NEW: Experimental support for Graw DFM-17 radiosondes added! Please test and report any issues! Using a DFM-17 as a primary flight tracker is NOT recommended yet!
NOTE: DFM-17 radiosondes require a GPS lock (and clear visibility to the sky) to calibrate its internal oscillator. DFM-17 transmissions, especially APRS, may not decode correctly because of incorrect timing before the internal oscillator has been calibrated.
NOTE: While this firmware has been tested (on RS41) with great success on a number of high-altitude balloon flights, it is still a work in progress and some features might not work as expected yet! In particular, the time sync (scheduling) features and use of an external Si5351 as a transmitter need more testing.
RS41ng is a custom, amateur radio-oriented firmware for Vaisala RS41 and Graw DFM-17 radiosondes. These radiosonde models have very similar hardware, so that it is relatively easy to support both with the same codebase. It is unlikely that RS41ng could support any other radiosonde hardware for now.
Some code is based on an earlier RS41 firmware project called RS41HUP, but most of it has been rewritten from scratch. The Horus 4FSK code has been adapted from the darksidelemm fork of RS41HUP.
Radiosondes, especially the RS41 and DFM-17, are used extensively for atmospheric sounding by the meteorological institutes in various countries and thus easily available to be collected once they land, an activity called radiosonde hunting: see YouTube presentation about Tracking and Chasing Weather Balloons by Andreas Spiess or Chasing Radiosonde Weather Balloons used in Meteorology for Fun by Mark VK5QI for more details!
You can track radiosondes without any additional equipment either via SondeHub or radiosondy.info that both use an existing network of receiver stations. Alternatively, you can set up your own radiosonde receiver station.
For your own receiver station, you will need:
The Vaisala RS41 and Graw DFM-17 radiosondes both use off-the-shelf 32-bit STM32F100-series microcontrollers, which can be reprogrammed using an ST-LINK v2 programmer or a smaller ST-LINK v2 USB dongle.
There is detailed information about the hardware of these radiosonde models on the following pages:
The radiosondes can be reprogrammed to transmit different kinds of RF modulations (morse code, APRS and different FSK modulations) on the 70 cm (~433 MHz) amateur radio band. The radiosonde contain Ublox GPS chips, so it can be used as a tracker device, e.g. for high-altitude balloons.
The RS41ng firmware is just one example of what can be achieved with the hardware of these radiosondes!
High-altitude balloon flights arranged by hobbyists are fun technical experiments. The flight goals are usually related to aerial photography, testing of radio tracker and transmitter hardware and different kinds of measurements with on-board sensors.
The following websites contain more information about planning and launching a high-altitude balloon flight:
The motivation to develop this firmware is to provide a clean, customizable and modular codebase for developing radiosonde-based experiments.
See the feature list below.
The main features the RS41ng firmware are:
config.c)Features available on RS41 hardware only:
Notes for DFM-17:
On the internal Si4032 (RS41) and Si4063 (DFM-17) transmitters:
On an external Si5351 clock generator connected to the external I²C bus of the RS41 radiosonde:
It is possible to connect external sensors to the I²C bus of the RS41 radiosonde.
The following sensors are currently supported:
Sensor driver code contributions are welcome!
config.h
// comment from either
the #define RS41 or #define DFM17 lines.CALLSIGNRADIO_SI4032_ to select transmit power and the modes to transmitRADIO_SI4063_ to select transmit power and the modes to transmitHORUS_V2_PAYLOAD_ID if you transmit Horus 4FSKAPRS_COMMENT if you transmit APRSconfig.c, depending on the modes you use.
You can customize the APRS and CW messages in more detail here.Power consumption notes (at 3V supply voltage) for RS41 by Mark VK5QI:
The variations seem to be the GPS powering up every second to do its fixes.
The time sync feature is a simple way to activate the transmissions every N seconds, delayed by the TIME_SYNC_OFFSET_SECONDS setting.
Please note that the time sync requires a stable GPS signal (good visibility to the sky) to work correctly!
For time-slotted modes like FT8 and WSPR, there default configuration file (config.h) already contains useful defaults.
The default FT8 configuration is:
#define FT8_TIME_SYNC_SECONDS 15
#define FT8_TIME_SYNC_OFFSET_SECONDS 1The above means that transmissions should start every 15 seconds (counting from the beginning of each hour), but delayed by 1 second. As an example, transmissions after 12:00:00 (hh:mm:ss) would happen at 12:00:01, 12:00:16, 12:00:31; 12:00:46, 12:01:01 and so on.
