How to start i2c communication between NodeMcu and Wemos D1?

Question 1

Share GND. Connect SDA to SDA and SCL to SCL (D2↔D2, D1↔D1 on these boards). Use 4.7 kΩ pull‑ups to 3.3 V on SDA and SCL. In code, call Wire.begin(D2, D1) to map SDA=D2 and SCL=D1. Use a known 7‑bit address for the slave (e.g., 0x08). [Elektroda, omnixcrs, post #18474243]

Answer

Share GND. Connect SDA to SDA and SCL to SCL (D2↔D2, D1↔D1 on these boards). Use 4.7 kΩ pull‑ups to 3.3 V on SDA and SCL. In code, call Wire.begin(D2, D1) to map SDA=D2 and SCL=D1. Use a known 7‑bit address for the slave (e.g., 0x08). [Elektroda, omnixcrs, post #18474243]

Question 2

Return 2 means the master "received NACK on transmit of address." The slave did not acknowledge that address. Confirm the slave address matches and the slave is actually on the bus. Initialize the slave with its address. How‑To: 1. Print the return code. 2. Verify the address in both sketches. 3. Initialize the slave as Wire.begin(sda, scl, address). [Elektroda, khoam, post #18474382]

Answer

Return 2 means the master "received NACK on transmit of address." The slave did not acknowledge that address. Confirm the slave address matches and the slave is actually on the bus. Initialize the slave with its address. How‑To: 1. Print the return code. 2. Verify the address in both sketches. 3. Initialize the slave as Wire.begin(sda, scl, address). [Elektroda, khoam, post #18474382]

Question 3

Tests show master↔slave works on 2.5.2 with minor repeats, but fails on 2.6.3. The newer NonOS‑SDK changed timing, and ESP8266 lacks hardware I2C. The Wire library bit‑bangs, so timing tightens and breaks. Quote: "default speed of 100 kHz is too high." Lower the clock to 50 kHz. [Elektroda, khoam, post #18475388]

Answer

Tests show master↔slave works on 2.5.2 with minor repeats, but fails on 2.6.3. The newer NonOS‑SDK changed timing, and ESP8266 lacks hardware I2C. The Wire library bit‑bangs, so timing tightens and breaks. Quote: "default speed of 100 kHz is too high." Lower the clock to 50 kHz. [Elektroda, khoam, post #18475388]

Question 4

Use 50 kHz. The default 100 kHz often causes lost bytes when both sides are ESP8266. Set Wire.setClock(50000UL) on the master before transmissions. This reduces timing stress from bit‑banged I2C and improves reliability across boards. [Elektroda, khoam, post #18475388]

Answer

Use 50 kHz. The default 100 kHz often causes lost bytes when both sides are ESP8266. Set Wire.setClock(50000UL) on the master before transmissions. This reduces timing stress from bit‑banged I2C and improves reliability across boards. [Elektroda, khoam, post #18475388]

Question 5

Partially. On Arduino core 2.5.2 it can work but shows duplicated or garbled bytes. On core 2.6.x, slave mode breaks. The ESP8266 has no hardware I2C, so stability depends on timing of the bit‑banged Wire library. Reduce clock to 50 kHz if you must try. [Elektroda, khoam, post #18475388]

Answer

Partially. On Arduino core 2.5.2 it can work but shows duplicated or garbled bytes. On core 2.6.x, slave mode breaks. The ESP8266 has no hardware I2C, so stability depends on timing of the bit‑banged Wire library. Reduce clock to 50 kHz if you must try. [Elektroda, khoam, post #18475388]

Question 6

Your code may be fine; the platform is not. On ESP8266 Arduino core 2.6.x, slave mode is broken, so begin(..., address) won’t help. Downgrade to 2.5.2 and lower the clock to 50 kHz to test. Expect occasional repeats due to bit‑banging. [Elektroda, khoam, post #18475388]

Answer

Your code may be fine; the platform is not. On ESP8266 Arduino core 2.6.x, slave mode is broken, so begin(..., address) won’t help. Downgrade to 2.5.2 and lower the clock to 50 kHz to test. Expect occasional repeats due to bit‑banging. [Elektroda, khoam, post #18475388]

Question 7

The ESP32 hardware supports I2C slave, but Arduino’s ESP32 Wire library does not implement slave mode. You cannot use Wire as a slave from the Arduino IDE today. Consider other transports or firmware stacks if you need slave on ESP32. [Elektroda, khoam, post #18504298]

