Project - Simple Electronic Lock

There are six (or more) push switches. To 'unlock' you must press all the correct ones at the same time, but not press any of the cancel switches. Pressing just one cancel switch will prevent the circuit unlocking. When the circuit unlocks it actually just turns on an LED for about one second, but it is intended to be adapted to turn on a relay which could be used to switch on another circuit.

Please note: this circuit just turns on an LED for about one second when the correct switches are pressed. It does not actually lock or unlock anything!

Parts Required

resistors: 470Ω, 100kΩ ×2, 1MΩ
capacitors: 0.1µF, 1µF 16V radial
red LED
555 timer IC
8-pin DIL socket for IC
on/off switch
push-switch ×6 (or more)
7/0.2mm stranded wire (for links off board)
battery clip for 9V PP3
stripboard 12 rows × 25 holes

Parts from Rapid Electronics

resistor 470 (pack of 100)
resistor 100k (pack of 100)
resistor 1M (pack of 100)
capacitor 0.1µF (pack of 10)
capacitor 1µF radial (pack of 5)
red LED (pack of 100)
555 timer IC (pack of 5)
8-pin DIL socket (pack of 60)
on/off switch (pack of 5)
push-switch (pack of 10)
7/0.2mm stranded wire pack (assorted colours)
battery clip (pack of 10)
stripboard 24 rows × 37 holes (larger than necessary, cut to size)

Most parts are supplied in packs but the extras are likely to be useful for other projects. Also see advice for building up a starter kit of parts.

Simple Electronic Lock Project

Parts Required

Parts from Rapid Electronics

Stripboard Layout

Circuit diagram