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Timer Circuits or PIC

Discussion in 'Electronic Basics' started by Rob Convery, Sep 13, 2005.

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  1. Rob Convery

    Rob Convery Guest

    I am working on a project where I am going to be controlling a number of
    rams. These are triggered using solenoids. I am trying to work out the best
    method of controlling these. The whole setup will have 5 instances of the
    setup described below (this may effect how you suggest doing this). I am
    working in a environment with a supply voltage of +12v.

    I have a single pulse trigger which I need to subsequently operate 2 outputs
    using delays using a 2nd input to decided what to trigger. In Summary.

    Trigger input pulses High
    If Input Z if ground Then
    Output A must go high for X (approx 5-10) seconds
    Output C must delay for X (probably 2), then high for X seconds
    (probably 2)
    Output B must go high for X (approx 5-10) seconds
    Output C must delay for X (probably 2), then high for X seconds
    (probably 2)
    end else

    or pictorally

    Trigger ___|-|_______________________
    InZ _____________________________
    A ____|-------------------|____
    B _____________________________
    C __________|--|_______________


    Trigger ___|-|_______________________
    InZ -----------------------------
    A _____________________________
    B ____|-------------------|____
    C __________|--|_______________

    (Copy above to notepad if it displays incorrectly)

    So what is the best way of implementing this. Should I use a combination of
    timer circuits to do this but with having 5 of these it would become a mass
    of timer circuits. Alternatively I could program a PIC or PICs do to this (I
    have never done PIC programming - well other than some traffic light thing
    during electronics at Uni, but should be able to pick it up as I am a
    programmer/tester by day)

    Cheers for any advice

  2. John Fields

    John Fields Guest

    Copying to notepad won't help...

    If this is what you mean:

    t0-->|_ t0-->|_
    Trigger ___| |_________________..._____| |_____________________
    ____ __________________________
    InZ ____|______________________...__|
    A _________| |___..._____________________________
    |<--- 5-10s --->|
    B _____________________________..._____| |_______
    |<--- 5-10s --->|
    ___ ___
    C _____________| |___________...________| |________________
    2s-->| |<-- 2s-->| |<--
    -->| |<--2s -->| |<--2s

    If you build it out of glue logic then you'll need a timer for A,
    one for B, one for C, and one for the delay before C. You'll also
    need an inverter to select between A and B, so if the timers are
    dual one-shots like 4538's or HC123's it'll cost you 4 chips per
    channel plus four timing caps, four timing resistors (probably pots
    if you're not sure what you timing requirements will be). Also, for
    the board, one hex inverter and one RC for the power-on reset.

    That's 11 chips and 42 discretes total, versus a single
    microcontroller and a ceramic resonator if you need better accuracy
    than you can get with the µC's internal clock oscillator.

    If you write code for the µC, the choice of which way to go is
    pretty much a no-brainer, huh?

    BTW, you could use a single timer for A and B, but then you'd have
    to steer its output, which would cost you three quad 2-input ANDs.
    So your savings in one-shots(2 chips) would be offset by the need
    for the three quad 2-input ANDs, so that would cost you an extra
    chip. You'd save ten discretes, though...

    Still a no-brainer, I think.
  3. ehsjr

    ehsjr Guest

    I agree strongly with John. Even if the hardware did not present
    such a compelling case, I still think a micro-controller would be
    better in this case, based on your requirements. They included the
    terms "approx" and "probably" 6 times, indicating there is some
    possible variability in what you need to do.

  4. ___
    Trigger ______| |___________________________

    InZ _______________________________________

    A _______| |________

    B ________________________________________

    C __________________| |______________

    Chelp ________| |_____________________

    Redraw (part of) your pulse diagrams to make sure I understand what you want
    to achieve. A circuit that behaves like this can be build using two dual
    monostable ICs like the old CD4098B or the CD4538B along with four Rs and
    four Cs for the timing and one inverter. One IC should be used to make the
    A- and the B-pulse. Connect the TR+ inputs to the Trigger, one TR- input to
    InZ and the other TR- input to the inverted InZ. The second IC can make the
    C-pulse. One monostable (making Chelp) is triggered by the raising edge
    Trigger, the second is triggered by the falling edge of the first. If the
    circuit is one of a kind *and* you have plenty of space for the components
    *and* you have neither the skills nor the equipment to program PICs this is
    the way to go. But in all other cases I'd prefer an eight pins PIC (or a
    collegue, a tiny AVR) to do the job. Keep in mind that a PIC requires 5V
    (common types) power. Which means an 7805 and two caps. PICs also do not
    like pulse >5V on their inputs so you may need a voltage divider for both
    inputs. You will also need output transistors as neither the monostables nor
    the micros are able te drive a solenoid.

    petrus bitbyter
  5. mike

    mike Guest

    Your use of the word "ram" conjures visions of maiming
    or other destruction when things go horribly wrong.
    Might want to invest in some position sensors, watchdog
    timers and maybe even external solenoid drive gates in case
    the processor goes horribly wrong. A cap on the gate function
    of a solenoid driver kicked by a watchdog timer gives you two
    levels of protection.
    PIC lends itself well to including these safety featurs
    at virtually no extra cost or complexity. Writing the code
    forces you to think about what might go wrong and what
    might be done to minimize the destruction.

