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Using TLC TLC59711 with common-cathode RGB LEDs
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Using TLC TLC59711 with common-cathode RGB LEDs

by Bautastein on Sat Apr 10, 2021 7:52 am

Hi

I'm planning a project with a kind of LED light-show for a small sculpture. I'll be using an Arduino Nano Every. It only has 5 PWM outputs, so I was looking for a board to expand my PWM outputs, and saw that the Adafruit TLC59711 looked promising.

The LEDs will be lighting up a sculpture, which is different from how LEDs are normally used in electronic circuits. For that purpose, I've purchased some very bright LEDs, on the order of 20-30 cd at 20 mA (small viewing angle). I'm waiting for them to arrive, so I don't know exactly how bright that really is, and whether I'll need more in series or parallel. They need not be able to light up the sculpture in a brightly lit room, but it should be possible to see it in a dimly lit room, with a 10-20 cm distance between LED and sculpture.

Anyway, I didn't know that there were different types of RGB LEDs, and it turns out the ones I've ordered are common cathode LEDs. It seems they can't be used directly with the TLC59711. However, I was wondering whether it might be possible with some extra components to use them anyway? Without much wasted power? Unfortunately, this type of LEDs have to be ordered in packets of 50 from my local supplier, and their common-anode counterparts from the same manufacturer have much lower brightness ratings (not sure why).

If that's not possible, maybe there is a better suited product? Also, I wonder whether it might be possible to use three single color LEDs (Red, Green, Blue), and mix them, since people are not supposed to look directly at the LEDs, but instead see the mixed results on the sculpture.

Bautastein
 
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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by adafruit_support_bill on Sat Apr 10, 2021 8:24 am

It is possible, but not very practical to drive common cathode RGB LEDs with the TLC59711. But you would need at minimum 3 transistors & 3 resistors for each RGB LED.

Single color LED are an option. That would also give you the possibility of running 4 LEDs in series per channel with a 12v power supply.

For high-output RGB illumination, we have 3W chainable Neopixels. That is about 10-15 times the output you would get from a typical RGB LED.

And you can drive a whole string of them with just one pin from your Nano: https://www.adafruit.com/product/4544

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by Bautastein on Sat Apr 10, 2021 10:38 am

WOW, the 3W Neopixels looks like an awesome product!

For my project I think it would be overkill, since it would require a big power supply and I'd have to start worrying about heat.

I'll wait untill the LEDs arrive to make some experiments to know better what my requirements are.

For now I have my eyes on the PCA9685: https://www.adafruit.com/product/815#technical-details

Bautastein
 
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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by adafruit_support_bill on Sat Apr 10, 2021 10:51 am

The PCA9685 is a possibility. It can work with the common cathode LEDs.

How many LEDs do you anticipate will be required for your project? You may not need 3W Neopixels. But you may still want to consider using regular Neopixels. It would simplify your wiring considerably - and it gives you lots of flexibility if you find that you need to add more. These are available in many different forms ranging from individual pixels to strips, rings etc.
https://www.adafruit.com/category/168

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by Bautastein on Sat Apr 10, 2021 3:50 pm

I was thinking 4-5 independent light sources, with some of them possibly consisting of more than one LED in series or parallel, depending on whether the brightness of one LED is sufficient. But now I'm not so sure anymore, I took a look at that NeoPixel page and WOW... that stuff might be perfect for the project. Maybe I ordered those other LEDs a little too soon... :)

I will be waiting for the LEDs to arrive, to experiment a little before I make any further decisions. Thank you for all your help!

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by Bautastein on Sun Apr 11, 2021 7:47 am

Well I couldn't stop myself, so I have been playing around in my head about incorporating the NeoPixels in the project.

After skimming through the document "Sipping Power With NeoPixels", I think it's feasible to have 60-70 NeoPixels powered by AA alkaline batteries, which is what I was hoping for. My Arduino wants 7-21 Vin, so I was thinking I might use three cells to power the NeoPixels, and three extra cells in series with those to power the Arduino, for a total of 9 V for the Arduino, which will also allow a little voltage drop as the batteries get discharged. So the Arduino and NeoPixels would share the GND terminal, but have different V+ terminals.

Would this setup work?

