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DiscoverCircuits.com -- Hobby Corner
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Tuesday, June 01, 2021 03:06 PM
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Remote Control
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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 Circuit Below to view PDF of Schematic |
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Remote Control
Switches
Hobby Circuits List
eMail David A.
Johnson, P.E. about this circuit |
