I didn’t really like the yellowish backlight on my VHF/UHF SWR Meter so I opened it up and grabbed a blue LED to replace it with. I added a small toggle switch as well so I can power the backlight off without having to unplug the power from the back.

It had 12volts already coming in from a power supply so I had to find the right resistor to use on the LED. It is a basic formula:

To calculate the resistor needed for a simple LED circuit, simply take the voltage drop away from the source voltage then use Ohm’s Law.

- Es is the source voltage, measured in volts (V)
- Eled is the voltage drop across the LED, measured in volts (V)
- Iled is the current through the LED, measured in Amperes (Amps/A)
- R is the resistance, measured in Ohms (Ω)

so.. R=(Es – Eled) / iled

If you don’t want to bother with that you can go HERE

I needed a 560 Ohm resistor to make my LED work on 12volts

I just like the blue backlight!

Wish I had a little smaller switch to use but it gets the job done.

-KG7FDJ