[sdiy] Using a stepper motor as an data entry wheel

[Eric Brombaugh]

Roy J. Tellason wrote:
> On Wednesday 13 September 2006 01:30 pm, John Speth wrote:
>>
>> A few years ago somebody on SDIY noted a web site that presented a DIY
>> design for using a stepper motor as an input device for a data entry wheel. 
>> I've since lost the link.
> 
> I don't recall where it was,  but the only thing that I remember reading that 
> was anything like that said that if you connected two similar motors 
> wire-to-wire you could spin one and the other one would move.

I've got a pair wired up like this - it works. One thing you'll find 
though is that the system is somewhat resonant and there is an optimum 
rate to turn without missing steps. Too slow and the driving motor 
doesn't generate enough EMF to kick over the driven motor. Too fast and 
the driven motor can't keep up.

> Me,  I'd just use some sort of an optical encoder.  That's what they did in 
> the Moog Source,  if I'm remembering right,  with a bit of weight added to 
> the shaft so you could spin it nicely.  You can probably salvage enough parts 
> for a couple of these from a mouse,  ignoring the mouse chip itself and using 
> the outputs of the actual optical encoders fed into some sort of processor or 
> other logic...

Seconded. I'd imagine that the bipolar nature of the stepper output 
signal would tend to make interfacing it more complex than simply using 
an optical encoder. Plus, if you spin the stepper too slowly the output 
signal won't trip your sensor circuit. An optical encoder won't suffer 
from that.

Eric