Answer

The ESP32 hardware supports I2C slave, but Arduino’s ESP32 Wire library does not implement slave mode. You cannot use Wire as a slave from the Arduino IDE today. Consider other transports or firmware stacks if you need slave on ESP32. [Elektroda, khoam, post #18504298]

Question 8

Use I2C multi‑master (master‑to‑master) techniques. Both nodes act as masters and arbitrate bus access. This avoids relying on the missing or broken slave implementation. See the referenced master‑to‑master pattern for Arduino‑style setups. [Elektroda, khoam, post #18505237]

Answer

Use I2C multi‑master (master‑to‑master) techniques. Both nodes act as masters and arbitrate bus access. This avoids relying on the missing or broken slave implementation. See the referenced master‑to‑master pattern for Arduino‑style setups. [Elektroda, khoam, post #18505237]

Question 9

Add a bidirectional 5V↔3.3V level shifter on SDA and SCL. Uno/Mega use 5V logic and can damage the 3.3V ESP pins. Power pull‑ups to the correct rails on each side. Keep grounds common. This prevents over‑voltage on the ESP. [Elektroda, khoam, post #18476437]

Answer

Add a bidirectional 5V↔3.3V level shifter on SDA and SCL. Uno/Mega use 5V logic and can damage the 3.3V ESP pins. Power pull‑ups to the correct rails on each side. Keep grounds common. This prevents over‑voltage on the ESP. [Elektroda, khoam, post #18476437]

Question 10

Print the result of Wire.endTransmission(). A 0 indicates success. Any value above 0 indicates failure, with 2 meaning NACK on the addressed device. This simple check narrows wiring or addressing mistakes fast. [Elektroda, khoam, post #18474289]

Answer

Print the result of Wire.endTransmission(). A 0 indicates success. Any value above 0 indicates failure, with 2 meaning NACK on the addressed device. This simple check narrows wiring or addressing mistakes fast. [Elektroda, khoam, post #18474289]

Question 11

Use typical 4.7 kΩ pull‑ups to 3.3 V on SDA and SCL when linking ESP8266 boards. Place them near the bus and keep wires short. Ensure both boards share ground and connect SDA↔SDA, SCL↔SCL. [Elektroda, omnixcrs, post #18474243]

Answer

Use typical 4.7 kΩ pull‑ups to 3.3 V on SDA and SCL when linking ESP8266 boards. Place them near the bus and keep wires short. Ensure both boards share ground and connect SDA↔SDA, SCL↔SCL. [Elektroda, omnixcrs, post #18474243]

Question 12

Use Wire.begin(D2, D1). This maps SDA to D2 (GPIO4) and SCL to D1 (GPIO5) on common ESP8266 dev boards. Keep the same mapping on both boards so SDA connects to SDA and SCL to SCL. [Elektroda, omnixcrs, post #18474243]

Answer

Use Wire.begin(D2, D1). This maps SDA to D2 (GPIO4) and SCL to D1 (GPIO5) on common ESP8266 dev boards. Keep the same mapping on both boards so SDA connects to SDA and SCL to SCL. [Elektroda, omnixcrs, post #18474243]

Question 13

Yes, on ESP8266 core 2.5.2 tests showed repeating strings and occasional corrupted characters. That’s a symptom of bit‑banged I2C timing. Lower the clock to 50 kHz and expect occasional retries. Avoid core 2.6.x for slave links. [Elektroda, khoam, post #18475388]

Answer

Yes, on ESP8266 core 2.5.2 tests showed repeating strings and occasional corrupted characters. That’s a symptom of bit‑banged I2C timing. Lower the clock to 50 kHz and expect occasional retries. Avoid core 2.6.x for slave links. [Elektroda, khoam, post #18475388]

Question 14

Yes. Create multiple OneWire instances on different pins and segment the network. For long runs, follow 1‑Wire cabling rules: use bus topology, short stubs, and consider strong pull‑up. Typical well‑designed segments can reach around 100 m. [Maxim, 2007]

Answer

Yes. Create multiple OneWire instances on different pins and segment the network. For long runs, follow 1‑Wire cabling rules: use bus topology, short stubs, and consider strong pull‑up. Typical well‑designed segments can reach around 100 m. [Maxim, 2007]

How to start i2c communication between NodeMcu and Wemos D1?

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