Once you have hardware tested and working, and you've also got WiFi connected - its time to explore deep sleep modes. When in deep sleep, the ESP32-S2 is basically completely off, it uses a tiny amount of power just to keep track of time so you can wake up after some amount of time.
When the ESP32-S2 comes back from deep-sleep it essentially does a hard-reset and begins over from scratch, so you don't get to keep your WiFi connection active. However, its pretty fast to re-connect so as long as you are only waking up about once a minute, your battery will last a lot longer!
Good Quality Sleep
Before you go into deep sleep, make sure you shut down the E-Ink display, NeoPixels, light sensor, and speaker with the following instructions:
display.powerDown(); digitalWrite(EPD_RESET, LOW); // hardware power down mode digitalWrite(SPEAKER_SHUTDOWN, LOW); // off digitalWrite(NEOPIXEL_POWER, HIGH); // off
Then enter deep sleep mode with
esp_sleep_enable_timer_wakeup(1000000); esp_deep_sleep_start();
the esp_sleep_enable_timer_wakeup(10000000); line tells the ESP32-S2 to restart in 10000000 microseconds, a.k.a 10000 milliseconds or 10 seconds
Here's an example sketch that wakes up, turns on the speaker and NeoPixels, draws a bitmap onto the EPD and then goes to sleep for one second. We use this demo to do power monitoring tests.
// SPDX-FileCopyrightText: 2020 Limor Fried for Adafruit Industries
//
// SPDX-License-Identifier: MIT
#include <Adafruit_ThinkInk.h>
#include <Adafruit_NeoPixel.h>
#include "magtaglogo.h"
Adafruit_NeoPixel intneo = Adafruit_NeoPixel(4, PIN_NEOPIXEL, NEO_GRB + NEO_KHZ800);
ThinkInk_290_Grayscale4_T5 display(EPD_DC, EPD_RESET, EPD_CS, -1, -1);
void setup() {
//Initialize serial and wait for port to open:
Serial.begin(115200);
pinMode(BUTTON_A, INPUT_PULLUP);
pinMode(BUTTON_B, INPUT_PULLUP);
pinMode(BUTTON_C, INPUT_PULLUP);
pinMode(BUTTON_D, INPUT_PULLUP);
pinMode(13, OUTPUT);
digitalWrite(13, LOW);
// Neopixel power
pinMode(NEOPIXEL_POWER, OUTPUT);
pinMode(SPEAKER_SHUTDOWN, OUTPUT);
digitalWrite(NEOPIXEL_POWER, LOW); // on
digitalWrite(SPEAKER_SHUTDOWN, HIGH); // on
intneo.begin();
intneo.setBrightness(50);
intneo.fill(100, 0, 100);
intneo.show();
display.begin(THINKINK_MONO);
display.clearBuffer();
display.drawBitmap(0, 38, magtaglogo_mono, MAGTAGLOGO_WIDTH, MAGTAGLOGO_HEIGHT, EPD_BLACK);
display.display();
delay(1500);
display.powerDown();
digitalWrite(EPD_RESET, LOW); // hardware power down mode
digitalWrite(SPEAKER_SHUTDOWN, LOW); // off
digitalWrite(NEOPIXEL_POWER, HIGH); // off
esp_sleep_enable_timer_wakeup(1000000);
esp_deep_sleep_start();
}
void loop() {
}
Be sure to download the sketch including the logo header file by clicking Download Project Zip and verify that in the Arduino IDE you have both tabs:
This example will go to deep sleep for only one second, you can change that by adjusting the number in this line:
esp_sleep_enable_timer_wakeup(1000000);
When using deep sleep, the power draw drops to about 250uA. These are the approximate current uses:
- 40uA are used by the onboard green OK LED (you can remove the LED with a soldering iron)
- 120uA are used by the EPD in deepsleep/reset mode (we couldnt figure out how to reduce this any more but tested suggestions are welcome!)
- 50uA are used by the 3.3V regulator
- 10uA are used by the VBat resistor divider
- 30uA are used by the ESP32-S2 in deep sleep
