construction, a soldering iron, side cutters, long nose pliers and a mini heat gun or lighter to heat the shrink tubing.
If you have any questions just add them to the comments below...
Andy Mechanic