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Need a little help building a 12 volt timer

Discussion in 'Electronic Design' started by Ryan Ashline, Oct 11, 2004.

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  1. Ryan Ashline

    Ryan Ashline Guest

    I am looking for a 12 volt timer or looking to build one. What I
    would like it to do is when powered wait for approx 3 mins (doesnt
    have to be close 15 sec or so +- would be ok) Then trigger a light I
    have for 2-3 secs shut off then repeat the entire sequence again. 3
    mins off 3 secs on. Would some please point me in the right
    direction?

    Thanks for your time

    Ryan Ashline
     
  2. mike

    mike Guest

    Dig up a 555 datasheet and build the astable.
    mike
     
  3. Rich Grise

    Rich Grise Guest

    http://www.national.com/pf/LM/LMC555.html

    There's a circuit in there, and a chart of RC values, from there it's
    just a little arithmetic. I'm not sure what the best caps are these
    days - it used to be polyester, but I've been out of the loop for
    awhile - look for "low leakage".

    Failing that, look for the 4020/4040/4060 - the 4060 has its own
    internal oscillator. You can get an arbitrary time delay with one
    of these and a little bit of logic.

    Have Fun!
    Rich
     
  4. Joerg

    Joerg Guest

    Hi Rich,
    Excellent advice. When stuff goes past the one minute marker these 4000
    logic choices are clearly better than some RC combination on a one-shot.

    Regards, Joerg
     
  5. CFoley1064

    CFoley1064 Guest

    Subject: Re: Need a little help building a 12 volt timer
    Joerg speaks truth -- the longer the time delay, the more chance of something
    coming around to mess timing up like electrical noise from the relay you're
    driving, power supply hash, you name it.

    A lot of time delay relays built in the 1970s and 1980s were based on the 4060,
    mostly because if noise from the relay caused the oscillator to add a count,
    well, there are always 16383 other counts to keep timing stable. These relays
    were never specified at better than 1% repetitive anyway.

    Here's something that should work for you (view in fixed font or M$ Notepad):


    VCCVCC
    + +
    | |10K VCC VCC VCC VCC
    .-..-. + + + +
    VCC 270K| || | | | | |
    + | || |.----o-----o----. | |
    | '-''-'| 8 4 | | C|
    .-------o---------. | | | | 1N4002- C|RY1
    | 16 | | | | | ^ C|
    | |.001uF | | | | | |
    | | | | | | | |
    | | || | | | | | |
    | 3o---||--|--o-o2 3o------. '---o
    | 4060 | || | | | | |
    .-o8 | | | 555 | | |
    | | | o----o6 | | |
    | | | | | | .-. |
    | | | | | | 1K| | |
    | | 11 10 9 | o----o7 | | | |
    | '-o------o------o-' | | | '-' |
    | | | | 10uF| | | | |/
    | .-. .-. | --- | | o-----|2N3904
    | | | | | --- --- | 1 5 | | |>
    | | | 50K| | --- | '----o-----o----' .-. |
    | '-' '-' |0.1uF | | 1K| | |
    | |220K | | === === | | |
    | | | | GND GND '-' |
    | '------o------' | |
    | | |
    === === ===
    GND GND GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de


    You're using the built-in oscillator on the 4060 to generate a 91 Hz clock with
    the .1uF cap, the 50K resistor, and the 220K resistor. That gets rolled around
    in the divide-by-2^14 ripple counter in the 4060, coming out as 1/180 Hz (do
    the math). That means you get a NGT to trigger the 555 through the .001uF cap
    with the 10K pullup once every 3 minutes. The values of the 555 are set for a
    3 second pulse, which drives the relay through the transistor. Try to find a
    relay with a coil that needs 100mA or less.

    A few notes here. For the 50K resistor in the 4060, you might want to use a
    39K resistor and a 25K pot. For the 270K resistor on the 555, you might want
    to use a 220K resistor and a 100K pot. Use a CMOS 555 if you can -- leakage
    currents on a regular 555 might cause you problems. But the main caveat is,
    don't use electrolytics for either cap, especially the 555. Use a tantalum if
    you can -- it will generally have lower leakage current. Also, keep your
    circuit board clean and out of high humidity environments.

    I hope this has been of use. Questions of this type generally receive a better
    response on sci.electronics.basics.

    Good luck with your project
    Chris
     
  6. Tam/WB2TT

    Tam/WB2TT Guest

    Ryan
    If you are AC powered, and don't have to be exact, just take the power line
    frequency and pass it through a 12 bit binary counter. You will get a cycle
    time of 68 seconds at 60 Hz, and 81 seconds at 50 Hz. Divide that by 2 or 3
    to get a roughly 3 minute trigger.

    Tam
     
  7. Rich Grise

    Rich Grise Guest

    Thank you.
    What???!!!!???? A 555????? We don' need no steeenkeeeng 555!
    Modified by Rich Grise v0.999.69 Alpha 3 ;-)

    * component values for proper timing are left as an exercise for the
    reader. (I didn't even check yours, and am too lazy to figure it out
    for whatever freq you'd need for the above)

    Cheers!
    Rich
     
  8. Not for the application and precision requested by the OP. Quite
    unnecessary. The 555 itself is capable of 1% accuracy (2 secs in 3
    mins). With a modern low-leakage electrolytic as timing capacitor, and
    reasonably careful construction, you could expect close to that even
    for monostable or astable periods of the order of an hour.
     
