Previously I have created a simple radio receiver using the schematic below (based off a crystal radio), and I was wondering if the modified circuit which is also below would work for a simple morse-code like transmitter that the receiver could pick up and display on an LED.

This is the receiver I built before: receiver screenshot

For clarification C1 is part of the LC oscillator, and C2 is just a small capacitor to reduce noise. I will be making some modifications like taking out the speaker and replacing it with a transistor that turns on an LED, as well as replacing variable capacitor C1 with a standard capacitor as the circuit will now only be receiving from the transmitter (with an identical oscillator), not radio stations.

And this is the proposed transmitter: proposed transmitter schematic

In this the LC circuit is the same as in the reciever.

I looked at tutorials for this sort of thing but they all seemed very complicated and all I need is a very simple one that doesn’t need to work super well. My intention for this was that when the button is pressed down on the transmitter the LED should light up on the receiver. Is this plausible?

  • \$\begingroup\$ Look into ambient backscatter techniques. I think the University of Washington will figure into some of that. But absolutely do NOT stop there. There have seen been much advancement in the field. So it's worth time for study. The transmitters are even simpler. \$\endgroup\$
    – jonk
    Jan 10, 2022 at 8:52

1 Answer 1


Your transmitter will, at best, generate short, exponentially decaying radio frequency pulses, when the switch is closed and most of the time when the switch is opened again. An AM receiver, like your crystal diode receiver, will, with a bit of luck, "click" at the start of each of these pulses, i.e. when the switch is closed, and then again, when it is re-opened.

Other than clicks, that is all you will hear with that transmitter and that receiver. To hear a tone, you will either need to use a more complex transmitter, or a more complex receiver.

Incidentally, your transmitter will be quite wasteful of your battery power.

  • \$\begingroup\$ Thanks for the response, would this receiver work better if instead of a speaker I had an LED (or similar component that doesn't require an input oscillating within the range of human hearing) in the circuit? \$\endgroup\$ Jan 10, 2022 at 3:08
  • \$\begingroup\$ @LukeCampbell Crystal radios are rather finicky, so I don't know if you can get one to work with an LED. However, even if you are able to, the pulses from your transmitter will still be short because the transmitter relies on the natural oscillation after an impulse. It will decay exponentially with time fairly quickly. It will not be continuous. \$\endgroup\$ Jan 10, 2022 at 4:50

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