This document describes an electronic bicycle lock circuit that provides an affordable anti-theft alternative for bicycle owners. The circuit uses a 9V battery, key lock switch, and tone generator integrated circuit to sound an alarm if the security loop between its two input jacks is broken. The simple circuit can be assembled on a small printed circuit board and housed in an enclosure to attach to bicycles in place of a standard lock.

1. circuit
ideas
ELECTRONIC BICYCLE LOCK
 T.K. Hareendran J2 are two standard RCA sockets. A
edi
home-made security loop can be used s.c. dwiv
T
he electronic bicycle lock de- to link these two input points. Around
scribed here is a worthwhile 50cm long, standard 14/36 flexible
alternative for bicycle own- wire with one RCA plug per end is
Fig. 3: Lock fitted on the bicycle
tone generator UM3561 (IC1). IC1
Fig. 1: Circuit of electronic bicycle lock remains enabled until power to the
circuit is turned off using switch S1
ers who want enough for the security loop. or the loop is re-plugged through J1
to make their Fig. 1 shows the circuit of the and J2.
bicycles ‘intelli- electronic bicycle lock. It is powered Assemble the circuit on a general-
gent’ at reason- by a compact 9V battery (6F22). purpose PCB and house in a small tin-
able cost. One Key lock switch S1 and smoothing plate enclosure. Fit the system key lock
of the benefits capacitor C2 are used for connect- switch (S1) on the front side of the en-
of building it ing the power supply. A connected closure as shown in Fig. 2. Place RCA
yourself is that loop cannot activate IC1 and there- sockets (J1 and J2) at appropriate posi-
Fig. 2: Lock box the circuit can fore the speaker does not sound. tions. Now, mount the finished unit in
be used for vir- When the loop is broken, zener diode place of your existing lock (as shown
tually any make of bicycles. ZD1 (3.1V) receives operating power in Fig. 3) by using suitable clamps and
In the circuit, input jacks J1 and supply through resistor R2 to enable screws. 
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