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Key Light Project

Key Light Project

This is a VW Passat Key. It used to have a 1.5V incandescent bulb which could be used to illuminate the keyhole on the car. This bulb burnt out, and I wanted to replace it with a super bright LED.
Unfortunately, I couldn't find a 3mm super bright LED which operated at or under 1.5V, which was a problem, as the battery is integrated into the switch mechanism in such a way that replacing it with a 3V battery would be very difficult.
The lowest voltage LED I could find required at least 2.1V.

Luckily, Linear Technologies makes a small chip called a "Charge Pump" which will boost 1.5V up to 3.3V with the help of a few external capacitors.

All I had to do was figure out how to fit the circuit (and the LED & Battery) inside of the key...

Time to use surface mount (SMT) components!

After Tinning the pads...

...it's easy to build 3D circuits with SMT components...

..especially if you have a few helping hands.

The finished circuit. Technically I'm supposed to use a resistor between V+ and the LED to limit the current to the LED to keep it from burning out, but as this is a momentary pushbutton light, and engineers always give you plenty of extra tolerances, I just drive the LED at the maximum output of the charge pump for extra light.

The LED has been attached. Note the power "leads" that interface with the battery/switch mechanism.

After testing and final fitting, epoxy is used to hold the circuit in place. Note the added yellow positive wire to the LED. (click image for details)

The finished product. Total Cost: 1.00 for the LED, 2.30 for the charge pump, 3.29 for the capacitors, 350 billable time for the work, total of $356.59


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