6. LED feedback

The Pololu Isolated USB-to-I²C Adapter has several LEDs to indicate its status as shown in the pictures below.

Pololu Isolated USB-to-I²C Adapter pinout and LEDs.

Pololu Isolated USB-to-I²C Adapter with Isolated Power pinout and LEDs.

Status LEDs

The green USB status LED indicates the state of the USB connection. When you connect the adapter to a computer via a USB cable, the green LED will start blinking slowly. The blinking continues until the adapter gets a particular message from the computer that indicates that the adapter is recognized. After the adapter gets that message, the green LED will be on, but it will flicker briefly when there is USB activity. During suspend mode (e.g. when the computer has gone to sleep), the green LED will blink very briefly once per second.

The yellow status LED blinks rapidly when the adapter reads data or acknowledgments from a target device.

The red status LED blinks rapidly when the adapter attempts to write data or acknowledgments to a target device. Also, if the last I²C read or write command resulted in an error, and the command was not zero-length I²C write, then the red LED blinks once per second with a 50% duty cycle.

When the yellow and red LEDs are both blinking rapidly, the relative durations of the blinks reflect the ratio of read events to write events.

Power indicator LEDs

On an adapter without isolated power, the green VCC (IN) LED turns on when power is supplied to VCC. It is directly connected between VCC and GND, so the brightness of the LED is higher when the VCC voltage is higher.

On an adapter with isolated power, green and blue LEDs by the voltage selection slide switch indicate the voltage that the adapter is supplying to VCC through its isolated DC-DC power module. The green LED indicates that the VCC output is 3.3 V, while the blue LED indicates that it is 5 V. The voltage setting is latched when the VCC output turns on, so toggling the switch when VCC is already on will not immediately change the voltage, and the LEDs will reflect that behavior. (When VCC turns on at 5V, the green LED might also light briefly.)