multi relay boards and a Duet

jens55

I have one of those 'dime a dozen' relay boards that has 4 relays on it. The inputs are 'ground, in1 through in4'. The idea was to run the signal from a Duet output to the relay board and have the other three relays as spares for future use.
I just received some buck converters to bring the signal voltage from my normal 24V down to 5V for the relay board when it occurred to me that there is a rather basic flaw in my plan that I should have seen before .... the outputs of the Duet are all switched via the ground side of things rather than the high side.

Question: Is there any way I can use the outputs of a Duet to run the relays on this board that assumes a common ground and a +5V or 0V at the signal input pins?

I think I know the answer but before I start over from scratch, I thought I would check here to see if there is some sort of a magic work-around.
Has anyone managed to run a multi relay board that has a common ground and expects a 5V signal to activate the relay?

jens55

After some contemplation, I think the best and most logical way for me to proceed is to use an individual 24V relay connected directly to the output of the Duet instead of using the opto isolated multi relay board.

dc42

@jens55 that's probably the simplest solution. However, your relay board might work if you connect the + input to an IO_OUT pin and the common ground to GND on the same IO connector.

luca Massimiliano

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jens55

@dc42 said in multi relay boards and a Duet:

@jens55 that's probably the simplest solution. However, your relay board might work if you connect the + input to an IO_OUT pin and the common ground to GND on the same IO connector.

I am not sure I understand. I had planned to use a 2 pin fan output on the 6hc board. The + pin is connected to Vin and is not switched and the actual switching happens on the low side where ground is either grounded (on) or left floating (off).
Are you suggesting to use one of the nine 5 pin io connectors instead? I see that pin 4 is the io out pin. Are you saying that on pin 4, the signal is an active high signal and that it is switched on the high side unlike the fan outputs that are switched on the low side? If that is so then yes, that would work.
What is the pin 4 voltage if the output is switched on?
Looking at the schematic, it looks like the signal on pin 4 is a 5V high output which would work perfectly with the relay board. Am I reading this correctly?
The only thing I have to watch is the available power (or lack thereof) since those io_out pins come directly off a 74HCT365 with no buffering.

Thanks!

dc42

@jens55 the signal on pin 4 of a 5-pin IO connector when high is 3.3V from the microcontroller through a 470 ohm resistor. That may or may not be enough to trigger the relay board.

Some Duets also have a LASER/VFD output which is a 5V signal. That one comes from a 74HCT365 and should definitely be sufficient.

Phaedrux

@luca-massimiliano Start a new thread please.

jens55

@dc42 said in multi relay boards and a Duet:

the signal on pin 4 of a 5-pin IO connector when high is 3.3V from the microcontroller through a 470 ohm resistor. That may or may not be enough to trigger the relay board.

That worked perfectly (once I got the pin name right and figured out that the 'invert' command is '!' and not '^')
Thanks again!