Recycling of Vaisala RS-41 meteorological radiosonde


    Since I succeeded in capturing a few Vaisala RS-41 meteorological radiosondes, I decided to look for some usefulness for them. Since the frequency at which these radiosondes are transmiting, is protected and allocated to meteorologists, it is necessary to find a way to shift the frequency into the amateur or ISM band. The radiosonde uses a Si4032-type radio IC so this job is only a question of programming. Unfortunately, it is usual practice that the program in these devices is protected so that only one way can be walked - the whole program must be re-written. During the search on the net I came across a program published by a Polish radio amateur, SQ5RWU. I programmed a radiosonde with this software and started testing it. The program worked, but it was unconfortable that every time I wanted to change some parameters, it was necessary to change the source code and compile it and then re-write the new program into the processor. This is a time-consuming process, and the flash memory on the other hand does not like the frequent rewriting. Since the whole program was simple and the possibilities it provided me were not enough, I decided to re-write the entire program. The final result of this development is this program. It is quite large, barely fitting in the flash, but the advantage is that you does not have to constantly re-write the radiosonde. The program should be put once into it, then the parameters can be changed at any time through the serial line on the port of the rs41 connector. Before the first programming, the flash memory must be deleted completely with the "Full chip erase" command so that the originally protected memory parts are released. Otherwise, the program will not save our own parameters due to lack of space!




Description:

    The radiosonde can be switched on by the pushbutton in the lower right corner. If the battery voltage is sufficient (the radiosonde can be powered by two NiMH batteries), the green LED on the lower left corner of the PCB will start to flash. If the radiosonde has a good view on the GPS satellites, the green LED will light up permanently after finding it's position. The red LED near to it lights up when the transmitter is working. The original sensors are not used, so they must be removed. If the BUTTON parameter is set to ON, the radiosonde can be switched off by pressing and holding the button. Push the button until the green LED starts blinking rapidly. After the button has been released, the radiosonde switches off. If the BUTTON is OFF, the radiosonde can only be switched off by removing the batteries from the battery holder.
    The radiosonde can operate in RTTY, APRS and CW mode. These modes can be switched on or off individually. The RTTY text is compatible with UKHAS recommendations. The APRS packet may be decrypted and encoded according to Mic-E variable. Sonde transmissing APRS data only if the coordinates are valid. Each parameter can be changed by sending a command and its parameters by the serial port. To do this, the radiosonde and computer should be connected via a COM-TTL or USB-TTL converter. Please note the radiosonde connector on the UART port is 3.3V! You can use any terminal program on your computer. The speed is 9600 baud, 8 data bits and 1 stop bit without parity and hw control (9600 8-N-1). As every other parameters, this can be changed too. The possible speeds are from 300 to 115200 baud. Communication is interactive. All issued commands will be answered. If the processor has understood and executed the command, then the answer will be an OK. Otherwise, we'll get an error message telling you where we made a mistake. After turning on the radiosonde, we need to see this welcome text on the screen, if the radiosonde and computer are properly connected:

STM32 CW, RTTY & APRS tracker v. 2.5 by OM3BC...
cmd>

If you need help, you can use the HELP or the ? commands. After this command we get the following text:

cmd>help

Allowed commands (not case sensitive):

