Pro Mini as node in sensor network

Hi,

I would like to use a Pro Mini as a node in a sensor network. Each node will need to be able to:

  • communicate (two way) with a Raspberry Pi via two nRF24L01+
  • control a 5V relay
  • use a temperature sensor (recommendations?)

My main issue is, as usual :~, power.

  • Batteries? Would need to be high capacity as I don’t want to be charging them every day.
  • Mains? Limited as there aren’t many sockets near where I want the nodes to be.

All advice greatly welcomed!

Can use a big lithium battery, can get very high capacity packs that won't need recharging often. 3.7V-4.2V would be fine to run a 8 MHz promini from battery directly.
nrf24L01+ can be powered from that, will need 74HC4050 or equivalent to keep SCK, MOSI, CS at 3.3V level tho. Or maybe get by with resistor divider if running SPI at slower speed.
A relay like this

can be driven directly until the battery voltage starts dropping.
What's the relay switching?
What's the temperature range to be monitored?

Thanks for your help, I understand that I need a big battery - could you recommend one?
The relay switches on a circuit for a boiler, which then heats the room.
The range would be about 10C to 30C (room temperatures), would this be ok http://www.ebay.co.uk/itm/281196485870?var=580242591095 ?
I don't understand about that resistor or level shifter, please could you explain?

Oops, had that backwards:
nrf24L01+ needs power of 3.6V max, while it’s input signals can be higher, up to 5V.
Use a low dropout 3.3V regulator with enable pin, can turn it off when not planning to Tx or Rx to save some power. If it has to be able to receive anytime, well, your big battery can cover for that.
I have a huge LiPo at home, like the size of 3 decks of cards, and 6 AH capacity or something like that. That would run a long time. Found it thru a google search for LiPo batteries.
Comparable to this, but I think was 11.4V (for driving LED strings) and came with a charger.

or this

and get a charger for it.
Sensor, I can’t open ebay from here, can look when I get home.

So what you're saying is that the Arduino itself could turn the power on for the RF module? Why couldn't it use the 3v3 pin on the Arduino?
Do you know how much current a Pro Mini would draw if it was controlling a relay, RF module and temperature sensor?
Because if I know that, I can work out how big a battery I need for, say, a week.
Also, what is the capacity of 2 AAs? Or 4, in parallel to double the ampage?

I am a noob, but you might want to check out the Moteuino at “lowpowerlab.com” and the forum there as the Moteuino was designed to be a very low power Arduino and you can choose which RF module is built into it when you purchase it. The RF module and the Moteuino itself can be put to sleep and consume very little power. A small battery could possibly power one for months. If you used something like a “latching” relay I think it could stay either “closed” or “open” while the Moteuino was powered down (sleeping) without changing the state of the relay until you wanted to. You could also use a Pro mini with a latching relay to accomplish the same thing I think. If using a Pro Mini, you could use a digital pin to power the radio up and down when you needed to transmit…

xavbabe:
Thanks for your help, I understand that I need a big battery - could you recommend one?
The relay switches on a circuit for a boiler, which then heats the room.
The range would be about 10C to 30C (room temperatures), would this be ok http://www.ebay.co.uk/itm/281196485870?var=580242591095 ?
I don't understand about that resistor or level shifter, please could you explain?

Those DS1820's are very common and used all the time plus there are libraries to support them so yes it would work. Plus they work from I think 3V to something like 5.5V so it would be in your range as well.