[Viacheslav] built a keypad that uses human capacitance to detect key presses. Unlike normal keys which close a physical connection, his project detects touch through the PCB substrate. He uses the ADC capabilities of an AVR ATmega8 to measure a change in capacitor charges for each sensor in the keypad.
He’s posted the schematic, Eagle files, and source code with his writeup. He also points to a document on the theory behind this: QMatrix Technology White Paper (PDF). We’re impressed at how simple the circuit is: a microcontroller, capacitors, resistors, and a homemade PCB.

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[Michael] has a keypad in his previous car’s door and he missed it enough to hack one into his Dodge Caliber. He bought a Ford keypad and mounted it inside his door with some custom electronics. He started with an Arduino nano to receive and authenticate button presses. This then splices into wires in the door that control the door lock. The program has a 5-digit code to unlock the door, but simply pressing 1 twice will lock the doors. He also implemented a lockout feature to prevent people from brute-forcing the combination. Although it isn’t wireless, it’s significantly…

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Price: $2,094.00Ships: In stock. Usually ships the same business day. SAVE $100 via mail-in rebate*24-inch glossy widescreen display 3.06GHz Intel Core 2 Duo Processor 4GB (2×2GB) of 1066MHz DDR3 memory 1TB 7200-rpm SATA hard drive 8x slot-loading SuperDrive NVIDIA GeForce GT 130 with 512MB of GDDR3 memory Apple Keyboard with Numeric Keypad and Mighty Mouse

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