DFM-17 Radiosonde

The DFM-17 is a balloon-launched radiosonde manufactured by GRAW Radiosondes GmbH & Co. KG, and used for meteorological sounding.

The label side view of a DFM-17 Radiosonde

Overview

The DFM-17 radiosonde succeeds the DFM-09 radiosonde. Graw began a contract with NOAA in the US to provide radiosondes. As of Late 2021, several sites have made the transition as part of NOAA’s Operational Test and Evaluation (OT&E) program. 45 CONUS sites are expected to use these radiosondes in early 2022.

Specs

• Weight: 63g
• Size: 90 x 67 x 44 mm
• Power supply: 2 CR123A batteries
• Estimated runtime: ~240 minutes
• Transmission rate: 1 packet/sec
• Bandwidth: ~10 kHz (Website lists <12)
• Frequency range: 400 - 405.99 MHz
• Modulation: GFSK
• TX Power: ~100mW
• Error Correction: Code-spreading, interleaving
• SoC: STM32F100R8T6B, 24MHz, 8KB RAM, 64KB Flash
• GPS: U-Blox MAX-M8C-0-10
• Transmitter: Si4063

Peripheral attachment points

LED's and Buttons

• Button = PC8
• LED_Y = PC7
• LED_G = PC6
• LED_R = PB12

uBlox GPS (USART_2)

• PA3(RX) = GPS TXD (Pin 2)
• PA2(TX) = GPS RXD (Pin 3)
• PB8 = GPS 1pps (Pin 4) (LED next to flex cable connector)

UART via USB Port (USART_1)

• PA9(TX) = USB D+
• PA10(RX) = USB D-

Si4063 (SPI_1)

• PB2 = CS/nSEL (Pin 15)
• PC3 - SDN (Pin 1)
• PA7 = SDI (Pin 14)
• PA6 = SDO (Pin 13)
• PA5 = SCLK (Pin 12)

NFC/RFID 4k EEPROM

• PC13 = RF WIP/Busy
• PB6 = SCL
• PB7 (needs confirmed, signal routes under STM) = SDA

STG719 (DPST) - U2

• PC11 = IN

STG719 (DPST) - U3

• PD2 = IN

STG719 (DPST) - U4

• PB5 = IN

STG719 (DPST) - U5

• PB4= IN

DG636 (Dual DPST) - U6

• VDD = ENABLE (always HIGH)
• PA10 = A0
• UnknownPin#1 (routes under STM) = A1

STG719 (DPST) - U7

• UnknownPin#1 (routes under STM) = IN

SN74LV4053 (Triple 2Ch Mux/Demux) - U8

• PB13 & PB14 = A
  • connected by trace
  • Why? Read back?
• UnknownPin#1 (routes under STM) = B & C
  • connected by trace

Identified Supplementary IC's

• 

  Top view of PCB with U reference designators overlaid

IC Part Numbers and Markings

	Manufacturer	Part Number	Description	Package	Part Marking	Datasheet	Note
U1	STMicroelectronics	STM32F100R8T6B	ARM MCU, 24MHz, 8KB RAM, 64KB Flash	LQFP48	ARM 32F100R8T6B	Mouser	Some recent batches of the DFM-17 have been using knockoff STM32s! The chip shortage strikes again!
U2, U3, U4, U5, U7	ST	STG719	STG719STR Low Voltage 4 Ohm SPDT Switch	SOT-23-6	V719	Mouser	Analog ADG719 pin compatible equivalent?
U6	Vishay	DG636E	0.3 pC Charge Injection, 100 pA Leakage CMOS ± 5 V / 5 V / 3 V Dual SPDT Analog Switch	TSSOP14	636EE	Mouser
U8	Texas Instruments	SN74LV4053A	Triple 2-Channel Analog Multiplexer/Demultiplexer	SOT-23-6	LW053A	Texas Instruments
U9	Texas Instruments	LMV761	Low Voltage Precision Comparator with Push/Pull Output	SOT-23-6	C22A	Texas Instruments
U10	Silicon Labs	Si4063	High Performance, Low Current Transmitter	QFN20	40632A C01Q81 2217	Silcon Labs
U11	u-Blox	MAX-M8C-0-10	u-blox M8 GNSS module, ROM, crystal		MAX-M8C-0-10	u-Blox
U12	STMicroelectronics	M24LR04E-R	Dynamic NFC/RFID tag IC with 4-Kbit EEPROM, energy harvesting, I²C bus and ISO 15693 RF interface	UDFN8	4BEB 8150	STMicroelectronics	Needs verification. DFM-17 does not boot when removed; I suspect the serial and calibration is stored in the EEPROM here - Trevor229
U13	STMicroelectronics	LD series, unsure on specific part	3.3V Low Drop Out Voltage Regulator	DFN6	33R		Needs verification, appears to provide 3.3V for GNSS
U14							Looks like a high side current monitor amplifier, need more information
U15	ABLIC	S-8200A Series, unsure on specific Part Number	BATTERY PROTECTION IC FOR 1-CELL PACK		VDL	Mouser	Needs verification, Potentially a Winsok WSTDW01 Battery Protection IC?
U16					AL W24		In-line with battery power, need more information; chip marking
U17							Connected to USB data lines, likely a UART, isolation, and/or level shifter

