Programmable electronic time delay initiator

Abstract

A programmable electronic time delay initiator includes a digital time-delay circuit that counts in response to a dual-resonator clock and, at the end of the programmed time delay, gates the pre-stored charge on a capacitor to a semiconductor bridge initiator to fire an explosive. The timer circuit includes a combined crystal/RC oscillator that provides high accuracy oscillations from the crystal or oscillations from the RC components in the event the crystal fails. The timer circuit functions in response to multi-part serial commands delivered on a conventional two-wire path. The timer is initially powered-on to provide power to a capacitor that supplies power to the time-delay and related circuits. An initial ATTENTION pulse initializes the circuitry and starts a watchdog timer that counts a fixed number of clock cycles and resets the logic if a following WRITE, ARM, or FIRE command is not received. A WRITE pulse and following programming pulses programs a fusible link memory with time-delay information, an ARM pulse effects charging of a firing-charge capacitor, and a FIRE pulse gates the firing-charge to the bridge initiator to fire the explosive.