Retino

The poor man's radiosonde receiver

What is it

An alternative firmware for the HC-14 LoRa modules for receiving and decoding meteorological radiosondes. To be used in conjunction with a USB TTL serial adapter. Part of the code for the decoding is adapted from sondedump. Inspiration was also taken from the rs1729 demodulators

Currently able to receive the following radiosondes:

• Vaisala RS41¹
• Meteomodem M10
• Meteomodem M20
• Graw DFM09

In case you don't own a NuLink programmer, the HC14Prog directory contains a sketch that enables an Arduino Nano (or similar board) to reprogram the HC-14 module. Requires installation of the CRC library. You need to connect 3 test points and power/ground to the Arduino as follows:

Arduino	HC-14
5V	VCC
GND	GND
D2	nRESET
D3	ICE_CLK
D4	ICE_DAT

This is only for the first time programming since you will be able to upgrade via a bootloader with the NuvoISP utility.

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⚠ Needless to say the original firmware will be lost forever, you will not be able to use your HC-14 module as before

Building

You will need SDCC, python 3 with the urllib3 and crc libraries. MCU support must be installed too, it should reside in the parent directory. After building the firmware binary you will be able to compile the Arduino sketch for programming the board.

How to connect to the USB TTL serial adapter

HC-14	adapter
VCC	+5V
GND	GND
TX	RX
RX	TX

Input "protocol"

Line oriented

• ? request settings
• • request build time
• $ request instantaneous RSSI measurement
• = force print last position data
• !ttttttffffff 6 characters that represent the sonde type, case insensitive (rs41,m10,m20,dfm09), right padded with blanks, followed by 6 charactes indicating the requested frequency in kHz
• @ reboot in bootloader mode (for firmware updates)

Output "protocol"

Line oriented, first character specifies record type:

• D: decoded data. Followed by key:value pairs separated by commas
• P: raw packet. Followed by data in hex. Data is already "massaged" (manchester decoded and dewhitened)
• #: current settings. Followed by sonde type and frequency in kHz separated by '@'

Reverse engineering of the HC-14 module

• Processor: Nuvoton MS51XC0BE
• Radio module: Semtech SX1278
• PG2179TB RF switch

Other connections:

Function	Pin
SX1278 DIO0	P0.4
SX1278 DIO1	P0.3
SX1278 NRESET	P0.5
SX1278 MISO	P0.1/SPI0_MISO
SX1278 MOSI	P0.0/SPI0_MOSI
SX1278 SCK	P1.0/SPI0_CLK
SX1278 NSS	P1.2
SX1278 RXTX/RFMOD	P1.3
PG2179TB vcont2	P1.7
PG2179TB vcont1	P1.5

Userful links

• MS51_BSP
• HC-14 – the simple LoRa module
• Nuvoton8051ProgrammingLib

Footnotes

1. Receive only, no decoding. Raw packet transmitted to host ↩