The voltage of 30 V indicated in this project, shown in the figure, depends on the diac used. It should be slightly lower than the one needed for your shot. P1 adjusts the trigger voltage. This voltage is added to that of the battery to arrive at what is necessary to trigger the diac. When this occurs, there is the conduction and polarization of the transistor that has a relay as collector load. The potentiometer or trimpot P2 must be adjusted to obtain the saturation current of the transistor as a function of its gain. The relay used depends on the voltage used in its supply and the load current that must be controlled.
