Whitebeard's Workshop: Arcade1Up Coin Door Lights

My Mortal Kombat II Deluxe cabinet in now Komplete with lit coin return plates (not functional buttons on this cabinet).

This is a really quick mod if you can use a soldering iron. I did this mod with my son and did not pause to take so many pictures.

Beginnings

I popped out the coin return faux buttons, replaced the coin door on the front panel, and marked points in the center.

The original idea was to drill holes the same radius as the LEDs in those spots. This worked really well. My standard LEDs pushed through to be stopped on the back side by a build in collar (the LED gets a little wider at the bottom), and were held securely.

Unfortunately, we were losing some light because the LEDs were too far back and blocked by being half embedded in the front panel. To resolve this we decided to counterbore (countersink) the LEDs by drilling a larger hole approximately half the depth such that the LED pushed farther out the front of the panel. This worked great. But when I drilled out the second hole, the drill caught and I ended up going all the way through. :(

And this is where a better design comes in. I drilled out the first hole completely to match the second.

LED Placement

Since my holes were now large enough to pass through an entire LED, I decided to use a piece of bass wood as a mounting plate for my LEDs and circuitry. I taped the plate inside the cabinet, marked the holes, then drilled two small holes for each of the LED leads and mounted them with hot glue.

The hot glue will allow the LEDs to protrude further through the front panel and illuminate the coin returns better. This setup was test fit back into the cabinet and worked great.

The Circuit

There are two basic power options inside the cabinet.

12 Volts can be obtained by splitting off from the DC power supply
5 Volt power can be grabbed directly from the PCBs USB port.

The original plan was to use the 12V power, but the simplicity and elegance of the USB connector option won me over. The Coin lights will turn on and off automatically with the PCB if the USB is used. To do this with the 12V power it would require splitting the power wire for the Marque, which are parts I do not have on hand.

For the USB, we just need to be sure not to draw a meaningful amount of power away from the PCB. Two LEDs should be no problem.

To right size the LEDs for power consumption, I tested various resistors to see what an acceptable light level would be versus power consumed.

I found that for the red LEDs I had on hand, a 1k Ohm resistor had a 3.14V drop across it, meaning that the circuit was pulling 3mA. And I will have two of these, so a single 6mA draw. This is very small.

Note: It is important to avoid the temptation to wire a single 500 Ohm resistor to power the two LEDs. Each LED is different due to manufacturing/lifetime variability and one LED will draw more current and wear out faster. It is best to provide separate resistors for each LED.

I cut the end off of an old USB cable, wired it up, and soldered it.

Final Installation

I used hot glue to attach the circuit to the board, and built up an attachment to the board for the connector cable which serves as strain relief. The strain relief protects the circuit in case the cable is pulled on.