I have a homebrew motorized hf tuner which is controlled by coupling dc from the shack through two BiasTs - one topside, the other in the shack.

As I reverse polarity to adjust tuner, will two LEDs, one LED reversed from the other, connected in parallel to the DC line at the shack end, work well to indicate when rotary inductor reaches its limit switches, so I may then know to reverse polarity to adjust the tuner toward resonance?

thanks in advance

  • $\begingroup$ Is this the same as ham.stackexchange.com/questions/17428/…? $\endgroup$ Commented Dec 13, 2020 at 19:30
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    $\begingroup$ Please edit your question to give us details about how your tuner is controlled so we can give you advice. A schematic would be best; the editor includes a schematic tool. Does the DC current drive the motor, or switch relays? What's the typical current? Does the current get shut off by the limit switches? Does the current reverse when the motor switches direction? So far all we can tell you is that your back-to-back LED idea could work if the current is about 10-20 mA, the current switches off when the motor hits a limit switch, and the current reverses when the motor changes direction. $\endgroup$
    – rclocher3
    Commented Dec 15, 2020 at 17:48
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    $\begingroup$ I'm not sure what you are asking here. Are you trying to make a limit switch with LEDs? Are you trying to use the LEDs to indicate the condition of a limit switch? Could you edit the question to clarify, especially by adding a schematic of the circuit in question? $\endgroup$ Commented Dec 15, 2020 at 18:03

1 Answer 1


Parallel LEDs across the power source will only indicate the presence of voltage and its polarity.

Parallel LEDs in the line can indicate current flow and its direction. However, the LEDs cannot carry the motor current.

The LED in the following circuit will be lit as long as the motor is running in either direction.

enter image description here


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