BUTTON on/off - use button to turn off
LEDS on/off - use LEDs
POWER n - rf power n = 0 to 7 (7 is max.)
HOLDOFF n - n = time between two rtty messages in seconds
SERCOM n - speed of serial communication port (n = 300 to 115200)
RTTY on/off - send rtty message
RTTYFRQ n.n - n.n = rtty and cwid frequency in MHz
RTTYCALL string - rtty callsign (up to 15 characters)
BAUD n - n = rtty baudrate (max. 300)
DBITS n - n = rtty databits (7 or 8)
SBITS n - n = rtty stop bits (1 or 2)
SHIFT n - n = 1,2,3,4 or 270,540,810,1080 Hz
TEMP (or TEMPERATURE) on/off - send temperature in rtty messages
ALT (or ALTITUDE) on/off - send altitude in rtty messages
SPEED on/off - send speed in rtty messages
COURSE on/off - send course in rtty messages
UBAT on/off - send battery voltage in rtty messages
RTTY_WWL n - n = characters of wwlocator (only even numbers) in rtty messages
RTTY_TIME on/off - send time in rtty messages
SAT (or SATELLITES) on/off - send heard satellites in rtty messages
APRS on/off - send aprs messages
APRSFRQ n.n - n.n = aprs frequency in MHz
APRSCALL string - aprs callsign (up to 6 characters)
SSID n - aprs ssid n = 1 to 15
APRS_ALT on/off - send altitude in aprs ttext
SYMBOL string - symbol from aprs symbol table (2 characters)
RELAY string - aprs relays (WIDE1-1,WIDE2-1)
APRS_EVERY n - time between aprs messages is n x holdoff
TAIL_EVERY n - time between tail text is n x aprs time, 0 = no tail text
TTEXT string - tail text (up to 100 characters)
APRS_UBAT on/off - send battery voltage in aprs ttext
APRS_TEMP on/off - send radio chip temperature in aprs ttext
CWID on/off - send cwid messages
CWIDMESS string - cw message (up to 25 characters)
CWID_ALT on/off - send altitude via cw
CWID_UBAT on/off - send battery voltage via cw
CWID_WWL n - n = characters of wwlocator (only even numbers) in cw messages
CWID_EVERY n - time between cw messages is n x holdoff
CW_SPEED n n = cw speed in wpm
DISP - show parameters
DEF - set default values
SAVE - save parameters to flash
cmd>

Available commands:

BUTTON - this parameter specifies whether the push button can be used to turn off the radiosonde or not.
LEDS - you can save energy when you do not use LEDs. Nobody sees them anyway when the radiosonde is flying. After switching on, the LEDs always work, but when set to OFF, they automatically turn off after 10 minutes of operation.
POWER - output power setting 0 = smallest, 7 = maximum power (approx. 40 mW).
APRSFRQ - APRS frequency (recommended frequency is 432,500 MHz)
RTTYFRQ - RTTY frequency. This frequency is also valid for CW identification.
APRSCALL - APRS call sign.
RTTYCALL - RTTY call sign.
CWIDMESS - the text of the CW identification. If you write a > at the beginning of the text, the broadcast will begin with a "attention" (-.-.-) sign, which facilitates machine decoding (MixWin, Dl-FlDigi, etc.).
RTTY - RTTY Text On / Off.
HOLDOFF - the time between the two RTTY broadcasts.
BAUD - RTTY transmission speed in baud (max. 300).
DBITS - number of data bits. Possible values ​​are 7 or 8.
SBITS - number of stop bits. Possible values ​​are 1 or 2.
SHIFT frequencies. Possible values: 1-270, 2-540, 3-810, 4-1080 Hz
TEMP - to transmit the temperature in the RTTY text. (The value is the temperature of the radio chip, not the environment.)
ALT - enable altitude transmission.
SPEED - enable speed transmission.
COURSE - enable motion direction transmission.
UBAT - enable battery voltage transmission.
SAT - the number of GPS satellites heard.
APRS - Enable APRS transmission.
SSID - the caller ID of the APRS. Possible values from 0 to 15.
RTTY_TIME - send time in RTTY messages.
SYMBOL - two characters that determine how the radiosonde appears on the www,aprs.fi website. Icon from the symbol table
RELAY - aprs relays (WIDE1-1,Wide2-1).
APRS_EVERY - APRS packages are not required to be given too often. This parameter specifies the time between the two packets.
TAIL_EVERY - frequency of transmission of the attached information text (comment field).
TTEXT - the attached information text (comment).
APRS_UBAT - Send battery voltage in aprs text.
APRS_ALT - Send altitude in aprs ttext.
APRS_TEMP - Send radiochip temperature in aprs ttext.
CWID_WWL or RTTY_WWL- Send n charakters of WW Locator. n = 0 for no WW Locator
CWID - Enable CW Authentication.
CWID_EVERY - Frequency of CW identification.
CW_SPEED - the CW identification speed in WPM.
DISP - shows the set parameters.
SERCOM - speed of serial communication port (n = 300 to 115200).
DEF - set parameters to default values.
SAVE - stores the set parameters.

