Counting slave flash unit back to projects
|the following schematic is a slave flash unit. The design is meant to run from a battery voltage ranging from 3 to 10 volts DC. starting on the left a circuit for biasing a phototransistor can be seen consisting of Q1,R1,R2 and C1. when slow licht changes take place this circuit can compensate for the changing current trough the phototransistor. however fast changes will end in a change og voltage at the base of Q2. Q2 will start conducting and the voltage on its collector will rise causing a trigger pulse on the clock input of the 4017. this device will start counting flashes. when the desired number of flashes is reached (to be set by the switch) the triac will trigger, on its turn triggering the flash unit. furthermore the circuit will reset itself when there is no pulses are received within one second after the first, this is accomplished by mosfet transistor M1 and the time delay consisting of R5 and C3.|
|Adjustments can of course be made, for example adding a ac-dc diode bridge
between the flash unit and the triac, then the polarity of the flash unit is
not important anymore.
furthermore the whole circuit can be run from the trigger voltage of the flash unit, the not batteries are required. this is done by removing all LEDs and R6, placing a capacitor of 10uF across the power supply together with a zener diode of 5 to 10 volts, and probably increasing the values of resistors R4 and R5, and decreasing the value of C3. This is however not working on all flash units.
|Photo; the flash-unit mounted on top of an existing flash.|