Okay so I have an UNO that has an nrf24l01+ attached. I want it to be completely wireless so free of the 5v USB power and the 12V wall plug. In this case what can I use? I do not wish to plug the power directly into the Vin as I am relatively new and afraid that it might fry the board. So I wish to plug it into the barrel jack. So I have read that using a 9v battery to power UNO is a waste of power as most of the power is translated into heat. Also, using 4 AA batteries seem to be a good solution except that I'm not sure if it has enough power for nrf24l01+ as I've read that an arduino with nrf24l01+ on batteries creates an unstable wireless node. I would like some help on what I can power the UNO with.
Vin is the same as the barrel jack (they are directly connected on the PCB). The NRF24L01 requires at least 2.7v. The uno board is however very inefficient (e.g. the usb-to-serial chip is always powered).– GerbenMar 24, 2015 at 15:12
Oh I thought that the Vin bypasses the voltage regulator but it turns out that its the 5v and 3.3v that does bypasses it, not the Vin. Despite the fact that the uno is inefficient, thats the board that I need to use. So back to the question, since it requires at least 2.7v, 4 AA batteries of 6V should be enough right? I am unable to try it out as of now as I do not have the time to buy the necessary things to try...– suckmsMar 25, 2015 at 4:32
That is kind of pushing the limits. 6v is the absolute minimum the voltage 5v regulator requires. If the batteries are drained a bit, they will go under this 6v limit. You could use 4 rechargable (1.2v) batteries to give you 4.8V, which you can connect directly the the 5v rail. But don't expect to get more than a day of battery life.– GerbenMar 25, 2015 at 15:19
Hmmm... Alright. Thanks for the advice. I guess if no one else has solutions I will use 6 AA batts of 9V instead of a straight 9v batt since I need a high current. Thanks!– suckmsMar 26, 2015 at 3:42
I've used the usb battery chargers (marketed to recharge cell phones) with great success on many different Arduino boards. They come in a variety of mAH capacities and are easily recharged with any powered USB port/power adapter.
Here's a link to one I've used. (I'm not affiliated with Duracell in any way).
this is certainly a easy off the shelf solution, which likely suits this user Mar 29, 2015 at 22:51
Sorry for the long wait in accepting your answer. I was setting up the exhibition in a location that was devoid of Wifi. I eventually went for the 6AA batts. But seeing your solution, I think it is the best and easiest solution. And its off the shelf as well!– suckmsApr 10, 2015 at 6:27
Brilliant, much easier than trying to get batteries into the DC barrel adapter, which is what I was trying to do (and can’t find the barrel size/type anywhere!)– DemisJun 27, 2021 at 17:06
To get an idea of run time, I used this battery to power an Uno with a photocell attached for at least 16 hours. I was running a sketch to record the amount of sunlight to determine the best place for some tomato plants. The sketch didn't use any low power techniques. github.com/linhartr22/LightMeterLogger Jun 28, 2021 at 19:11
Firstly if you only need short runs, go with the usb battery pack answer, but if you need the longest time from least batteries:
As has been pointed out, for best battery consumption an arduino board is not efficient due to power regulators and led lights. For best performance you want a standalone 328 chip with its BOD (brown out detector) reduced to 1.8v and then you can run it and the nrf24 chip off 2x AA batteries.
But all this might be a bit beyond you.
One thing though that will help your battery life is a PNP transistor or Mosfet on the +ve of your nrf24l01+ module triggered by a arduino io pin. as these power amplified versions dont sleep (per say, the chip does but not the PA) so it will always be consuming a large amount of power regardless of state. So just use your io pin to power it on and off for each use.
(that is unless you need it on always for recieving, in which case this wont help)