Wednesday, 25 November 2015

Using node.dsleep() in NodeMCU to extend battery lifetime in ESP8266 projects

For some applications, like checking sensors, the ESP8266 does not need to run permanently with all it's bells and whistles on. The datasheet claims 10uA when in deep sleep mode.
NodeMCU, currently my preferred firmware, does support that sleep mode, but I've never tried using it. Mainly because it is a pain to modify the ESP-01 which used to be my perferred module.


With the Olimex modules, I aquired a while ago, trying this out is a piece of cake. Both the reset-pin and GPIO 16 are freely accessible. The ESP8266 wakes up from deep sleep on a falling edge on the reset pin. This signal does not necessarily need to come from GPIO16, but can also be generated externally.

The brown wire does it all

NodeMCU syntax

It is explained in detail here. Basically it is:

node.dsleep(Time-In-uSecs , option)

Where "option" can be 0-4. But I don't quite understand the "0" option yet.
If you send it to sleep for 0 useconds, you'll need to trigger the wakeup from an external source.

Power considerations

In my experiments, the running module took around 70mA from it's 3,3V supply.
In deep sleep mode, the module draws a little less than 0.8mA which is great and will run the system for months with a good 18650 rechargeable battery. Still it is quite a bit more than the 10uA from the data sheet.
Looking at the Olimex datasheet, two things come to mind:
  • The SPI Flash memory (W25Q16BVSSIG) has a 25-50 uA standby current and can peak to 25mA when active.
  • There is a power LED with a 2k resistor that is constantly on and will probably account for most of the current
Another interesting option to node.dsleep() ist option 4, which leaves WiFi disabled when waking up. This saves a lot of power while the system can read sensors or process other information. I've seen it draw around 12mA in this mode.


I've also documented that in a short video on my youtube channel.


Try the same with an ESP-12 that has no LED

1 comment:

  1. Hi there,
    thank you very much for your explanation and especially the video :)
    Can you tell me how to wake up the wifi? Is it done by running the code to connect to an AP?