Hello there.

This is a fork of Tech Tangents Floppy Switch Board, video about that here!

Basically his board is a passive board to switch between two floppy drives and makes it work with some software magic. It made me wonder just what it would take to make the switching automatic in the sense then when you switch to another drive; the diskchange line is pulled low until a step command is issued.
I took this as a bit of a personal challenge to make the circuit work with just a 555, transistors and passives. Using an MCU would probably be the more correct way to go but where's the fun in that?

So all this is is a 555 in a bistable state that opens an n channel mostfet to pull the disk change line low, when the step line is pulled low by the floppy controller, the 555 closes the mosfet and the disk change line is controlled by the floppy drives once again. There is some extra fluff to translate the latching of the switch into a pulse for the 555, plus some more mosfets to keep the switch to a DPDT. The circuit says I'm using some BSS138 but I switched that out for 2n7002's for the sake of the SMT ordering, it should be fine either way.

As for power, what I want is power in and a power out for a pass through or something. Originally I was thinking of a berg for power in and a molex for power out so the end user can just use a molex to berg connector to power their floppy drive. Female surface mount molex sockets are a little hard to find, so I'll have to think of something else. Maybe just a single Berg and expect the end use to use a berg slitter or something. It is just powering a 555 and some transistors so a few milliamps at most is all it needs.

I wouldn't count the PCB as finished but the circuit itself should be finished. Still, I think there's enough here to show what I have already. I hope it is of interest to people. Please let me know if you see something wrong with the PCB or the circuit.

• Links
• GitHub Fork URL
• Original GitHub URL
• Tech Tangents Video

-Lime