I have a circuit with a single momentary on switch that causes a solenoid to change position. I need to be able to see which position the solenoid is in. I've looked at the circuits for motor control LEDs on and off and I don't think that that will work for me.

I need the LEDs to indicate both states of the solenoid. One LED (green) = ON when the solenoid is on (red is off), and the other LED (red) = ON to indicate when the solenoid is off (green is off). I can't get this with a single LED because the off state would not be indicated.

I can't change the switch to a double throw switch I have to use the single pole single throw momentary switch. I can get back 12V indicating the solenoid is on or off from the live terminal. I can't use a relay in the space I have, I would like a diode biased solution if possible. I have 12 volts at the Led position which is remote from the solenoid.

  • \$\begingroup\$ You must show the datasheet and wiring \$\endgroup\$ Commented May 31, 2019 at 2:29

1 Answer 1



simulate this circuit – Schematic created using CircuitLab

  • SW2 indexes the solenoid.
  • D3 lights when SW1 is open.
  • When SW1 is closed the forward voltage drop of D1 will be lower than the combined forward voltage drop of D4 and D3 so D1 should light and D3 turn off.

If D3 is still glowing when it should be off then add another diode in series in the D3, D4 branch.

  • \$\begingroup\$ Thank you for the reply. I don't think this will work if I understand this correctly. L1 is a latching state solenoid. When the momentary switch is pulsed once the solenoid changes / toggles state. The normal state of SW1 is open. When L1 is latched on, then I would have 12v on the output of L1 which would drive D1 ON. But when L1 is at 0V (ie open) and SW1 is in its normal state which is open wouldn't both D3 and D1 be ON? \$\endgroup\$ Commented May 31, 2019 at 0:07
  • \$\begingroup\$ I may have misunderstood your answer. If I used the output of the solenoid as SW1 and disregard L1, would that work? The sense circuit on the solenoid changes the state of the solenoid based on a momentary closure, but that may be irrelevant to the solution and therefore L1 could be ignored; \$\endgroup\$ Commented May 31, 2019 at 0:28
  • \$\begingroup\$ Updated after additional information supplied. \$\endgroup\$
    – Transistor
    Commented May 31, 2019 at 6:35

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