A basic dark room timer circuit for photographers works on a solitary 1.5V cell and flashes a neon light is detailed below. As the time frequency are visible, it is quite simple to record time lapsed even in darkness. Transistor Tl actuates transistor T2 instantly. Output of the
A transistor pair is within phase having its input. Transistor T2’s output is linked back via the capacitor. This leads to sporadic blocking of the triggering at a level based mostly on the RC time constant. The output will be boosted by the transformer to some level adequate to flash the neon lamp. Using offered component values, the circuit offers approximately one pulse per second, that is most ideal for timing exposure of enlargements and additional unusual tasks. By making use of a potentiometer rather than l80k resistor, the period could be established in virtually any precise value. The flashing rate, for instance, may be designed speedier by decreasing the value of resistance in circuit. A low current holding 230V to 12V step-down transformer may possibly be applied for Xl. The transformer’s larger voltage winding ought to be attached to the neon in addition to its lower voltage winding into the remaining circuit. Also, the presented dark room timer circuit's flashing level could be adjusted broadly. Using a 100,000—ohm resistor, the flashing rate may be reduced into one blink every 5 seconds. As well as through adjusting the measure of capacitor to 0.22uF, the neon could be constructed to shine constantly.
