GoRailPager_BLE

A device for receiving and repeating POCSAG formatted ChinaRail "LBJ" message which has the meaning of train arrival alert. The project is based on TI CC1101 RF solution and STM32F070F6P6 microcontroller. First, the apparatus receive and decode the 2-FSK modulated digital baseband raw data using CC1101. Besides, the programs parse the raw data according to the POCSAG formate regulations. Finally, repeate the LBJ message via Bluetooth 4.0 smart (BLE) interface to data receiving terminals (e.g. mobile phones) for further post processing or storge. This project is the practical and extended version of project "CC1101_Rx_LBJ".(See [email protected]:XieYingnan-Hideo/CC1101_Rx_LBJ.git) For the hardware design, such as schematic diagram and printed circuit board layout of this device, please visit the repository hosted by lceda.cn.

Basic infomation

• Project Name: GoRailPager_BLE
• Revise version: V1.0
• Created date: 2021-08-20
• Author: Xie Yingnan ([email protected])

Hardware requirements

0. CPU

ARM Cortex-M0 STM32F070F6P6 (Package:TSSOP-20)

1.TI CC1101 RF solutioin(Operated on STM32F070F6 SPI1)

fCLK = 6MHz

Function	MOSI	MISO	SCLK	CS	IRQ(GDO2)
Pin	PA7	PA6	PA5	PA4	PB1

2.BLE interface module HC-08

Function	HC-08 Rx (USART2 Tx)	HC-08 Tx (USART2 Rx)
Pin	PA2	PA3

Pattern: 9600 bps, No parity, 8 bits, 1 stopbits

3.Serial Port(For debug info print)

Function	UART1 Tx	UART1 Rx
Pin	PA9	PA10

Pattern: 115200 bps, No parity, 8 bits, 1 stopbits

4.Serial-Wire Debug(SWD)

Function	SWDIO	SWCLK
Pin	PA13	PA14

5.Indicators (Status LED)

Function	Pin on MCU
STATUS_LED	PA1

6.ADC input for battery voltage check

Function	Pin on MCU	Function
BATT_CHK	PA0	ADC input of Vbat/2

Details

1. About the Rx procedure and cofiguration of CC1101

The train arrival alerting message is transmitted by locomotive on 821.2375MHz using 2-FSK modulated POCSAG formate. The FSK frequency deviation direction of LBJ systems on locomotive is obeying POCSAG standard. i.e. F+f signifies logical 0, and F-f signifies logical 1. It is exactly reversed to the FSK pattern that CC1101 holds. CC1101 regarding F+f as logical 1 and F-f as logical 0. So we need to do bit reverse operate for receiving LBJ message correctly. The implement method is: change sync code from 0x15D8 to its bit reversed value 0xEA27 and make raw data bit reversed before POCSAG parsing.

Notes: value 0x15D8 is the lower 16bits of standard POCSAG sync code 0x7CD215D8, for CC1101 does not support 32-bit sync code, we only intersect its lower 16 bits.

According to the standard TB/T3504-2018, LBJ systems on locomotive publish two kinds of message on two POCSAG address: 1234000 and 1234008. The former POCSAG message contains traincode, train speed and milesmark that the train just passed. The latter POCSAG message just for time sync utility. The structure of two messages are listed as following chart.

Train arrival alert @ 1234000
576bits preamble+32bit sync(0x7CD215D8)+1 Address codeword(4 bytes)+3 Message Codeword(12 bytes)+3 IDLE Codeword(12 bytes)

Train arrival alert @ 1234008
576bits preamble+32bit sync(0x7CD215D8)+1 Address codeword(4 bytes)+1 Message Codeword(4 bytes)+5 IDLE Codeword(20 bytes)

We can summerize that we only need to receive bytes size of 16(containing 1 Address codeword and 3 Message codeword), the packet size of CC1101 is set to 16, with fixed length mode.

CC1101 receiving package pattern
16 bytes of preamble+16bit sync code (0xEA27)+16bytes of payload(containing 1 address codeword and 3 message codeword)

CC1101 shoud be configured an follow:

CRC Filtering	Package mode	Sync word	Preamble length	FSK Freq deviation
OFF	Fixed length, 16bytes	0xEA27	16 bytes	4.5kHz

2. About the communication protocals between PC and Microcontroller

The communication between PC and MCU is done via serialport (parrtern: 115200,N,8,1), for the ending of each command string, both '\r' or '\n' as well as '\r'+'\n' is OK. Here listed below are the command strobs, note that they are case sensitive. The messages during self-check after power-up as well as POCSAG decoding will also be printed via serialport.

Command	Function	Expected ack from MCU
$NAME	Show BLE name	(e.g.)BLE name:LBJ_Pager
$NAME=xxx	Set BLE name to "xxx"(max. length is 12)	OK
$BATT	Show battery voltage in mV and level	(e.g.)Vbat:3750mV,Level2
$V	Show firmware version	version string
?	Show command help	command help string

3. About the communication protocals between Microcontroller and HC-08 BLE module

The communication between MCU and BLE module is based on serialport (pattern: 9600,N,8,1). Before BLE connected to data receiving terminals(e.g. mobile phone), protocals are AT+something, as listed below.

Command	Function	Expected ack from HC-08
$AT	Check HC-08 module presence	OK
$AT+NAME	Get BLE name	(e.g.)LBJ_Pager
$AT+NAME=xxx
Set BLE name to "xxx"	OKsetNAME

After BLE connected, we can transmit the raw data what we want the data terminal be received directly through the serial port, for this pattern of data transfer, please view next section for details.

4. About the data transfer between HC-08 BLE module and BLE termial (MobilePhone)

Content	Function	Example	Direction
${train direction:X,S},{train code},{speed},{miles},{RSSI in dBm},{RSSI level}$	LBJ alerting message	$S,4230,104,168.0,-105.0,2$ $X,47963,45,22.5,-85.5,3$	HC08 -> Terminal(MobilePhone)
#VBAT:{battery voltage in mV},{battery level}#	Report battery voltage and level	#VBAT:3756,3#	HC08 -> Terminal(MobilePhone)
#BATT_ALM:{battery voltage in mV}#	Low battery alarm	#BATT_ALM:3456#	HC08 -> Terminal(MobilePhone)
#VBAT_CHK#	Check battery voltage	#VBAT_CHK#	Terminal(MobilePhone) -> HC08

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End of file (Edited by XieYingnan)