ULP wakes ESP32

[HOUS2020]

Dear all,

Our set-up: ESP32, LiPo battery, load cell, HX711.
ESP32 is in deep sleep.
We want to wake CPU up when the ULP sees a change on the load cell >10 grams and smaller <200grams.
Objective is to save battery life.

Is this possible?
If so: how?

Hope there is a solution!
Best regards Fred

[wevets]

Hi,

I find myself in the same situation, wanting first to interface an HX711 to an ESP32, and wanting to wake the ESP32 from deep sleep on seeing a significant change in mass on the loadcell.

Have you found a solution?

wevets

[boarchuz]

It's definitely possible. If you look at the datasheet, especially the c reference driver, its data output is very simple and will be easy to bitbang. Of course writing the ULP program is still going to be a bit of work.
I got halfway through writing a library to make this stuff easier but haven't worked on it for a while. Anyway, here's something to get you started:

Code: Select all

#define I_READ_PIN(pin) \
    I_RD_REG(RTC_GPIO_IN_REG, RTC_GPIO_IN_NEXT_S + rtc_gpio_desc[pin].rtc_num, RTC_GPIO_IN_NEXT_S + rtc_gpio_desc[pin].rtc_num)

#define I_WRITE_PIN(pin, val) \
    (val) ? (ulp_insn_t) I_WR_REG_BIT(RTC_GPIO_OUT_W1TS_REG, RTC_GPIO_OUT_DATA_W1TS_S + rtc_gpio_desc[pin].rtc_num, 1) : (ulp_insn_t) I_WR_REG_BIT(RTC_GPIO_OUT_W1TC_REG, RTC_GPIO_OUT_DATA_W1TC_S + rtc_gpio_desc[pin].rtc_num, 1)
    
#define CLOCK_PIN GPIO_NUM_X
#define DATA_PIN GPIO_NUM_Y

#define WAKE_THRESHOLD_VALUE 12345

void setup() {
    ulp_insn_t ulpProgram[] = {
    	I_READ_PIN(DATA_PIN),
    	M_BGE(1,1), //If no data available, go back to sleep
    	  I_HALT(),
    	M_LABEL(1),
    	  I_STAGE_RST(),
    	  I_MOVI(R1,0),
    	  M_LABEL(2), //Read 16 bits
    	    I_WRITE_PIN(CLOCK_PIN, 1),
    	    I_LSHI(R1,R1,1),
    	    I_STAGE_INC(1),
    	    I_WRITE_PIN(CLOCK_PIN, 0),
    	    I_READ_PIN(DATA_PIN),
    	    I_ADDR(R1,R1,R0),
    	    M_BSLT(2,16),
    	    M_LABEL(3), //Ignore 8 bits
    	    I_WRITE_PIN(CLOCK_PIN, 1),
    	    I_STAGE_INC(1),
    	    I_WRITE_PIN(CLOCK_PIN, 0),
    	    I_DELAY(1),
    	    M_BSLT(3,24),
    	    I_SUBI(R0,R1,WAKE_THRESHOLD_VALUE), //Compare to threshold
    	    M_BXF(4), //Go to wake if value > threshold
    	      I_HALT(),
    	    M_LABEL(4),
    	      I_WAKE(),
    	      I_HALT(),
    	};
    	//Initialise pins
        rtc_gpio_init(CLOCK_PIN);
        rtc_gpio_set_direction(CLOCK_PIN, RTC_GPIO_MODE_OUTPUT_ONLY);
        rtc_gpio_set_level(CLOCK_PIN, 1);
        rtc_gpio_init(DATA_PIN);
        rtc_gpio_set_direction(CLOCK_PIN, RTC_GPIO_MODE_INPUT_ONLY);
        //Load and run
    	size_t programSize = sizeof(ulpProgram) / sizeof(ulp_insn_t);
        ulp_process_macros_and_load(0, ulpProgram, &programSize);
	ulp_set_wakeup_period(0, 1 * 1000 * 1000);
	ulp_run(0);
   }
 

I don't have a HX711 to test so this probably isn't even close to working, but it should be a good starting point. It will read the most significant 16 bits (discarding the lower 8) and comparing to a (16 bit) threshold, waking if the read value exceeds that threshold. Needs the updates I've submitted here to work https://github.com/espressif/esp-idf/pull/3580 (you'll need to replace your ulp.h and ulp_macro.c with those if you decide to use it)

[wevets]

Thanks, boarchuz.
This is a great start. I'm not quite ready to digest it yet, having just starting on getting the HX711 up and working. But I wrote my post asking for this info as I know that's the direction my project is headed. I'll be into this before too long.

wevets (stevew backwards. Hey, all the other variations of Steve W were already taken. My folks weren't too original when it came to name-picking time and the world is full of Steve W's. But I love them anyway.)

[stock86c]

have you guys looked at this ?
viewtopic.php?f=2&t=4170&p=47306&hilit=hx711#p47306