David put this circuit together yesterday. It models a surface controller and components on the ROV using two independent sets of 555 timers, surface and craft, linked via fiber cable. When one set is selected, the frequency of the surface timer is fed into a comparator on the ROV and matched with corresponding timer on the craft to produce a true signal. We are working the problem of synchronizing the surface and craft timers as phase drift could cause the comparator to change state. We'll also prototype an alternative design with a frequency-to-voltage IC.
