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Latching Flip Flop For Continuity

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mhensell

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Was hoping to get some help on a circuit design. Thanks!

Application: An electronic panel used for fireworks. Electric matches are connected. 20mA@1.2v is then passed through them (led is in series) for continuity. Good continuity lights the LED at the panel. To fire the match, we touch a probe to to a small protruding pin. Contact between the probe and pin bypasses the led and sends 24vdc through the match and fires it. In a perfect world, the match head would open the continuity circuit and the led would go out. Unfortunately, about 20% of them stay closed after being fired.

Circuit: Would anyone know of a simple latch/flip flop that could replace our current continuity circuit? It would have to power up in the ON condition and immediately send 20-25mA@1.2-1.5v through the connected matches and light up a closed circuit. The momentary application of 24vdc (probe to pin) would then change the state to OFF, regardless of whether the match is opened or closed. A reset switch could be added to the panel if needed.

Any help would be greatly appreciated. Thanks, everyone.
 
Let's see if I have understood you.

What you have now is:
  • Some sort of panel (and a bunch of wires).
  • A led
  • A fire stick that burn when 24V DC is aplied
  • A return wire from the stick that change state somehow
 

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**broken link removed**

Here's a simplified diagram of my current circuit. The LED lights when the match head is closed and passes the 25mA test current to ground. Problem is, is doesn't always OPEN the circuit after being fired. We then have a light indicating a 'live' circuit when there is none. For the record, our concern isn't the state of the loop. It's whether the match on that loop has or hasn't been fired. But if we KNOW it hasn't been fired (say-before the display even begins and we're going through, testing all the matches), we want a light to indicate good - no light for bad. What we need is something that will pass that 25mA in a power up state. An input voltage (24v) changes the output state to kill the LED, thus indicating that particular circuit has been fired.
 
Your image is totally useless. What is that, something that's supposed to look like an old-fashioned blueprint?

In any case, seems you ought to be able to use a regular old D-type flip-flop here. Wire it so that the "set" input is activated at power-on, to illuminate the LED. Connect the "reset" input through a resistor (and a diode if necessary) to your 24V "firing pin" so that it will extinguish the LED when the fireworks goes kablooey.
 
you can make a timer with monostable. when you press it will give a short pulse ON-OFF regardless of the lenght of time pressed. then comes ready for next shot after relasing the switch..
 
The circuit you are using is pretty straightforward and simple. The problem is that it relies on the match burning open. While not familiar with the match itself I would venture a guess it is a small section of fine Tungsten or Nichrome wire. The problem is that the wire does not always (about 1 in 5) burn open. If the match burns into a short the LED will remain illuminated. So yes, a Flip Flop in there would at least tell you when a fire pin had been touched. Each pin fired respectively turns off a LED. Then you could have either a master reset or individual reset buttons.

Ron
 
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