We developed a six-digit cipher lock for a museum kiosk where the visitors needed to enter a six-digit number, which they calculated, and if correct it would release a magnetic lock.  The device can use most 12-button multiplexed button pads.  The cipher can easily be placed into non-volatile memory by the user.  They simply input the correct number and press a small button on the component side of the PCB to save it.  The relay output can handle up to 30vdc at 2.0 amps.   Other features can be customized into the firmware.  For instance, in this case, we gave the visitors a hint when their input guess was wrong by appropriately flashing “—HI—“ or “— LO—“ briefly on the display upon evaluating a wrong answer.

This display provides not only numeric input but also the ability to clear the display (zero it out) and a button (”E”) to press when they are ready for an evaluation of their number.  The display digits are 5/8″ tall and are multiplexed to reduce current draw.  The display scrolls if more than six digits are input:  it dumps the most significant digit to make room for the last digit entered which is the least significant digit.

The power supply requirement for the cipher electronics is 12vdc at 500ma and does not include power for the locking mechanism.

The solder side and component of the PCB is shown below.

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Click on this link to download flier on this device: Six Digit Cipher Lock