  9. After switching on power, is it important that the delay before the
    first 3 sec ON should be (approximately) 3 minutes?

    If NO, a simple astable (oscillator) could be used, with a roughly
    1:60 duty cycle (3 mins OFF, 3 secs ON).

    If YES, a monostable (one-shot or timer) needs to be added. This is
    because a simple astable, such as from a 555 or 1/2 x 4001 or 4011,
    starts at an unpredictable position in its cycle. So the delay could
    be *anything* up to 3 mins. As an added complication, if you used a
    555 the delay could be over 4 mins, because the *first* cycle of a 555
    astable is always 30-40% longer than all subsequent cycles.

    You also need to be clear we understand your skill level. Given a
    suitable astable or mono+astable circuit, can you add appropriate
    lamp-driving circuitry yourself? If not, you need to specify more
    details of the lamps and your power supply voltage and current.
     
  10. Tam/WB2TT

    Tam/WB2TT Guest

    How about a compromise desig,:
    1. Build an oscillator with a period of 3 seconds. Easily doable with
    standard component. ( 1 ufd mylar cap + few megaohm)
    2. Feed the output to a 6 bit counter.
    3. Connect the reset lead of the counter to an RC network so it powers up
    000000.
    4. Detect the 111111 state to turn on the light.
    5. This gives 192 seconds OFF, 3 seconds ON.

    Tam
     
  11. Joerg

    Joerg Guest

    Hi Rich,
    To be honest, I have never really used one in a design for a customer
    and if I ever did it would only be the CMOS version. Whenever I needed
    timing I used CD chips, usually Schmitts. If you take a hex chip that
    gives you a timing capability for a silicon cost share of under 2 cents.

    Long timers are usually better done using dividers. After all, the cost
    impact of a polyester cap or larger varieties in other technologies is
    nothing to be sneezed at.

    Regards, Joerg
     
  12. Joerg

    Joerg Guest

    Hi Terry,
    For a one-up project and in a home environment with fairly constant
    temperature and humidity, maybe. But when you look at the cost of low
    leakage electrolytics the picture can change for a commercial product.
    Also, ideally you do not want trim pots and I believe it is nearly
    impossible to obtain an electrolytic under 5% tolerance at reasonable
    cost. Even with polyester that is a challenge as they often cost more
    than two resonators would. I guess that's why someone came up with the 4060.

    Back in my days at the university one of our professors used to joke
    that the quality of a digital designer is inversely proportional to the
    number of one-shots he or she uses. Now I don't quite agree with that
    and I use them a lot myself, even though they will be "home made" rather
    than a 555 or HC123. It's just that the cost picture changes with longer
    timings and cost is usually the predominant factor in a commercial design.

    Regards, Joerg
     
  13. The labor cost of calibrating an analog timer in the minutes can be a
    factor too. For our 3 minute analog timer modules I did a circuit that
    would track and then freeze the capacitor voltage in time long enough
    that the calibration pot could be trimmed (turned out to be trickier
    than it sounds). With digital timers you can bypass most of the
    divider chain to speed up testing. Reset of the capacitor voltage
    becomes a non-issue.
     
  14. Joerg

    Joerg Guest

    Hi Spehro,
    That is probably the reason why most of the start-up delay relays for
    motors use the 4060 or something along those lines.

    Testing can often be done with a poor man's spectrum analyzer: One of
    those radios from Europe that have the long wave band. Just look where
    the harmonics come out. If you let an IF stage oscillate a bit it can be
    even easier to detect. I guess nowadays a sound card with enough dBs of
    preamp would do.

    Regards, Joerg
     
  15. National (IIRC) patented a method of calibrating digital watches by
    optically picking up the multiplex frequency of the LED (yes, early
    watches) digital display and using something like a period counter as
    a display while the trimcap was being tweaked.


    Best regards,
    Spehro Pefhany
     
  16. Peter

    Peter Guest

    A little program like this into a PIC would do the trick.

    main: low 0
    wait 180
    high 0
    wait 3
    goto main

    "wait" counts in seconds, Just add a transistor or a relay to drive the
    load.

    If you are in Australia I could supply the complete unit you are after,
    including the programmed chip. I have about 100 of these PCB's hanging
    around. 12V ac/dc in, same out, max load 5A.

    Just a thought.
     
  17. Joerg

    Joerg Guest

    Hello Spehro,
    Hey, if they were able to patent that scheme I could have patented my LW
    receiver gimmick. Too late, I guess I just spilled the beans ;-) Oh, well.

    Regards, Joerg
     
  18. Rich Grise

    Rich Grise Guest

    Hey, I posted this circuit yesterday, ASCII art and all! Where did my
    post go?

    Thanks,
    Rich
     
  19. Rich Grise

    Rich Grise Guest

    Right here: <[email protected]>

    Cheers!
    Rich
     
  20. Joerg

    Joerg Guest

    Hi Spehro,
    Just wondering: I remember when a friend in high school had one of
    these. Holding it next to an AM radio would muffle all the stations and
    you could hear distinct harmonics between all the pulsating hash when
    turning the AM dial. They could have just picked a harmonic as well and
    attach a pickup coil to the radio, plus feed in a correct frequency or
    harmonics off a "golden watch" for beat. Then it's just a simple tuning
    to zero, "weeeeoooupp...", done. Acoustic feedback usually works fastest
    in a production environment. It does tend to go on other peoples nerves
    though.

    Now don't ask how I tune our piano. Any pro would get goose pimples.

    Regards, Joerg
     
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