|
Simple
Code Lock
|
| The
circuit described here is of an electronic combination
lock for daily use. It responds only to the right sequence
of four digits that are keyed in remotely. If a wrong
key is touched, it resets the lock. The lock code can
be set by connecting the line wires to the pads
a, b, c, and d in the figure. For example, if the code
is 1756, connect line 1 to a, line 7 to b, line 5 to c,
line 6 to d and rest of the lines—2, 3, 4, 8, and 9—to
the reset pad as shown by dotted lines in the figure.
|
| The
circuit is built around two cd4013 dual-d flip-flop ics.
The clock pins of the four flip-flops are connected to
a, b, c, and d pads. The correct code sequence for energisation
of relay rl1 is realised by clocking points a, b, c, and
d in that order. The five remaining switches are connected
to reset pad which resets all the flip-flops. Touching
the key pad switch a/b/c/d briefly pulls the clock input
pin high and the state of flip-flop is altered. The q
output pin of each flip-flop is wired to d input pin of
the next flip-flop while d pin of the first flip-flop
is grounded. Thus, if correct clocking sequence is followed
then low level appears at q2 output of ic2 which energises
the relay through relay driver transistor t1. The reset
keys are wired to set pins 6 and 8 of each ic. (Power-on-reset
capacitor c1 has been added at efy during testing
as the state of q output is indeterminate during switching
on operation.) |
| This
circuit can be usefully employed in cars so that the car
can start only when the correct code sequence is keyed
in via the key pad. The circuit can also be used in various
other applications. |
|
|
Click on the Image for its larger version
|
