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E-paper temperature card

Show a DS18B20 reading on a 2.9 inch e-paper panel that keeps its image with the power off, refreshing only when the value changes.

Intermediate30 min115200 baud

Board

ESP32

3V3

GND

CMD

CLK

Fig. 1. Pins this project uses on the ESP32-DevKitC V4, 38 pin. USB connector at the bottom.

Wiring

From	To board	Note
Display VCC	3V3
Display GND	GND
Display CLK or SCK	GPIO 18
Display DIN or MOSI	GPIO 23
Display CS	GPIO 5
Display DC	GPIO 17
Display RST	GPIO 16
Display BUSY	GPIO 25
DS18B20 DATA (yellow)	GPIO 4	4.7 kΩ pull-up to 3V3. Red to 3V3, black to GND

Tested on this board

Not run on this board yet. Treat the wiring and code as a first draft.

Firmware, Arduino sketch for ESP32 Dev Module

#include <SPI.h>
#include <GxEPD2_BW.h>
#include <Fonts/FreeSans9pt7b.h>
#include <Fonts/FreeSansBold24pt7b.h>
#include <OneWire.h>
#include <DallasTemperature.h>

// Pick the class for your panel. GxEPD2_290_T94_V2 suits the common 2.9 inch SSD1680
// modules (Waveshare 2.9 inch V2 and similar). See GxEPD2's display selection list for others.
GxEPD2_BW<GxEPD2_290_T94_V2, GxEPD2_290_T94_V2::HEIGHT> display(
  GxEPD2_290_T94_V2(/*CS*/ 5, /*DC*/ 17, /*RST*/ 16, /*BUSY*/ 25));

OneWire oneWire(4);
DallasTemperature probes(&oneWire);

float shown = NAN;
unsigned long lastRead = 0, lastDraw = 0;
uint32_t refreshes = 0;

void draw(float c) {
  refreshes++;
  char line[48];
  display.setRotation(1);
  display.setFullWindow();
  display.firstPage();
  do {
    display.fillScreen(GxEPD_WHITE);
    display.setTextColor(GxEPD_BLACK);
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 24);
    display.print("ESP32 Bench");
    display.setFont(&FreeSansBold24pt7b);
    display.setCursor(10, 84);
    if (isnan(c)) {
      display.print("no probe");
    } else {
      snprintf(line, sizeof line, "%.1f C", c);
      display.print(line);
    }
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 118);
    snprintf(line, sizeof line, "up %lu min, refresh %lu", millis() / 60000, (unsigned long)refreshes);
    display.print(line);
  } while (display.nextPage());
  display.hibernate();  // the image stays with the panel powered down
  shown = c;
  lastDraw = millis();
}

void setup() {
  Serial.begin(115200);
  SPI.begin(18, -1, 23, 5);  // before init, so the display uses these pins
  display.init(0, true, 2, false);  // 0: no library diagnostics on the serial port
  probes.begin();
}

void loop() {
  if (lastRead != 0 && millis() - lastRead < 30000) return;
  lastRead = millis();

  probes.requestTemperatures();
  float c = probes.getTempCByIndex(0);
  if (c == DEVICE_DISCONNECTED_C) c = NAN;
  if (isnan(c)) Serial.println("no probe: check the data wire and the 4.7 kOhm pull-up");
  else Serial.printf("temp %.2f C\n", c);

  // Full refreshes flash the panel and wear it, so only redraw on a real change,
  // at most every three minutes, or every half hour regardless.
  bool changed = isnan(c) != isnan(shown) || (!isnan(c) && fabs(c - shown) >= 0.2);
  unsigned long since = millis() - lastDraw;
  if (refreshes == 0 || (changed && since > 3 * 60000UL) || since > 30 * 60000UL) {
    draw(c);
    Serial.printf("display refreshed, %lu so far\n", (unsigned long)refreshes);
  }
}

3V3

GND

3V3

RST

GND

Fig. 1. Pins this project uses on the ESP32-S3-DevKitC-1, 44 pin. USB connector at the bottom.

Wiring

From	To board	Note
Display VCC	3V3
Display GND	GND
Display CLK or SCK	GPIO 12
Display DIN or MOSI	GPIO 11
Display CS	GPIO 10
Display DC	GPIO 17
Display RST	GPIO 16
Display BUSY	GPIO 15
DS18B20 DATA (yellow)	GPIO 4	4.7 kΩ pull-up to 3V3. Red to 3V3, black to GND

Tested on this board

Not run on this board yet. Treat the wiring and code as a first draft.

