Audio / Log taper confusion

Re: Audio / Log taper confusion

John Roberts said:
One apparent difference between using a pot (to A/D) versus digital encoder is that the pot will provide absolute information.
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Good point. The absolute nature of position from a pot can be a plus or a minus. On the plus side, there is no need for homing upon power-on -- persistent position memory, if you will. This is good for mission critical stuff, like position feedback on a missile vane servo, for example.

As you point out, a gray-code digital encoder also gives absolute position, and I suppose these days there's a built in gray-to-serial encoder so that it's down to one or two wires no matter how many bits.

I'm straying pretty for off topic here. Maybe I'm a little starved for this kind of talk :)

--Frank
 
Re: Audio / Log taper confusion

drew gandy said:
Interesting, Frank. It seems to me that another couple reasons that pots may be chosen as encoders for digital systems is that control can be accomplished with one gpio pin (well, gpio's with a/d convertors anyway) and with simplified decoding in the microcontroller. btw, wikipedia says that most consumer audio controls are mechanical rotary encoders. I must say, the radio in my now defunct 2003 Dodge Grand Caravan was getting difficult to work. Sometime a clockwise turn would result in a reduction of volume rather than an increase. I had the opposite problem with a rack mount digital audio recorder the other day. I couldn't get the record level to adjust any lower than about -5db (and I needed something closer to -12db). In both cases I have to wonder if a pot would have been better.
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Drew, this anecdote is a perfect illustration of what's happening to our digital encoders, and the reason we're considering going analog. So really it's a physical robustness issue, and advantages of absolute levels vs relative levels for certain kinds of non-tech-savvy users.
 
Re: Audio / Log taper confusion

Daniel Postilnik said:
Drew, this anecdote is a perfect illustration of what's happening to our digital encoders, and the reason we're considering going analog. So really it's a physical robustness issue, and advantages of absolute levels vs relative levels for certain kinds of non-tech-savvy users.
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This sounds like a dirty contact in a quadrature encoder. If this were a potentiometer, it would also be scratchy and jumpy (although may not have gone through quite as many mechanical cycles).
 
Re: Audio / Log taper confusion

Tim Padrick said:
That graph looks way off to me. With a linear rotary, attenuation at 12:00 is 6dB. With an audio rotary, attenuation at 12:00 is commonly 20dB.
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There is no 12 o'clock on the graph in this thread.

for linear taper .5 rotation = .5 voltage division which is -6dB
for log/audio taper .5 rotation= .1 voltage division which is -20dB.

JR
 
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