    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    Wanted, PCMCIA SCSI Card for HP m820 CDRW.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Wanted 12" LCD for Compaq Armada 7770MT.
    Bunch of stuff For Sale and Wanted at the link below.
  6. Rob Convery

    Rob Convery Guest

    Thanks - I suspected so. Now the nest question. As I have not done PIC
    progamming since uni what is the easiest way to get into this? Is there a
    decent kit out there etc? Also any specif place for support i.e.


  7. John Fields

    John Fields Guest

    I don't do PICs because I like Motorola (Freescale) better, but this
    will get you going if you want to use Microchip's stuff...

    Also, some of the other guys around here and on sed use PIC's so
    maybe you'll get some info from them.

    Then there are also the comp.arch.embedded newsgroups.
  8. Rich Grise

    Rich Grise Guest

    John gave you the link to the microchip site, but here's a sample of
    what's out there:

    I've also download their MPLAB IDE package, although I haven't got
    too heavily into it yet.

    Have Fun!
  9. mike

    mike Guest

    If you're comfortable with assembly language programming, maplab will do
    what you need for free. There are also several other free or cheap
    programming environments. But if this is your job and your boss cares
    about your efficiency, go buy PIC Basic Pro. It turns fairly complex
    situations into simple statements and can dramatically reduce your
    error rate.

    Use a 16F877A 40-pin dip. Download a free bootloader.
    Once you get the serial port hooked up, you'll be able to modify the
    program and be back testing it in seconds. The serial port connection
    comes in very handy to report real-time status of your system. You only
    need the PIC programmer to install the bootloader the first time.
    After you get it all debugged, you can think about switching to a
    smaller part, but it's probably not worth the effort unless you wanna
    make thousands...or the big chip won't fit in the box. There are newer
    parts, but then you gotta go find newer tools...

    I've made a lot of assumptions about what you're doing and made
    recommendations on what I KNOW works. You'll get lots of arguments
    over individual pieces, but you need a system that works. YMMV

    Email me if you wanna discuss further.

    Return address is VALID but some sites block emails
    with links. Delete this sig when replying.
    Wanted, PCMCIA SCSI Card for HP m820 CDRW.
    FS 500MHz Tek DSOscilloscope TDS540 Make Offer
    Wanted 12" LCD for Compaq Armada 7770MT.
    Bunch of stuff For Sale and Wanted at the link below.
  10. A PIC-AXE (Google it) is by far the easiest way to program a micro. No
    harwdare needed and it uses simple commands in BASIC.
    A PIC-AXE is a regular PIC chip with a BASIC interpreter pre-programmed
    into it. So you don't need to know anything about the PIC architecture
    in order to program it. They are CHEAP too.
    A PIC-BASIC Pro compiler with the PIC hardware programmer is more
    complicated than a PIC-AXE.

    BASIC-Stamps are similar but are a more expensive "module" solution.
    PIC-AXE kills it for an apllication like this.

    Dave :)
  11. Jasen Betts

    Jasen Betts Guest

    use a PLC :)
    if you know PIC assembler (or programming and any assember) it shouldn't be
    a tough task to implement each on a separate microcontroller

    if you want to make it a tougher task implement all 5 on a single chip :)

  12. Jasen Betts

    Jasen Betts Guest

    There's comp.sys.embedded but I stopped reading that as *.electronics.* is
    keeping me busy enough.

    as for hardware any serious electronics store (amy many hobbiest electronics
    stores) will have development kits of some kind. there's plenty of software
    out there on the internet.

  13. quietguy

    quietguy Guest

    I would suggest using a PICAXE rather than a PIC - they are just as cheap, but
    the mfg provides a free programmer which allows you to program in BASIC on a
    Windows box, and you only need a simple Serial port lead and two resistors to
    enable on board downloading. And of course there is lots of free stuff on the
    web to get you started

    They also have a number of development boards, kits etc

    As a starting point have a look at - you will
    find other links there as well

  14. Rich Grise

    Rich Grise Guest

    Oh, yeah, sounds great, except for the "step-by-step" instructions:

    Step 1, select a chip,
    Step 2, write the program,
    Step 3, connect the cable directly to the project board...

    Wait a minute? Where did this "project board" come from????

  15. It appears as soon as the right amount of money disappears?


  16. quietguy

    quietguy Guest

    The project board can be one they sell, or you just use some veroboard etc or
    any project type board you may have. Depending on the PICAXE you buy - eg 8
    pin, 18 pin etc, the board needs to have a socket for the PICAXE, 2 resistors
    (serial input for programming) , and the usual provision for connecting a 5volt
    supply. Plus of course you might want some leds etc to play with. You also
    need to make up or buy a lead - serial (RS232) plug one end, perhaps a 3.5mm
    stereo plug the other end - so you can program the PICAXE

    I gather you thought it was some expensive rip off thing, but that isn't the
    case. I did buy a (18X) project board, but am also making another one from a
    small piece of veroboard for the 08M PICAXE (A$4.95) to make a musical toy for
    my grandson.

  17. Rich Grise

    Rich Grise Guest

    I've got the serial cable, a protoboard (The white rectangular one
    with the strips of plug-in contacts), and a supply - are you saying
    that I can plug in the chip, power it, two resistors, and plug in the
    serial port, and I'm ready to go? That'd be kewl. Where's the schematic
    for this arrangement?

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