Electronics Concept
Inside the chip, we can find the two processing cores, the RAM and ROM memory, the WiFi module, the Bluetooth Module, a hardware acceleration module for cryptographic applications, the RTC module, and a lot of peripherals. Inside the RTC module, we can find a PMU (Phasor measurement unit) a small and very low power 32-bit co-processor, and 8Kbs of RAM memory. This small amount of memory is very useful as you are going to find out in a moment.
The WiFi modules, the Processing Cores, and the Bluetooth module require a lot of current to operate. So, if we want to conserve power we have to disable them when don’t use them. We put the ESP32 to deep sleep mode, where it disables everything except the RTC module. There is a light sleep mode and the Deep sleep mode. In Deep Sleep mode the chip offers the lowest power consumption. It just needs 0.01 mAs of current in Deep Sleep mode and that’s the purpose of the tutorial.
Prerequisites
Arduino IDE
Components
- Electronics Club Custom Development Board (CDB)
- LED
- Resistor - 10k
- Jumpers
- Breadboard
- Multimeter
Schematic
Code
#define uS_TO_S_FACTOR 1000000 /* Conversion factor for micro seconds to seconds */
#define TIME_TO_SLEEP 3 /* Time the board will go to sleep (in seconds) */
RTC_DATA_ATTR int bootCount = 0;
int LED_PIN_1 = 25;
int LED_PIN_2 = 26;
void setup(){
pinMode(LED_PIN_1,OUTPUT);
pinMode(LED_PIN_2,OUTPUT);
delay(500);
if(bootCount == 0) //Run this only the first time
{
digitalWrite(LED_PIN_2,HIGH);
bootCount = bootCount+1;
}else
{
digitalWrite(LED_PIN_1,HIGH);
}
delay(3000);
digitalWrite(LED_PIN_1,LOW);
digitalWrite(LED_PIN_2,LOW);
esp_sleep_enable_timer_wakeup(TIME_TO_SLEEP * uS_TO_S_FACTOR);
esp_deep_sleep_start();
}
void loop(){
}
When we use the deep-sleep function, each time the ESP32 wakes up, it executes the setup function again. The loop function is never called. All the variable values are lost, except if we save them in the RTC memory using this prefix.
Follow-up Problem Statement
Measure the current that the board takes when it is used in active mode and deep sleep mode using a multimeter. Also, we see that after a random number of wakes up, the board goes to sleep and it won't wake up again. How do we solve this bug?