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Insoluble Conundrum? (switching relays)

Gentlemen,

I can't come up with a straightforward solution to what ought to be a simple problem so I'm posting this in the hope that intellects greater than mine can crack it. I've acquired an HP RF attenuator, but it wasn't the one I wanted. I wanted the manually-switched version with a knob you can twist to select the degree of attenuation required, but I've ended up with the electronic one instead. Anyway, even the plugs for these things are made of pure unobtainium, so I'm going to have to re-work the damn thing from scratch. So here's the problem. The attenuator provides from 10db to 70db attenuation depending on which resistances are selected by sending a short pulse to the relay for that particular resistance card. Sequential pulses toggle the relevant resistance in and out of circuit. You only have to momentarily ground one end of the relay to flip it from one state to the other - and therein lies the problem. I'd like some LEDs as status indicators to show which resistances are 'in', but in a system such as this, I can't figure out how to readily implement that. Any ideas? Here's the internals of the attenuator:

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Reply to
Cursitor Doom
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From the schematics, it appears to have a 'set' contact and a 'reset' contact. It will only take a brief current pulse to change state, but there is nothing that prevents you from leaving the coil contacts energized. You can control it with four spdt switches and the same switches can drive your status LEDs too. Easy.

Jeroen Belleman

Reply to
Jeroen Belleman

A relay coil has one end that will be +24 volts when the solenoid is in the "in" position; the opposite side from the one that you just blipped to ground. So a resistor+LED to ground will indicate the position.

You can verify that with a DVM.

1 mA, 22K resistor, would be plenty bright but not influence the solenoid.
Reply to
John Larkin

Okay, well, I don't understand how I missed that. After that conspicuous display of ignorance, I shall bow out ungracefully. Thanks, chaps.

Reply to
Cursitor Doom

I like this circuit and the way the relay disconnects itself once it has flipped. As you say, that lets you ground the active input continuously. If that is an option, then yes, you can put an LED across the two inputs and 24V. The activated input will pull the LED to ground as well lighting it.

But, if the control signal is only a momentary for whatever reason, an LED can be connected from ground, to the input that is now connected to 24V. As Larkin has said, you need to size the LED resistor so it draws very little current compared to the pull in current of relay. I don't recall about latching relays, but I expect they don't have drop out current ratings. The LED current should be less that this if they specify it. If the relay current is anywhere near a mA, it would require a transistor to drive the LED.

Reply to
Ricky

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