From the clues (there are at least four of them) hidden in the schematic above, what would you say are the most likely loads for the drains of transistors Q1 and Q2 connected to EdgeConn1 and EdgeConn2, respectively? Also, please describe what led you to your conclusions.
I don't see why you would need to prevent the two transistors from turning on at the same time in a motor. I think a two phase motor would have its coils driven 90 degrees out of phase not 180 degrees.
As seen from the protection stuff on the outputs I think it is driving a small transformer, probably center tapped. This transformer is driving 2 nasty devices capable of giving a big burst of energy back to the primary drivers. It might be 2 enormous MOSFET's or IGBT's that -depending on the speed and load- are able to destroy direct logic driving. I think at least I should win half a pint of lukewarm beer....(Yikes! ;-)
@betajet My other off-beat guess is a flipper torpedo, with a single tail fin powered by alternating electromagnets.
This would be great if used on one of those helium-filled air-floating sharks that Max wrote about a while back. The 400 Hz tone would be a bit annoying, but at least would give warning that the beast was approaching - from miles away! And could also double as a fire alarm bell if two gongs were located near the tailfin. :^}
As for the red connection points, thay are just part of the net naming symbol in TinyCAD schematic drawing software. One has to position the red connection point on the wire to give it a name, so there really is a connection.
If you look closely at the schematic, you'll see that the connection points on the four off-page connectors are red, which means they're not actually connected. [PCB designer rule #1: never trust the schematic. Always check the netlist!] This means there's no power in, no connection to loads be they inductive or otherwise, and no connection to ~Alarm.
Actually, I'm going to go with a couple of off-beat guesses. Since the input voltage is +48V, that sounds like four 12V batteries, which is a common configuration battery back-up of serious electronics. I'm guessing a really loud alarm bell, actually a pair of bells with a hammer between them which is driven by two electromagnets alternating at 400 Hz. I mean really loud, the kind of alarm that clears a building in case of fire.
My other off-beat guess is a flipper torpedo, with a single tail fin powered by alternating electromagnets. The reason for a flipper rather than a circular propeller is so that it has a passive sonar signature that sounds like a fish.
I'm going to guess, based on the 110V zener diodes in the output, that the load is around 45mA (since that's what the zeners are going to be conducting when the JFETs are off and the opposite rail is active).
The alarm goes low whenever the pulsing AC voltage quits on either EdgeConn1 and/or EdgeConn2. This means that if the 555 fails, or the external inductors blow open, or the external voltage being supplied from somewhere to the inductor-loads (may not be the same 48v+ supply) fails, then the alarm goes low (asserted).
That makes much more sense. I missed that red bar over the ALARM.