Connecting 12V open collector output to LM Reactor input

[Regis]

Hello,
I am not sure if this is the best place to ask but I don't know anyone locally to ask this question.

I have a device (EVVA EMZY motorized lock) which has an open collector output described as "max 12V / 300 mA" which I would like to connect to one of the LogicMachine Reactor inputs. The ampere rating is fine but LogciMachine is 24V and this device clearly expects 12V max.

I have tried reading up on open collectors, etc. but I really lack the basic electrical engineering knowledge to even understand most of what I can find about this. I think I need a pull up resistor and probably an optocoupler or a transistor to convert the voltage, but that is about it.

I tried to ask for someone around here who can design this for me but so far no luck. I am really reluctant to just try something, considering both LM and the lock are pretty expensive.

Any ideas? I am sure it is a really simple job for someone who knows what they are doing but that is not me...

[admin]

Which Reactor version are you using? Newer versions with 1-Wire have +5V output which you can use for pull-up resistor.

[Regis]

Thanks for the reply. I do in fact have the GND and +5V terminals. It is a great idea.

So the connection would be:
1st wire:
LM +5V out <-> pull up resistor <-> open collector on the lock <-> LM digital input
2nd wire:
GND next to the 1wire terminal <-> ground on the lock power supply

Correct?

I assume I need to connect the grounds but that should be fine since both devices are powered by (presumably floating ground) transformers. Right? And I also assume the GND next to the 1wire is connected to the 24V ground which the digital inputs use...?

Any suggestions for the value of the pull up resistor? I am not sure what is the specification of the +5V output. Assuming simple Ohm's law, 10k Ohm resistor should result in 0.5mA draw which should definitely be OK, right?

[Regis]

Alright, here is a picture:
   


I understand if nobody wants to check my circuitry, but can you (admin perhaps?) confirm, the 1-Wire GND terminal is floating ground? I.e. not connected with the 24V - (ground) terminals? My measurements suggest that is the case which in turn means I have to connect the 1-Wire GND to the 24V - terminal for the digital input to properly work... I think.

[CHOUAIBOU]

Alright, here is a picture:



I understand if nobody wants to check my circuitry, but can you (admin perhaps?) confirm, the 1-Wire GND terminal is floating ground? I.e. not connected with the 24V - (ground) terminals? My measurements suggest that is the case which in turn means I have to connect the 1-Wire GND to the 24V - terminal for the digital input to properly work... I think.

Hi Regis,
If you need help, please post the EVVA EMZY motorized lock datasheet and give the version of your reactor logic machine. 

I am not sure your wiring is correct at this point.

BR,
Chouaibou.

[admin]

All GND terminals on LM are connected to PSU minus output via a ferrite chip filter. There's no need to connect GND to PSU minus.

[Regis]

Thanks for the replies.

Here is all the EVVA EMZY documentation I could find:

User manual (contains most of the info):
https://www.evva.com/fileadmin/user_uplo...l_1-04.pdf

Datasheet:
http://www.evva.se/fileadmin/files_all/D...35i_EN.pdf

Mounting manual:
https://www.evva.com/fileadmin/user_uplo...139.02.pdf

Sadly none of those contain any examples of the open collector connection. Only the specification (12V 300mA).

I came up with a simplified wiring which I think might work. However it all depends on whether my understanding of how the open collector works in general is correct or not...
   

Basically I am pulling the +12V from the EVVA PSU rather than the +5V from LogicMachine. It increases the draw current but it should still be negligible I think... (1.2 mA)


EDIT: Also I don't know how to find which LogicMachine version I have. It is about a year old, revision 5, Reactor model, CPU (from system info): ARMv7 Processor rev 5 (v7l). It looks more or less like the LogicMachine5 Reactor IO v2 on the OpenRB web page, but without the BNC connector on top.

[admin]

Open collector output is either floating or connected to GND. This is why you need a pull-up. The advantage is that external input voltage can be freely chosen. In case of LM inputs any voltage below 30 is fine. Your scheme looks correct.