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Timer problem with Parallel port monitoring

Discussion in 'Electronic Basics' started by [email protected], May 13, 2013.

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  1. Guest

    Hey everyone,
    I'm very much so a newbie at electronics, but figured I'd try and tacklea problem for my scout group: making a pinewood car timer.

    I found this schematic online that uses optical transmitters:

    I have hooked everything up as seen in the schematic to the best of my ability... I have hooked up the parallel port grounds (Pins 18-25) also to thenegative row at the bottom of my breadboard, so all the grounds are on thesame line (I couldn't figure out how else to do that).

    Here's my problem: Using parmon to monitor the parallel port, when I hit any of the sensors (say the start gate for example), it changes the status on all the pins that are hooked up.

    Pins 10,11,12,13, and 15 all read "1". I trigger the start gate switch (hooked up to pin 15). Now ALL of my pins (10,11,12,13, and 15) all toggle over to "0". Similar thing happens if I hit just ONE photoelectric diode with a flashlight, ALL trip to 0, not just the one pin that that diode is hooked to.

    I've written my matlab code to poll everything and run the race, but since I can't differentiate which sensor is getting twigged, I can't determine which sensor came across first...

    Any help/suggestions would be fantastic.

    Thanks in advance,
  2. Daniel Pitts

    Daniel Pitts Guest

    When you toggle the "start gate" switch, only pin 15 should change from
    high to low (voltage, I don't know whether that means 0 or 1).

    If more than that switches, check the voltage levels from ground to the
    rest of the pins. It could be that your "power supply" just can't handle
    the load.

    Make sure you're using 10kΩ resistors (brown black orange). Test them
    with an ohm meter (removing them from the circuit first).

    Make sure your not inadvertently shorting the signal lines some how.

    Try disconnecting all the phototransistors. With-out them in the
    circuits, you should read all high-level except for the start-level
    switch. If that *isn't* the case, start removing all the other line
    connections until it is the case.

    Perhaps you could upload a photo of your protoboard somewhere for us to
    look at. Sometimes you think you've wired it one way, but it is actually
    wired a different way.

    Anyway, I hope my suggestions help you. I'm somewhat new to this myself.

    Good luck,
  3. Guest

    Thanks so much for your response. I will check this out, hopefully I can squeeze it in over lunch.
  4. Guest

    Thanks so much for your input. I thought I'd have time on my lunch break to test some things but couldn't squeeze it in. I'm going to go through these tests this evening and try to isolate/debug it.

    Thanks everyone for the help!

  5. P E Schoen

    P E Schoen Guest

    wrote in message
    I was not familiar with parmon so I looked into it and it seems like a
    useful program. I also found many other helpful tutorials and applications.
    Interfacing to the parallel port was pretty easy with MSDOS and early
    computers as were standard when I developed some products in the early
    1990s, but after Win98 and the ubiquitous USB port, the LPT port vanished
    and I had to redesign my hardware and software. Here are some links that may
    help: (updated version with bug fix) (Jan Axelson)

    Good luck with your project!

  6. Jasen Betts

    Jasen Betts Guest

    "GND" at the bottom if the diagram should be connected directly to "GND"
    on the parallel port and to nothing else.

    +5V should always measure about 5V to gnd (parport pin 25)
    any voltage from (3.5 to 5.5V) should be ok.

    the device can probably be powered from pins 1-5 of the parallel port
    instead of from an external supply. to do this: to set those pins to
    output and high. Then disconnect the top end of each resistor and
    reconnect it to diffetent parport pin.
  7. tuinkabouter

    tuinkabouter Guest

    The RS-232 standard defines the voltage levels that correspond to
    logical one and logical zero levels for the data transmission and the
    control signal lines. Valid signals are either in the range of +3 to +15
    volts or the range -3 to -15 volts with respect to the ground/common pin;
    consequently, the range between -3 to +3 volts is not a valid RS-232 level.


    Some PC builders cut corners and then it may work.
    So try another PC or redesign the schematic.
  8. P E Schoen

    P E Schoen Guest

    "tuinkabouter" wrote in message
    The OP is using the Centronics parallel port and not the RS-232 serial port.
    Older computers used a 25 pin Dsub connector for both, but the serial port
    was male while the parallel port has always been female. The early parallel
    ports used an 8255 PIO which could be reconfigured by writing to the control
    port address, but in later machines it was usually incorporated into
    proprietary chips on the motherboard (or on plug-in ISA or PCI cards).

    There were some improvements (enhancements) to the parallel port such as
    EPP, which I think was faster and designed for bidirectional data transfer.
    But it had to be compatible with old versions of software and hardware so
    there is usually a BIOS option for SPP or EPP. AFAIK all of them use TTL or
    CMOS logic levels of nominally 0 and 5 VDC with transition at about 0.7V.

    I have also found that some parallel ports work much better if pull-up
    resistors of 4.7k or so are added.

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