USB Voltage Clarification

[andy902]

Hi Guys,
New to Teensy, great active forum, congrats I think I've answered most questions already by searching, but I'm only 99% sure on the last question.

Project - I'm looking at Teensy LC + physical buttons to emulate keystrokes

Topic - I think I understand the difference in 3.3 and 5v used at the same time

Clarification - If I connect USB from PC, that should power the LC without issue (even though LC is 3.3v and USB is 5v)... as well as transmit keyboard keystrokes back up the cable?

So all that's needed is

PC USB Port (2.0 or 3.0) <--USB Cable--> Teensy LC <---two core cable--> plastic momentary switch

Many Thanks
Andy

 

[MichaelMeissner]

Hi Guys,
New to Teensy, great active forum, congrats I think I've answered most questions already by searching, but I'm only 99% sure on the last question.

Project - I'm looking at Teensy LC + physical buttons to emulate keystrokes

Topic - I think I understand the difference in 3.3 and 5v used at the same time

Clarification - If I connect USB from PC, that should power the LC without issue (even though LC is 3.3v and USB is 5v)... as well as transmit keyboard keystrokes back up the cable?

Yes, the LC has a voltage regulator that converts 3.7-5.5 volts from USB (or VIN) to 3.3v volts for the Teensy to use.

My notes say that the LC's voltage regulator can handle roughly 350ma. For keyboard stuff this is not an issue, but it might be an issue if you use a lot of ws2812b (neopixel) or apa102 (dotstar) lights that you illuminate at full power. From a computer, you might not get that much power (100ma is more likely), but still it is more than enough to power the LC to act as a keyboard.

 

[andy902]

Legend, thankyou sir!