Photos

• 

  Internal view of the DFM-17

• 

  The bottom side of the PCB in the DFM-17

• 

  The label sticker NOAA(US) puts on the back of their DFM-17 radiosondes

• 

  A view of the DFM-17 Radiosonde showing both layers to better assist tracing connections while reverse engineering the hardware.

• 

  Possible meanings of the internal labels and values. The date code in particular which may be useful to date production times. NWS sondes have the same cryptic string printed on the outside of the sonde where the mfg. date normally is on other countries'. "TU" may just indicate the board comes with sensors according to a third party source.

• 

  Pinout of the DFM-17 sensor stalk. Not all pins are used, and some seemingly are connected to a trace but end abruptly.

• 

  V719 SOT-23-6 packages removed as well as 636EE (SPDT Switch) and LW053A (Mux/Demuxer)

• 

  Mapping of the pins on the sensor stalk to the connector and their corresponding IC/IO lines. Top of sensor stalk corresponds to bottom of pictured connector!

• 

  Back of the DFM PCB without CR123A battery holders

Disassembly

1. Examine rope, parachute and parachute rigging lines for viability. Neatly organize the flight rigging if usable. Discard if not viable for reuse.
2. Cut the zip tie surrounding the Styrofoam from the top portion by the rope loop.
3. Pull the rope loop out, there should be little to no resistance.
4. Make a slice in the sticker where the two pieces of Styrofoam meet.
5. Pull apart the two Styrofoam pieces to reveal the circuit board.
6. Pull the circuit board out. There will be some resistance.
7. The board is now separated from the Styrofoam shell, reuse if desired.
8. Pull the two CR123A batteries out, keep or discard them. The board can run off USB power. Batteries are not necessary for development on this board.

Reassembly

1. Insert two fresh CR123A batteries into the board.
2. Line up the board to the IO cutouts in the Styrofoam, begin to push into the slots. Make sure the antenna wire comes through.
3. Press the top piece of Styrofoam into place.
4. Tape or apply another sticker onto the back label. (Optional)
5. Insert the plastic rope loop piece.
6. zip tie the shell together, the zip tie end should end up on the edge nearest to the power button.
7. Rope on a balloon/drone/kite/etc.. to the rope loop.
8. Power on the device by pressing and holding the button, you will see a yellow light blink, hold until the light turns solid.

Mini USB Port

The mini USB port on the board does not use the USB protocol for communication, it is a UART bus. However using USB to power the board should not harm the board in theory.

In order to use it, splice a USB cable and wire up a USB<->TTL adapter with the following pins:

• VBUS: 5 Volts DC
• D-: TX
• D+: RX
• GND: GND

The board will communicate with the official GRAWMET software using this approach. Reverse engineering of the port's protocol is underway, however it is believed to use a similar, if not the same protocol the PS-15 uses.

Hardware modifications

SMA Port to replace antenna & SWD header:

The DFM-17 has solder pads for an SMA port and a SWD header. An Adafruit Skinny SWD SMT connector and a generic SMA connected was used in the photo.

Minimizing transmit range:

As amateurs we are not licensed to transmit in the 400-406MHz band, so for testing purposes one should perform this mod. Unsolder the antenna wire and take two 100 ohm resistors and twist them in parallel, then solder them to the center pad and one of the side pads on the SMA footprint. This creates a 50 ohm dummy load for the Si4036 to transmit into. The range is reduced to a couple tens of feet. Also if you are running a radiosonde_auto_rx instance, don't forget to turn it off during testing to avoid feeding erroneous data to Sondehub!

• 

  MrARM's modified DFM-17 with a SWD connector and an SMA antenna port

• 

  Trevor229's DFM with ST-Link SWD pins connected to debug interface and 50 ohm dummy load mod.

Developing and Programming the board

A very crude diagram showing the standard SWD pinout overlaid onto the DFM-17 board

When lab testing, you can power the board from the USB header. It also appears to run fine supplying 3.3V to the SWD port(STLink clones do this).

The board uses a STM32, and requires a ST-Link to program. The process used to upload code to the MCU is the same as the Vaisala RS41 radiosonde, you will need to solder and connect the VTRef(3.3V), Ground, SWDIO, SWDCLK and RST pins to your ST-Link.

The board can run without external power being supplied when programming. This board has read-out protection enabled similar to the RS41 and this must be disabled before you can flash firmware to the board.