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Circuits designed by David Johnson,
P.E.
Last Updated on:
Saturday, December 23, 2017 03:21 PM
Master Category List - Dave's Circuits
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More
Remote Control
Switches |
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Isolated Remote Switch Circuit
January 4, 2009 |
There are many applications when a remote switch’s on/off status needs to be
monitored. Reed relay sensors, toggle control switches and security alarms
contacts are just a few examples. Routing a switch directly to a computer
system hundreds of feet away can often lead to erratic operation and noise
problems. If such a control switch is required, a fully isolated circuit is
strongly recommended. The circuit below provides such isolation. When
properly wired, it will have 5000 volts of isolation and can be positioned 1000
feet away. |
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The circuit uses a custom ferrite toroid type transformer. About 20 turns of
magnet wire forms the primary winding and 10 turns forms the secondary winding.
A simple Schmitt trigger oscillator drives the primary winding of the transformer with
a 100KHz signal. The voltage at the transformer secondary is rectified to
produce a DC voltage. That voltage is routed to the remote switch and is used to drive
the LED side of an optoisolater. The phototransistor side of the optoisolator
can be used in either a source or sink type logic level swing. Both type
circuits are shown. |
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Click on Drawing Below to view PDF version of Schematic |
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