Powering a standalone ATMega project at 3.6V

Projects General Guidance
1

I have a project that needs to run of a battery. It has been designed to sleep and only work on interrupts to conserve energy. My problem is this:

The project uses a NRF24L01 wireless module, which has a power rating of 1.9V - 3.6V.

How should I power this? I was hoping to use a 3.7V Li-Po cellphone battery, but then I am afraid of the 0.1V too much damaging the wireless module. Could I use an output pin of the atmega to power this module, so that i can switch on the module when i actually need it? And then use a voltage divider to achieve the 3.6V?

Or would you rather go for 3x 1.5V batteries?

Additionally how can i regulate the power to the entire project? I do not mind if the voltage drops over time, but I do not want it to be too high at any moment. Is that even possible? if it is would a 3.6V zener diode be a solution?

Thanks for your help.
Michael

2

Use a coin cell, CR2032. Its a 3V cell, is small, cheap and perfect for battery operated circuits.

And yes, you can power up the RF module from the arduino pin itself to save further power.

Make sure to use a 8Mhz crystal/oscillator in place of a 16 Mhz, as it can't operate below 4.5V as per the datasheet.

3

Good idea on the 3V cell. Also thanks for the information on the crystal. I was unaware of that.

4

As far as I remember, the NRF24L01 is fussy about the supply voltage on Vin but will tolerate higher voltages on the signal lines. Does your Arduino provide a 3.3V output? If so, that's perfect to power the radio module. The other lines can use plain old digital pins. If you don't already have a 3.3V supply then you can put your 3.7V Li-Po through a couple of diodes to drop the voltage slightly (I seem to remember silicon=0.7v, germanium=0.3v).

5

Thanks for the response, but I am not actually using an entire Arduino, but just the chip, ATMega328. So whatever I power this project with is the voltage I will have to work with. Since it will run on a battery I need power consumption to be quite low.

6

If you're planning to actually power down the nRF module it might make sense to supply it from an Arduino digital output pin (as long as the nRF module is not the amplified type, it doesn't need much current). I haven't measured the voltage drop between the Arduino's logic supply and a digital output but presumably there will be some. You could just leave the nRF disconnected, power it up and see what voltage you actually get on the digital output. If you need to drop it slightly I'd suggest one or more diodes in series, but it may be that it's already within the safe range for the nRF. If you decide to power it directly from the battery then most likely you will need to drop the voltage slightly and a couple of diodes would do that nicely.