I'm wondering about one thing: In the NeoPixel Überguide, it says "If powering the pixels with a separate supply, apply power to the pixels before applying power to the microcontroller". Does this advice apply to the above scenario, and how would I achieve that? The obvious way to wire a power switch would be to use a double pole switch, which would power on the Arduino and the NeoPixels simultaneously. Would that be OK? Or could I have the power to the NeoPixels always connected, without draining the batteries? Is this best practice advice in the Überguide actually meant for cases when you power on the NeoPixels and the microcontroller independently, or should it always be followed?

A little background: While I have great skills in programming, and good soldering skills, my circuit design skills/electronic knowledge is only rudimentary, but I'm a quick learner... :)

EDIT: As to why I don't just use the 5V output pin on the Arduino, it's because with the setup above I don't have to think about the max current limitations or power dissipation from the Arduino, as long as the average current usage by the NeoPixels is low enough to provide good battery life.

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by adafruit_support_bill on Sun Apr 11, 2021 10:14 am

Would this setup work?

That setup should work fine. But 6 cells for the Nano is more than you need. The Nano will only draw 20-30mA, so those cells will easily outlast the ones powering the Neopixels.

Another approach is to use a 3.3v processor and power both processor and pixels with the same 3.7v LiPo cell. That is how we do most of our battery powered pixel projects these days. https://www.adafruit.com/product/3675

I'm wondering about one thing: In the NeoPixel Überguide, it says "If powering the pixels with a separate supply, apply power to the pixels before applying power to the microcontroller". Does this advice apply to the above scenario, and how would I achieve that?

Yes, it does apply. The pixels can be damaged if the voltage on the signal pin exceeds the voltage on the power pin.
A double-pole switch to switch them simultaneously would be OK. You don't want to leave the pixels powered full-time. The idle-current when the LEDs are all off is about 1mA per pixel, so you would have a 60-70mA drain on your battery pack.

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by Bautastein on Tue Apr 13, 2021 3:26 pm

adafruit_support_bill wrote:Another approach is to use a 3.3v processor and power both processor and pixels with the same 3.7v LiPo cell. That is how we do most of our battery powered pixel projects these days. https://www.adafruit.com/product/3675


That looks like an optimal solution, but I decided not to go for it, because if the LEDs draw a few hundred milliamps, and I charge the battery at say 100 mA, you'd be spending more time charging than using it(?) If I try to charging it at maybe 500 mA, inside the enclosure, I'll probably have to do some thermal analysis. I'll just go for the alkalines to make it simple. Plus I already have the nano, I'll go with it. For future projects I'll probably go for a Featherboard with support for your LED Animation Library.

I have received the LEDs now. Not the NeoPixels, but the ones mentioned earlier in the thread. They totally exceeded my expectations, and I want to use them. Not the RGB ones, but the single colour ones.

The sculpture is a skeleton playing an electric guitar, and the plan was to make a light show for it, like the light shows at a rock concert. The LEDs are fantastic to mimic miniature coloured stagelights used on rock concerts, because they spread the light in a sharply distinguished cone, of only 15 degrees, but inside that cone the light coming from just a few milliamps is impressive, it can easily light up and colour a small object even in a normally lit room. These will only be to illuminate, not to look at directly.

In addition to that, the NeoPixels could provide a light show to look at directly. Also, I'd like to experiment with your micro servos, and your pan-tilt package, to move around the "stage lights". https://www.adafruit.com/product/1967

So now my setup is ready:
1x Arduino Nano Every (which I already have)
1x TLC59711 to drive single colour LEDs for illumination
NeoPixels for light show
2x Pan-tilt kit, to be controlled by the Nano's built-in PWM outputs.

Are these parts all compatible with my Arduino board, and will the micro servos draw much current? They will only be slowly moving around a few grams from time to time.

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Re: Using TLC TLC59711 with common-cathode RGB LEDs

by adafruit_support_bill on Tue Apr 13, 2021 3:35 pm

All those parts should be compatible with your Nano.

Current draw from the micro-servos is 'peaky'. They should idle at maybe 40-50mA. You will probably see spikes up to 500mA or more as they start to move. If they are lightly loaded, those peaks should be pretty brief.

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Please be positive and constructive with your questions and comments.