This simple board allows you to neatly and painlessly install LEDs on top of a rotary encoder for use with transparent/translucent knobs.
I designed this board when building a MIDIbox SID synthesizer based on the MB6582 design. The idea was inspired by Hawkeye's control surface build tutorial for the MB6582, but I didn't think I'd personally be able to do a very neat job with enamel wire, and so I decided to design a simple PCB to make it easier to achieve this kind of lighting.
The PCB has been verified to fit perfectly over Alpha Taiwan RE160F-40E3-20A-24P-003 and Bourns PEC16-4220F-N0024.
- I have several spare sets available to anyone who wants them - contact me on Twitter if you'd like to buy some!
- I've also added the PCB to OSH Park as a shared project if you'd like to order from there.
- Alternatively, you can download this repository and place your own order with a PCB fab service.
The PCB has space for three surface-mount LEDs and one resistor. The size of all parts is 0603 imperial (1608 metric).
There are multiple + (positive) terminals that you can use to daisy-chain multiple PCBs together if you need to.
The three LEDs are wired in series, and share a common resistor (R1). The proper value for R1 will vary depending on the specifications of your LED and the voltage of your power source.
If your LEDs have a low enough voltage drop, you may be able to just bridge R1 (or use a 0 ohm resistor) and use a 5V power source. The amber LEDs I used did not light up at all this way however, and so I chose to use a 9V source instead.
You can use a simple LED calculator to help choose the right value for R1. In my case, using the datasheet for my amber LEDs I entered the following information into the calculator:
- Source voltage: 9V
- Diode forward voltage: 2V
- Diode forward current (mA): 20mA
- Number of LEDs in your array: 3
The result was 150 ohms, and so that's the value I used for R1.
- Solder a wire to one or more of the + (positive) terminal of the PCB. If space is limited above the encoder, it's recommended to solder the wire from the back of the board.
- Take a small piece of rigid wire (the excess leads cut off from through-hole resistors or LEDs are ideal for this), and solder it to the ground terminal of your rotary encoder.
- Bend a small "knee" in the wire so that it is fairly close to the "tongue" sticking out of the encoder, but not touching (see photo).
- Place two small strips of adhesive foam on the front and back of the encoder (see photo). I recommend 3M PE foam tape for this - it's very strong and thick enough to prevent shorts.
- Place the PCB down over the encoder, ensuring the wire you soldered goes through the - (negative) hole.
- Push down on the PCB to ensure it sticks nicely and then solder the negative wire.
- Cut off the excess wire with a pair of wire cutters.
- Make sure there are no shorts between the metal chassis of your encoders and any of the wires you have attached.
- Repeat as necessary, daisy chaining the PCBs together via the + (positive) terminals. The result should look like the photos below.
Note: In the last photo above, the wires are shown above the PCBs. This was a mistake, as when test-fitting the metal front panel, there wasn't quite enough clearance, and so I moved them below the PCBs instead. I recommend you do the same.