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Timer chips?

Discussion in 'Electronic Basics' started by BR, Nov 6, 2004.

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  1. BR

    BR Guest

    Could anyone please post some info on timer chips? I'm looking for
    timers controlled by PC serial port. Need three timers on a common
    crystal osc base that are low jitter. Only 0 to 200 Hz pulse train
    and a lot of control resolution over that range, like 16bit. And also
    some provision to initially sync the three timers as in an absolute
    hardware sync, not software, and then the ability to adjust the
    timing of each. Do I have to roll (learn to program) my own?

  2. Marlowe

    Marlowe Guest

    It appears what you are asking could be accomplished by a Microchip PIC
    device. Go to Microchip's web site and look up the specs for the 16F628
    chip. It has three internal timers that can be slaved to an external
    oscillator. Two of the timers TMR0 and TMR2 although they are eight bit
    timers can be quite versatile because they have pre and post scalers. In
    effect they can count to 16 bits. TMR2 is a 16 bit timer. They can
    generate interrupts and TMR2 can interrupt at a loadable value, PR2. And
    the 16F628 is dirt cheap. Costs less than a couple of LEDs. There may be
    other PIC chips that could be better suited for your purposes, I'm only
    familiar with the 628. Oh, the 628 has a built in USART capability which
    can communicate with a PC via a serial port.

    I'm working on a 16F628 electronic ignition project where I use TMR0 to
    count the time between revolution pulses and TMR2 to count down the
    necessary spark delay time. The beauty of using these timers is that once
    loaded and started that keep on counting regardless of what the rest of the
    software is doing. They just keep on ticking.

    Of course to utilize all these features you have to roll your own code and
    then download it onto the PIC.
  3. BR

    BR Guest

    Yes, I believe hardware timers is the only way to provide steady
    pulse trains regardless of all other code execution. I'm looking
    for the minimum needed to provide three variable pulse trains
    controlled by the PC serial port. What about using a Basic stamp
    (easier for me) for the serial stuff and separate chip with 3
    timers? What timer chips should I be considering? Someone had used
    an 82C54 with a stamp. I've been fooling around with CMOS 4000, so
    what do I know. They do function well for low freq stuff, but
    changing divider outputs on a breadboard is getting tiring and I
    can't keep track of what changes are made verses time. It's like
    the stone age here.

  4. Marlowe

    Marlowe Guest

    The BASIC STAMP is certainly a possibility, but out of my area of expertise.
    It does have a PIC embedded in it so you might to look into the PIC on the
    STAMP to evaluate the number and capability of the internal timers. If it
    is using something like the PIC 16F628 or the 16F648 you can possibly do
    everything (serial IF, timers, etc) within the STAMP. The other possibility
    is to use the PICAXE system. Do an internet search on this keyword. The
    last time I looked on Ebay they had several for sale.

  5. BR

    BR Guest

    Just realized that MBASIC was available for the 16F628. I wanted to
    avoid ASM if possible.

    PICAXE looks like a good cheaper alternative to the STAMP (despite
    falling dollar). I like the built-in bootstrap and no need for
    programmer board. Thanks for the info.
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