Relay Matrix Board

Hey,

I approached the forum before with an idea I had with an audio relay matrix. Audio goes in one end of the board, is routed through a 32x32 matrix of relays and returns to an output at the other end. After some help from some forum members I had a design that worked pretty well on a breadboard small scale. I had to work out some kinks and have reworked the design to a modular design of 8x8 cards. Each card has four edge connectors which will each plug in to a backplane to route signals from card to card.

I’m attaching the schematic and board I’m working on now. I am using latching relays so that digital signals can be limited to pulses which should cut down on issues with noise reaching audio signals.

The backplane cards will have 4 db25 connectors to input audio and 4 db25 connectors for audio output. The backplane will house an atmega328p and shift registers to source and sink the relay current.

I just need some reassurance on the design maybe some help on what sort of grounding might be best for this circuit. I was thinking of using a star ground to the chassis. I would have a ground pour at the db25 connectors which would then connect to the star ground, keeping it isolated from the power section.

hopefully this makes sense, I know the schematic is not finished but is a start to show where the audio and digital paths will be located

vwyf11: I am using latching relays so that digital signals can be limited to pulses which should cut down on issues with noise reaching audio signals.

So switching a relay on requires a pulse which goes on and off and switching it off again requires a pulse which goes on and off. That's twice as much noise as just switching it on and off. The digital transitions make noise. A digital output which is stable at either on or off doesn't make any noise.

The pads you've put for the DB25 connectors aren't correct. They look more like edge connectors where the PCB is the connector. Or maybe 30-pin Centronics connectors? Either way, it looks like you're only using just over half of the pins - can you combine connectors and reduce the number of connectors?

It looks like you have connections on all 4 sides of the box. That's going to be trouble. Try to put all connectors on one side, maybe two sides in complex cases. Anything with connectors on 3 or 4 sides is almost impossible to put into a box.

Your schematic doesn't show any information about these relays, so I can't look up a datasheet to find them. I think you're using them wrong or you're missing a lot of wiring. There's no individual control wires going to the coils. The other wires that go through diodes aren't connected to anything except the relays so there's obviously no power supply connected. It's a bit early with that schematic to lay out traces on the PCB. you should only start drawing copper once you have all the nets on the schematic.

Do you want to always connect only one input to one output? Then a better design can select one of 32 inputs and connect it to one of 32 outputs. This design also can be implemented with 8 analog multiplexer chips, instead of the many more relays.

I really need to explain more...

The connectors shown are 30 pin edge connectors. The backplane I speak of is not shown as this card will plug into that. The DB25 connectors will be located on that backplane.

I understand that I’ve been laying this out way out of order. I’ve ripped up traces multiple times. I laid out these traces with the only intent being to upload here and see if I may run into trouble with the audio and power signals. The relays are nec ea2-5tnj. No power is shown, but will be across pins 1 and 5 and pins 6 and 10.

Noise will not be much of an issue through the pulse on and off. The unit will be used as a digital patch ya to route audio signals. It will not be used in real time, so signal can be routed and then used after the switch

I left pins open on the edge connectors to carry the switch pulse signals.

Drdiettrich, If you think there’s a better way to route using the relays, in all ears. I want to avoid the multiplexer chips as most of the higher end gear seems to favor relays in place of them.

32 inputs can be multiplexed by 16 relays onto 16 outputs. These 16 are multiplexed by 8 relays into 8 outputs and so on, until 1 output remains. The exactly same scheme can be used to distribute that signal to one of 32 outputs.

DrDiettrich: 32 inputs can be multiplexed by 16 relays onto 16 outputs. These 16 are multiplexed by 8 relays into 8 outputs and so on, until 1 output remains. The exactly same scheme can be used to distribute that signal to one of 32 outputs.

Wouldn't this require the same amount of relays for 32 inputs routing to 32 outputs?

I'm attaching another schematic that shows switches wired to the first vertical row of relays. When S1 and S3 are switched on audio will pass from In1+ and IN1- to OUT1+ and OUT1-. When S1 and S2 are switched on, the coil will reset on the first relay and audio will no longer pass.

relay board v2.png|9002x4812

Count yourself: 31 relays for inputs and 31 for outputs, that's less than you need for only 8 inputs and 8 outputs.

DrDiettrich: Count yourself: 31 relays for inputs and 31 for outputs, that's less than you need for only 8 inputs and 8 outputs.

I get what you mean now. When you said one input to one output, I thought you meant for each input to only be routed to one output. I would need to route route multiple inputs to multiple unique outputs. No single input would need to go to multiple outputs at once. I think this was where the discrepancy was for me.

You also can build a multiplexer for one output to one of 32 inputs (31 relays), and duplicate that for each output. This model prevents shorts between inputs in case of bad swtiching.

Hey,

So I’ve updated the board and designed the audio portion of the motherboard.

I moved all of my input and output connections to one side of the board on a 36 pin edge connector. The cards will then plug in to the motherboard section which will route audio to the appropriate card based on which relay is turned on.

There is still no power section here, but I am trying to see if the audio paths will cause any issues with how they are routed. Crosstalk, etc.

The left side db25 connection is where all audio will output. The right is the input side