PARALLEL PORT INTERFACING

Discussion in 'General Electronics Chat' started by arunk, Nov 11, 2008.

  1. arunk

    Thread Starter New Member

    Nov 11, 2008
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    hi,

    i want to interface my adc 0804 to a parallel port in a windows pc and use c to aquire and manipulate the data.
    and i need information regarding that

    Thaks In Advance
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    I dont know about the programming needed to implement the control of a PC parallel port but for the hardware i suggest you to use opto-isolators to interface the outputs of the ADC to the parallel port because any fault voltages on the ADC board will destroy your mother board.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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  4. wskehr52

    New Member

    Nov 10, 2008
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    It would seem that about any existing circuit that connects directly to the parallel port could be made more robust if that circuit was isolated so that any appropriate power supply could be used, without reguard to possible damage to the parallel port or attached motherboard.

    Does anyone have any suggestions or examples of circuits for opto-isolators?

    There seem to be plenty of examples of opto-isolators used to isolate signals coming from the parallel port to external devices (for example transistors that drive relays). But there don't seem to be examples of opto-isolators used to isolate incoming signals.

    It seems that this might be a harder project to do. Many circuits show using one of the parallel port signals as the positive power supply so this seems like there might not be enough current to drive the transistors in the output part of an opto-isolator.

    I suppose that a battery could be added to the circuit. That may seem crude but it would help satisfy any requirement that the external circuits (including the power) are isolated from the parallel port.

    There are several examples of using an ADC on a parallel port for Windows, some that are referenced are LPTScope or ScopeOnPc. There also seems to be sufficient Linux resources for this application. But these don't show using opto-isolators in the circuits.

    So it seems that isolating the parallel port would both protect the port and also allow more current (if necessary) to the driver circuit.
     
    Last edited: Nov 17, 2008
  5. Wendy

    Moderator

    Mar 24, 2008
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    The main thing is don't make a mistake wiring it. I don't see a major advantage between optoisolators and transistors as long as you don't slip, make a mistake either way and the port is toast. Which brings us back to the sacrifical port.

    If you are controlling AC then SSRs (Solid State Relays) are ready made optoisolators, no extra circuitry needed for the port side. You need be extra careful, of course.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    Bill,
    I agree that if you connect either optos or transistors wrong on the port it will be destroyed but, in my opinion, optos offer greater protection against voltage spikes than single transistors.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    BE junctions are pretty safe, IMO. The resistors will provide some buffering too.
     
  8. wskehr52

    New Member

    Nov 10, 2008
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    For circuits where the parallel port is controlling something, there is probably more protection in the circuitry than in this case where the data is coming into the parallel port. When the port is expected to control devices, there will be transistors and/or relays designed into the circuit to match the expected use. For a relay there could also be seperation of the power supplies on both sides of the relay.

    But for input, the control circuitry isn't there to take any misfortunate power. An ADC and a few resistors seem to be a lot less of a buffer than a relay. And if the grounds are tied together between the port and the signal being measured, that's just another potential problem.

    Think about a current surge protector that has protection on the AC line, phone or ethernet connection, and the cable connection. The basic idea is to have all possible routes protected.
     
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