Teensy 2.0 and VBAT

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tptompkins
 
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Teensy 2.0 and VBAT

Post by tptompkins »

Hey Guys,

I picked up a couple of Teensy's from you guys and have modified them to run at 3.3v with a regulator per the instructions here:

https://www.pjrc.com/teensy/3volt.html

Now that I've done this, I'm not sure how to wire up a 4.2v lithium battery to the Teensy 2.0. It appears that the regulator is only for the USB input power. I don't see a VBAT pin anywhere on the pinout list:

https://www.pjrc.com/teensy/pinout.html

Does anyone know which pin I should use to wire up a 4.2v battery to this board? Or is there a different recommended method of doing so?

BTW - I posted the question on their forums as well but they don't seem to answer questions very quickly.

Thanks!

Tommy

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Franklin97355
 
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Re: Teensy 2.0 and VBAT

Post by Franklin97355 »

You would hook to VCC and GND

tptompkins
 
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Re: Teensy 2.0 and VBAT

Post by tptompkins »

I actually just did that and tested the voltage coming out of the LED pin with a simple blink sketch and the voltage was the same as my battery (3.8v) so it doesn't look like it goes through the regulator like it does when plugged in through USB. I did everything that they mentioned in the 3.3v conversion instructions but it does appear that it only works when powering through USB. Seems very odd. Can anyone confirm this?

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adafruit_support_mike
 
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Re: Teensy 2.0 and VBAT

Post by adafruit_support_mike »

Looking at the traces on the board, the VCC pin connects directly to the 3.3v/5v pads at the regulator's output. Connecting a battery to VCC will bypass the regulator.

Let me check with Paul Stoffregen and see if he has any suggestions.

tptompkins
 
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Re: Teensy 2.0 and VBAT

Post by tptompkins »

Thanks Mike. Nobody has answered me yet on their forum so I'm looking forward to seeing what Paul has to say.

Tommy

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paulstoffregen
 
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Re: Teensy 2.0 and VBAT

Post by paulstoffregen »

Sorry about my very delayed response. I've been working very hard on SPI library improvements, just barely keeping up with forums.

The MCP1825 modification for Teensy 2.0 is meant to let the board run on 3.3V when you power from USB. There's no specific pin or pad on the board for supplying external, non-USB power. This is one of the many small changes that went into the Teensy 3.x design...

If you're powering from a battery on Teensy 2.0 with the MCP1825 regulator, you have (at least) 2 less-than-ideal choices. You could chop a USB cable in half and apply power to the red and black wires. Or you could solder the battery positive directly to the bottom of the PCB, right at the input of the MCP1825, or at the 5V pad that was cut away. Of course, refer to the schematic for details.

Image

tptompkins
 
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Re: Teensy 2.0 and VBAT

Post by tptompkins »

Thanks for the response Paul. Since I had a few extra MCP1825 regulators, I soldered some pins on one and basically converted it from surface mount to a through hole version that plugs into my breadboard. I soldered a couple of extra pins on the heat sink side to help dissipate any generated heat and it seems to work well. Now I can power off battery or plug in through USB to program.

It's not ideal to have to use two regulators, but for my purposes it'll get the job done. Thanks!

tptompkins
 
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Re: Teensy 2.0 and VBAT

Post by tptompkins »

I made a change to my setup and soldered the battery power directly to the input of the regulator on the bottom of the board just as you suggested. But that poses another question:

Is it harmful / bad to be plugged in via USB and have the battery plugged in at the same time? I actually have 4-AA batteries in a pack that's going through a 5v regulator, which is supplying 5v to a couple of sensors as well as supplying 5v power to the 3.3v regulator on the bottom of the Teensy. I want to use Serial for debugging and need the sensors to be powered at the same time. Can the 3.3v regulator handle power being fed in from two sources?

Thanks!

Tommy

tptompkins
 
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Re: Teensy 2.0 and VBAT

Post by tptompkins »

Nevermind. I was being dumb. When powered by USB, it also powers my sensors without the battery being connected since those are also connected to the input of the 3.3v regulator.

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