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Interfacing 24V IO + Isolation


#1

Hello,

I would like to read and write 24V digital IO for an external device. I found the Load module that could fit my need for the Output but I don’t know how to handle the inputs. Is there any off-the-shelf module that I can use for Raptor? And I would be more happy if only one additional device can handle the IO together.

I2C interface is free to use. The device below is more or less fine, but I need your suggestions and advice:

http://www.ereshop.com/shop/digital-inputs-c-143_181/?zenid=0cc6ca3426200d61aa4bb4dd31440d10

Isolation is required of course.


#2

@ durnek60 - Those devices look like they will work. However, if you need high speed or an Input to fire an interrupt then they won’t work. You will have the overhead of polling the inputs over I2C.

There are not a whole lot of 24Vdc industrial type offerings out there yet for .NETMF. Hopefully that will change with some time. I have made a shield for the Cerbuino that has 24Vdc I/O but it’s not isolated. I am waiting for bare boards to arrive so I can test my updated version. https://www.ghielectronics.com/community/forum/topic?id=16885
I chose not to isolate I/O because of cost and that in my applications the I/O is powered from the same 24Vdc that powers the Cerbuino.


#3

@ durnek60 - Correction.
I do see that they have an interrupt line that comes back from the I2C chip. This will help a lot if you need to get a notification of Input changes. Still not as fast as local, on chip I/O, but better than polling.


#4

Dear skeller,

Thank you for your answers. I have a similar case where the NETMF device is powered from the controlled machine.

also I do really like your device too, good luck with it. :slight_smile:

Is there any other way to connect 24V to my Raptor? Unfortunately I can not create custom PCB so I am searching a good commercial product.

What does GHI offer? Are they planning to produce any module for this purpose?


#5

@ durnek60 - I am not aware of any upcoming modules from GHI. My guess would be no, they just did a major revamp of their catalog that actually removed a lot of low selling modules.

Depending on your application another option would be to use MODBUS, either RS485 or Ethernet. There are a lot of companies that sell MODBUS enabled I/O.

Option 2 would be to use 24Vdc relays for the inputs. Your Input device would control the coil and the contacts would switch the 3.3Vdc or 5Vdc inputs.


#6

Is there a reason for this ? Is it your required time-to-complete, an expertise gap, or some other factor/concern ?


#7

There are plenty of rs485 interface devices that provide all kinds of isolated inputs and outputs, including connecting 24v. Any these would be a perfect solution.