AC Cycles for Clock

benha

Joined Jan 4, 2011
69
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

Joined Jul 18, 2013
27,648
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.

KMoffett

Joined Dec 19, 2007
2,918
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

Lestraveled

Joined May 19, 2014
1,946
Here is a simple zero crossing circuit. The opto isolator helps keep you safe.

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hp1729

Joined Nov 23, 2015
2,304
Here is a simple zero crossing circuit. The opto isolator helps keep you safe.

< > I thought we didn't like the idea of running an LED off of mains? How does this differ? </ >

benha

Joined Jan 4, 2011
69

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!

SLK001

Joined Nov 29, 2011
1,548
Here's a circuit that will give an output pulse once every cycle:

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

atferrari

Joined Jan 6, 2004
4,700
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
Were you controlling exactly what? The time the voltage was applied to the piece being weld?

Joined Jul 18, 2013
27,648
When I started out we would use a Dekatron counter tube for this!
Output on any selected pin.

Max.

benha

Joined Jan 4, 2011
69
Were you controlling exactly what? The time the voltage was applied to the piece being weld?
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.

cmartinez

Joined Jan 17, 2007
8,100

It's an excellent zero crossing detector that I've been using safely and reliably for years.

Joined Jul 18, 2013
27,648
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.
What device are you using to trigger the primary on?
Max.

benha

Joined Jan 4, 2011
69
It'll be an SSR.

Joined Jul 18, 2013
27,648
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.

benha

Joined Jan 4, 2011
69
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

Joined Jul 18, 2013
27,648
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.

Threeneurons

Joined Jul 12, 2016
30
When I started out we would use a Dekatron counter tube for this!
Output on any selected pin.
View attachment 100218
Max.
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:

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:

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.

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.