Digital Output (Open Collector) to Analog Ground?

[twixx]

Hi,

I have a home automation peripheral that has a digital output (Digital output - Open collector. Maximum 3.3A DC.), that I am trying to connect to another peripheral which is listening for a Ground Connection.

The digital output, I assume is High/Low, whereby "logically" Low would be ground, but it's not seemingly as simple as that.

How and what can I use to read the High/Low (1/0) signal from the digital out, and convert this into a traditional ground??

Kind regards and Thanks in advance!

 

[RandomGrinch]

How and what can I use to read the High/Low (1/0) signal from the digital out, and convert this into a traditional ground??

You can treat an open collector as a simple switch connecting your circuit to ground.

If you have a device connected to +V and the other side to the open collector, when the open collector is turned on, the circuit is made and the device is powered.

If you don't want to power a device, you will need a pull-up resistor to to create a high or low level output - at Vout in this case...

More info here:

Open Collector Outputs - Circuits Geek

Open Collector Outputs are increasingly common in digital chip design, operational amplifiers and micro-controller (Arduino) type applications, for either interfacing with other circuits or for driving high-current loads such as indicator lamps and relays which maybe incompatible with the...

circuitsgeek.com

 

[bernardgreen]

Have you connected the ground of the peripheral to the ground of the peripheral which is listening for a Ground Connection ?

home automation

 

[twixx]

Appreciate your replies! Very much so!

How would this/that look here??

 

[bernardgreen]

Try adding the ground return connection, it might work,

 

[twixx]

I've tried that, sadly it doesn't

Can I use a multimeter to detect High/Low? (Although unsure how that will help)

 

[RandomGrinch]

Pull up resistor!

 

[twixx]

What exactly will that do? What's it pulling up?

If I said I can invert the DOUT signal, does that matter at all?

Also, this DOUT trigger is software controlled. Again, unsure if that matters.

 

[Harry Bloomfield]

As above, you need a pullup resistor, but the resistor needs to be connected to the positive rail, of the equipment which is sensing the change.

Without the pull up, the output level would just float, rather than rising to the positive level.

 

[bernardgreen]

Better to put the pull up resistor at the input end so that the voltage matches the supply voltage at the input device. The driving device at the other end may have a voltage that is higher than the input can cope with.


(( beaten to it by Harry ))

 

[twixx]

Ok, many thanks...! Round 2...

Is a pull up resistor, a specific kind of resistor, or?
And how could I calculate the resistance required? I guess the "Max 3.3A DC" on the DOUT comes in to play?

 

[twixx]

Better to put the pull up resistor at the input end so that the voltage matches the supply voltage at the input device. The driving device at the other end may have a voltage that is higher than the input can cope with.


(( beaten to it by Harry ))

As above, you need a pullup resistor, but the resistor needs to be connected to the positive rail, of the equipment which is sensing the change.

Without the pull up, the output level would just float, rather than rising to the positive level.

So that would just be a case of wiring one leg to the + on the left device (Pin 10) and one leg to the Brown (Pin 2), and then connecting the Brown + Grey?

 

[Harry Bloomfield]

Is a pull up resistor, a specific kind of resistor, or?
And how could I calculate the resistance required? I guess the "Max 3.3A DC" on the DOUT comes in to play?

No, they are just a perfectly normal resistor - anything between 1k and 10k will suffice usually.

So that would just be a case of wiring one leg to the + on the left device (Pin 10) and one leg to the Brown (Pin 2), and then connecting the Brown + Grey?

It's not clear to me in your diagram, which side is sending the instructions, and which is receiving them, but...

The resistors needs to be on the receiving device, connected between the receiving devices input pin and it's positive supply.

The idea is - the output is allowed to float, unless pulled to ground. There is nothing to pull the output up, which is where the need for the resistor comes in, to pull the output up. Depending on the receiving device type, anything above 1.7 is seen as a 1, anything below that is seen as a 0.

Open collector, allows multiple devices to all be on the same data line, each able to pull the line down to ground when they signal, but only one input needs to have the pull up resistor.

 

[twixx]

Lovely! You're all stars! Superb.

I've even managed to dig out some resistors from the bottom of a cupboard (10R, 100R, 1K, 10K, 1M and 10M)... based on your reply above, do I need something between 1k and 10k, or would/could a 1/10k work? That said, I assume a few 1K in series would theoretically allow me to land between 1 and 10...

For what its worth, the sender is on the right in this image example. Grey (DOUT) going in to Brown (GND).

So I guess we get this...

I'm assuming this will mean there's /some/ voltage going IN to the line... are any of my devices at risk here, potentially?

 

[Harry Bloomfield]

based on your reply above, do I need something between 1k and 10k, or would/could a 1/10k work? That said, I assume a few 1K in series would theoretically allow me to land between 1 and 10...

Sorry, I don't understand any of that, but do not put any resistors in series - just the one resistor in your final diagram, will work fine.