Brad took my idea of a haptic blindspot sensor for the car and started to run with it a couple of weeks ago. Using an Arduino Duemilanove controller board, an ultrasonic sensor with a 3m range, and a little variable speed motor, we were able to prove that we had enough hardware on hand to put together a prototype.
Last night, Brad and I spent about 5 hours working on the first prototype. Brad wired up a car lighter adapter to power the thing. We used 4 wire telephone cable and audio jacks to modularize the 3 parts (sensor, controller/power, and motor). Some parts weren't pretty. (There's probably a better way of cutting the prototype boxes than using a Dremel.) However, we persevered and got something built.
This morning I went by Walmart and found a massaging lumbar support with 3 massage points for about $20. I ripped out one of their motors, put our motor in the housing, and tested. Everything worked.
After that, it was a simple matter of mounting the sensor to under the left rear bumper using some double sided tape. I was able to run the cable behind the bumper. My car happens to have an electrical housing that goes out through the spare tire well. I was able to plug in to an outlet in my cargo space. Everything sits in one of the floor storage compartments.
Now for the first drive!