# What is the simplest possible circuit for a wireless on-off switch [closed]

On one side I have 5V DC powering an LED, and on the other side I have a button (switch/latch/whatever). What's the simplest circuit for this button to control the state of the LED (hopefully without OpAmps)? Range is not important, just the principle. Not including electromagnetic induction...

## closed as too broad by markt, Andy aka, Daniel Grillo, Scott Seidman, Matt YoungMar 12 '15 at 13:59

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• Is IR allowed? There are very simple detectors which just detect the presence of an IR carrier signal. – mkeith Mar 1 '15 at 6:24
• @mkeith, yeah sure. – Sparkler Mar 1 '15 at 6:25
• I just re-read your question. Is the switch on the same board as the LED? If so you can use an opto-coupler IC to keep them totally electrically separate. This would basically be a photo-transistor and an LED inside a single package. – mkeith Mar 1 '15 at 7:03
• Google TSOP38238 from Vishay. When it detects the carrier, it sets the output low. When the carrier is absent, the output is high. – mkeith Mar 1 '15 at 7:12
• LED to photo transistor, LDR, light sensor, ... . Sound - audible with transducers (speaker/beeper/mic ...) , ultrasonic. Piezo or other vibration. Capacitive coupling. Small RF modules for maybe $2-$4. SAW oscillator TX, regen/super-egen RX. |Spin a magnet (alternator). Electrostatic. ... – Russell McMahon Mar 1 '15 at 7:55

If you have to use radio waves within a short range, you can look into TA7642-based AM receiver and a single transistor AM transmitter. Feed the output of TA7642 into a Schmitt trigger and control a MOSFET with the output of it. This is good within up to a few tens of meters, about covering your house and maybe include your neighbor in the range. If you have some elderly living within that range this can be a very Good Samaritan project.