how to power arduino plus transistor load with 3.7v batteries

hey guys i I have a project where Im powering few ir leds from arduino pin. I want to use max two 3.7 lipo batteries to power my 5v arduino project. I know I can't connect ir leds directly to arduino due to its current limit. So my question is if I power arduino with two 3.7v batteries in series, can I then connect the transistor (collector) load to the same batteries + supply? Since I am not connecting transistor load directly to arduino 5v output pin rather to the same power supply, then I shouldn't have to worry about max arduino current draw, right??

or would I need a separate 3rd battery for powering my transistor load??? If so, then what would be the best way to power 5v arduino and transistor load using two 3.7v batteries??? thanks.

Your Arduino won't work on that voltage. Get an 8 MHz, 3.3V Pro Mini instead. Those should work just fine on 3.7V batteries, just connect it to the Vcc pin. One battery will do. You can then power the IR LEDs directly from the pin - just make sure you don't exceed the 20 mA pin limit.

I have to use like a transitor because I am using ir leds which draw more current plus I want to power all of them from single arduino pin.

Thats why I want to know if I power the transistor load (collector side) from the same battery that is powering arduino, would that current drawn be separate from the arduino max current since I dont want to burn it.

but yes if I use the 3.3v mini pro that will solve my problem but I don't know how 8 MHZ is going to affect the on off timing of my ir leds because I want it to remain exactly same.

kashi786:
I don’t know how 8 MHZ is going to affect the on off timing of my ir leds because I want it to remain exactly same.

If you tell the Arduino IDE your using an 8Mhz Pro Mini, it will make the adjustments.

You dont need to change the program.

kashi786:
So my question is if I power arduino with two 3.7v batteries in series, can I then connect the transistor (collector) load to the same batteries + supply?

Yes, you can power a +5V Arduino with 2X3.7 volt batteries wired in series and, from your description, you can power the xistor circuits from the battery.

kashi786:
Thats why I want to know if I power the transistor load (collector side) from the same battery that is powering arduino, would that current drawn be separate from the arduino max current since I dont want to burn it.

Then don't have the current run through the Arduino. Just use separate wires.

Idahowalker:
Yes, you can power a +5V Arduino with 2X3.7 volt batteries wired in series

True - if you connect it to the Vin and are happy to waste battery power.

wvmarle:
Then don't have the current run through the Arduino. Just use separate wires.

So if I power my load attached to transistor from the same power source(battery) that is also powering the arduino, so in this case the current drawn by load/transistor is also running through the arduino?? Or is it separate??

wvmarle:
True - if you connect it to the Vin and are happy to waste battery power.

sry Im confused, how does that waste power??

If your Arduino needs say 20 mA, then in the single battery scenario you take 20 mA from one battery, in the other scenario you take 20 mA from two batteries - so two batteries power the 5V one as long as one battery can power the 3.3V one. Well, it's actually even worse, as at 8 MHz an Arduino takes less current than at 16 MHz. That means one battery can power a 3.3V 8 MHz Arduino longer than two batteries in series can power a 5V, 16 MHz Arduino.

Also if you feed 7.4V to Vin this gets stepped down to 5V by the regulator, meaning about 1/3 of the power taken by the Arduino goes straight to heat, without doing anything useful. That's another way battery power gets lost.