The pitch preview display -- how it should be

I should make love to my theremin by rubbing my lobes on its attractive antenna ;) Making little love squeaks.

Obviously, I need serious meds...

"TOO MUCH INFORMATION !!!"

"I suggest ... No stepping behavior or thresholding, just continuous PWM." -- dewster

As it turned, this is not so cool in practice because of:

1. the different LEDs  (even within the same batch) have different luminous efficiency. This leads to the misperception of actual values "between" the LEDs.
2. The linear law "PWM vs cents" works poorly because the slightest deviation from the clean note (not yet marked by ear) lead to the noticeable lighting of the second LED.  This is disorient a bit.

Also I tried the "blink PWM" technique. When the deviation is 50 cents, both LEDs are alternately blinking, say, at 10 Hz (almost together for eyes) . As you approach the clean note the frequency is reduced (down to 1 Hz and even fraction of a hertz) and one LED is lighted longer than the second. The results are unsatisfactory because of interference  between the blinking freq and, say, the vibrato freq.

Now I have stayed on the 1st version with a slight modification: when the deviation is within +-10 cents, the second LED is forced to "off".

ILYA, in my LED brightness PWM adventures I've found that response is rather non-linear.  As you state in (2) "barely on" looks a whole lot more "on" than it should.  And "fully on" is not very distinguishable from "mostly on".  You can exploit this, and you can also make it so the bare LEDs don't need to be exposed for positional feedback when they are off:

Make it so all LEDs are "on" and the important one or two giving the information go "dark" to do so.  The eye is much more sensitive to PWM "off" levels than "on" levels, and the user will be able to easily see the pattern of the tuner LEDs under colored/smoked/diffused plexiglas.  I believe you always want a sheet of something light conducting over the LEDs as this can increase contrast - it also makes it easier to manufacture and keep clean, and it looks nicer IMO.

So I stand by my statement that stepping / thresholding is not necessary, and that continuous PWM is a viable solution.

Also, if you stagger the LEDs the eye will see useful patterns in what is transpiring.  Neither a simple ring of 12 LEDs nor a simple line of octave LEDs will do this very well.  We are creatures of pattern if nothing else.

Just made a crummy video of Hive doing "bouncing ball moving dark spot PWM":

My camera doesn't capture it very well, but maybe you can get the idea.  The pattern is quite clear even through red diffused Plexiglas, and the contrast is enhanced as well.  It really looks like something is moving if you don't look directly at it (use peripheral vision).

If driving the display with logic all kinds of things are possible.  You could light up half of the LEDs to either side of the active indicator instead of the whole thing (with the center LED black), etc.  I've decided NOT to use different colors to differentiate things.

Hi Dewster,

Hmmmm...

I agree that it "It really looks like something is moving " - But would be unable to say what was moving.. I think it may just be that the "ball" is "bouncing" too quickly.. Would be real interesting to see it slower, then switch to a moving illuminated LED (rather than a dark one) and compare them.

When you first suggested the idea, I thought it was a good one - but Im not so sure anymore.. I wonder if having a load of LEDs on, and one off, will cause a "wash" of brightness which will make the "identity" of the off indicator more difficult to see.

But it is real difficult to assess from a video - there is all the scatter from the lens and distortions of scale.. Im almost tempted to quickly knock a demo together on my PSoC board (would take about 15 minutes) - but Im not even thinking about a display, so it would just be an excuse to side-track again ;-)

Nice to see Hive actually running! ;-) Its always a big step forward when one has a development actually doing something, even it that's just flashing a LED or making a beep! ;-)

Fred.

"But it is real difficult to assess from a video - there is all the scatter from the lens and distortions of scale."  - FredM

Yeah, it's a crummy video.  My camera does a fairly good job in better lighting but LEDs give it fits. The shutter doesn't seem to get involved enough.

Anyone know if there are USB cameras that can do a better job for not too much money?

It's high time I made a real prototype for show and tell.

"Anyone know if there are USB cameras that can do a better job for not too much money?"

Dewster,

I strongly suspect that even a "good" camera could give crap results for something like this.. Also, dont take my judgment too seriously - I have quite bad astigmatism, so whilst my vision is not "impaired" its really not even close to average when it comes to things like this.. I often get blurring even on text on my monitor, the combination of short-sightedness and astigmatism are corrected by my specs - but not in the field of vision where monitors, scopes, DVMs etc usually sit!

Fred.