The offset of 1 second is just to make sure the transmission starts strictly after the 15-second periods and never before.
If the offset was 5 seconds, transmissions would happen at 12:00:05, 12:00:20, 12:00:35, 12:00:50 and 12:01:05.
In order to transmit only in even or odd time slots of FT8, you could use:
// Transmit every 30 seconds, even time slot
#define FT8_TIME_SYNC_SECONDS 30
#define FT8_TIME_SYNC_OFFSET_SECONDS 1// Transmit every 30 seconds, odd time slot
#define FT8_TIME_SYNC_SECONDS 30
#define FT8_TIME_SYNC_OFFSET_SECONDS 16The latter (odd time slot) example would transmit at 12:00:16, 12:00:46, 12:01:16, 12:01:46 and so on.
For WSPR, the transmissions happen every 120 seconds, so the configuration has to be:
#define WSPR_TIME_SYNC_SECONDS 120
#define WSPR_TIME_SYNC_OFFSET_SECONDS 1The above means that transmissions should start every 120 seconds (counting from the beginning of each hour), but delayed by 1 second. As an example, transmissions after 12:00:00 (hh:mm:ss) would happen at 12:00:01, 12:02:01, 12:04:01 and so on.
The offset of 1 second is just to make sure the transmission starts strictly after the 120-second periods and never before.
Sometimes it is necessary to set transmission time slots when using multiple payloads/transmitters on the same frequency. The time slots guarantee that the transmissions from different payloads will not happen simultaneously.
The time sync settings can be used to configure this type of time slots.
In this example, we configure 3 payloads to transmit every 120 seconds, so that each payload is scheduled to transmit evenly across the 120-second period, every 40 seconds (120 / 3 = 40).
First, the TIME_SYNC_SECONDS setting of the particular mode has to be set to the full interval where all payloads are expected to have their transmissions finished.
This setting has to be the same for every payload. Do also remember to take into account transmission length too (depending on the mode).
Next, the TIME_SYNC_OFFSET_SECONDS needs to be set independently for each payload. The first payload would have
an offset of 0, the second an offset of 40 and the third and offset of 80.
As an example, transmissions after 12:00:00 (hh:mm:ss) would happen at:
The configuration with 3 payloads using Horus 4FSK V2 mode would be the following.
Payload 1:
#define HORUS_V2_TIME_SYNC_SECONDS 120 // everything happens at 120 seconds interval
#define HORUS_V2_TIME_SYNC_OFFSET_SECONDS 0 // the first payload will transmit at 0 seconds within the 120 second intervalPayload 2:
#define HORUS_V2_TIME_SYNC_SECONDS 120 // everything happens at 120 seconds interval
#define HORUS_V2_TIME_SYNC_OFFSET_SECONDS 40 // the second payload will transmit at 40 seconds within the 120 second intervalPayload 3:
#define HORUS_V2_TIME_SYNC_SECONDS 120 // everything happens at 120 seconds interval
#define HORUS_V2_TIME_SYNC_OFFSET_SECONDS 80 // the third payload will transmit at 80 seconds within the 120 second intervalThe easiest and the recommended method to build the firmware is using Docker.
If you have a Linux environment -- Windows Subsystem for Linux (WSL) or macOS might work too -- and you feel adventurous, you can try to build using the Linux-based instructions.
Using Docker to build the firmware is usually the easiest option, because it provides a stable Fedora Linux-based build environment on any platform. It should work on Windows and Mac operating systems too.
The Docker environment can also help address issues with the build process.
docker build -t rs41ng_compiler .docker run --rm -it -v $(pwd):/usr/local/src/RS41ng rs41ng_compilerOn Windows, run:
docker run --rm -it -v %cd%:/usr/local/src/RS41ng rs41ng_compilerbuild/src/RS41ng.elfNow you can flash the firmware using instructions below (skip the build instructions for Linux).
Software requirements:
arm-none-eabi-gcc)
On a Red Hat/Fedora Linux installation, the following packages can be installed:
dnf install arm-none-eabi-gcc-cs arm-none-eabi-gcc-cs-c++ arm-none-eabi-binutils-cs arm-none-eabi-newlib cmake openocdmkdir build
cd build
cmake ..
makebuild/src/RS41ng.elfHardware requirements:
Follow the instructions below for the radiosonde model you have.
The pinout of the RS41 programming connector (by DF8OE and VK5QI) is the following:
______________________| |______________________
| |
| 9 7 5 3 1 |
| |
| 10 8 6 4 2 |
|_______________________________________________________|
(View from the bottom of the sonde, pay attention to the gap in the connector)The DFM-17 programming connector is an unpopulated group of pads on the circuit board between the sensor boom connector and the main STM32 microcontroller.
