I would have thought this a common circuit, and maybe I’m searching wrong, but what logic method are people using to trigger a mechanical relay to switch between a transformer secondary and a 1/4” instrument input? In my case the load is a tube grid but I think it doesn’t matter. The jack is on the front panel, the transformer and tube are deeper into the PCB, and I don’t want to send signal out to the front panel from the transformer.
The rest of the relays in the system are on a ULN2004, and I have a spare channel. I’m working in through hole, and logic voltage is 6V, though I could add a little 5V regulator if need be.
I’d like to use either the shield normal or ring normal on a regular PCB mount TRS jack. Maybe a little trickle of voltage through the normal, and when the ring goes low it triggers an inverter feeding the spare ULN2004 channel, to pull it high? It’s just not coming together visually for me and I need an example.
[It came together in Post #23]
It would be nice to avoid running any voltage through the jack if possible. I have looked at audio sense circuits (rectifier, smoothing, comparator), but I think the potential for flutter is too great. We don’t just run the cold side of a coil to an open ring contact, do we? That’s like 20mA at 5V that the tip has to pass through…
The rest of the relays in the system are on a ULN2004, and I have a spare channel. I’m working in through hole, and logic voltage is 6V, though I could add a little 5V regulator if need be.
I’d like to use either the shield normal or ring normal on a regular PCB mount TRS jack. Maybe a little trickle of voltage through the normal, and when the ring goes low it triggers an inverter feeding the spare ULN2004 channel, to pull it high? It’s just not coming together visually for me and I need an example.
[It came together in Post #23]
It would be nice to avoid running any voltage through the jack if possible. I have looked at audio sense circuits (rectifier, smoothing, comparator), but I think the potential for flutter is too great. We don’t just run the cold side of a coil to an open ring contact, do we? That’s like 20mA at 5V that the tip has to pass through…
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