Hey.
I'm about to build an amp, in which I'll be able to switch channels using a latching relay - both from a momentary switch on the front, and from a pedal (also momentary switch).
(I want to use the single coil latching relays that stay in place after power is turned off).
I found a nice driver circuit for it, that works off of the 5V winding of the power trafo. So far so good.
However, I realized I want to be able to switch something else too, so I need another relay. As for the pedal, that just means putting another momentary switch in there - no prob...
But I would hate to have to run two jack cables from the amp to that one pedal...
Anyone have a good suggestion for a circuit that can control both relays, but could be done using a simple stereo jack cable???
Regards
Anders
driver circuit for two latching relays?
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martin manning
- Posts: 13210
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: driver circuit for two latching relays?
Does the latching relay just need a momentary pulse to change state? If so then a TRS setup would be simple, using the tip to ground for one and ring to ground for the other.
Re: driver circuit for two latching relays?
Thx - but unfortunately for the circuit I found, the switch isn't going to ground.
You can see the circuit in this schematic of the amp:
https://www.dropbox.com/s/yiaovf24a9xfq ... 3.pdf?dl=0
The switch shorts out a capacitor, so I fear that particular circuit would require 4 wires out to pedal switches :-/
You can see the circuit in this schematic of the amp:
https://www.dropbox.com/s/yiaovf24a9xfq ... 3.pdf?dl=0
The switch shorts out a capacitor, so I fear that particular circuit would require 4 wires out to pedal switches :-/
Re: driver circuit for two latching relays?
Would this work?
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Re: driver circuit for two latching relays?
Can't you just use a stereo footswitch cable and have it so that the alternate channel switching is energised from one control voltage (i.e. 1 footswitch cable - see Fig 13.9 and 13.10 in Merlin Blencowe's pre-amp book - 2nd edition), with the 3rd relay operated by the 2nd footswitch cable?
He who dies with the most tubes... wins
Re: driver circuit for two latching relays?
These are latching relays, and I need to control two independantly, so it's a bit different from normal non-latching relays.
That's why I wonder if the circuit I drew up would work?
That's why I wonder if the circuit I drew up would work?
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martin manning
- Posts: 13210
- Joined: Sun Jul 06, 2008 12:43 am
- Location: 39°06' N 84°30' W
Re: driver circuit for two latching relays?
I replied to the same question when you posted over at diystompboxes.
The approach ought to be the same: think of what function you want done, and where you start, then go fill in between them.
The toggled-capacitor trick for flipping a single coil latching relay works because the driver circuit pulls the cap alternately up to the + supply and down to the - supply. the circuit you've shown does this, but uses a complementary two-transistor latch/filpflop. The two MOSFETs and that diode do the pull up/down. The PNP and the bottom MOSFET do the latch/filpflop. The switches shorting or not shorting the caps provide little pulses the PNP/MOSFET flipflop to make it flip.
If your issue is the non-grounded switch, there are lots of ways to make that work. One is to simply replace the switches in the schematic with some kind of a remoted switch. One way is with a second, very small, cheap relay that is not latching. You use the footpedal and panel switches to momentarily kick the new small relay, and its isolated switch contact makes the bigger relay flipflops work.
Another variant of this is to use an LED/MOSFET optoisolator instead of another small relay. The ...um... TS222G??.. device is an LED and an isolated MOSFET in the same package. Make your pedal/switches drive the relay, it drives the bigger flipflops. Costs about the same as a little US$0.50 to US$2.50 relay, though. Surplus relays would make it cheaper.
Another option is to redesign it to not be so convoluted. Recognize that what you're trying to do is drive a relay coil in series with a capacitor, and arrange a suitable IC to do that. Then, put a real, logic flipflop in front of it, and have your panel switches and pedal switches drive the logic flipflop. Sounds complicated, but it's actually about the same cost and probably less complicated to understand.
I personally would use an 8-pin PIC microcontroller. These US$0.75 devices would take in switch closures, and then convert that to the complementary drive the relays need. The big hill to climb there is that to use a single 8-pin package to do the job, you need to be able to program them.
The approach ought to be the same: think of what function you want done, and where you start, then go fill in between them.
The toggled-capacitor trick for flipping a single coil latching relay works because the driver circuit pulls the cap alternately up to the + supply and down to the - supply. the circuit you've shown does this, but uses a complementary two-transistor latch/filpflop. The two MOSFETs and that diode do the pull up/down. The PNP and the bottom MOSFET do the latch/filpflop. The switches shorting or not shorting the caps provide little pulses the PNP/MOSFET flipflop to make it flip.
If your issue is the non-grounded switch, there are lots of ways to make that work. One is to simply replace the switches in the schematic with some kind of a remoted switch. One way is with a second, very small, cheap relay that is not latching. You use the footpedal and panel switches to momentarily kick the new small relay, and its isolated switch contact makes the bigger relay flipflops work.
Another variant of this is to use an LED/MOSFET optoisolator instead of another small relay. The ...um... TS222G??.. device is an LED and an isolated MOSFET in the same package. Make your pedal/switches drive the relay, it drives the bigger flipflops. Costs about the same as a little US$0.50 to US$2.50 relay, though. Surplus relays would make it cheaper.
Another option is to redesign it to not be so convoluted. Recognize that what you're trying to do is drive a relay coil in series with a capacitor, and arrange a suitable IC to do that. Then, put a real, logic flipflop in front of it, and have your panel switches and pedal switches drive the logic flipflop. Sounds complicated, but it's actually about the same cost and probably less complicated to understand.
I personally would use an 8-pin PIC microcontroller. These US$0.75 devices would take in switch closures, and then convert that to the complementary drive the relays need. The big hill to climb there is that to use a single 8-pin package to do the job, you need to be able to program them.