How-To: Finger-Gesture Lock Box

Want to ditch that combination lock and bring your lock box into the 21st century? California-based best selling tech author Gordon McComb shows us how to pair an optical finger navigation (OFN) module with an Arduino and a small motor to create a lock box that reads your finger gestures across a small optical window, opening only to a combination you create. You can build your own by checking out Gordon’s how-to, which originally appeared on the pages of MAKE Volume 32.

In the intro, Gordon writes:

The OFN sensor works much like an optical mouse, except it’s intended to be used in direct contact with your finger. They are used in handheld devices where a trackpad would be too large, but because they are more expensive than trackballs, they’re not common in consumer products. Movement across the small surface of the sensor is converted to X and Y distance measurements — up, down, left, and right. Sequences of these movements make up the combination of the lock.

For this project I’m using the Parallax OFN module, which puts a commercial OFN sensor on a breakout board that provides connectors for power (3.3V to 5V), ground, and 6 signal lines. The OFN module uses 2-wire I2C to communicate with a microcontroller, and has additional I/O pins for such things as the momentary pushbutton switch that engages when you push the optical sensor down.

The locking mechanism uses a standard-size R/C servomotor that’s glued into the bottom of the box. To lock the box, the turning servo engages a metal arm attached inside the box’s lid. Turning the other way, it frees the bar, letting you open the lid.

An Arduino microcontroller works as the main brain of the lock box, handling all the communications with the OFN module, controlling the servo, and even making musical tones on a small piezo speaker.

For my box, I used a plain 8″ square cigar box from a craft store — no need to smoke a bunch of stogies. The wood is unfinished; stain or paint to suit. You don’t get Fort Knox with these boxes, but they’ll keep out the casual thief.