Intelligent Relay Bypass - More than 1 relay

tiefschwarz73

New member
Hi Folks,

will a single ATTINY85 be able to drive (make them change the switching status) 2 latching relays?

For example...
I have in mind to build a booster pedal with an output which can be used to switch channels on my amp. So I can switch the booster on an change from clean to drive channel with a 'flick of a kick'...

Of course, I can do it with a 4dpt footswitch. But I will like it more to do it with the Intelligent Relay PCB.

Greetings from Germany
 
Not sure if this will help. There’s a small company that makes DIY audio equipment, and one of their projects uses the tiny to control MANY relays. I have the parts, have been planning to build this for quite some time… I’ll be building a balanced stereo set, so I think 2 relay boards, 8 relays on each, all driven by one tiny, So-it can be done; but I can’t help with the how.

 
Yes, but not (safely) with the existing Intelligent Relay Bypass PCB.

The SideEffect module drives two relays directly from a single ATTINY but it uses separate pins of the IC for each relay.

There are a couple issues with directly driving two relay coils in parallel from the same pin of the microcontroller...

1) You'll most likely be pulling more than the maximum rated per-pin current of the microcontroller
2) When the coil is de-energized it will kick back a voltage that theoretically could trigger the other relay coil

You can drive them both from the same pin of the IC but you'll want to add a couple drive transistors to take the load off of the microcontroller.
 
Not sure if this will help. There’s a small company that makes DIY audio equipment, and one of their projects uses the tiny to control MANY relays. I have the parts, have been planning to build this for quite some time… I’ll be building a balanced stereo set, so I think 2 relay boards, 8 relays on each, all driven by one tiny, So-it can be done; but I can’t help with the how.

Boom... I think it's slightly over the top for me. But thank you
 
Yes, but not (safely) with the existing Intelligent Relay Bypass PCB.

The SideEffect module drives two relays directly from a single ATTINY but it uses separate pins of the IC for each relay.

There are a couple issues with directly driving two relay coils in parallel from the same pin of the microcontroller...

1) You'll most likely be pulling more than the maximum rated per-pin current of the microcontroller
2) When the coil is de-energized it will kick back a voltage that theoretically could trigger the other relay coil

You can drive them both from the same pin of the IC but you'll want to add a couple drive transistors to take the load off of the microcontroller.
Wait, so if I’m understanding correctly, the issue is that one relay could mis-trigger while the other doesn’t, putting the two relays out of sync? Couldn’t a design be done for two non-latching relays so they’re always synced? I’m assuming that the use of two relays is in reference to getting 4pdt functionality without having to do an expensive and bulky 4-pole relay
 
Wait, so if I’m understanding correctly, the issue is that one relay could mis-trigger while the other doesn’t, putting the two relays out of sync?

That's one of the issues, the other being that a single microcontroller pin can't supply enough current to open/close two relays simultaneously.... I mean it probably could, a few times, but you better socket it. ;)

If you use non-latching relays it'd be continuous current instead of surge current, and that makes current consumption an even bigger issue.

Microcontrollers weren't designed to drive significant amounts of current. Just driving a single relay per pin is abusing the microcontroller (but we do it anyway)...

I have some relay utility boards worked up that would help this situation... Basically you have a logic module that contains the microcontroller and footswitch connections, and multiple relay modules that each take a control line from the microcontroller board. The relay, I/O, and drive circuitry is contained on each relay module so there is no load on the microcontroller.
 
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