un code lua pour nodemcu récupéré bien pratique , http://www.esp8266.com/viewtopic.php?f=19&t=1049

id=0  -- need this to identify (software) IC2 bus?
gpio_pin= {5,4,0,2,14,12,13} -- this array maps internal IO references to GPIO numbers

-- user defined function: see if device responds with ACK to i2c start
function find_dev(i2c_id, dev_addr)
     i2c.start(i2c_id)
     c=i2c.address(i2c_id, dev_addr ,i2c.TRANSMITTER)
     i2c.stop(i2c_id)
     return c
end

print("Scanning all pins for I2C Bus device")
for scl=1,7 do
     for sda=1,7 do
          tmr.wdclr() -- call this to pat the (watch)dog!
          if sda~=scl then -- if the pins are the same then skip this round
               i2c.setup(id,sda,scl,i2c.SLOW) -- initialize i2c with our id and current pins in slow mode :-)
               for i=0,127 do -- TODO - skip invalid addresses
                    if find_dev(id, i)==true then
                    print("Device found at address 0x"..string.format("%02X",i))
                    print("Device is wired: SDA to GPIO"..gpio_pin[sda].." - IO index "..sda)
                    print("Device is wired: SCL to GPIO"..gpio_pin[scl].." - IO index "..scl)
                    end
               end
          end
     end
end