Relay-like interface

Discussion in 'General Electronics Chat' started by drkblog, Dec 3, 2013.

  1. drkblog

    Thread Starter Member

    Oct 4, 2012
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    I've built a sensor (an infrared barrier) for replacing an old one, and it's almost done. But I have to interface it with a input/output board for PC (which is legacy too) and have almost no documentation. The old barrier had a relay and was connected to the board with that. But I don't want to use a mechanical part here so I thought I could replace the relay with a simple transistor working like a switch. I have to measure it yet, but I don think the board works with voltage above 12V (maximum).

    What do you think about it?
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    Based on information provided, I don't see a problem.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    I think it's pretty tough without more detail. Was this relay meant to be controlled by a parallel port, or a special interface board, or what?

    A relay can usually be replaced with a transistor if you are switching a DC load. Your relay was probably meant to switch and AC load?

    [edit] Oh, I see you have an interface board. Maybe a search for documentation would be worth some effort.
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    Does the relay has three contacts for one set or six contacts for two sets?

    And how is the voltage of relay, 6V or 12V, if you can't make sure then you have to unsolder it from the PCB and using the power to measure it.

    And how is the load current of the relay contacts?
     
  5. drkblog

    Thread Starter Member

    Oct 4, 2012
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    Thank you all!

    I posted it as a generic question. I'm going to add some detail tonight as soon as I receive the board (I just saw the board some days ago and have no further information yet).

    I assume the board won't use more than 12V to sense the relay state. The old barrier used a solid state relay. But it was intended for handling other devices different from this board. I mean, the manufacturer built the barrier in order to be connected to non-digital devices working at line voltage. (220/110V)
     
  6. BReeves

    Member

    Nov 24, 2012
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    The I/O cards I have worked with have resistor networks on the input of the optoisolators that can be changed to determine the working input voltage.
    This is a link to an example from Sealevel, on page 11 is the resistor chart. Maybe you can compare your board to this and determine what input voltage your board is expecting.

    http://www.sealevel.com/support/getAttach/59/AA-00253/3096.pdf
     
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  7. drkblog

    Thread Starter Member

    Oct 4, 2012
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    The board you linked seems to expect a given voltage at the input. But I think (I mailed someone to check this) this board provides its own voltage and expects the circuit to be closed or opened in the other end. According to a connection scheme I have, they are using to wire connection between the board and the sensor. So my assumption should be correct unless they have an external power supply in the middle. For simplicity I asked them to measure the voltage over the pins connected to the sensor (with and without the sensor connected to it). That should give me enough information, I guess. So I don't have to go and see for myself. :)
     
  8. inwo

    Well-Known Member

    Nov 7, 2013
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    Seems you need an open collector output on your device. Which is pretty standard.

    Use an opto-isolated open collector if you need isolation.
     
  9. drkblog

    Thread Starter Member

    Oct 4, 2012
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    That's what I think. I will have more detail after this Saturday.

    I guess I can skip the opto-isolation as I know this will be connected to this specific board only. The only case for a destruction I can think of is the wire getting in contact with a high voltage source (220V line, for example) but it's unlikely this could happen.
     
  10. BReeves

    Member

    Nov 24, 2012
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    Wonder if they are using the PC Parallel port for DIO. We went to the p-port when we no longer needed more than one input. Still used an opto to pull the pin low, built the opto into the shell of a 25 pin connector.
     
  11. drkblog

    Thread Starter Member

    Oct 4, 2012
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    No, I have the actual board in my hands (but this one is not working). It's interfaced through the serial port and has its own opto-isolation.
     
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