One possible setting:

cmd>disp

Current parameters:

BUTTON ON
LEDS OFF
POWER approx. 100 mW
UART 9600 8-N-1
HOLDOFF 10 s
RTTY ON
RTTY and CWID FREQUENCY: 434.500 MHz
RTTY CALLSIGN: OM3BC/AM
RTTY BAUDRATE: 100 Bd
RTTY SHIFT: 540 Hz
RTTY DATA BITS: 7
RTTY STOP BITS: 2
RTTY TEMPERATURE: OFF
RTTY ALTITUDE: ON
RTTY SPEED: OFF
RTTY COURSE: OFF
RTTY BATTERY VOLTAGE: ON
RTTY SATELLITES: ON
RTTY WWL: OFF
RTTY TIME: ON
APRS ON
APRS FREQUENCY: 432.500 MHz
APRS CALLSIGN: OM3BC-11
APRS RELAY: WIDE1-1
APRS SYMBOL: /O
APRS EVERY: 1
APRS ALT: ON
APRS TAIL TEXT EVERY: 1
APRS TAIL TEXT:  Modified RS-41 balloon tracker
APRS UBAT: ON
APRS TEMP: ON
CWID ON
CWID MESSAGE: TEST DE OM3BC/AM
CWID speed: 60 WPM
CWID EVERY: 5
CWID WWL: 6 characters
CWID UBAT: OFF
CWID ALT: OFF
cmd>

Closing remarks:

The original source can be found here.
Hex file can be found here.
For programming, I use the ST-LINK V2 programmer, which can be obtained from aliexpress, for example.

HG8LXL, Laci's report on the balloon, he has launched.

Wiring:

RS-41 connector:

| ----------- |
|  2 4 6 8 10 |
|  1 3 5 7 9  |
| ------ ---- |

1 - GND
2 - Uart3 Rx
3 - Uart3 Tx
4 - PB1 * (10k + cap + 10k)
5 - Vcc (Boost out)
6 - VBAT
7 - RST
8 - SCL
9 - SDI
10- GND

The Programer cable connections:

 RS41 ----- ST-LINK
===================
Pin 1 ----- GND
Pin 5 ----- 5.0V
Pin 8 ----- SWCLK
Pin 9 ----- SWDIO

USB - TTL converter:

RS41 ------ USB-TTL
===================
Pin 1 ----- GND
Pin 2 ----- TxD
Pin 3 ----- RxD

    From January 2024, a new type of processor will be installed in the RS41. It has a larger flash memory and consumes less power. Although the old and new processors are pin-compatible, unfortunately, the same pins are not used in all cases. Because of this, the old program cannot be used in the new hardware. Since the firmware had to be modified anyway, it was time for a little wrinkle-removal. Lately, the RTTY mode has been pushed into the background, and HORUS is used instead. This is understandable to a certain extent, although I don't appreciate the fact that an identifier has to be requested centrally, and someone else decides what identifier a probe can fly with. Since HORUS uses 4FSK modulation, the transmission of a packet takes much less time than in the case of RTTY. That is why this mode was also included in the new firmware.
    The information and advice written about the hardware are also valid here.
    This firmware can now handle external sensors, so if the sensor is not damaged, we can use it (although this increases power consumption).

The serial port parameters are still 9600N1.
After switching on, the probe logs in with the following message: RS41 based payload for STM32F100 (RS41 based payload for STM32L412).

You can use the HELP, H or ? command to find out what commands to use and in what form.

You can view the current parameters with the DISP command.
As a first step, we change N0CALL to our callsign (APRS and RTTY).
After that, we can modify the other parameters. After programming, none of the modes are enabled. Enable the ones we want to use.

If the program does not start after loading, check whether the correct config bits are set in the programmer.


                                STM32L412                                                                    STM32F100

firmware for probes before 2024 (STM32F100 with V included).

firmware for probes from 2024 and later (STM32L412 starting with W).