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Magnetic proximity sensors Click here for the circuit diagram
an interesting circuit for a magnetic proximity switch which can be used in
The magnetic proximity switch circuit, in principle,
consists of a reed switch at its heart. When a magnet is brought in the vicinity
of the sensor (reed switch), it operates and controls the rest of the switching
circuit. In place of the reed switch, one may, as well, use a general-purpose
electromagnetic reed relay (by making use of the reed switch contacts) as the
sensor, if required. These tiny reed relays are easily available as they are
widely used in telecom products. The reed switch or relay to be used with this
circuit should be the ?normally open? type.
When a magnet is brought/placed
in the vicinity of the sensor element for a moment, the contacts of the reed
switch close to trigger timer IC1 wired in monostable mode. As a consequence
its output at pin 3 goes high for a short duration and supplies clock to the
clock input (pin 3) of IC2 (CD4013?dual
D-type flip-flop). LED D2 is used
as a response indicator.
This CMOS IC2 consists of two independent flip-flops
though here only one is used. Note that the flip-flop is wired in toggle mode
with data input (pin 5) connected to the Q (pin 2) output. On receipt of clock
pulse, the Q output changes from low to high state and due to this the relay
driver transistor T1 gets forward-biased. As a result the relay RL1 is energised.
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