Digital Pot - need help

[Rancor]

hey guys, im pretty new to this stuff so i need help.
What i got here is a digital volume control, its got 3 pins - common, vol up and vol down. You can use a pushbutton to make it go up / down. (i havent built the thing yet) Before i start buying the chips ill need, i wanna make sure i can make it work.
What i wanna do is take the pushbuttons and replace them with some sort or a rotary switch. Clockwise volume up, counterclockwise volume down. So one direction it would pulse (on/off) pins lets say.. a and c and the opposite direction it would pulse pins b and c. That would replace the pushbuttons.
Ive seen these controlls lots of times in stereos, amps etc..
Im also holding a stepper motor in my hand wich makes those same clicks as the volume controls on amps and stereos that i just mentioned... So im thinking maby they use stepper motors? If so.. is there a circuit that i can use to intergrate into my digital pot?
I would rather use the rotay switch that i was talking about earlier (i dont know if they exist but i would assume so.... do they?)
by the way heres the schemtic im going to use (gonna make 2 of these for stereo) http://www.aaroncake.net/circuits/volume.htm

[purplepeople]

You need a rotary encoder and circuit to convert the pulses for S1 or S2. Look inside your mouse, it has an at least two encoders.

There are two problems with a rotary switch. The first is ergonomic - even a 12-position switch needs 30deg rotation to make one connection. That's 3 full rotations for any kind of loud/soft volume change on the DS chips. The second, and bigger, problem with is that there is no facility to determine direction. When you connect the switch and don't care that it takes up to 6 rotations for full volume swing, you find that you still need two rotary switches - one for up and the other for down.

:)ensen

[Rancor]

yeah i found some stuff on rotary encoders already .. wasnt sure if i needed that much.. i just though there was a simpler solution. i wasnt talking about that kind of rotary switch.. i though theres the kind that as ure turning it left it clicks alot like a stepper motor and sorta sends on/off pulses in 2 leads and other direction 2 diff leads.

btw, isnt there only 1 encoder inside the mouse>? the mouse wheel

[till]

what about using one of those instead: http://focus.ti.com/docs/search/para...e&familyId=588

[Rancor]

what is that? i see an ic on the datasheet..
anyways i guess ill use purplepeoples' idea, know any place i can find a shematic for it? so it converts the signal to SW1 ans SW2 according to direction?

[apollyon25]

Hi,

The TI digital pot is a nice bit of silicon. The AD one is more expensive and good luck trying to get samples out of them!
I would use it (TI) to do the actual attenuation as the internal attenuator array is laser trimmed and at 0.5dB steps is good enough for reasonably fine control.

As the options have been discussed (encoder vs switch) I wont suggest them again except to say that whilst a typical 512 ppr encoder (the type used for motor positioning) is preferable from having the signals already decoded for you, they are quite expensive. The another option is to use a set of rotary switches, whoever again these are expensive for good quality ones, and as mentioned have very coarse rotational steps. This is easily overcome by stacking them with offset angles and using the angle offsets to calculate the direction. A bit of a pain is the a$$ mechanically though. Also by the time you buy 10 to reduce the rotational coarseness problem you may as well buy an encoder.
There is another option that was hinted at by purplepeople. Use the encoders from your mouse (assuming it isnt optical) and adopt a similar approach. Use two of them and make the dual strip pulsewheel (laser print onto some transparency) yourself. use one encoder to do fine, the other to do coarse, and the angle differences can be used to work out the direction.

It basically comes down to the time/effort vs money problem.

Oh and stick a micro in there - makes the decoding really easy (a PIC would do).

Have fun!

apollyon25

[Rancor]

thanks dude, really usefull info
however i gave up on the project because i found a mixer for $24.99 which was perfect for my purpose.

-Alex