Control Unit

What the control unit does, and why it is important.

Powering the Sensor

The control unit has several important functions. It features a built-in DC/DC converter that takes input voltage (ranging from 9 to 36V) and provides a steady voltage to the radiometer. Additionally, there are two power inputs on the controller that can be used to supply power. The input with the higher voltage is automatically utilized to power the sensor. One input can be connected to the drone battery, while the other is used only as a backup during battery swaps. This means that the radiometer continues to run while the drone pilot changes the drone battery. A low-capacity NiMH or LiPo battery with a 12V rating would keep the radiometer running while the drone is on the ground. Although it is not mandatory, keeping the sensor running throughout the mapping process is highly recommended to maintain consistent internal temperatures.

Indicator LEDs

On the controller, there are two LEDs located at the front. The first LED is labelled "System" and it starts blinking as soon as the power is supplied and the processor is booted up. Once the GPS has acquired a fix, the "System" LED will turn steady. The second LED is labelled "WiFi" and shows that a connection to the telemetry unit has been established.


The controller also has a GPS receiver (Antenova M20048-1 [^1]), which adds position and timestamp metadata with an accuracy of 2.5 meters or better and ±1\pm 1 second to the raw data.


The controller has enough memory to store radiometer data for approximately one hour. The memory is a ring memory, meaning new data overwrites the oldest data once the memory is full. When the controller connects to the ground station, the data is transferred to the storage on the ground station.

WiFi Module

The control unit is equipped with a WiFi module (ESP8266), which will attempt to establish a wireless connection to the ground station using 2.4 GHz WLAN. The module is programmed to search for the access point provided by the ground station unit and automatically log in whenever the control unit comes within range of the ground station.

As a side note, the control unit can connect to any access point that operates at 2.4 GHz, provided that the SSID of that access point matches "SkahaDrone" and the password is the same as the one printed on the ground station. Once connected, the control unit will search for an MQTT broker on port 1883. The sensor settings can be configured, and raw data can be received via MQTT.

Cable Connection to Antenna

A CAT-7 Ethernet cable is required to connect the sensor antenna to the control unit, as the cable shield is used as ground. The sensor will not function with CAT-6 or lower cables that have plastic connectors.

Do not connect the controller or radiometer to a router or computer. The CAT-7 cable between the antenna and the control unit is not an Ethernet connection!

A longer cable can be used for bench testing the sensor as long as it is CAT-7 or higher.

Firmware Updates

Two microprocessors are running on the control unit. The first is an STM32 processor that handles housekeeping tasks, and the second is a WiFi module (ESP8266). Sometimes, these two processors may need firmware updates, which can be done over-the-air when connected to the ground station. The ground station can receive the latest firmware files whenever it is connected to the Internet.

Over-Temperature Protection

The radiometer powers down automatically whenever the internal temperature of the FPGA or the ADC reaches 75°C.

After a thermal shutdown, the sensor will remain off for 5 minutes and will resume data acquisition unless the temperature is too high. However, the airstream should cool the sensor during flight, so this should not be an issue.


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