A few "design" notes

Design is probably too grand a word for it but I decided to buffer the rotary encoder inputs via a Schmidt trigger buffer. When I was using a mouse as the encoder this wasn't strictly necessary as it already had a nice well defined levels. But I decided to do this so I could try out other encoders.The two Schmidt level inputs and +v and gnd are brought out to a four pin socket to allow me to try out other encoders.

I've found an encoder off an old junk-box Sony HiFi. This isn't quite a nice as the mouse - it doesn't have as many pulses per turn and it is just some metal contacts instead of an optical arrangement. But it does have the advantage that it has a standard 1/4" shaft and a big shiny knob!

This has its own little board with a couple of capacitors and resistors to try and smooth out switching bounce/spikes. This works OK, and the Schmidt trigger inputs are happy but I need to have a proper look at the circuit as the arrangement is causing a lot of "sparking" at the contacts - this can be picked up on an AM radio a few feet away!

The other use for the other two gates in the Schmidt package are as I/O buffers for the FSK input and SYNC output.

On the FSK input this will be a front panel input and as I tend to play with a lot of vintage gear and some of the test equipment in the workshop is a bit dodgy and capable of floating quite high I decided this should be protected as well as I can manage. The FSK input has two protection diodes and a 100k "snubber" this should hopefully work up to the speeds I'm interested in (RTTY type speeds) and provide a reasonable amount of protection. If it isn't fast enough I may need to reduce the resistor.

The Sync output goes through the buffer also - this is not strictly necessary but hopefully if I do manage to connect it up to the 300V supply by accident it will blow the one penny buffer chip instead of the £5 uController!