|
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 |