Project to change the backlighting on a car radio to use blue LEDs. I orginally wrote and posted this on my blog and can be found at:
The radio is the Delco AM/FM/CD model that appeared in many GM models anywhere from 1996 - 2002. The buttons and labels on the faceplate are backlit with a number of 12V incandescent bulbs. I initially set out to do a direct replacement of the bulb on the circuit board. In the end, the implementation was a little different. Due to the space constraints, right away I knew I would need to find an LED with an integrated resistor. They do exist, but they are quite expensive and I could not find any in blue. So at this point the best thing to do was to remove the incandescent bulbs and glue the LEDs into the faceplate, creating wire leads to solder to the circuit board.
Step 1: Disassembly
For this particular radio, the faceplate essentially snaps on to the front of the body. A flat screwdriver easily pries it off. Four screws remove the bottom of the body that exposes the two connectors that interface to the faceplate. Those easily disconnect and the new faceplate can be removed. Additional hex screws attached the circuit board to the faceplate. Remove these, and the front of the circuit board is now exposed. The incandescent bulbs are removed very quickly and easily with some solder wick.
The first image shows the front of the circuit board. The second image is the back of the faceplate where the circuit board connects to.
Step 2: LED Placement
The next step is to group the LEDs. Based on the specifications of the LEDs you can wire them in series with a single resistor. In my situation, I could only put them in groups of three. You can find a website to help you calculate the resistor value. (http://ourworld.compuserve.com/homepages/Bill_Bowden/led.htm) Obviously use 12V as the total voltage. Also, I didn't max out the current on the LEDs. Theoretically they will last longer and I really didn't need them to be THAT bright.
I installed the LEDs in the faceplate, routing the wires as tightly as possible and keeping the power and ground wires together. The faceplate is a very tight fit to the circuit board so routing the wires efficiently is very important. A single pair of wires connects the power and ground to the circuit board in the place where one of the incandescent bulbs was. The picture is showing the LED grouping and placement. Much more work was done later to get the wires routed tightly. The blue LEDs and wires were glued in using some silcone glue.
Step 3: Installation
Installing the modified faceplate was easy after I got all the wire routing issues resolved. It's important to make sure all of the faceplate buttons are able to make contact with the actual switches on the circuit board. Do this before you put it all back together. :)
I've got more pictures and details on my site at:
I also have info on how I added a blinking security light.