Init commit with many years of arduino sketches and projects. I dont know if the esp8266 includes much, but there are also libraries. I hope they dont have crazy automatic versioning through the Arduino IDE.

libraries/NewliquidCrystal/thirdparty libraries/SoftI2CMaster/examples/I2CScanSoft/I2CScanSoft.ino

@@ -0,0 +1,91 @@
+// Scan I2C bus for device responses
+
+#define SDA_PORT PORTD
+#define SDA_PIN 3
+#define SCL_PORT PORTD
+#define SCL_PIN 5
+#define I2C_TIMEOUT 100
+#define I2C_NOINTERRUPT 0
+#define I2C_SLOWMODE 1
+#define FAC 1
+#define I2C_CPUFREQ (F_CPU/FAC)
+
+
+/* Corresponds to A4/A5 - the hardware I2C pins on Arduinos
+#define SDA_PORT PORTC
+#define SDA_PIN 4
+#define SCL_PORT PORTC
+#define SCL_PIN 5
+#define I2C_FASTMODE 1
+*/
+
+#include <SoftI2CMaster.h>
+#include <avr/io.h>
+
+//------------------------------------------------------------------------------
+void CPUSlowDown(int fac) {
+  // slow down processor by a fac
+    CLKPR = _BV(CLKPCE);
+    CLKPR = _BV(CLKPS1) | _BV(CLKPS0);
+}
+  
+
+
+void setup(void) {
+#if FAC != 1
+  CPUSlowDown(FAC);
+#endif
+
+  Serial.begin(19200); // change baudrate to 2400 on terminal when low CPU freq!
+  Serial.println(F("Intializing ..."));
+  Serial.print("I2C delay counter: ");
+  Serial.println(I2C_DELAY_COUNTER);
+  if (!i2c_init()) 
+    Serial.println(F("Initialization error. SDA or SCL are low"));
+  else
+    Serial.println(F("...done"));
+}
+
+void loop(void)
+{
+  uint8_t add = 0;
+  int found = false;
+  Serial.println("Scanning ...");
+
+  Serial.println("       8-bit 7-bit addr");
+  // try read
+  do {
+    if (i2c_start(add | I2C_READ)) {
+      found = true;
+      i2c_read(true);
+      i2c_stop();
+      Serial.print("Read:   0x");
+      if (add < 0x0F) Serial.print(0, HEX);
+      Serial.print(add+I2C_READ, HEX);
+      Serial.print("  0x");
+      if (add>>1 < 0x0F) Serial.print(0, HEX);
+      Serial.println(add>>1, HEX);
+    } else i2c_stop();
+    add += 2;
+  } while (add);
+
+  // try write
+  add = 0;
+  do {
+    if (i2c_start(add | I2C_WRITE)) {
+      found = true;
+      i2c_stop();
+      Serial.print("Write:  0x");    
+      if (add < 0x0F) Serial.print(0, HEX);  
+      Serial.print(add+I2C_WRITE, HEX);
+      Serial.print("  0x");
+      if (add>>1 < 0x0F) Serial.print(0, HEX);
+      Serial.println(add>>1, HEX);
+    } else i2c_stop();
+    i2c_stop();
+    add += 2;
+  } while (add);
+  if (!found) Serial.println(F("No I2C device found."));
+  Serial.println("Done\n\n");
+  delay(1000/FAC);
+}