Abstract: This invention provides modules and a system for sequentially activating a series of detonators. The modules and the system rely on a transistor in which the base-collector junction is caused to change state by a current pulse of suitable magnitude so that it presents a low resistance. Similarly, the base-emitter junction is also caused to change state to present a low resistance path in both directions. Such transistors are utilized to steer signals through a module in which they are used to activate a detonator associated with that module and then to steer a further signal to a next module in the series.