A few months ago a friend of mine -car mechanical at profession- told me that he had problem with some car sensors. He couldn't check, with a simple multimeter, if a sensor was working properly. I advised him to buy a LCD oscilloscope instead of a normal oscilloscope, because of its small size. The use of an oscilloscope is very helpful because you can see the waveform that is produced by a "healthy" in-circuit-sensor* and you can compare it with the waveform of a "suspect" in-circuit-sensor.
After that, he told me that this oscilloscope costs a "fortune" for him as he has a small car service shop. I offered to help him by designing and constructing a small, cheap and workable LCD oscilloscope for him.
*in-circuit-sensor is the sensor which is connected on a board (PCB) or it's connected somewhere in the car. It's not a disconnected sensor.
You can download the source code, hex, schematic diagram,PCB and picture of the circuit .