Philip Cowley wrote:

> the availability of many cheap mice that work decently proves
> that even junky 2 bit encoders can be made to work reliably.

I don't dispute that for optical ones.
The mouse industry quickly ditched mechanical ones.

> I am building a computer control system
> for a 1-tonne astronomical optical telescope.

Cool. Whereabouts? I'm in cycling distance of the RGO.

Someone else suggested using the Hewlett-Packard HCTL2016.

They do look neat, and for a one-off design this could be
the most labour-effective solution.

Depends on how frequent the pulses are.
A modest rate would be fine when tracking, but you probably
want to slew at many times sidereal rate, and the pulse
rate should rise in proportion. In which case, the HCTL2016
comes in handy.

A friend (ex-radio astronomer) and I were discussing
automating scopes. He said there was a neat chip
called a Universal Pulse Processor (UPP) that looked
ideal for jobs like that. The only snag was it was
single-sourced. From Hitachi, I think.