Abstract: A circuit for use in the sequential initiation of explosives comprises an up-down counter having a first input terminal at which an up-count is initiated, a second input terminal at which a downcount is initiated, and an output terminal, an energy storage capacitor for powering the counter, a first resistor which has a low impedance for a fixed time to current of a particular value and of a first polarity and which thereafter has a high impedance connected to one of the input terminals of the counter so that when current of the first polarity and of the particular value is passed through the first resistor a signal is applied after the fixed time to the input terminal to initiate a count in an up direction, and a second resistor which has a low impedance to a predetermined voltage of a given polarity connected to the other input terminal of the counter so that when the predetermined voltage of the given polarity is applied to the second resistor a count is initiated in a down direction, the counter generating