Wednesday, 27 November 2013
The basis for the control was an Arduino Uno with an Adafruit RFID Shield. Some of the pins were pulled out to some right angled header on the end for power and control to a servo. A MOS-FET was added to switch the servo power on and off as needed under control from a digital pin.
The servo is a Tower Pro with a max rating of 6 volts. Powered at 5 volts it is working hard and drawing quite a bit of current, so the board has to be powered through the USB port. If you try an external source, the current draw overloads the regulator on the Arduino and it resets.
The frame is from a tomato can and mounts between the latch knob and the door. The knob is a spare that I drilled a couple of holes in, leaving the original safe in the closet, and the actuation is with nylon blind cord.
The code gets the servo to back off and take a run at the actuation, then slack the cord after it's done. By turning the servo power off between actuations we save electricity and make it easy to operate the lock by hand or with an old fashioned mechanical key.
Owen helped me make the video by swiping cards while I tried to hold the camera steady.