As the direct result of a question in the Instructables forum, for a bargraph to display data on the dashboard of a car, a custom electronics instructable.
Here, for your delectation is the Car-barDuino, a simple display system for analog and digital stuff, for a car, for a timer, for a thermometer, for whatever. I built it for a manifold pressure meter for friends car, I'm going to use it at work for some monitors in a research instrument.
Under the hood, it uses a micro configured to run "Arduino" sketches, so anyone can play with the code. All the spare I/O has been brought out to connectors to play with.
In its current form, we can drive 2, 7 segment displays and a 30 element bargraph. We can mix LEDs from red/green/yellow, but it can't drive white or blue. If there was enough interest, I'd redo the design to allow higher voltage LED technology to be used. The current design is open ended, since each MAX7221 can be connected to the next over just 5 wires, and each can drive 64 LEDs at once.
There are 15 levels of digital control of LED brightness, and a SINGLE resistor to set the maximum brightness of all of the LEDs on one chip.
The processor can be any standard Arduino (Atmega 168 or 328) and with the ICSP connector, you can burn your own bootloaders.
The input interface uses a simple current limiting resistor and two diode clamps to the 5V rail. DON'T make a habit of driving into the clamps !
There are no input scaling resistors on the circuit at the moment.