On Mon, Dec 31, 2007 at 03:37:46PM +0000, Stuart Henderson wrote: > On 2007/12/31 15:07, chefren wrote: > > And look at the workings of your heartbeat monitor: I bet it needs a loop in > > the software that "pings" it. With software failures: Big chance that loop > > still works and thus the heartbeat monitor isn't triggered while the system > > as a whole can be considered broken.
Put it somewhere in the main software loop. Hook up a second trigger off the money-detector. The computer decides what tune to play and plays it. The heartbeat monitor can detect the money and listen for any sound out of the speaker. > > Even so, it still allows recovery from some serious problems without > touching the machine. There are quite a few situations where this could > be very useful, though it might not be worth the extra expense and > complexity of adding an external device, watchdog timers aren't too > uncommon in PC hardware these days. > > > Your heartbeat monitor also needs a way > > to power-cycle the whole system. Relays? How is/are these powered? Don't > > forget for all the cables and connectors needed. > Last time I needed such a timer was about 20 years ago. Used a mil-spec 556 TTL dual-timer IC and appropriate caps, resistor, and relay. Fit it inside a small box with a 110V recepticle and a power cord, and connected with a serial cord. Powered it right off the serial port. Doug.
