Simple electronics Code Lock System

SIMPLE ELECTRONIC
CODE LOCK
The circuit diagram of a simple electronic
code lock is shown in figure.
A 9-digit code number is used
to operate the code lock.
When power supply to the circuit is
turned on, a positive pulse is applied to
the RESET pin (pin 15) through capacitor
C1. Thus, the first output terminal
Q1 (pin 3) of the decade counter IC (CD
4017) will be high and all other outputs
(Q2 to Q10) will be low. To shift the high
state from Q1 to Q2, a positive pulse must
be applied at the clock input terminal (pin
14) of IC1. This is possible only by pressing
the push-to-on switch S1 momentarily.
On pressing switch S1, the high state
shifts from Q1 to Q2.


Now, to change the high state from
Q2 to Q3, apply another positive pulse at
pin 14, which is possible only by pressing
switch S2. Similarly, the high state can
be shifted up to the tenth output (Q10)
by pressing the switches S1 through S9
sequentially in that order. When Q10 (pin
11) is high, transistor T1 conducts and
energises relay RL1. The relay can be
used to switch ‘on’ power to any electrical
appliance.
Diodes D1 through D9 are provided
to prevent damage/malfunctioning of the
IC when two switches corresponding to
‘high’ and ‘low’ output terminals are
pressed simultaneously. Capacitor C2 and
resistor R3 are provided to prevent noise
during switching action.
Switch S10 is used to reset the
circuit manually.

Switches S1 to S10
can be mounted on a keyboard panel,
and any number or letter can be used to
mark them. Switch S10 is also placed
together with other switches so that any
stranger trying to operate the lock frequently
presses the switch S10, thereby
resetting the circuit many times. Thus,
he is never able to turn the relay ‘on’. If
necessary, two or three switches can
be connected in parallel with S10 and
placed on the keyboard panel for more
safety.
A 12V power supply is used for the
circuit. The circuit is very simple and can
be easily assembled on a general-purpose
PCB. The code number can be easily
changed by changing the connections to
switches (S1 to S9).