rotary encoder sales site?

[Hank Fletcher]

ALthough, that could be said for the analog system too if you sample fast enough and average consecutive readings to combine them into a single reading.

Yes, I remember doing this with the Sharp IR displacement sensors, but as I also remember, it was more trouble than the result warranted. Thanks for your encouragement to explore the PWM option - I'll definitely check that out!

 

[CheapSlider]

Have you considered making your own encoder ?

It seems that cost is an important factor in this project.

If the size is not important then a positional encoder can be made using very basic tools. Its a disc with concentric slotted circles. The innner circle has a slot cut along half its circumference, the second circle has 2 slots cut in alternate quarters, and so on each sucessive circle is divided by 2. The number of circles corresponds to the number of bits.

A row of light detectors is positioned in a line, from the centre of the disc, over each slot. A light shone from the other side of the disc can picked up through the slots by the detectors .

attached are 2 pictures of 170mm (7") disc prototypes:
The first picture shows a disc made from cardboard as a 'proof of concept'. This was a 5 bit encoder. It used different detectors salvaged from various items. A mains reflector light provided the illumination. (This worked OK but the disc did get rather hot)

The second picture shows a marked up 9 bit encoder disc. -This was never made as the 170mm (7") diameter was too big.

The final encoder used 2 CD discs. After cleaning (to make them see through) they were glued together between a piece of opaque paper which had been cut and drilled to make the slots and holes. It had originally been intended to print the pattern on a overhead projector slide or on a photographic film but the cardboard version worked the best.
LED and Detector pairs, salvaged from mice, were seperated and then glued to 2 booms, one placed on each side of the disc.

The final version (which is still working) was used in a wind vane to give wind direction. Althought it was able to give a 7 bit output only 6 bits are used. Thr eason was that it was fed with a 4 pair alarm cable. After one pair was used for power there was only 3 pairs left. It was decided to keep the external head as simple as possible as I don't like heights.


I trust the above is useful and gives you some ideas.

If the detectors are mounted on independant arms the offsets could be varied. So could the lengths of the slots. The ideal may be to get outputs that correspond with the musical intervals.

It could be possible to use 2 discs: one for lower bit values and a geared disc for higher values.

Good luck with your project!

 

[Hank Fletcher]

Have you considered making your own encoder?

Yes, I had thought about this, and for a long time until I knew about the $30 encoder mentioned above, I thought it was my only solution. But $30 kind of changes things - the only thing I hate worse than wasting money is wasting time, and it would take me a fair bit of time to construct my own encoder for this project (although I'm sure it would be more satisfying in its own way!).

The problem is, I'm really going for as good as one millimetre resolution over the length of the slide, which the $30 encoder can do as long as some PID adjustments for the velocity of the slide are made. If I wanted to do that with my own encoder, I'd have to have very fine intervals in the encoder wheel, and trust that vibration would not interfere, and that the hardware hacked from a mouse would be up to the job (i.e. max rpm of the wheel).

Your idea of making intervals in the encoder wheel specific to the slide positions is interesting, but I'm aiming for the next level beyond that even with the first prototype. In practice, trombone players can make small adjustments to fine-tune the slide from note-to-note, depending on the musical context (much like vocalists in a choir), which is why a trombone ensemble can be the most beautiful of all homogeneous brass ensembles. Moreover, having the better-than-one-millimetre feedback resolution will allow programming for that most tromboney of trombone sounds, the glissando! Even in a single tune of constant tempo, the rhythm (i.e. how fast) and the pitch (i.e. how far) between two notes in the trombone part will be quite various, and presuming that there might be glissandos between some of them, then quite fine (in time and space) measurements of the slide are necessary.

If I just wanted to clumsily snap the slide between seven different positions, I might as well just build something simple like an autonomous recorder player. Which I am doing.

 

[dknguyen]

You could just use a potentiometer. The resolution and sampling time is limited by your ADC...just remember to calibrate the center position or end for it first since they can vary by 10%

 

[Hank Fletcher]

Well, I've been thinking along that line for a long time now, but I can't find anything (other than the Atari paddles) that's close to what I could use. I'm a little perplexed by all the info on pots, particularly the specs on accuracy over the full scale. Suppose a pot is only accurate to 5%fs and it rotates a total of 345 degrees. Does that mean that I can expect at best 345/20 = 17.25 degrees accuracy? That's nowhere near good enough, but maybe I'm interpreting specs wrong?

 

[jbeng]

If you're wanting a quadrature rotary encoder, you could look at **broken link removed** These encoders cost about $80US. Here's a page from Bourns that has some pots you could probably use. The linear motion pots they show (on another page) may have too short of a travel to be of use to you (1/2 inch). Bourns also makes optical encoders.
Jeff

 

[1Steveo]

Check out this link, **broken link removed**
He has a rotary encoder design program.