# How to power an Arduino Uno with 3 1.5V batteries?

I have an Arduino Uno (a SainSmart model, actually). I intend to power it with three 1.5V batteries. I measured them and they yield 4.67V in total. The Arduino requires 5V.

# The question is, if the arduino will work this way.

I'm not powering complicated microcontroller components here. These components are used:

• A buzzer
• An LED
• A unit of 4 seven segment displays
• A couple of buttons as input elements

If the volume or brightness of these components is slightly decreased, it doesn't matter at all. But I would like to know if it will work in the first place.

# And also...

Where exactly do I plug the power source in? The power jack, the USB jack, pins, somewhere else?

The schematic looks like this, just to illustrate it. I'm not a good drawer, but you'll get the idea...

• According to the datasheet of the ATmega 328P (figure 29-1, page 303), you need at least 3.78 V to run the Arduino at 16 MHz. This is 1.26 V per battery. Many 1.5 V batteries will drop below that level way before being exhausted. You can use the clock prescaler (c.f. chapter 9) to throttle down the clock to 8 MHz (minimum = 2.4 V), at which frequency you can use the full capacity of your batteries. But your timing functions will be off by a factor 2. – Edgar Bonet Jun 17 '16 at 8:43

The Arduino doesn't require 5V.

The Atmel chip on the board requires somewhere between 1.8V and 5.5V, the Arduino just happens to have chosen 5V as a good common widely used voltage to run at.

If you provide a voltage within that range to the +5V pin the board will operate. There's a couple of caveats though:

• Anything below about 4V will mean the 3.3V regulator won't be working right, so the 3.3V pin won't be functioning properly
• At lower voltages the Atmel chip can't operate reliably at higher frequencies, which is why 3.3V Arduino boards operate at 8MHz instead of 16Mhz.

So 3 x AA batteries is a perfect power source for running the Arduino, direct into the 5V pin. Just make sure that you don't power it any other way at the same time or you'll be pumping 5V into your batteries. You may want to add a Schottky diode in series with your battery + (between battery + and the 5V pin) to stop that ever causing a problem. Choose one with a very low forward voltage drop though, otherwise you could end up dropping too much of your precious voltage over the diode.

By the way, when you're powering it from USB the 5V could be anywhere between 4.75V and 5.25V.

• So the 5V output pin is a 5V input pin at the same time? – bytecode77 Aug 19 '15 at 22:18
• @bytecode77 The 5V pin doesn't have a "direction". It's just a connection to the 5V power rail. You can use power from it, or you can give power to it, depending on what power you have where. – Majenko Aug 19 '15 at 22:25
• Good. Very nice answer by the way. Lots of facts, information beyond the asked question. +1! – bytecode77 Aug 19 '15 at 22:26

As per @Majenko's answer, yes, this will work fine.

Some caveats: the Atmel chip at the center of the Arduino has brown-out detection - if it drops below a certain voltage, the chip will shut down. This voltage is selectable: 4.3v, 2.7v, 1.8v, or off. The factory default for the chip is "off", I found a reference that the Uno sets this at 2.7V.

Also, if you are powering anything else with your battery, e.g. a motor, the voltage is will drop - if it drops below the brownout, the arduino will shut down (usually also shutting down the external device, causing the voltage to rise again, causing it to power up again). An LED (with a correct resistor) should be fine.

• 2.7V as the threshold sounds fair. And my components draw constant and very low current (I think). – bytecode77 Aug 19 '15 at 22:31
• Just something to remember if your project seems to be randomly resetting. – AMADANON Inc. Aug 19 '15 at 22:33
• While I have your attention: How long do you think I can operate an LED, 4 seven segment displays and a buzzer (buzzer has a duty cycle or 7,5%) with 3 1.5 AA batteries? – bytecode77 Aug 19 '15 at 22:35
• @bytecode77 That depends if you invest some time in learning how to use sleep mode or not. I am in the process of designing a PIC32 based system with LCD screen and all sorts that can run for a month off a small PP3 9V battery. – Majenko Aug 19 '15 at 22:43
• You mean that the Atmel chip doesn't consume energy when it doesn't do anything? As far as I saw it, `delay()` does nothing more than a blocking for-loop. But that's a different question, I will also look into that. Does the Arduino drain much current when running? – bytecode77 Aug 19 '15 at 22:45

For battery-operated Arduino Uno's I recommend thinking bigger (in terms of power, not physical size).

I power several by using 3x 18650 batteries in series, (providing about 14 Volts, connected to a 4x USB 5 Volt module.

The Unos are connected to power by a standard USB cable (into the programming port), and then you also have 3 other 5V USB charging or power ports available.

Or you can get a small converter unit that provides just one 5V USB.

Either way, bringing the power to the UNO is as simple as using the programming cable that comes with the board.

Or you can use any other converter and use wires to bring in Vin and GND.

You don't need to use 3 of the 18650s. 2 will do fine. Or 4 in series/parallel for longer battery life. No converter would be needed but again you would need wires to bring the voltage into the Unos.

18650s are very common, and are inexpensive. They pack a whole lot more mAh than any AA battery you will find.

One warning about buying 18650s: There are Chinese companies that advertise 9,800 mA batteries. Don't believe it. 3,000 is about the max any reputable manufacturer will claim.

You can power the Arduino via the 5V pin - but you need make sure you disconnect it when you are connected via USB - ie. don't power both the 5V pin and via the USB.

Any even better way is to power it from the USB socket - I use those emergency Phone battery packs, but you could cut up a usb cable and use that - this is a much better socket fit to use than the 5v pin and more energy efficient than passing a higher voltage through the 9V supply.

• The requirements of my project are tight and therefore batteries are the only options. But still useful information to keep in mind, thanks. – bytecode77 Jun 17 '16 at 9:12
• @user23096 - are you suggesting you could use the USB power socket and still use batteries by wiring a AA batteries to a USB cable that is cut off at one end and the other end plugged into the board? (I am a noob - forgive the stupid questions) – DanCaveman Dec 22 '18 at 15:34