Here is a simple circuit able to sync many type of flash. It cannot works with some old unit that has a negative voltage between the batterie's negatve pole and the minus of the triggher command.

C1 and R2  are optional, thay must be used for the unit with a low voltage triggher (usually the same of the batteries).

Clik here to download the EXPRESS PCB schematic.

Disclamer:

The circuit is as is. I am not responsable of its use. In particular some old unit can use as triggher the same voltage of the lamp (sometimes 300V) that could be very dangerous!!!!