Interlocking Relay Monitor

[ruffrecords]

I have been thinking about monitor switching for the EZTubeMixer. A convenient way to do monitor selection is with mechanically interlocking push buttons such as those made by ITT (Schadow) and Lipa Isostat. However, these seem to be rather hard to come by but momentary action push buttons are readily available. So I wondered if I could come up with an interlocking relay logic based system that did the same thing using momentary push buttons. Here's the schematic of what I came up with:

Assume all the relays are unenergised to start with and none of the push buttons S1 thru S3 is pressed. V+ is the relay supply input.

If you push S1, RLA is energised via D1 and R1. Contact A2 connects C1 across the relay and C1 charges up through R1. Contact A1 closes. When you release the button, the +V supply is removed but the relay is kept closed by the charge on C1. When the switch is fully released the +VR supply is restored via the daisy chained switches on the top row and RLA remains energised via D2 and contact A2. The relay is thus latched on.

If you then press any other switch, +VR disappears, C1 discharges and RLA drops out. Contact A2 opens so it will no longer latch. Contact A1 disconnects the capacitor and discharges it through R2. The relay whose switch was pressed gets enegised and latches just as RLA did before.

D3 is to protects against reverse volts when the RLA turns off. D1 may not be necessary but D2 is there to prevent +V getting to +VR when a button is pressed.

OK, I know this would be trivial with a micro but I am old school and I don't really want a crystal oscillator sitting inside my mixer.

I think this would work but I am not sure. Comments??

Cheers

Ian

 

[shabtek]

I like it, clever seems self debouncing--needs 4p2t relay to switch anything besides itself.

...When the switch is fully released the +VR supply is restored via the daisy chained switches on the top row and RLA remains energised via D2 and contact A2. The relay is thus latched on.

via D2 and A1 innit;

what would happen if 2 buttons pressed simultaneously.

Keep it up--we love you

 

[Rochey]

Ian,

I had the same concern with the MSP430's that I use on the Expat Audio switch controllers. Those devices have an integrated oscillator, which doesn't see any pins. (all inside the package).

the one's i use come in DIP or SMT packages.

Go get an eval baord for $4.30 -- google msp430 launchpad.

/R

 

[gemini86]

I like it. I too am curious what would happen if two switches are pressed simultaneously. My guess is that C1 would keep all activated relays on until the switch is returned to normal position and VR+ is restored to keep them all on. So you could in fact have all of your monitors on by pressing all buttons and once, as long as you release them all at once. I guess this would also be dependent on the size of C1, which I like. (fine tune the amount of time you need to hold a button down to drain C1 on an unwanted selection.)

 

[ruffrecords]

Ian,

I had the same concern with the MSP430's that I use on the Expat Audio switch controllers. Those devices have an integrated oscillator, which doesn't see any pins. (all inside the package).

the one's i use come in DIP or SMT packages.

Go get an eval baord for $4.30 -- google msp430 launchpad.

/R

I think you may be right. It's like the PIC with an on board RC oscillator. Ideal for none time critical applications like this. The 4 into 2 mixer I am building right now would be a good test bed.

Cheers

Ian

 

[ruffrecords]

I like it, clever seems self debouncing--needs 4p2t relay to switch anything besides itself.

...When the switch is fully released the +VR supply is restored via the daisy chained switches on the top row and RLA remains energised via D2 and contact A2. The relay is thus latched on.

via D2 and A1 innit;

what would happen if 2 buttons pressed simultaneously.

Keep it up--we love you

Ah, you spotted the 'deliberate' mistake - I suspect if you press 2 keys you get 2 sources shorted together - not a good thing.

Cheers

Ian

 

[Rochey]

Ian,

drop me a PM, for something like this, I could put a tiny module together for you, preassembled and programmed. It could be teeny tiny, and powered from a separate digital supply (heck, even a USB wall wart...).

/R

 

[Brian Roth]

Actually, having the ability to have more than one source selected at the same time can SOMETIMES be useful.  I've seen that on recording desks using mechanical Schadow switches that were "interlocked, but not locked out".  In those desks, all of the sources fed through the switches onto a summing bus.

Bri

 

[warpie]

I have been thinking about monitor switching for the EZTubeMixer. A convenient way to do monitor selection is with mechanically interlocking push buttons such as those made by ITT (Schadow) and Lipa Isostat. However, these seem to be rather hard to come by but momentary action push buttons are readily available. So I wondered if I could come up with an interlocking relay logic based system that did the same thing using momentary push buttons. Here's the schematic of what I came up with:

Assume all the relays are unenergised to start with and none of the push buttons S1 thru S3 is pressed. V+ is the relay supply input.

If you push S1, RLA is energised via D1 and R1. Contact A2 connects C1 across the relay and C1 charges up through R1. Contact A1 closes. When you release the button, the +V supply is removed but the relay is kept closed by the charge on C1. When the switch is fully released the +VR supply is restored via the daisy chained switches on the top row and RLA remains energised via D2 and contact A2. The relay is thus latched on.

If you then press any other switch, +VR disappears, C1 discharges and RLA drops out. Contact A2 opens so it will no longer latch. Contact A1 disconnects the capacitor and discharges it through R2. The relay whose switch was pressed gets enegised and latches just as RLA did before.

D3 is to protects against reverse volts when the RLA turns off. D1 may not be necessary but D2 is there to prevent +V getting to +VR when a button is pressed.

OK, I know this would be trivial with a micro but I am old school and I don't really want a crystal oscillator sitting inside my mixer.

I think this would work but I am not sure. Comments??

Cheers

Ian

Hi Ian, just wondering whether you still have this image as it doesn't load on my browser and I believe it's long gone from the server you uploaded it. Thanks.

 

[abbey road d enfer]

Last century, I built a number of monitor selectors.
I didn't use relays, FET's and later CMOS switches.
Originally I used a chip that was for TV sets but they were phased out then I used a bunch of CD4011's to do that.
I would need to think it over. But I believe there are references to that type of circuit in cookbooks.
I don't see why you couldn't use that to drive low-power relays.