The pinout of the DFM-17 programming connector is the following:
_____
| |
| S | _____________________
| e | | |
| n | | 1 2 |
| s | | |
| o | | 3 4 | ________________________
| r | | | |
| | | 5 6 | | STM32 microcontroller
| b | | | |
| o | | 7 8 | |
| o | | | |
| m | | 9 10 | |
| | | | |
| | |____________________ |
| |
|___|
(The sensor boom connector is on the left and the main microcontroller unit on the right side)openocd -f ./openocd_rs41.cfg -c "init; halt; flash protect 0 0 63 off; exit"63 with either 31 or the number the error message suggests:
openocd -f ./openocd_rs41.cfg -c "init; halt; flash protect 0 0 31 off; exit"openocd -f ./openocd_rs41.cfg -c "program build/src/RS41ng.elf verify reset exit"It is possible to receive log messages from the firmware program and to perform debugging of the firmware using GNU GDB.
Also, please note that Red Hat/Fedora do not provide GDB for ARM architectures, so you will need to manually download and install GDB from ARM GNU GCC toolchain. Pick the latest version available for your operating system.
Semihosting allows the firmware to send log messages via special system calls to OpenOCD, so that you can get real-time feedback and debug output from the application.
Semihosting has to be disabled when the RS41 radiosonde is not connected to the STM32 programmer dongle, otherwise the firmware will not run.
config.h by uncommenting the following lines
#define SEMIHOSTING_ENABLE
#define LOGGING_ENABLEopenocd -f ./openocd_rs41.cfgarm-none-eabi-gdbbuild directory with Makefiles from CMake ready for build)
target remote localhost:3333
monitor arm semihosting enable
make
load src/RS41ng.elf
monitor reset halt
continue # this command runs the firmwareTo load debugging symbols for settings breakpoints and to perform more detailed inspection,
use command file src/RS41ng.elf.
Notes by Mikael OH3BHX:
The idea behind the APRS / Bell 202 modulation implementation is based on RS41HUP project and its "ancestors" and I'm describing it here, since it has not been documented elsewhere.
The Si4032 chip seems to support only a very specific type of FSK, where one can define two frequencies (on a 625 Hz granularity) that can be toggled by a register change. Because of the granularity, this mechanism cannot be directly used to generate Bell 202 tones.
The way Bell 202 AFSK is implemented for Si4032 is kind of a hack, where the code toggles these two frequencies at a rate of 1200 and 2200 Hz, which produces the two Bell 202 tones even though the actual frequencies are something else.
Additionally, the timing of 1200/2200 Hz was done in RS41HUP by using experimentally determined delays and by disabling all interrupts, so they won't interfere with the timings.
I have attempted to implement Bell 202 frequency generation using hardware DMA and PWM, but have failed to generate correct symbol rate that other APRS equipment are able to decode. I have tried to decode the DMA-based modulation with some tools intended for debugging APRS and while some bytes are decoded correctly every once in a while, the timings are mostly off for some unknown reason.
Currently, the Bell 202 modulation implementation uses hardware PWM to generate the individual tone frequencies, but the symbol timing is created in a loop with delay that was chosen carefully via experiments.
Here are some tools and command-line examples to receive and debug APRS messages using an
SDR receiver. There are examples for using both rx_tools
and rtl-sdr tools to interface with the SDR receiver.
The example commands assume you are using an RTL-SDR dongle, but rx_fm (from rx_tools)
supports other types of devices too, as it's based on SoapySDR.
Dire Wolf can decode APRS (and lots of other digital modes) from audio streams.
rx_tools:
rx_fm -f 432500000 -M fm -s 250000 -r 48000 -g 22 -d driver=rtlsdr - | direwolf -n 1 -D 1 -r 48000 -b 16 -rtl-sdr:
rtl_fm -f 432500000 -M fm -s 250k -r 48000 -g 22 - | direwolf -n 1 -D 1 -r 48000 -b 16 -SigPlay is a set of tools for DSP and signal processing. SigPlay also includes a command-line tool to decode and print out raw data from Bell 202 encoding, which is really useful, as it allows you to see the bytes that actually get transmitted -- even if the packet is not a valid APRS packet!
rx_tools:
rx_fm -f 432500000 -M fm -s 250000 -r 48000 -g 22 -d driver=rtlsdr - | ./aprs -rtl-sdr:
rtl_fm -f 432500000 -M fm -s 250k -r 48000 -g 22 - | ./aprs -