Sorry, my bad. Eyes are too old, I guess.

Let's try this: Voltage Comparators

I really think this site will help you.

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All those who believe in psycho kinesis, raise my hand.

 

Great site! Should be required reading after (or before) a couple of questions!

It will be my reading for tonight. Thanks
Michael

 

Here is a timing diagram of my understanding of your input signal to the comparator. If you can add a line to show what you need the output signal or relay closure to do, it would be helpful.
The squiggly lines just mean the time interval is indeterminate.

Attached Images

flash timing.PNG (2.9 KB, 8 views)

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Ron

 

I added the timeline in the lower portion of your image showing that the relay gets energized when the flash goes into sleep mode. (I might have to also try it that the relay is de-energized when it goes into sleep mode.) The flash goes into sleep mode when there has been no activity to fire the flash within these 90 sec. The same momentary switch that is used to fire the flash is then be used via the energized relay to now connect the 6v supply to the extra wakeup contact. When the momentary switch is pressed and the flash is in sleep moed, the flash will first wake up and stay awake for another 90 sec. The relay will be de-energized connecting the momentary trigger switch so that the next time it is pressed, the flash will fire, as long as 90 sec have not elapsed, and the flash went back into sleep mode.

If this couldn't work because of something to do with the flash circuits, my next test is to use an optical sensor taped against the flash ready light. When the flash goes into sleep mode, the ready light (usually a red or green LED) will be off. The disadvantage here is that while the flash is powered on and charging the main capacitor, the ready light is off, until the flash is actually ready to fire, so the relay would cycle many more times this way.

Attached Images

flash timing copy.jpg (48.5 KB, 5 views)

 

I'm still not getting the big picture. Can you describe what you are really trying to accomplish, independent of how you think it should be done? Do you want the flash to fire every 90 seconds, repetitively, with no external controls (I'm guessing not)?
I'm just confused by your description of what you want.

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Ron

 

Here is the setup and what happens with the flash itself:

Turn the flash main power on and leave it on. The flash is not connected to a camera in any way, but the flash terminals are connected to a momentary contact firing switch.

The flash will charge the capacitor, and when it is ready to fire, the ready light will be lit. As soon as the main power switch is turned ON, the voltage across the terminals of the momentary switch is 4.5 volts. The momentary switch is external to the flash unit (2 wire connection). If you press the momentary switch (when the ready light is on) the flash will fire and then recharge the main capacitor. As long as you press the momentary switch at least every 90 seconds, the flash will remain awake. If the momentary switch is not pressed within 90 seconds, the flash will go into sleep mode, but the master power switch has not been physically moved, and the flash will not fire if the momentary switch is pressed. To wake up the flash and allow the momentary switch to again fire the flash, either you 1) physically turn the master switch OFF, and then ON again, or 2) physically hit a RESET button to wake the flash up, or 3) add a small voltage to a secondary contact.

Here is what I am trying to accomplish:

It is this item # 3) which is what the relay will allow me to do, using the same momentary switch that can normally fire the flash. If the flash is awake and powered on, this switch will connect through the NC contacts of the relay to the pos terminal of the flash with the ground of the flash connected to the other side of the momentary switch. Any press of this momentary switch will fire the flash if it is charged up (ready light on).

After the 90 sec of inactivity, when the flash goes into sleep mode, the relay will energize, connecting the NO contacts of the relay to the "wakeup terminal" through the 6v supply. The next press of the momentary switch will send the 6v on to the "wakeup terminal" of the flash, which will then wake up, energize the relay which will disconnect the connection to the "wakeup terminal" and then the next press of the momentary switch will again fire the flash.

There is the possiblity that the relay will need to be energized not when the flash is in sleep mode, but in awake mode. I attached a rough drawing showing the relay, flash, and momentary switch.

Thanks,
Michael

Attached Images

FlashRelayTrig.jpg (86.3 KB, 7 views)

 

In your timing diagram, you showed that the momentary contact closure would last about 10mS. How is this controlled? What if the relay switches faster than this? If this is a problem, we could probably add a little delay to the comparator.

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Ron

 

Well, it might be a problem, in that when the flash fires, the voltage drops to zero, and the relay would try to energize briefly, which technically should be ignored, but the circuit isn't working yet, so I don't know if it is a problem. Right now the momentary switch is just a pushbutton.

Any other ideas of things to check here?

Michael

 

I just realized that making the comparator ignore the momentary closure will allow the comparator to trigger only on the transitions to sleep, which I believe is what you want. Otherwise, it will trigger whenever the input goes low. Unfortunately, you can't possibly make the contact closure as short as 10ms. It would be easier for the comparator if the contact closure time was consistently the same, but this would require putting some circuitry between the switch and the flash. Short of that, we could make the comparator ignore anything shorter than, say, 100ms, but you would have to be certain to make all your contact closures shorter than that.

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Ron

 

I think I am understanding, but let me ask what might be an elementary question: Does this have to do with the momentary switch being open most of the time?

To trigger the flash, the momentary switch is pressed, normally just a brief push, by hand at maybe 0.1 sec, or by an auto trigger which would be a duration of about 0.01 sec, I think. When the switch is not pressed, the voltage across the flash terminals is the 4.5 volts.

From what I understand, the way the circuit is currently setup, comparator output is OFF (and should de-energize the relay) when the voltage at the PLUS input is greater than the reference voltage at the MINUS input. Measuring the voltage at the MINUS input as you asked (having a 4 AA battery supply) gave a reading of +2.61v. Since this is less than the +4.5v of the flash, the relay should NOT be energized, but unfortunately, as soon as the 6v supply is connected, the relay immediately energizes.

This seems like it should be so simple already, and the tutorial referenced from AllVol was very helpful in getting a better understanding of all this, but obviously, something still is amiss. Does it indeed have to do with the momentary switch? Sorry, but I am at a loss for what else to check to make this work correctly.

 

Sorry for the silence. I was away from my computer all day yesterday.
I'm working on what I hope is a final schematic. Will the flash unit spend more time asleep or awake? We can design the circuit so that the relay is off most of the time, saving power.

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Ron

 

I have been using the time to read more about these circuits, and make notes and order components!

I think the flash usually spends more time on, but would want to be able to try it the other way also. Thanks!

Michael

 

You should have some LM339's on hand, as I think I might use one in the circuit.

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Ron

 

Have some, and more are on order!

 

If I understand what you are trying to do, I think this will work.
I'm sure this could be done without a relay, but I haven't put any thought into it.

Attached Images

flash unit controller.PNG (32.1 KB, 5 views)

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Ron