can I supply my teensy 3.2 with 1.5 volts or 3 volts(not 3.3)?

Status
Not open for further replies.
H

harambeCute101

Member
Hi,
I'm making a wristwatch with my teensy, I'm designing a custom PCB and everything.
I'm planning to supply power to my watch with two aaa batteries. each battery has a 100mah capacity with a voltage of 1.5v.
If I connect the two batteries in parallel, I will get a 3V input and 1000mah capacity.
If I connect them in series, I will get a 1.5V input and 2000mah capacity.
Is it possible to drive the teensy with a 1.5v or 3v supply? or does it have to be above 3.3v?
Also, I don't know how to calculate my watch's power consumption. It has a teensy 3.2, an i2c 128x32 oled, 5 leds, and 1 neopixel.

Thanks for everything!
 
3.0 volts works fine, but below 1.7 volts definitely will not work.

Reverse polarity will destroy the chip, so make sure you use battery holders that prevent reverse polarity connection. Or plan to add a reverse polarity protection circuit to your design.
 
Thanks Paul!
Sorry, what is a reverse polarity? Is it basically when I connect - to + and vice versa?
Also...
1. how long do you think my watch will last with 1000mah?
2. I connect my batteries to Vin, not 3.3v, right?
 
Last edited:
harambeCute101 said:
Sorry, what is a reverse polarity? Is it basically when I connect - to + and vice versa?
Click to expand...

Yes.

This happens if a person accidentally put the batteries in backwards!

1. how long do you think my watch will last with 1000mah?
Click to expand...

Running at 96 MHz without using the Snooze library, the power usage is approx 45 mA. So a 1000 mAH battery would last about 22 hours.

You can lower the power by reducing the speed in Tools > CPU Speed. Lower speeds use less power. This is very easy, just click the menu and see if you code is still able to work at the slower speed.

You can dramatically lower the power by using the Snooze library put Teensy into deep sleep modes when your code does not need to run. This is harder, because you need to learn how to use the Snooze library, and then structure your program around how the low power features work.

2. I connect my batteries to Vin, not 3.3v, right?
Click to expand...

If you're sure the voltage will not be more than 3.6V, you can connect directly to 3.3V for best performance.
 
If you need to generate 3.3V from a 1.5V battery, I would recommend something like this: https://www.pololu.com/product/2561
Hook that into the 3.3V pin of the Teensy, and you'll do fine!

Snooze can extend runtime by almost the ratio of sleep-to-awake. I e, if you use 48 MHz frequency, and get 2 days of runtime; if you end up deep-snoozing 90 milliseconds and being awake 10 milliseconds, you could extend time up to 20 days in the optimal case. Less deep modes of sleep will extend less, and depending on what your actual power consumption is (peripherals, pull-ups, etc,) you may get much less.
 
Keep in mind that most displays use a lot of power. With Snooze the Teensy can use significantly less than 1mA, but most displays will use 20mA or more.

Also keep in mind that brand new alkaline AAA can have a voltage of 1.7V or even higher, so you might exceed 3.3V if you use two AAAs in series. Battery voltage drops during their lifetime, and in order to use most of the battery charge your watch should be able to use them at least down to 0.9V per cell.

And finally, a step-up regulator usually needs at least 1mA for itself. So in a low power project you should try to do without them.
 
Status
Not open for further replies.
Back
Top