Abstract: An electronic delay circuit for firing an ignition element. The delay circuit includes a capacitor which stores electric energy supplied from an electric blasting machine, an oscillator generating a clock pulse train, a circuit for over-exciting the oscillator, a counter which counts clock pulses of the clock pulse train, and a circuit for maintaining a reset state of the counter for a predetermined time period after the electric energy is supplied. The counter produces a trigger signal when it counts a predetermined number of the clock pulses, and the electric energy stored in the capacitor is discharged to the ignition element. Since the oscillator enters into the steady state in a very short time by the over-excitation, the delay circuit has large resistance to external noise.

Abstract: An electronic delay detonator for igniting an ignition resistor a predetermined delay time after supply of electric power from a blasting machine comprises two input terminals for receiving the electric power supplied from the blasting machine, a diode-bridge circuit connected to the input terminals, a power supply capacitor connected to the output of the diode bridge circuit, an RC charging circuit connected in parallel with the capacitor and having a predetermined time constant, and a monolithic IC.