Hi @bjmcontrols You could check if GND is the same (host-device), also check your wires SCL and SDA are not broken.
I have used I2C devices between 5V and 3V3 and they works well, I mean ESP8266 as Host (3V3), and sensors as Devices (5V). If you are using Arduino IDE, could try with “i2c_scanner.ino” test.
// --------------------------------------
// i2c_scanner
//
// Version 1
// This program (or code that looks like it)
// can be found in many places.
// For example on the Arduino.cc forum.
// The original author is not know.
// Version 2, Juni 2012, Using Arduino 1.0.1
// Adapted to be as simple as possible by Arduino.cc user Krodal
// Version 3, Feb 26 2013
// V3 by louarnold
// Version 4, March 3, 2013, Using Arduino 1.0.3
// by Arduino.cc user Krodal.
// Changes by louarnold removed.
// Scanning addresses changed from 0...127 to 1...119,
// according to the i2c scanner by Nick Gammon
// https://www.gammon.com.au/forum/?id=10896
// Version 5, March 28, 2013
// As version 4, but address scans now to 127.
// A sensor seems to use address 120.
// Version 6, November 27, 2015.
// Added waiting for the Leonardo serial communication.
//
//
// This sketch tests the standard 7-bit addresses
// Devices with higher bit address might not be seen properly.
//
#include <Wire.h>
void setup() {
Wire.begin();
Serial.begin(9600);
while (!Serial); // Leonardo: wait for serial monitor
Serial.println("\nI2C Scanner");
}
void loop() {
int nDevices = 0;
Serial.println("Scanning...");
for (byte address = 1; address < 127; ++address) {
// The i2c_scanner uses the return value of
// the Write.endTransmisstion to see if
// a device did acknowledge to the address.
Wire.beginTransmission(address);
byte error = Wire.endTransmission();
if (error == 0) {
Serial.print("I2C device found at address 0x");
if (address < 16) {
Serial.print("0");
}
Serial.print(address, HEX);
Serial.println(" !");
++nDevices;
} else if (error == 4) {
Serial.print("Unknown error at address 0x");
if (address < 16) {
Serial.print("0");
}
Serial.println(address, HEX);
}
}
if (nDevices == 0) {
Serial.println("No I2C devices found\n");
} else {
Serial.println("done\n");
}
delay(5000); // Wait 5 seconds for next scan
}
I am not sure if the MCP9600 can be powering by 3.3V.
It does work with the Arduino. So, this is an IOT project for a customer. I have a number of other signals coming into the ESP. I could try an ESP32. Using an Arduino is not my first choice. Any suggestions?
I finally got the system working connected on a breadboard, but somewhere between there and moving it over to a solder board I did something to break it. I can no longer communicate with the MCP9600. The “I2C Address Find” routine does not find the board. I have ordered another one but I thought I would check with you to see if there is anything I can do to see if this board is salvageable.
Huh! I tried it again this morning and its working fine. I have no idea why it stopped the other day and now is working fine. Anyway, thanks for your attention.