New Guy Here...First Micro Controller Project - Teensy LC Midi

[TeleRay]

Hi everyone. Glad to have found this resource. I'm working on building a MIDI Controller using a Teensy LC nearly exactly as this...

https://ask.audio/articles/how-to-build-a-simple-diy-usb-midi-controller-using-teensy

The only difference is I'm planning to use LED Arcade Buttons which will simply be lighted at all times (no control needed). These...

https://www.adafruit.com/product/3490

I'd like to power the entire box with one USB connection from a powered hub advertised to provide 900mA per output. This one...

https://www.apple.com/shop/product/HHM72ZM/B/belkin-aluminum-usb-30-4-port-hub?afid=p238%7Cs9WxpDgaK-dc_mtid_1870765e38482_pcrid_246387003261_&cid=aos-us-kwgo-pla-btb-3pp--slid--product-HHM72ZM/B

Also connected to the hub will be an iPod Touch running Loopy HD to be controlled with this MIDI controller.

So far I'm pretty solid on the code and loading it into the Teensy LC. My only real question is about powering the LED's. Here's my (ahem) wiring diagram...



The LEDS are rated for 10mA/5v and 2mA/3.3v - eight of them total. I'm going to run a 900mA USB to the Teensy and power the series/parallel LED's (2.5v each) between pin 17 (5v) and the nearby adjacent GND pin. So, assuming the LED's aren't too dim at 2.5v, I should only need less than 16mA for the LED's. If I need to run the eight LED's at 5v, then it will be 80mA. Will pin 17 cary 80mA?? Or even 16mA for that matter?? Reading the documentation it seems the pin 17 output is only good for 20mA. Or am I missing something? Is pin 17 simply a parallel connection to USB power?

Cheers! And thanks in advance.

 

[GremlinWrangler]

The pin 17 5V output is the logic output from pin 17 level converted up to 5V and current limited. If you want control of the LEDs better option would be a transistor on the low side controlled from a pin. If you just need them to light when project is powered then connect to the Vin pin and they will get 5V USB power - limited by the 500mA the USB port can provide but a lot more headroom there.

 

[TeleRay]

Thanks GW. Now I see why that Vin pin is labeled "17". So Plan A is out. You're saying Plan B is USB power in parallel 5v/500mA ? I'm now thinking I'll just wire the LED's all in parallel for 3.3v/16mA and pin to Plan C. Will that work?

 

[GremlinWrangler]

As long as you stay under the 100mA limit, that should work. Issue with 3.3V usage is that the regulator is inside the main IC, so it does not fail gently under load and when if it does fail you need to ditch the board. For indicator (vs illumination) LEDs should work ok.