AC Cycles for Clock

Discussion in 'General Electronics Chat' started by benha, Feb 7, 2016.

  1. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    Hi, folks.

    I have a project in mind wherein I would need to leave a circuit energized for a specific number of AC cycles. I think I've got my head around most of the counting part, but what I haven't been able to figure out is how to create a trigger that fires once per cycle. I'd prefer to do this based on witnessed cycles as opposed to using a timer set to fire at 1/60th (or 1/50th) of a second.

    Basically, the goal here is to create a CLK trigger once per AC Mains cycle.

    Anyone able to point me in the right direction?

    Thanks,
    -Ben
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    Use a zero crossing detection set up, you could probably do it with a variation of the triac trigger circuits in Fairchild App note AN-3006.
    Integrating with either a logic IC or microchip.
    Max.
     
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    I did that for a Miller spot welder at work. Thumb wheel switches and a down counter. One pulse/cycle from a half-wave rectifier and transistor off of the low voltage DC supply transformer. I'll see if I can find the schematic Monday.

    Ken
     
  4. Lestraveled

    Well-Known Member

    May 19, 2014
    1,957
    1,215
    Here is a simple zero crossing circuit. The opto isolator helps keep you safe.

    [​IMG]
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
    1,938
    218
    < :) > I thought we didn't like the idea of running an LED off of mains? How does this differ? </ :) >
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
  7. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    Super helpful, thanks folks!

    Ken, I suspect your solution is the best fit for my project. I suspect I can figure out the details, but if you have a diagram lying around I'd love to see it!
     
  8. SLK001

    Well-Known Member

    Nov 29, 2011
    810
    224
    Here's a circuit that will give an output pulse once every cycle:
    ZERO_CROSSING.jpg

    R6 and R7 are only needed for simulation purposes. Here is a simulated output of this circuit:

    SIMULATE.jpg
     
  9. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,645
    759
    Were you controlling exactly what? The time the voltage was applied to the piece being weld?
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    When I started out we would use a Dekatron counter tube for this!:p
    Output on any selected pin.
    upload_2016-2-7_11-51-59.jpeg
    Max.
     
  11. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    I suspect so. A spot welder is, in fact, the exact thing I'm building.

    The standard unit of measure for a spot welder's weld time is the number of AC cycles power is applied.
     
    atferrari likes this.
  12. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    3,555
    2,511
    MaxHeadRoom likes this.
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    What device are you using to trigger the primary on?
    Max.
     
  14. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    It'll be an SSR.
     
  15. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    Do you need that much precision with for any simple spot welder? most weld take place over many cycles, and is commonly done in the industry with a simple timer to control the firing element, often a large contactor.
    Pulse counting is usually done with seam or projection welding where the weld repeats and cycles rapidly.
    Max.
     
  16. benha

    Thread Starter Active Member

    Jan 4, 2011
    35
    1
    No. But for better or for worse I'm seldom guided by "need." It's fun to set goals like this to learn new stuff.

    Didn't need to build a boat either but: http://www.buildaboatwithben.com

    :)
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    Iv'e built a few boats in my time, mostly sail, I still have 1/2 ton of lead that was intended for a keel, and Sitka spruce spars, but never made it.:(

    This is how they sing it in Newfoundland Ca.

    I's the b'y (boy) that builds the boat
    And I's the b'y that sails her
    I's the b'y that catches the fish
    And brings them home to Liza
    Max.:)
     
    cmartinez likes this.
  18. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
  19. Threeneurons

    New Member

    Jul 12, 2016
    19
    10
    On a "selector" type dekatron, yes. Tubes such as the GS10C, 6476A, and Z504S.

    I used both the AC line, for the time base, and a dekatron, in the timing chain, of my nixie clocks:
    [​IMG]
    Dekatron Plugs into P5. Anode goes to the anode. G1 and G2 go to the two guide pins. NDX typically ties to K0, and RTN ties to all the other Kx cathodes. A simple common emitter transistor stage is used to extract the 60Hz. btw, its all powered of a 9VAC wallcube.

    For a zero crossing, here is a non-isolated circuit I use for an "improved" version of the old fashion thyristor-incandescent color organ:
    [​IMG]
    Its key to the "improved" part. The original SCR driven color organ had no phase control. Brightness was due to statistics. More ON cycles for loud noises, and fewer for quieter sound. My improved unit actually modulated the pulse width to the sound.
    [​IMG]

    I don't know why a true PWM circuit wasn't used in the old days. The technology was available, and that's how thyristors are to be driven.
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    The machines I had knowledge of back then that used dekatrons were usually used to fire thyratrons and ignitrons, equivalents to the thyristor family and function the same way.
    PWM was rare and Mosfet's did not exist and transistors were impracticable replacement for these devices.
    Max.
     
    cmartinez likes this.
Loading...