ESP8266: Differentiate wakeup due to sleep interval vs button press

Question

I have an ESP8266, ESP-12F modules that is in deep sleep mode.

It wakes up every 6 hours to read the humidity sensor, display it on LED and then post to IFTTT. Because it is every 6 hours, it actually wakes up every hour just to check an EEPROM stored counter to see if the 6 hour has elapsed. Otherwise, it will increase or reset the EEPROM counter accordingly.

I also want the user to press a button to wake up the ESP, read the humidity sensor, display it on the LED and send to IFTTT even if the 6 hours have not elapsed.

Is there a way to differentiate wakeup due to sleep interval vs a button press reset? In both cases the reset reason is 5.

I'm open to both hardware and firmware solutions.

I have also tried to simulate a possible circuit. But the GPIO12 (which I am trying to read as LOW right after ESP wakes up) does not hold on to the LOW value long enough for me to read it right after wake up.

Answer 1

One hardware solution is to use SR Latch. From description it look like the NAND one (/S, /R) would be suitable in this situation. You should be able to find a chip with such latch or build one from gates using for example 74HC00 (4 nand gates out of which 2 would be used). However one extra pin to reset the SR latch after power up caused by the external button is needed.

Connection could be as follows:

• /S - connected to wake up button connected also to ESP8266. Assumed the ESP8266 wake up (/RESET) is active low, momentary switch pulls to GND, and this line is normally pulled up (like in the falstad schematic from question).
• /R - connected to some output of the ESP8266 (GPIO) - you would need pull up on this pin too, so it is defined when ESP8266 is in power down
• Q (SR output) - connected to some input of the ESP8266 (GPIO)

Operation would be as follows:

1. Pressing the momentary switch (shorting to GND) - would change state of the SR output to 1.
2. After boot up is finished software would read state of the Q - if it is "1" this is power up due to switch/if 0 this is power up due to timer.
3. Before going to sleep again, you would arm the SR latch for next power up by applying short pulse to GND on /R pin so Q would be 0.

One drawback of this solution is that after first applying power to the system (3.3V ramp up) SR latch state is unknown (either 0 or 1). This means that you might misread first power up reason but later on would be OK.

Standard disclaimer - solution provided w/o any simulation or prototyping - you should think it through, check if works at all and if is suitable for your application.

Answer 2

An easy answer is to use diode steering and a delay cap.

Wake from a button... Your reset button goes to 2 diodes, one connects to the ESP RST pin, the other connects to any other GPIO (lets say GPIO 6). GPIO-6 has a cap to gnd, and a slow pull up resistor. Pressing the button brings both pins lo and discharges the cap, releasing the button releases the reset pin, the cap holds GPIO 6 low for some time, you sample GPIO 6 during boot before the cap charges.

Wake from timer... GPIO 16 from the ESP goes to the RST pin. When this goes lo, GPIO 6 does not go lo. Maybe use a diode here too so pressing the reset button does not pull GPIO 6 low (it is set as an output, best not to over current it.)

Of course, you can do the opposite, GPIO16 pulls both RST and GPIO 6 low, the reset button pulls only the RST pin low.