Onboard Arduino and XBee

The "Arduino" that I'm using in this project is actually an arduino-compatible Really Bare Bones Board (RBBB). This was both cheaper and more appropriate for this project, because I would rather plug it into a regular breadboard to have more pins available. Luckily a breadboard I had already happened to have fit quite neatly into the car!

Since the control would be in the car, I had no use for the hacked handheld controller any more. I had to hack the car's receiver end instead and figure out how I could drive it. It had a number of transistors which appeared to form two variations of an H-bridge, one for the forward/reverse motor, one for steering. It also had a small PCB offshoot which probably did the signal processing. It connected to the main PCB with a number of pins. I made use of an oscilloscope which had been recently loaned to the hackerspace, and mapped out the pins as follows:

If we make the top left pin 1 and the top right 18 (going down and back up the other side), then pins 1, 3, 4 and 10 are of interest. All I have to do is send a 5V signal from the arduino to drive the car that way. You also need to connect up the ground to make them common (or the 5V signal won't be registered). Also, being a H-bridge, you must be careful not to send both forward and reverse signals at once, which shortcircuits around the motor and causes "shoot-through", driving all the current straight to ground and possibly damaging or burning out components.

Unfortunately I didn't get a photo of the car's hacked circuit board before I closed it up to test it, but here are some photos of the mounted wireless circuit. Hmm... these seem to be mirrored. Stupid mac camera software. 

Controller mounted to car body and secured with electrical tape. That's the Xbee module sticking out the side.