Do I need a regulator at all?

Projects General Guidance
1

I would like to build a few sensors to use with a mysensors gateway.

I have some atmega328p chips lying around, I will use them to build a minimal Arduino (I have an external programmer, capacitors, etc)

The sensors will use a nRF24 radio to transmit the data back to the gateway. I would like to power the sensors with a CR2032 battery (ideally), or 2x AA Eneloops.

I read the MCP1700 is pretty good for that, but I also read about people feeding the project straight off the batteries without any regulator at all.

So, do I need a regulator for that? If a regulator is optional, what are the pros and cons of using one?

2

Neither the ATMegas nor the radio require a regulator. The sensors might.

See these excellent tutorials on low power operation, and on a solar powered remote sensor with Arduino.

3

You can certainly power an Atmega 328 and an nRF24 with 2 x AA alkaline cells without any regulator. i have built a few devices like that.

I don't know if a CR2032 could provide enough milliamps for the nRF24 when it is transmitting.

...R

4

The CR2032 will work, at least for a while.

From the data sheet:

11.3mA TX at 0dBm output power

5

jremington:
The CR2032 will work, at least for a while.

If it only needs 11 mA how come it is only marginally able to work with the Arduino 3.3v pin? I have a Mega clone that does not have enough mA on the 3.3v pin to work an nRF24.

...R

6

What is the measured TX current?
Are you using the PA version?

7

jremington:
What is the measured TX current?
Are you using the PA version?

If that is aimed at me I only have the low power versions with the PCB antenna. I never measured the current - I'm not sure that I have suitable equipment to do so.

...R

8

Yes, that was aimed at you. Based solely on the manufacturer's specifications, it is then very difficult to understand the following claim. Perhaps you have an out-of-spec NRS24 device or clone.

I have a Mega clone that does not have enough mA on the 3.3v pin to work an nRF24.

9

jremington:
Yes, that was aimed at you. Based solely on the manufacturer's specifications, it is then very difficult to understand the following claim. Perhaps you have an out-of-spec NRS24 device or clone.

I would not be at all surprised if the clone is out of spec.

...R

10

I think you should use "large" (a few hundreds uF) cap when using coin battery to help it cover the current spike needed by nRF when transmitting. Maybe it is problem with Arduino's 3V3 regulator too - step increase in current demand when nRF starts transmitting causes short loss of regulation?