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Discussion in 'Electronic Basics' started by Ed, Apr 13, 2007.

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  1. Ed

    Ed Guest

    (Earilier posted in .design - moved here by recommendation.)

    Many moons ago, I was an electronics repairman in the military. Most
    tubes had been replaced by then with solid state, which of course was
    gaining wide use in the commercial world! I was a dabbler in
    circuitry, and devoured the TTL Cookbook I bought at Radio shack
    with any component I wanted.

    25 years later, Radio Shack is something different and so is
    electronics. I'm sure E=IR still works, but I'm not sure what they
    with it any more! The most I get to do with "electronics" is change
    ballast in a flourescent light! Everything seems to be programmed -
    well, I dabble in VB6 and VBA macros, but that's it. But I've got a
    couple of things I'd like to see if I can cobble together, and I'm
    wondering if this is a good place for me to start.

    Two projects right now:

    Project 1: A digital metronome of sorts. A footswitch that would
    count the time intervals between successive taps of my toe, average
    the times, and flash a light at that interval. That would connect to
    a unit by my hand that would have buttons to increase and decrease
    time interval counts. I also want a number pad for direct entry of a
    number that would set a "beat time".

    I'm figuring I would need a stable frequency generator of some kind
    into a pulse counter. A tap on the foot button would zero the
    and open a gate for about 10 seconds - within that time, every
    successive tap would capture the number of pulses between taps and
    increment a tap counter, add the count to the previous one and divide
    by the number of taps to get the average. The average is fed into a
    counter that flashes a light after this many pulses.

    So far, not bad. I did things of that sort with 555s and TTL up/down
    counters. But adding and averaging weren't included. And now I want
    buttons that will increment that count by a plus or minus, and I want
    to directly enter a count. Which means I also need a display, and I
    need a circuit to convert whatever the actual pulse count is into
    something meaningful in my world, and convert my entered number into
    pulse count the unit can deal with.

    Am I out of my league yet?

    Project 2: A comparative thermostatic controller for an attic fan.
    live in the Arizona desert and want a fan in my attic to cool things
    down up there. If I set it for say 120 degrees, the thing will run
    day and night for months! So I'd lke to compare the attic temp to
    ambient temp, trigger it on when the attic raises maybe 20 degrees
    above and shut off when the temps are even.

    I have looked up temperature chips on the internet, but I've never
    worked with any. I imagine there would be voltage comparators and
    flip-flops (do they still use those?) to control the on/off.

    So how are we doing? Should I be here for help with these? Or over
    in the "wishful thinking" group?

  2. default

    default Guest

    I'm in a similar situation. Navy CTM. For the metronome a
    programmable chip is the answer and there will be plenty of folks to
    recommend one - I've used the basic stamp and it would do it at a cost
    of ~$50-100 with the hardware and a relatively steep learning curve
    if you aren't used to programming. But it is some fun learning to do
    it - and you'll likely spend hours just getting some leds to blink
    until you get proficient.

    Someone in the group has recommended the picaxe chip for simple tasks
    - I have no experience with it but had no problem convincing myself
    that it is so easy and inexpensive that I have to learn it. That chip
    is available in several flavors from 8 to 40 pins. It is just a
    programmable logic chip with a bootstrap loader burned into memory -
    the programming is done in Basic and a (free) compiler sends the
    machine language over to the chip on a serial cable from your

    All you need to start is the $3 chip and some breadboarding stuff and
    a cable - or for your metronome you'd likely need the $8 (18 pin
    version) All the manuals software and tutorials are on line and free.

    I ordered the stuff from on line and a $20 book
    from total cost with 3 chips, USB to serial cable
    and prototyping board was under $40 (minus the book - I like paper and
    have a cheesy printer)

    I don't know how one learns Basic these days - I learned with a Radio
    Shack Color Computer years ago - then an Action Instruments
    programmable industrial controller that used SYBLE (or something like
    that) it was easy to use and I had a robotic system running in a few
    weeks. SYBLE is BASIC with a few additional commands to turn things
    on and off and add time delays easily.

