# 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

![](https://1329960936-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-L9GLtb-Tz_XaKbQu-Al%2F-LVsF9QGtglk9CSM-Pf6%2F-LVsG4-IlVkx0kVV3QyQ%2FC-serial2irda.png?alt=media\&token=c7e35bca-6492-4d42-a01d-d29315c9c701)

## 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

![](https://1329960936-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-L9GLtb-Tz_XaKbQu-Al%2F-LOrvCVzlhjwif35PmiG%2F-LOruKQ_PGZfjdqely5h%2Firda.PNG?alt=media\&token=a7541362-b42b-46d8-8245-215e11ef70cb)