Dripping Device and Flash Trigger

Today I draw the circuits for the dripping device and the flash trigger. The dripping device itself is a 12V solenoid valve. It is normally closed. When it gets 12V it opens the valve and the liquid can flow. I will provide the 12V from a lead acid battery. I want galvanic isolation between the Arduino’s 5V circuit and this 12V circuit. I will use an optocoupler for that. Here is the circuit:

Dripping device

The optocoupler basically consist of a LED and a photodiode or phototransistor. From the Arduino’s side we have to switch this LED on and off. Accoding to the datasheet of the PC 725V optocoupler the led requires 10mA, so we would need 500 ohm resistor for the 5V. I will use 450 because I have lots of those If you use other optocoupler, check the datasheet. Pin numbering can also be different.

The flash trigger circuit will also be optoisolated:

Flash trigger

On the output side of the optocoupler we drive an SCR gate. When the flash is charged it has about 300V so we have to limit the current that flows through the phototransistor of the optocoupler. I will use 5.6K or bigger resistor for this. It limits the current to about 50mA. According to the datasheet of the SCR gate the typical gate trigger current is between 15mA and 35mA. The maximum value is 200mA. So 5.6K makes bit high current but it is still on the safe side. Maybe 10K would be better. Lets see.

And finally a disclaimer again. Playing with the flash is dangerous. 300V can give you a memorable moment I do not take any responsibility for any damage that you cause for yourself or your devices or someone else or someone else’s devices etc. Use these drawings on your own risk.