How major a project would it be to change the note lights on/off settings?

[Roger_Linn]

Hi Yin,

I’m afraid it’s not possible to implement variable brightness of the LEDs. The LED refresh is done in software and is therefore tied to the refresh rate of the touch surface scanning, and Geert took a long time to get it as good as it is.

LinnStrument uses very high brightness LEDs but only turns on for one column at a time, which is a 1/26 duty cycle on the large LinnStrument. This design permits powering all 208 RGB LEDs (624 individual LEDs) from a standard USB port, which provides only 500 mA. So yes, this low duty cycle can cause video flicker or photos with some dim LEDs, but that is easily fixed by using a longer shutter speed.

The Low Power mode is not to enable USB use but rather to reduce the power usage to about 275 mA, which permits LinnStrument to be powered by a Lightning iPad or iPhone through Apple’s adaptor. Normal Power mode works fine with USB ports and with any iPad or iPhone with USB-C. Low Power mode works by further reducing the LED duty cycle below the normal 1/26 duty cycle while maintaining the color balance of mixed colors (all colors except red, green and blue).

Given the above, trying to implement variable LED brightness would require further reducing the duty cycle. Geert found that a variable duty cycle was too difficult in consideration of maintaining the color mixing and the tight scanning loop of the touch surface. So we felt that two levels of LED brightness (normal and Low Power) were adequate.

[yinwang0]

Thanks for the explanation Roger. Indeed, I can't power my Launchpad Pro with iPhone. I wonder how the LEDs are different.

In low power mode, I found that I can only use non-compound colors otherwise my eyes can see the flickering of the compound colors such as lime and pink, although I don't really want to use lime and pink

I played with the parameters and found that if I modify LOWPOWER_LED_REFRESH to 120 (was 250), and then reduce the duty cycle of low power mode to 1/3 (was 1/2), then the flicker stopped and also seems to use very little power.

I tried my iPhone 8 and iPhone 11, and both seem to work. Previously they work with only non-compound colors. Once I change to pink, they will suddenly stop working. So I guess some colors use more power than others. The above change seems to be able to fix that also the flickering in the eyes.

I have no idea if changing LOWPOWER_LED_REFRESH will bring some other problems though. The code looks quite advanced so I still don't know how the operating system works. It seems to be doing multitasking in some way so I hope this won't break it.

I guess my intention is just to make the lights less flickering in low power mode. I'll play some music on it and seem if it still works.

[Roger_Linn]

My guess is that will reduce scan rate of the touch surface and therefore velocity accuracy, but you can try it out to see if it does.

[Tj Shredder]

What could help as well is lighting less notes. I find it less distracting to either only have the C, or C and A enlightened. But I use the sixth tuning which makes navigating much easier anyway... This also helps to learn playing in other keys than C-major or a-minor...

[yinwang0]

LOWPOWER_LED_REFRESH is actually the low power mode LED refresh time in milliseconds, so making it smaller will make the LEDs refresh more frequently. I thought this would use more power, but it turned out the smaller I change it, the stabler it works with iPhones. Still, some colors will suddently stop working.

My lightening->usb cable is not Apple official one, so maybe it is causing some trouble too. Maybe I can claim to have a good setup for cheap third-party lightening USB cables

Actually I'm planning to play the same way as Tj Shredder, just turn root note lights on. But even just the root notes with full power LEDs look too bright, so I prefer low power mode lighting all the time.

[Roger_Linn]

LOWPOWER_LED_REFRESH is actually the low power mode LED refresh time in milliseconds, so making it smaller will make the LEDs refresh more frequently. I thought this would use more power, but it turned out the smaller I change it, the stabler it works with iPhones. Still, some colors will suddently stop working.

The problem is that this change not only breaks the LED colors at low power, but will also increase processing requirements for the LED refresh, which will reduce available processing at peak playing load for the touch surface scanning. The scanning code is the result of many refinements that Geert made with considerable effort in balancing sensitive priorities, so I'd prefer not to change this code unless there's an important reason.
But I'm glad you're made this source code mod, so people can try it out and see how they like it. Thanks!

[yinwang0]

The problem is that this change not only breaks the LED colors at low power, but will also increase processing requirements for the LED refresh, which will reduce available processing at peak playing load for the touch surface scanning. The scanning code is the result of many refinements that Geert made with considerable effort in balancing sensitive priorities, so I'd prefer not to change this code unless there's an important reason.
But I'm glad you're made this source code mod, so people can try it out and see how they like it. Thanks!

Today I got an official lightening to USB cable from Apple. Interestingly with the original low power settings with no modification, some colors work okay, but some will stop working. Also the compound colors are blinking. For my usage I'll just turn off the note lights except the root note, then I can even use normal power mode with iPhones

But this seems to mean that for a "perfect" support of smart phones (which nobody else did), there might be a need for further tuning low power settings. Ideally all colors should work equally well. I have the impression that increased LED refresh frequency won't hurt midi processing, say reduce the time to 120ms. This should at least reduce blinking. Maybe we can get some ideas from Geert?

I should stop using LinnStrument as my coding toy

[Roger_Linn]

We do our best to make Low Power mode work with Lightning iPhones or iPads, but there's only so much we can do so there's no perfect solution, especially considering that iPads have already moved to USB-C and few people use LinnStrument with iPhones. I believe that the current LinnStrument software achieves the best possible compromise between color choice, low power, and fast LED refresh and surface scanning within the processing limits of the low power CPU. It's a delicate balance that I'd prefer not to change unless there is a new solution that clearly offers a significant improvement after extensive testing, especially considering that the programmer Geert's time is limited.
But I very much appreciate your willingness to take the time and effort to try to make LinnStrument even better.

[yinwang0]

Indeed supporting iPhones perfectly is of very little use. They don't have good speakers and now they don't even have headphone jacks. I should stop

[bkanzelmeyer]

I just updated firmware today to 2.2.2. After the update, which completed without issue, Ben's MAX app to set the LED note colors does not seem to be working. I'm running a Windows laptop and the MAX app seems to load just fine; I click my preset and the LED indicators in the app light up correctly, but the LinnStrument remains dark. Otherwise, everything seems to be working as it should and I can use Global settings to set note lights, etc.; but I use a 16 note per octave scale, and the standard settings don't work very well. Any thoughts? Did/does Ben have to update his app for the new firmware release? I emailed him but he hasn't gotten back to me yet. Thanks!

[bkanzelmeyer]

Sorry everyone! I forgot the old saying...if something's not working right, reboot! I rebooted my laptop and everything is working great! Sorry, rooky mistake!