alpha dials and inc/dec buttons

[Fraser, Colin J]

The rotary encoders I've looked at output two pulses. Pulse one leads pulse
two for one direction, and pulse two leads pulse one for the other.
To derive inc and dec pulses, you could use a dual monostable (eg 74ls221,
ls123 etc).

The ls221 has 3 inputs to trigger each monostable - you'll need to use two
of these and tie the other input to enable. 
If you connect one pulse from the encoder to trigger both monostables with
the same sense, and the other pulse triggers the monostables with opposite
senses, then you get an output pulse from one m/s for rotation in one
direction, and an output pulse from the other m/s for the other direction.
Output pulse length is set by a resistor and capacitor.

You might find that this won't work tho' - it will depend on how the device
you are modifying scans the inc and dec keys.
In the worst case you may need to modify the firmware too.

Alternatively - if you want to interface rotary encoders to a
micro-processor, you could salvage an old PC serial mouse.
I opened one up recently to find two rotary encoders, already connected to a
chip that outputs the rotation information via a serial output.
I'm looking at putting these in a box with knobs on soon...


Colin f


> -----Original Message-----
> From: Paul Perry [mailto:pfperry at melbpc.org.au]
> Sent: 10 September 1998 02:27
> To: cyborg0 at GlobalEyes.net
> Cc: synth-diy at mailhost.bpa.nl
> Subject: Re: alpha dials and inc/dec buttons
> 
> 
> At 05:59 PM 9/09/98 -0500, you wrote:
> 
> >basically, I just need this circuit to send pulses on the 
> inc line when
> >the pot is turned right, and pulses on the dec line when 
> turned left..
> >Is this possible? 
> 
> yes, look at "rotary contacting encoders".
> These come in various shapes, precision etc, priced down to $10 or so.
> As they rotate they put out binary output on 2 pins & the 
> phase says which way 
> it is rotating. The model robot guys love them.
> I'm not Mr logic, but it looks like an encoder and one logic 
> chip shd do it.
> I'd like to see a ckt too!
> 
> paul perry melbourne australia
> 
> And, I'd like to find a source of small rectangular 'chiclet' 
> buttond for 
> PCB mount, or similar, say 4mm by 8mm or around there.
>