If you are interested about parking radars, or any short range distance or object sensing, this is the right project for you. The author uses the SRF04 sonic module for ultrasound generation and reception, the controller used is ATmega128, but probably a smaller one would also do the job. The device is nothing less nothing more then a radar system, measures the time between the sent sound wave and the reflection, then calculates the distance.
Is is easy to extend this project to a parking radar for your car, not to mention the great potential it has in robotics. The schematics, source code is available for download.
Sonic distance measurement: [Link]
This is the most advanced DIY metering device I have seen on the web with open source hardware and software, it has two 0-10VDC range and one auto range 0-30VDC voltmeter, one channel 0-3A high side amp meter, four channel logic analyzer, pulse/sine/triangle waveform generator and frequency counter, it has a simple PC interface, which makes all the functions easily accessible. Did I mentioned that even the PC software is open source?
Be aware though that isn’t a hand held multimeter, it doesn’t have any protection for over voltage, and it is connected to your PC the trough the serial port, so be careful not to fry your computer, I recommend this instruments to people who work with micro controllers, or low voltage electronics powered trough a power supply which has a transformer, this way you and your computer are on the safe side of the wall outlet.
AVR bench instrument: [Link]