If you live in an area where golf carts are used to get around like Youtuber “ramicaza,” you might consider carrying a key around for your golf cart a hassle. I suppose one could simply install a switch instead of the key to start the vehicle up, but if you would like some semblance of security, you could hook up a finger print scanner as shown in the video below.
This biometric scanner, a “GT-511C1″ model from Sparkfun, is controlled by an ATTiny85 microcontroller (here’s the sketch). This simple controller then uses a relay to allow power to flow from the cart’s main battery to the motor. Additionally, it powers two LED lights, “green” for on, and “red” (or possibly orange), for off. In order to preserve the cart’s battery, when the nicely implemented plastic cover is pushed down, the whole circuit is turned “off. Cleverly, the circuit is designed that if the cover is pushed down with the power on, the circuit remains active. Someone with a registered thumb has to actually turn it off.
The implementation of this device is nicely done, and actually isn’t that noticeable. Unlike many creations where most of the fun is in building it, I could see this being quite useful!