Wakeup Pin ESP8266

Question

Is there a way to put an ESP8266 into a sort of "sleep" mode where it draws less power than usual, and then wakes up on a pin going high? I've tried doing this with delay, which still draws 20 mA, and with the deepsleep function that comes with the esp library, which can't sleep for short periods of time to watch for the pin going high. I'm building a watch, and power draw is of great concern to me. Is there possibly a way I could build or code this differently to make it more power efficient? Basically it works like this, but the full code (at it's current state) can be found here.

void loop() {
    delay(1);
    // check for power signal stuff
    if(digitalRead(0)) {
        // execute data fetching 'n stuff
    }
}

Answer 1

Without seeing the code and optimizing it I can tell you the following:

ESP8266 has three ways to save power:

1. Modem sleep - only wlan modem shutdown, connection kept open
2. Light sleep - less cpu usage, fast recovery
3. Deep sleep - suspend all, close wifi too, slow recovery

http://bbs.espressif.com/viewtopic.php?t=133

Answer 2

ESP8266 does have deep sleep mode. The link to http://bbs.espressif.com/viewtopic.php?t=133 posted earlier sums it up pretty well, despite being old.

However, a few things that are different from Arduino or should be considered if you're building a battery-operated device:

• when the MCU wakes up from deep sleep, the entire application is restarted. Yes, beginning from the setup() function - just as if it was reset. You cannot put it to the deep sleep and then resume from the same place keeping all variables etc. You can only detect that the device was woken up from the sleep by reading a flag in the setup() function.

• check your board. If you're not using bare ESP8266, but some development board such as NodeMCU or WittyCloud, it usually has number of other circuits powered on even when the MCU is sleeping. Particularly, USB-UART bridge and maybe power LED.

• check your power source. Again, if you're using a development board, very likely it has an inefficient LDO voltage regulator. Even when MCU is powered down, the LDO can still use a few mA just to power itself (quiescent current). There are special low quiescent current regulators exist, very useful for battery-operated application.

• finally, I see your code refers some OLED display. Just to be sure - is it powered down or excluded from the measurement? OLED doesn't need a lot of energy, but will drain a battery in a few days.

Personally, I do have experience creating a battery-operated device on ESP8266, which wakes up every few minutes, connects to wifi and sends some data. An old 700mAh Lithium battery is enough to run it for approximately a month. And I managed to get the sleep power to about 40 microAmps. Still a few times more than the chip itself needs, but good enough for me.