how to use esp32 ulp interrupt pulse counter and periodic wake up deepsleep mode

Question

I am trying to measure power usage using dds353 kWh meter. This meter has a pulse output. I am interested in using the esp32 since I can periodically send the data over the internet to nodered dashboard.I am also very interested in using the esp32 in low power mode and periodically wake up to send data over mqtt. I have tried out examples from github using espressif idf but I would not mind an arduino equivalent. I would like to do hardware interrupt which when one of the rtc gpio pin goes high a counter is incremented while a seperate timer interrupt run and occasionally wakes up the main xtensia cores which fetches data from the rtc and sends it over. I have looked at the pulse counter examples and with my limited knowledge can not tell if the interrupts are triggered when the ulp is in sleep mode or only when it is on. I would really be glad if someone would show me how to basically use the ulp for counting pulses even when it is sleep mode and periodically wake up the main cores. I am ok with IDF or arduino examples

Answer 1

If you want to count pulses while in deep sleep youuse the ULP. Code on the ULP continues to execute when the board wakes up and goes to normal power mode. So when it is awake, it will still run the counter on the ULP processor unless you stop the ULP periodic wake up timer, ULP will keep waking up and running while the main CPU is active.

As you gave already checked with this example , it should be pretty close to what you need. The only difference seems to be that the example is set to wake up after a given number of pulses, rather than a fixed amount of time. However it should be easy to change that, by enabling deep sleep wake up from timer.
For the Arduino you could check
Some additional info:
ULP doesn't have GPIO interrupts. So you use deep sleep wake stub (small piece of code which runs immediately after deep sleep, prior to loading application from flash into RAM) you can increment the pulse counter variable, and go to sleep again. This way you can get low power consumption (~5uA) between pulses and moderate power consumption while running the wake stub (around 13mA), for a very short time.
So its up to you to experiment with your specific scenario.

Answer 2

You can use Pulse Counter(PCNT) feature in ESP32 to count the number of pulse in background, Understanding by using same you can able to do some periodic wake-up and read the count.. Its also possible to configure event when number of counts reached certain threshold and had lot of options,

For get information and available Interfaces and API's for Pulse Counter(PCNT) please follow below link, https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/pcnt.html

Initially I faced lot of issue to make Pulse Counter(PCNT) work in Adrino IDE for ESP-32, After multiple attempt I make it working, And same sample code is uploaded in GitHub for reference. I have not use all the API's in the official documentation but but used few of them and are working..

I have created sample program for a water flow meter, there also we use to get pulse which needs to count to measure the water flow rate, understanding simile to kWh meter.

GitHub Sample code Path:- https://github.com/Embedded-Linux-Developement/Arduino_Sample_Programs/tree/main/ESP_32/Water_Flow_Pulse_counter_WithOut_Interrupt_Using_PCNT

I have not placing the code here, because its there in GitHub and not directly for the asked question, but simile one and can use it. Its a working code I tested in HW.

Hopes Its helpful, Regards, Jerry James