Brightest LED that Teensy 3.1 can drive?

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pjrcbear

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Hi,

I have a project that lights up LEDs from a Teensy 3.1 board, where each LED is driven out of an output pin (I do my own PWM to control intensity) and then located on a drum kit in such a way that each LED illuminates a drum kit piece (like the snare, tom, etc).
It's a Roland e-kit, so the snare/toms are made of mesh so they can be lit from underneath the mesh head.

So far the LEDs I've been playing with for this are the one from the Tutorial projects, or this one.

The lighting works appropriately (kit pieces are lit when they should), but these LEDs aren't very powerful. What's the brightest LED (or LED array) I can power from the Teensy board itself?

Thanks in advance.

-- Greg
 
Hi Greg,

The datasheet of the MK20DX256VLH7 states the following:
1. Id, Maximum current single pin limit (applies to all digital pins), –25, 25 mA.
2. Ioht, Output high current total for all ports, 100 mA.

Personally, I would not drive a LED with the maximum current of a pin, but stick to 20mA.
In that case you could theoratically drive 5 pins/LEDs for a total of 100mA, but you're at the limit of the chip.

But more important: the Teensy 3.1 outputs 3V3 max on a pin. So you can not really drive white LEDs reliable from a Teensy pin since you need a (mandatory) current-limiting resistor in series with a LED as well.
See the figure below that shows the forward voltage of a LED versus the color of a LED.

roygbuiw.png

I think you need to look for a different solution...NeoPixels perhaps?

Paul
 
To get a strong led visual effect, I think that you will need to separate out the power to the leds from the power to the Teensy, and not supply led power through the Teensy. The Teensy would be used to control the data to the leds, but not the power. You can still have separate leds on the same separate pins that you currently have, just using the data line (such as to a set of WS2811 / ws2812 / LDP / etc).
And for massive lighting rigs, you can use the teensy to manipulate relay switches for higher voltages.
 
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OK, so I added a ULN2803APG functioning as a relay, and combined 2 channels into one so I can get to 1A out to a 10W LED array that works out of a 12V external supply.
It works great! Here's a video comparing the LEDs driven by the Teensy board vs the 2803.

Cheers,

-- Greg
 
Nice to see that your cicruit is working!
That ULN2803 is an old animal but still useable. I also used them for several projects long time ago.
You may want to combine more than 2 channels though since you are on the edge of the max current per pin [500mA].
But you could also consider to use a FET like this: https://www.sparkfun.com/products/10213.

Paul
 
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