Electronic Edge Finder

[mr_modify1]

I use this mostly on my mill. It was cheaper to make than buy.

[Don42]

An LED driven by a 12-volt battery definitely requires a resistor if you want it to last. Most 5mm LEDs are quite happy running at 20 mA. A typical 5mm white LED has a voltage drop of 3.6 volts at 20mA, which indicates a resistor of 420 ohms. 430 ohms is a standard value. 470 would work fine too. Other colors have different voltages but 470 ohms would work OK with any of them.
A good source for LEDs is
https://www.ledsupply.com/5mm-leds
Good selection, reasonable small-quantity pricing, free first-class shipping.

[DIYer]

Thanks mr_modify1! We've added your Electronic Edge Finder to our Electronics category,
as well as to your builder page: mr_modify1's Homemade Tools. Your receipt:

Electronic Edge Finder by mr_modify1

tags: LED, edge finder

[mr_modify1]

Thanks for the info. I know enough about electronics just to get in trouble.