Firmware, Arduino sketch for ESP32S3 Dev Module

#include <SPI.h>
#include <GxEPD2_BW.h>
#include <Fonts/FreeSans9pt7b.h>
#include <Fonts/FreeSansBold24pt7b.h>
#include <OneWire.h>
#include <DallasTemperature.h>

// Pick the class for your panel. GxEPD2_290_T94_V2 suits the common 2.9 inch SSD1680
// modules (Waveshare 2.9 inch V2 and similar). See GxEPD2's display selection list for others.
GxEPD2_BW<GxEPD2_290_T94_V2, GxEPD2_290_T94_V2::HEIGHT> display(
  GxEPD2_290_T94_V2(/*CS*/ 10, /*DC*/ 17, /*RST*/ 16, /*BUSY*/ 15));

OneWire oneWire(4);
DallasTemperature probes(&oneWire);

float shown = NAN;
unsigned long lastRead = 0, lastDraw = 0;
uint32_t refreshes = 0;

void draw(float c) {
  refreshes++;
  char line[48];
  display.setRotation(1);
  display.setFullWindow();
  display.firstPage();
  do {
    display.fillScreen(GxEPD_WHITE);
    display.setTextColor(GxEPD_BLACK);
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 24);
    display.print("ESP32 Bench");
    display.setFont(&FreeSansBold24pt7b);
    display.setCursor(10, 84);
    if (isnan(c)) {
      display.print("no probe");
    } else {
      snprintf(line, sizeof line, "%.1f C", c);
      display.print(line);
    }
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 118);
    snprintf(line, sizeof line, "up %lu min, refresh %lu", millis() / 60000, (unsigned long)refreshes);
    display.print(line);
  } while (display.nextPage());
  display.hibernate();  // the image stays with the panel powered down
  shown = c;
  lastDraw = millis();
}

void setup() {
  Serial.begin(115200);
  SPI.begin(12, -1, 11, 10);  // before init, so the display uses these pins
  display.init(0, true, 2, false);  // 0: no library diagnostics on the serial port
  probes.begin();
}

void loop() {
  if (lastRead != 0 && millis() - lastRead < 30000) return;
  lastRead = millis();

  probes.requestTemperatures();
  float c = probes.getTempCByIndex(0);
  if (c == DEVICE_DISCONNECTED_C) c = NAN;
  if (isnan(c)) Serial.println("no probe: check the data wire and the 4.7 kOhm pull-up");
  else Serial.printf("temp %.2f C\n", c);

  // Full refreshes flash the panel and wear it, so only redraw on a real change,
  // at most every three minutes, or every half hour regardless.
  bool changed = isnan(c) != isnan(shown) || (!isnan(c) && fabs(c - shown) >= 0.2);
  unsigned long since = millis() - lastDraw;
  if (refreshes == 0 || (changed && since > 3 * 60000UL) || since > 30 * 60000UL) {
    draw(c);
    Serial.printf("display refreshed, %lu so far\n", (unsigned long)refreshes);
  }
}

GND

3V3

GND

RST

GND

Fig. 1. Pins this project uses on the ESP32-C3-DevKitM-1, 30 pin. USB connector at the bottom.

Wiring

From	To board	Note
Display VCC	3V3
Display GND	GND
Display CLK or SCK	GPIO 4
Display DIN or MOSI	GPIO 6
Display CS	GPIO 7
Display DC	GPIO 10
Display RST	GPIO 1
Display BUSY	GPIO 3
DS18B20 DATA (yellow)	GPIO 5	4.7 kΩ pull-up to 3V3. Red to 3V3, black to GND

Tested on this board

Not run on this board yet. Treat the wiring and code as a first draft.

