# Connect two different sources with two Digital Ouptuts using an Adam 4055

I would like to operate an Adam 4055 module to control two different applications having their own power supply.

Adam 4055 is Digital Input/Output control module over RS-485, I use only the DO part here. Reading the doc, Adam 4055 DO are Open Collectors.

I have adapted schematic from manufacturer documentation (page 81 in search bar, P.67 within the footpage, section 3.16.1, schematic is embedded bellow) which is using a single power supply:

Provided both load loops respect manufacturer prescriptions (power, voltage, drained current), is the following schematic correct and safe (nodes are labeled as they will be connected to the module):

simulate this circuit – Schematic created using CircuitLab

In this setup I could not use pin DO.COM (I currently do not know if I must use this pin, doc is not explicit about that) because sources have different voltages. I just connect Ground (D.GND) pin to make both power supply having the same potential reference.

Is this setup correct and safe? Will it require improvement?

• May I ask why my question is downvoted? I'll be glad to improve it. – jlandercy Jun 15 '18 at 9:37
• Show page 81 - don't expect ten guys using this site to trawl through that document looking for page 81. As it happens, it appears pg 81 is the wrong page. Show the circuit. – Andy aka Jun 15 '18 at 9:38
• I down voted it for obvious reasons (see above). – Andy aka Jun 15 '18 at 9:38
• @Andyaka, Sorry my schematic isn't clear? I found your path a bit rude, I am not used to EE, what can I do to make it suit EE guide lines? Should I remove the reference to the docomentation? – jlandercy Jun 15 '18 at 9:39
• @jlandercy What you did seems right at the first glance, but I can't be sure, because I found nowhere an explanation of the purpose of this DO.COM pin. The documentation is very explicit about the inputs (there are schematics of the internals of the inputs), but it is unclear about the outputs. Is the purpose of this DO.COM pin explicited somewhere? – dim Jun 15 '18 at 13:47

I am answering my own question because I think it fits better than updating the question. Feel free to comment I update the post accordingly if it does not suit the EE.SE guidelines.

As @dim suggested, I have contacted the manufacturer and I have received an answer. The IC inside the Adam-4055 driving Digital Outputs is a ULN2803 (specs, info). The reason why they connect the D0.COM pin is to take advantage of the built-in the fly-back diodes.

The Open Collector gate is a Darlington:

According to this new information, I think I can:

• Share the D.GND pin among power sources;
• Skip the D0.COM pin and miss the built-in fly-back diodes;
• Use different power sources (within the IC specification);
• Add additional fly-back diodes on inductive loads to protect the IC;
• Add Optocoupler if I want to completely isolate loads from IC.

A possible setup is now (I may have not chosen the best symbols):

simulate this circuit – Schematic created using CircuitLab

Now it is just about shipping compliant components provided they exist and are available. Thank you for your valuable feedback.

• Excellent. It makes sense, your solution is correct and you did well by answering your own question. – dim Jun 19 '18 at 10:28