Code lock

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< Digital Electronic ~ Code lock

eric

Posted: Sun Sep 10, 2006 9:24 am Post subject: Code lock

Site Admin Joined: 01 Jan 1970 Posts: 311

G. Vanderplancke
The combination of a couple of thyristors, key switches and a relay
as shown in the diagram forms a suitable, reasonably tamper-proof
code lock for use in, say, a car. To open the lock,a number of keys
must be pressed in a prescribed sequence to energize a relay,
whereupon the battery voltage is applied to the ignition switch.
The first key to be pressed is S4, whereupon capacitor C1 is
charged via resistor R1. The charge on this capacitor ensures that
transistor T1 is on for about 15 seconds, during which relay Re1 is
energized. However, within these 15 seconds, key S5 must be
pressed to switch on thyristor THR1. Then S6 must be pressed to
switch on THR2. Finally, S7 is to be pressed to switch on THR3.
When that is done, relay Re2 is energized, and the lock is open.
If within the initial 15 seconds the wrong key

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