Firmware, Arduino sketch for ESP32C3 Dev Module

#include <SPI.h>
#include <GxEPD2_BW.h>
#include <Fonts/FreeSans9pt7b.h>
#include <Fonts/FreeSansBold24pt7b.h>
#include <OneWire.h>
#include <DallasTemperature.h>

// Pick the class for your panel. GxEPD2_290_T94_V2 suits the common 2.9 inch SSD1680
// modules (Waveshare 2.9 inch V2 and similar). See GxEPD2's display selection list for others.
GxEPD2_BW<GxEPD2_290_T94_V2, GxEPD2_290_T94_V2::HEIGHT> display(
  GxEPD2_290_T94_V2(/*CS*/ 7, /*DC*/ 10, /*RST*/ 1, /*BUSY*/ 3));

OneWire oneWire(5);
DallasTemperature probes(&oneWire);

float shown = NAN;
unsigned long lastRead = 0, lastDraw = 0;
uint32_t refreshes = 0;

void draw(float c) {
  refreshes++;
  char line[48];
  display.setRotation(1);
  display.setFullWindow();
  display.firstPage();
  do {
    display.fillScreen(GxEPD_WHITE);
    display.setTextColor(GxEPD_BLACK);
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 24);
    display.print("ESP32 Bench");
    display.setFont(&FreeSansBold24pt7b);
    display.setCursor(10, 84);
    if (isnan(c)) {
      display.print("no probe");
    } else {
      snprintf(line, sizeof line, "%.1f C", c);
      display.print(line);
    }
    display.setFont(&FreeSans9pt7b);
    display.setCursor(10, 118);
    snprintf(line, sizeof line, "up %lu min, refresh %lu", millis() / 60000, (unsigned long)refreshes);
    display.print(line);
  } while (display.nextPage());
  display.hibernate();  // the image stays with the panel powered down
  shown = c;
  lastDraw = millis();
}

void setup() {
  Serial.begin(115200);
  SPI.begin(4, -1, 6, 7);  // before init, so the display uses these pins
  display.init(0, true, 2, false);  // 0: no library diagnostics on the serial port
  probes.begin();
}

void loop() {
  if (lastRead != 0 && millis() - lastRead < 30000) return;
  lastRead = millis();

  probes.requestTemperatures();
  float c = probes.getTempCByIndex(0);
  if (c == DEVICE_DISCONNECTED_C) c = NAN;
  if (isnan(c)) Serial.println("no probe: check the data wire and the 4.7 kOhm pull-up");
  else Serial.printf("temp %.2f C\n", c);

  // Full refreshes flash the panel and wear it, so only redraw on a real change,
  // at most every three minutes, or every half hour regardless.
  bool changed = isnan(c) != isnan(shown) || (!isnan(c) && fabs(c - shown) >= 0.2);
  unsigned long since = millis() - lastDraw;
  if (refreshes == 0 || (changed && since > 3 * 60000UL) || since > 30 * 60000UL) {
    draw(c);
    Serial.printf("display refreshed, %lu so far\n", (unsigned long)refreshes);
  }
}

Parts

Quantity	Part	Where to buy
1×	ESP32 dev board	Buy at Amazon
1×	2.9 inch black and white SPI e-paper module, 296 by 128, SSD1680 driver
1×	DS18B20 waterproof probe	Buy at Adafruit
1×	4.7 kΩ resistor, pull-up for the probe data line	Buy at Amazon
10×	Jumper wires

Amazon buy links may include an Associates tag, and this site may earn a commission from qualifying Amazon purchases at no extra cost to you. Adafruit links are direct.

Libraries

GxEPD2, Adafruit GFX Library, OneWire, DallasTemperature

Load it

In the Arduino IDE, install the esp32 board package and pick the board named above the sketch.
Install the libraries listed above from the Library Manager.
Paste the sketch, choose the board's port and upload. Hold BOOT if the upload stalls at Connecting.
Close the IDE's serial monitor, then open the bench here to watch the output.

Field notes

E-paper panels look alike but use different driver chips. If the screen stays blank or shows noise, the display class is wrong: GxEPD2's examples include a list that maps panel part numbers to classes.
A full refresh takes about two seconds and flashes black and white. That is normal. Panels are rated for a limited number of refreshes, which is why the sketch only redraws when the reading moves.
BUSY must be connected. Without it the library cannot tell when the panel has finished, and every refresh stalls until a timeout.
Most modules have a regulator and level shifting on board and are happy on 3V3. Bare panels with a 24-pin ribbon need a driver board.
The image survives power loss, so this pairs well with the battery deep-sleep sensor: draw, hibernate, sleep.

Not tested yet

Not tested on hardware yet. Compiles for every board listed with Arduino-ESP32 core 3.3.12.

Open the bench at 115200 baud

Built it? Send a build report with your board and what the serial port printed. Working reports become the "Tested on this board" entries above.