Saturday, January 21, 2012

Laser trigger for high speed flash photography, post-final

I adjusted the circuit a tiny bit. I added an LED and another potentiometer after ORgate1.  This works really well.  The additional 1 KOhm potentiometer allows for fine tuning of the resistance (and therefore the trigger delay).  The LED prevents current from the DelayCapacitor when it discharges (when the circuit gets reset) from flowing back towards ORgate1.  A regular diode should really be used instead of an LED as voltage drops significantly across an LED (but for my purpose, the LED works and I do not have any regular diode around.)

  • CircuitResetSwitch:  when the switch is closed, it will cause the DelayCapacitor to discharge quickly to ground, and it will cause XOR_OnOff to output a zero voltage.  The CircuitResetSwitch is implemented with a MOM (momentary) switch.
  • OptoIsolator:  triggers the flash to pop when a trigger voltage is reached, and protects the circuit from a possibly high current from the flash.
  • PhotoResistor:  when a strong source of light (i.e. the laser) hits it, its resistance goes down to 10 Ohms, directing most current to ground.  If the source of light is broken, its resistance goes up to 1 MOhm, directing most current to ORgate1.
Actual implementation:

Breadboard, laser pointer, and lego water dispenser

Components on breadboard

Breadboard on another angle

Breadboard from another angle

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