Controling 16 RGB LED stripes with Arduino Mega and Adafruit PWM extension

Other Hardware LEDs and Multiplexing
1

Hi guys,

I am new in this forum and don't have an overview yet. I read a lot of posts, but nothing was of help so far. In case this was already spoken about, please tell me.

For a project at the university, we need to controle about 90m of LED strips. 12V 5A = 60W (12W/m)
[We used these ones: https://www.amazon.de/gp/product/B01500WV74/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1]

Since they each need 4 pins (12V, R, G, B) we ran out of PWM pins on our Arduino Mega. It seemed to be a good solution to simply extend our PWM pins by this hardware: Adafruit PWM Arduino extension, 12 Chanels, 16Bit [Adafruit 12-Channel 16-bit PWM LED Driver - SPI Interface [TLC59711] : ID 1455 : $7.50 : Adafruit Industries, Unique & fun DIY electronics and kits]

To power all the LED strips we used the original power supplies and took care that each one powers a maximum of 5 meter LED strip. (Its a littly messy, but that was due to budget) The minus goes directly to the 12V of each stripe, all grounds are put together and connected with the arduino and extension board grounds. The RGB signals come from the extension boards. Each board covers 4 strips (12 Chanels, 4x RGB).

Now the problem: Everything works so far. We can controle all the strips, easy, BUT it seems that there is something wrong with the power supply. All LEDs seem to run with ~25% brightness, even set to 100% in our script. I am quiet sure that it is not a scriting problem, that why I havent put the code here. In case you think it could be the script, let me know and I will post it here.

Do we need to power the extension boards seperately with 12V 20A (4 stripes á 12v5A)?

In case you have an idea, I would really be grateful.
Best,

Daniel

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2

Wrong expander board.
That board can only sink <=60mA (1% of what you need).

You need mosfets to switch 5Amp.
There are most likely three of them inside that white box that came with the strip.

Not sure how to fix this.
You can try if that expander board can drive the gate of a mosfet.
You might need gate pull up resistors.

Leo..

3

Since they each need 4 pins

No they only need 3 Arduino PWM pins.

You need to post a schematic of what you have because your description sounds all wrong.
These strips ( not stripes a zebra has stripes ) work by sinking current, that is connecting the RGB lines to ground. I think you have underestimated the amount of current you need and that is why the LEDs are dim. You could also damage your power supply like this. What sort of FET are you using to drive the strips?

4

I didn't see any mosfets on the picture.
Just the LED stripes :slight_smile: connected to the outputs of a TLC59711.
Leo..

5

Thank you guys already!
I thought so, that the expander board was not correct. Please find attached to the first post a schematic drawing of the situation. As said, the controlling works, but the signals are too weak. You were probably right, that we underestimated the current needed. The 5A Mosfets seem to be a good solution. Let the soldering begin ... :slight_smile:

6

As said, the controlling works, but the signals are too weak.

The data sheet for that chip says:-

Current Capability: 60 mA per channel

So not only are you vastly overloading it, it is also a constant current output which in a way saves you from the consequences of your mistake, and also explains why the LEDs were dim. I think you are in for a shock at how bright they will be when you drive them correctly.

The 5A Mosfets seem to be a good solution.

Not for a 5A load they are not. Try not to run a component any harder than 80% of full current rating.
Make sure they are logic level FETs.

If you are using that expander chip then note you will need a pull up resistor to 5V from the output of each driver of about 1K as they are only sink outputs.