This is an I2C buffer / extender based on the P82B175 it has additional indicator LED's to show that the bus is high, when lock up occurs one of the LED's will be off indicating a problem. The input has 5k5 resistors and the output has 470R pull up resistors. With one buffer it should give a few meters range to I2C. If a buffer is used at either end then the data sheet for the P82B175 suggests up to 50 metres P82B175 Data sheet The input is duplicated so that it is easy to daisy chain the I2C bus. The actual length depends on the wire used and its configuration, Using one buffer as in the first image the distance can be extended to a few metres 'A'. For maximum range (50m according to the data sheet, use two buffers back to back as in 'B' In this test the wire is a flat 4 core telephone type cable but with stranded cores (7/0.15mm) to make it more flexible. On the reel there is about 10m left and using just 1 buffer (as A above) the signal at 100KHz and with a voltage of 3.3V the I2C drives the I2C display device perfectly well, At the other end of the buffer, acting as the master was an ESP8266 running micropython.
