Car Courtesy Light

  
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A car courtesy light in a standard car without a board computer is often a very simple thing: you open the door, the interior light is switched on, you close the door, the light is switched off. For convenience, it is very nice to have the light switched on a little longer after the door is closed, for instance to find your keys and start the engi
Car Courtesy Light - schematic

ne. There are many car courtesy light schematics and ready-to-use devices around on the internet, but this one has a few interesting properties that I could not find on any of them, and that I really wanted. That`s why I decided to build it myself. This circuit is based around the PIC18F2550 microcontroller. This chip is actually a small computer contained in a single chip, including RAM memory, EEPROM, I/O ports, CPU and so on. When you buy this chip, it comes empty with no program on it. You have to compile the source code and download the resulting machine code into it, using a PC and a small programmer attached to the PC and the chip. To get yourself familiar with this stuff, I suggest you first read this link: Getting started with microcontrollers. Using a microcontroller to design a car courtesy light extender/dimmer might look like overkill at first glance. A simple 555 timer or a few transistors/resistors/capacitors also might do the job, but considering the characteristics I wanted the device to have, a microcontroller really ended up to be the way to go. - Absolutely no change needed on the existing wiring, no need to interrupt the wire from door-switch to the light bulb or from +12V to light bulb. In fact, this device use only a one-wire interface to the existing car courtesy light (plus 2 wires for power) - Possibility to immediately switch off the light when an event takes place, for instance when the alarm...



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