[sdiy] Incremental encoder to up / down counter or pots and an ADC

rsdio at audiobanshee.com rsdio at audiobanshee.com
Sat Dec 3 09:49:41 CET 2016


Mike,

Take a look at the schematic for the Oberheim Xpander and Matrix-12. Although there are probably more modern options, Oberheim had a few gates between their rotary encoders and the CPU to change the quadrature signals into an interrupt and direction. This was basically more what was needed by the CPU - an interrupt to signal a change, and a direction to signal which way the encoder had been turned.

Note that modern products with encoders have a problem where rapid turns in one direction can appear to be a slower turn in the opposite direction. That's because quadrature has only four states, and if the CPU misses a single state then it becomes impossible to determine which direction the encoder was turned. One solution to this is an encoder with more than four states, but the cost of the hardware is several times more expensive, probably due to supply and demand (since the quadrature encoders are so massively popular, and therefore dirt cheap). I looked at one 4-bit encoder with 16 states, but that was around $5 to $7 each! I believe that the Oberheim logic translation solves this issue because if an interrupt is missed, the direction bit will still be accurate when read one or more steps later. Feeding the raw quadrature bits into software cannot achieve this.

Freescale Kinetis processors have quadrature encoder hardware peripherals, but those are often very limited (one to four encoders, maximum, and I assume you wants lots and lots of encoders). I think it's possible to solve the problem like Oberheim did without an expensive circuit and without leaving the software vulnerable to missing states and the ensuing confusion about direction.

Brian


On Nov 29, 2016, at 8:28 AM, Mike HEQX <mike at heqx.com> wrote:
> I'm building a sequencer and I want to use these Bourns illuminated incremental encoders to select the note values instead of pots.
> 
> http://www.bourns.com/docs/product-datasheets/PEL12S.pdf
> 
> My issue is spending over 3 dollars for this interface chip to drive an up down counter per step.
> 
> http://www.usdigital.com/products/interfaces/ics/lfls7183
> 
> 
> Is there a cheaper way to do this or is it easier to go back to using pots and a flash ADC.
> 
> Mike
> 



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