# Serial 2 / Telemetry 2 / IRDA

On older versions of the RDDRONE-FMUK66, this port could only be used as IRDA. Since RDDRONE-FMUK66 Rev. C, it is by default configured as a free UART, which can be used as Telemetry 2 in PX4. It can still be reconfigured to use it as IRDA or as an extra I2C bus, though pull-up resistors will have to be placed by hand.

## RDDRONE-FMUK66 Rev. C connector pinout

| Pin | Signal  | Voltage |
| --- | ------- | ------- |
| 1   | VCC     | +5.0V   |
| 2   | UART TX | +3.3V   |
| 3   | UART RX | +3.3V   |
| 4   | GND     | GND     |

## RDDRONE-FMUK66 Rev. C schematic

![](/files/-LVsG4-IlVkx0kVV3QyQ)

## RDDRONE-FMUK66 Rev. B connector pinout

{% hint style="danger" %}
Rev. B (and older boards) are **not supported** anymore. This information is left for reference.
{% endhint %}

| Pin | Signal  | Voltage |
| --- | ------- | ------- |
| 1   | GND     | GND     |
| 2   | UART RX | +3.3V   |
| 3   | VCC     | +3.3V   |
| 4   | IR-     | +5.0V   |
| 5   | IR+     | +5.0V   |

## RDDRONE-FMUK66 Rev. B schematic

![](/files/-LOruKQ_PGZfjdqely5h)


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