19-04-2012, 11:18 AM
ELECTRONIC WATCHDOG
Electronic Watchdog.pdf (Size: 136.96 KB / Downloads: 170)
Here’s an electronic watchdog for
your house that sounds to inform
you that somebody is at the gate.
TAPAN KUMAR MAHARANA
pillars of the gate such that the IR
beam gets interrupted when someone
is standing at the gate or passing
through it.
The transmitter circuit (see Fig. 1)
is built around timer NE555 (IC1),
which is wired as an astable
multivibrator producing a frequency of
about 38 kHz. The infrared (IR) beam
is transmitted through IR LED1.
The receiver circuit is
shown in Fig. 2. It comprises
IR sensor TSOP1738 (IR RX1),
npn transistor BC548 (T1),
timer NE555 (IC2) and some
resistors and capacitors. IC2 is
wired as a monostable
multivibrator with a time period
of around 30 seconds. The
melody generator section is
built around melody generator
IC UM66 (IC3), transistor T2
and loudspeaker LS1. Fig. 3
shows pin configurations of IR
sensor TSOP1738 and melody
generator IC UM66.
When somebody enters through the
door, the IR beam is interrupted and the
alarm sounds for 30 seconds. The alarm
keeps sounding as long as one stands
between the transmitter and receiver units.
Using preset VR1, you can set the volume
of the loudspeaker.
This circuit can also be used as a doorbell
or burglar alarm.