Powering Teensy 3.1 with 2s 3.7v batteries

[ddmods]

I've been researching the best way to power the teensy externally with 2s 3.7v batteries. I would use an lm7805, but under load the batteries can go down to about 6v which is under the minimum for the 7805. Thought about voltage divider, but not sure if that would be the best route. Is any of you using a voltage divider to power the teensy with 7.4-8.4v? If so, how high of resistor values?

I read that it can be powered with 3.3v, but I'd like it to run at its best performance. Some help is greatly appreciated. 3s 3.7v batteries would work with lm7805, but I don't have room in the enclosure I'm planning on using. Thanks!

 

[MichaelMeissner]

You can apply 3.7v to vin, and it should work just fine at full performance (unless you need higher voltage for servos). So you don't need 2 batteries (unless you need 2 batteries for capacity, but there it might be simpler just to get a larger li-poly battery).

You could use this battery connector with mini-charger from onehorse (https://www.tindie.com/products/onehorse/lipo-battery-charger-add-on-for-teensy-31/). I bought it, but unfortunately I had to clean the house for a party, and I put all of my stuff in a box to get it out of the way, and I need to get stuff out of the box and fire up the soldering iron.

 

[Jp3141]

Using a resistor divider to power somethingis not very practical.

Instead of a LM7805-type regulator, use a LM317 which is easily available and only requires 1.3 V 'extra'. You use some resistors to set the output voltage.

There are other regulators (LDOs and DC/DC converters) available --what's best depends on the effeciency (battery lifetime) you want. Consider using just one Li-Ion battery -- it's simpler, and you can get LDOs to regulate its (3.3 .. 4.4 V) output down to the 1.76 - 3.3 V that the Teensy can run from.

 

[ddmods]

Thanks! I actually have a lm317! Totally forgot about it. This project needs at least 7.4v. Thanks for the tips.