    I think they call the technique you mean digital smoothing or
    averaging. Measure the time between taps and average until you get to
    some number of total taps then start throwing out the first ones. Tap
    one and two are averaged, then three, four, five, then throw out five
    and keep averaging the last five counts. (or some number I
    arbitrarily said five) Subroutine takes the average time and
    calculates frequency based on period.
    The second project is very easy. Two temperature sensing chips like
    the LM318 (if I remember the # - National Semiconductor has it -
    they'll probably still provide free databooks or a CD with the entire
    searchable component line) or just a pair of thermistors and an analog
    comparator, feeding a solid state relay. You'd have to tinker with
    the calibration and deadband settings a bit. Op Amp Cookbook would be
    a good place to start if you haven't used them in awhile.

    I built a small incubator that does something like that - use two
    comparators with one pot to set temperature and another for deadband.
    As temperature drops, the heater comes on. When the ambient gets high
    enough it turns on a fan - a pot sets the difference between both
    control points and one sets the whole range.
  3. <snip for brevity>

    See, it's like the twilight zone (get it?) Same people, different tudes.
    ;-) Like Joerg said before, the TI MSP430 is a popular micro with
    hobbyists. You already know I do the PIC thing. There is another micro
    that has allot of popularity called an AVR. Pretty much equivalent to a
    PIC, but different. That's more of a Ford/Chevy issue than anything. The
    AVR is a little more friendly with C compiler expectations.

    Microcontrollers rock, learn to use them properly and you will agree. You
    will be able to build things you never thought possible.
  4. Ed wrote:
    Unless you want to wire up a square foot or so of logic
    chips, this really would be a nice project for a small
    microprocessor, like a PIC or AVR. But getting up to speed
    to load up the first one is a pretty steep climb. After
    that it just gets easier and easier.
    This is much simpler than project 1. A couple thermistors
    or integrated temperature sensors, or even a pair of
    transistors or diodes as temperature sensors, some opamps to
    build up any small signals to something robust, a comparator
    (or opamp operated as a comparator, since speed is not
    important) to make the decision and a solid state relay to
    drive the fan and you are there. I built one of these 10
    years ago, to heat a basement by ducting hot attic air to
    the basement any time the attic was warmer than the basement.

    To get started on either of these two projects or anything
    in between, I suggest you get familiar with operational
    amplifiers (and their comparator cousins) and the 4000
    family of CMOS logic, which is about as simple and forgiving
    as any logic will ever be. But don't wait too long to get
    your 4000 series parts in DIP packages. They are getting
    obsolete as we discuss.

    Here is an opamp tutorial to get you started.
  5. Randy Day

    Randy Day Guest

    Heh. It's a galaxy of choice out there, that's for sure.
    Fortunately, most of it's dirt cheap; perfect for
    So you know a bit of programming. That helps.
    Project 1 is tailor-made for a microcontroller;
    not only does it have a clock source on-chip,
    it'll count pulses, read buttons, flash leds,
    add/average and other math. It'll also drive or
    interface with any type of display you want.

    You'll want to get an idea how many inputs and
    outputs you'll need, pick a micro that has
    enough i/o ($2 to $20), then buy or build a
    programmer for it.

    The PIC, the Basic Stamp and the PicAxe are
    the three that get talked about most on s.e.b.
    Each family has small, cheap i/o devices, with
    a few K of memory; midrange devices with stuff
    like analog-digital conversion, USB and RS232
    i/o capability; high-end units with lots of
    i/o, onboard memory space and peripherals.

    Most uC's have flash memory versions, so you
    can burn (program) them thousands of times
    over and over; great for debugging.

    The 'net has lots of freeware compilers and
    schematics for uC burners, but you may need to
    spend time getting it all to work together.

    The commercial kits ($80 to $300) include
    software and the hardware necessary to program
    the chip. I bought a PicKit 2 for PIC's that
    programs via the USB port on my PC. I can
    compile and burn to chip with a few mouseclicks.
    Got a bug? Recompile, burn again.

    The downside? Learning curve. uC's like the
    Basic Stamp use a variation of the Basic language
    to program the micro, so there's a bit of
    familiarity for you. A purchased learners kit
    will have tutorials, and example code to flash
    led's, read buttons, that sort of thing.
    You tell us! ;)
    The only temp sensor I'm familiar with is the
    LM35, and only because I have one in my parts
    bin. Two of those in a window comparator
    circuit might work.
    This is definitely the place. No question is too
    simple, though some of the answers can be ;)

  6. Ed

    Ed Guest

    Okay - I feel that ~here~! <G>

    Thanks to everyone for all the tips. I'll look some things up and
    post back with each project as I come to it.


    "Just remember that everything electrical runs on smoke. If you ever
    let the smoke out, it will never run again!"
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