ESP32 Forum

Hello all,
This might be a stupid question but I'm getting bit overwhelmed with possibilities and would like to focus on one that is the best.

I need connect multiple ESP32 to local LAN ( or Internet ) but I need it at low power 3.3V batteries, this mean sleep for about 24hours than wake up, check server if something changed specifically for that device ( so it have to broadcast identification first and than read the response ), if something changed than do action and back to sleep...

I do not need long distances like LPWAN ( which sounds great, low power and long distance... but licensed and need expensive hub to talk to normal web servers... )
Bluetooth - nice low power consumption, range is not that great though and I'm not sure if it can be made in a sense Server + many clients checking from time to time ( possibly multiple clients checking at once )
WiFi - classic solution that I understand , its just AP and clients.. simple enough.. battery inefficient though.. ( would be nice to have wifi mesh capability, but since like 99% of the devices will be in deep sleep, it would not work. I don't know though...gathering information about it now )

What else is there ? Some low power radio communication like LPWAN. or just stick with wifi and get a bigger batteries ?

Does it matter how power hungry WiFi is if it's only going to be awake for 5 seconds once every 24 hours?

I have several battery-driven ESP32 boards running which wake-up, read sensors, start Wifi, send data with a single HTTP-request and go to deep sleep. That all takes 4 to 5 seconds. I made some calculations about battery consumption and the active Wifi part is the relevant part when you really power down all peripherals during deep sleep. For example I power the sensor chips with an output GPIO port which is possible if the sensor needs only a few mA. So in deep sleep there is no current to these modules.
Bluetooth communication would need much less power but is limited (as you wrote)

Thats what I'm looking into, I heard claims that somebody had the chip running over year on small button 3V batteries ( two), Basically I need the chip to wake up at night ( once every day ), connect to server via wifi, read reply and perform some action.. than immediately go to sleep, but I doubt that can be done one 3V batteries like CR2035 or something like that.. also I'm curious how would I go about disconnecting everything from power like sensor ( if they need more mA and can't be powered from output pin ) .. maybe some kind of relay ?

The WiFi hardware needs more than 150 mA for a few seconds, this peek needs to be handled by the battery. I thing a CR2032 / CR2035 coin cell cannot handle this.
See: https://electronics.stackexchange.com/q ... ifications

With the ESP32, sending Bluetooth BLE advertising seems to be the fastest and most battery-saving way, but this is just a connection-less "ping" used in the beacon devices.

For some use cases a smaller controller with a low-power transceiver in the 866 / 915 MHz band is a better solution. I have an old controller measuring temperature every 10 minutes and sending it to a special receiver board. It's running on one CR2032 for several years now!

Yes, I ended up with Lora module seems to be the only solution for now.