Abstract: A continuity checking system for detonating cord having four principle parts. The detonating cord has a fiber optic cord associated therewith to run from the blasting cap to a remote primer; a light return device is installed at the primer; a disposable testing head is installed at the end of the detonating cord adjacent the blasting cap; and a testing device is positioned a safe distance away from the disposable testing head. The testing head utilizes an LED with means for illuminating the end of the fiber optic cord, and a light sensitive device with means for sensing return light from the fiber optic cord. An electrical input signal, and an electrical output signal from the disposable testing head is communicated by electrical wires to the remote testing device.

Abstract: A sequencing system for a series of control circuits; each of which has its own control switch. A signal of spaced apart pulses is communicated simultaneously to all control switches. Separate normally closed grounding switches are provided for all but the first of the series of control switches to make them inoperative. Each control circuit after the first is provided with a connection which opens its grounding switch in response to power flowing through the preceeding control circuit of the series.

Abstract: A blasting machine comprising a pulse generator which delivers its pulses to a control signal transmitting circuit that in turn delivers the pulses to driven blast initiating circuitry. The control signal transmitting circuit includes an electronic switch which is not only turned on and off by the pulse generator but is also turned off by a deactivating circuit when the voltage of a power supply for the machine is below a predetermined level. When the voltage of the power supply is above this predetermined level, the deactivating circuit is made inoperative so that it can no longer turn off the electronic switch.