A versatile digital counter-timer circuit is described. The circuit simultaneously times and counts TTL pulse events in a single experiment under either timer or events counter control, or independently times and counts events in separate experiments. The total time duration (1 μs-999,999s) or total desired number of event pulses (1-999,999) can be preset by means of a 6-digit BCD switch. Initiation of the experiment controls both a timer relay and an events relay. When the preset timer or pulse count is reached, the corresponding relay is reset, allowing control of experiments. Applications to spectroelectrochemical coulometric titrations of cyfochrome c and methyl viologen are described. Applications to additional techniques such as anodic stripping voltammetry are suggested.