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LED guitar fingerboard
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Please be positive and constructive with your questions and comments.

LED guitar fingerboard

by Rymano on Fri Dec 20, 2019 5:30 pm

I'm looking to wire the DotStar Micro LEDs (APA102–2020) under a bass fingerboard to backlight the side and face dots with some 4 conductor ribbon cable (0.5mm pitch). I'm rather new to most of this tech but have a basic idea of where to start. Would like to hear any alternative LED options to consider before taking the plunge. Also the possibility of running 2mm fiber optic cable from the center dot/LED to illuminate the side markers. Lastly - what are the maintenance risks if one goes out...

Thanks a million in advance!
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LED fretboard.jpg
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Re: LED guitar fingerboard

by adafruit_support_bill on Sat Dec 21, 2019 8:36 am

Lastly - what are the maintenance risks if one goes out...

We'll take the last one first. Since it raises a number of related issues:

Is this a retrofit project, or are you building this up now? How do you plan to integrate the leds into the fingerboard and how will the fingerboard be attached to the neck?

Assuming that the fingerboard will be glued to the neck, you might be able to find a suitable thermal release adhesive that would allow removal for maintenance if needed.

LEDs do have a lifetime. If run at the rated current levels, they typically last for 100,000 hours or so. At decreased levels, they can last much much longer. Since you probably don't need them running at full blast, they should last a good long time. However, there can also be premature failures. Statistically, these tend to happen very early or very late relative to the average lifetime of a pixel. For that reason, it would be a good idea to allow some burn-in time for your pixels to shake out any possible early failures before installing the fingerboard. https://en.wikipedia.org/wiki/Bathtub_curve

Would like to hear any alternative LED options to consider before taking the plunge.

Dotstars or Neopixels are both viable alternatives. But the Neopixels require a decoupling capacitor for each pixel, so the APA102 DotStars would be simpler to wire up.

Also the possibility of running 2mm fiber optic cable from the center dot/LED to illuminate the side markers.

The radiation pattern from the pixels is Lambertian. That means that 90 off-axis, the light emitted will fall off to zero. But 2mm is fairly large relative to the chip, and if you locate the end of the fiber a little bit above the surface plane of the pixel you should still get significant light out to your side-markers.

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Re: LED guitar fingerboard

by Rymano on Mon Dec 30, 2019 2:37 pm

Thank you for the detailed breakdown of options. I run a guitar shop and intend (if things go according to plan) to offer this option for retrofitting existing guitars along with customs that we create. The standard adhesive tends to be titebond II for most builders for strength/work-ability and environmental stability. With some patience and heat it will come apart but is fairly arduous as far as maintenance due to the amount of precision fretwork that follows fingerboard removal/regluing. Hence the need for reliability and strong wiring.

Here is a 3rd rate MS Paint rendering of our plan:
Led fretboard layout.jpg
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Re: LED guitar fingerboard

by adafruit_support_bill on Mon Dec 30, 2019 3:33 pm

TB-II is tenacious stuff. I don't envy the removal task. But your general plan looks workable. You may need to experiment a bit with the positioning of the fiber-optics relative to the LEDs for best results with the side-indicators.

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Re: LED guitar fingerboard

by Rymano on Mon Dec 30, 2019 6:21 pm

My journey down the rabbit hole has given too many viable options but I've narrowed to the Diffused Rectangular 5mm, https://www.adafruit.com/product/2739 over the less-bright Dotstars. My fiber optics provider also mentioned trying piranha LEDs but they seem a bit large to embed into a thin fingerboard. Both seem applicable with mating FO tubing.

Thank you again for helping me field through the many possibilities.

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Re: LED guitar fingerboard

by adafruit_support_bill on Mon Dec 30, 2019 8:00 pm

Do you plan to drive those all in parallel? Or will they be individually controlled?
If driving in parallel, you will need some external drive circuitry (e.g. transistors). A single GPIO pin will not be able to drive more than one to full intensity.
If controlling individually, you will need a lot more wires - as well as PWM pins on your controller. Even then, you will likely run into the total current sinking limits of the MCU.

The advantage of the Dotstars is that they have their own built-in drive circuitry - and you can individually control a whole string with just 2 GPIO pins.

The brightness difference is not as big as the numbers make it look. The visual response is logarithmic. Doubling the mcd is like going from 10 to 11 on your amp.

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Re: LED guitar fingerboard

by Rymano on Mon Dec 30, 2019 11:44 pm

Lol! I like the 10 to 11 amp reference. Looks I'll be ordering some dotstars asap. I assume the 2mm should do the trick.

Thanks again for all the expert advice! I'll post some shots of the finished product as soon as it comes together.

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Re: LED guitar fingerboard

by adafruit_support_bill on Tue Dec 31, 2019 7:14 am

2mm is pretty small. I hope you have better eyesight and steadier hands than I. You might want to try some of the 5mm ones too for comparison.

