Graupner HoTT Telemetry

The Graupner HoTT range of transmitters and receivers support realtime transmission of data from the the receiver and connected telemetry modules back to the transmitter. The data is then displayed on one or more LCD screens on the transmitter.

With the addition of HoTT telemetry to the PX4 system the PX4 can transmit data back to the transmitter by emulating various Graupner modules.

Video Setup Tutorial

What you will need

  • Graupner HoTT Transmitter: MX-16, MX-20, MC-16, MC-20
  • Graupner HoTT Receiver: GR-12/12s, GR-16, GR-24
  • Telemetry cable (servo cable, only signal wire is needed)
  • Soldering iron

Setting up your Transmitter

You will need to make sure that telemetry is correctly configured. To do this you will need to:

  • Enter the telemetry menu by holding down the ESC button for a couple of seconds
  • Choose Sensor Select from the menu
  • Activate the Electric Air.Mod option
  • Activate the GPS option if you are using a GPS module.

Configuring Receivers

Make sure that you are using the latest firmware for your transmitter and receiver, especially if you are finding that can't get things working following this guide. Older firmware releases did not properly support telemetry.

The GR-12 and GR-12s receivers do not support telemetry on channel 5 by default. You must activate telemetry on this port in the transmitter telemetry settings.


Connect a single wire from the “T” pin on the receiver telemetry port to a free serial port on the PX4. On the PX4 side you will need to connect the single wire to the TX port only. On the PX4FMU you can choose from:

  • USART1 (/dev/ttyS0)
  • USART2 (/dev/ttyS1) [default]
  • UART5 (/dev/ttyS2)
  • USART6 (/dev/ttyS3)

See the Developer Wiring page for more information on ports and devices for the respective autopilots.

If you use the PX4FMU with the PX4IO you can connect it to the USART2 (/dev/ttyS1) port on the PX4IO using a Hirose DF13 5 pos (Digi-Key Link: DF13-5P-1.25DSA) connector. More information on the location of the port can be found in the PX4IO User Manual.

Manually Starting the HoTT Telemetry

It is assumed here that you have a working serial connection to your PX4FMU board on UART1.

To start the app on the px4fmu type:

nsh> hott_telemetry start

To check whether the app is running:

nsh> hott_telemetry status

To stop, use:

nsh> hott_telemetry stop


–device / -d

The default UART is currently set to /dev/ttyS1 (USART2).


Starting the HoTT telemetry app using an alternative UART, such as UART5.

nsh> hott_telemetry start -d /dev/ttyS2

Auto Starting the HoTT Telemetry

Add the following line to the etc/extras.txt file on your microSD card:

hott_telemetry start

Verifying HoTT Telemetry Operation

As soon as the telemetry app has started it will start broadcasting data to your transmitter. You should see something similar to the this on the transmitters display:

Telemetry Data

This is a work in progress. Currently the following information is transmitted:

  • Voltage
  • Altitude
  • Temperature (as measured by the receiver)
  • GPS

The following will be available shortly:


If you are a developer see the HoTT Telemetry developer page.

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