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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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Remote Control Switches
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