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Re: LED guitar fingerboard

by Rymano on Tue Jan 07, 2020 1:14 pm

5mm it is! Would you have any advice towards a proper tiny MCU? I was going to start with the Feather STM32F405 Express for simplicity and get and additional Feather nRF52 to experiment with bluetooth IOS/Android control. Would love to tie in the power into the bass's existing 9v preamp battery but it looks like a seperate 3.7v LiIo with higher mAh would be best suited.

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Re: LED guitar fingerboard

by adafruit_support_bill on Tue Jan 07, 2020 2:38 pm

If you are going to want wireless communication, one of the Feather processors with integrated wireless capability would be the way to go. Any one of them could handle the DotStars easily. The Feathers have a built-in charger circuit for a LiPo too.

You could use a voltage regulator between the 9v and the Feather. But those LEDs would drain a standard 9v cell pretty quickly. A LiPo would work better. And you probably also don't want any PWM noise from the LED coupling back into your pre-amp circuit.

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Re: LED guitar fingerboard

by Rymano on Mon Feb 10, 2020 3:28 pm

Alrighty then. I went and bought some components I probably have no business fooling with. Given I have absolutely no programming background, I purchased an Adafruit Feather STM32405, itsybitsy nRF52840 and some single dotstar 5050s (I wired test leads to the 5v, GND, CI and DI of 1 dotstar).

After many hours of setting up Arduino IDE, STM32 Cube Programmer and Circuitpython Mu, eventually getting the feather to connect and receive "Blinky" code, I have hit an absolute wall with adding the single dotstar to run a simple test code.

I know dotstars need 5v (3.3v feather board) but have read it can operate for testing purposes off the feather's 3.3v pin. -Also purchased some 74HCT125 logic shifters once the board is ready to control more dotstars off the 1200mah Lipo.

I believe I'm out of my league at this point after many hours of searching every tutorial/write-up I could find. I'm definitely lost as to what pins my dotstar leads need to connect or if this is even a feasible project. Had no clue what I was getting myself into... A point in any direction would be incredibly helpful.

Thanks a million

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Re: LED guitar fingerboard

by adafruit_support_bill on Mon Feb 10, 2020 3:45 pm

Your Dotstars will run fine from the 3.7v LiPo. You do not need 5v. You can use the output of the 3.3v pin for a few pixels for testing. But best not to overdo it and overload the regulator.

Each pixel requires 6 connections. Power and Ground are wired in parallel. You can wire GND and BAT (or 3.3v for testing) from the Feather to the GND and VCC pins on all the pixels..

Then you will need to wire 2 of the GPIO pins from your feather to the DI (data in) and CI (clock in) of the first pixel. From there you will daisy-chain DO (data out) of the first pixel to DI of the next. And CO (clock out) from the first pixel to CI of the next. Then repeat for all the pixels in the chain.

The GPIO pins you connect to will need to be specified in the code. Best to start with the "strandtest" example in the library. That uses pin 4 for data and pin 5 for the clock.

You can find the pinout diagram for your pixels in the data sheet linked here: https://learn.adafruit.com/adafruit-dot ... l-dotstars

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Re: LED guitar fingerboard

by Rymano on Tue Feb 11, 2020 2:29 am

20200211_011810.jpg
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I've tried tried strandtest several times with different 5v locations (bat, 3.3v, usb; GPIO DI4&CI5) and IDE gives, "Start operation achieved successfully," prompt at end of upload with no effect on the dotstar. Only edited strandtest line: "NUMPIXELS 1" instead of 30.

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Re: LED guitar fingerboard

by adafruit_support_bill on Tue Feb 11, 2020 6:52 am

A couple of things:

1) To avoid confusion, it is best to stick with standard wiring color codes. The standard convention for low-voltage DC circuits like this is black = GND and red = V+.

2) Looks like you are using A4 and A5. Those are not the same as GPIO4 and GPIO5 (in fact, the STM32405 has no GPIO4). Keeping the same wiring, you would need to change your code to reference the GPIO numbers for those pins which are A4 = GPIO20 and A5 = GPIO21. (Sorry, I know this is confusing!) https://learn.adafruit.com/adafruit-stm ... ss/pinouts

3) We can't see in the photo, but double check that you have the correct orientation of the chip. The notched corner on the face of the pixel aligns with DI - https://cdn-learn.adafruit.com/assets/a ... 1574117503

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Re: LED guitar fingerboard

by Rymano on Tue Feb 11, 2020 2:01 pm

Thank you for the references. Luckily I've been staring at those this past month and only fried 1 dotstar before getting the pinouts right. I did, however, completely miss the proper GPIO references til now.

Seems I'm probably typing something incorrectly and receving: "strandtest:16:25: error: 'GPIO20' was not declared in this scope; did you mean 'GPIOH'?" for DI and CI. My coding journey is off to a rough start. I really appreciate your patience with my severely novice approach.

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Please be positive and constructive with your questions and comments.