Is putting an ATTiny85 sensor to sleep during the day worth it?

My project consists of a mains powered host and multiple (about 30) battery powered sensors.

The sensors are standalone ATTiny85 "Arduinos" running off 3xAA batteries.
Sensing is either via a mini PIR or a magnetic reed switch (think burglar alarm).
Each sensor has a 433RF transmitter.

The sensors are only required to be active at night, say from 7:00 pm to 7:00 am.
I am considering putting each sensor to sleep during the day to conserve battery power.
Sleep mode would need to be initiated "automatically".

So the questions that come to mind are:

  1. What are the different viable options to track time and invoke sleep/awake mode?
  2. Is it worth doing?

My thinking so far has been :

  1. Equipping each sensor with a RTC.
  2. Using transceivers rather than transmitters and have the host send a sleep/wake-up signal.

Input appreciated.

I think that in your case having the tiny check it’s sensor one every second and sleep for the rest of the time would be the best power saving option.

If you are really trying to make an alarm system then you must use a transceiver, as this allows the master unit to check that the slaves are still working.


If you are going to use a Transceiver, then you will have to factor in its power consumption.
The receiver component will consume power all the time .

It is not a burglar alarm, but it works on the same principle.

FWIW I was looking at using transceivers when I was considering using nRF24L01+ modules. My concern however was range which is why for now I am favouring 433MHz RF.

Nonetheless I am keeping an open mind...

The receiver component will consume power all the time .

It doesn't have to!

Either the master can periodically send an idle signal which lasts longer than the sleep cycle of the slaves, which allows them to "wake up and take notice" after which it polls each in turn for a report, or it can with some accuracy, know their sleep cycles and transmit when it expects them to be active.

However there is no advantage to having the master poll the slaves, over having them poll themselves, that is, emit a periodic beacon without having any receive function.