HSC025A-an-one-dollar-Bluetooth-SoC

Introduction

HSC025A is a Bluetooth Audio System-on-Chip (SoC) delivering wireless audio with a UART interface that supports creation of your featured audio player. With a firmware developed on top of the Bluetooth SoC (AC6925A) fabricated by Zhuhai Jieli Technology Co. Ltd., HSC025A provides the following features:

• Stand-alone operation with push buttons or slave operation with MCU control through UART interface
• Bluetooth Classic - BR/EDR with three profiles supported
  • Headset profile (HSP)
  • Hands-free profile (HFP)
  • AudioSink - Advanced Audio Distribution Profile (A2DP - SNK)
  • Audio/Video Remote Control Profile (AVRCP)
• 1 USB 2.0 OTG host controller for USB mass storage connection (up to 64GB)
• 1 microSD/SD card controller (up to 64GB)
• Audio file playback from USB or microSD/SD card in MP3/WAV/WMA/FLAC/APE formats
• FM radio supporting worldwide frequency band 87.5-108.0MHz
• Integrated 16-bit stereo DAC with headphone amplifier (SNR>=95dB)
• 1 channel MIC input with an integrated amplifier for hands-free phone call
• 1 integrated low dropout regulator (LDO) delivering 3.3V that sources up to 150mA
• Current consumption less than 10mA @5V in sleep mode

Pin Configuration

Pin No.	Name	I/O Type	Function
1	SDCLK	O	Serial clock for microSD / SD card
2	SDCMD	O	Command output for microSD/SD card
3	SDDAT	I/O	Data Line [Bit0] 1
4	USBDM	I/O	USB negative data line
5	USBDP	I/O	USB positive data line
6	MICIN	I	Mic input channel
7	DACR	O	DAC right output channel
8	DACL	O	DAC left output channel
9	DACVDD	Power	DAC power. Bypass this pin with a 1uF ceramic capacitor.
10	VCOM	Power	DAC reference. Bypass this pint with a 1uF ceramic capacitor.
11	DACVSS	Power	DAC ground
12	VDDIO	Power	3.3V LDO power output (150mA max loading)
13	BT_LED	O	GPIO pin configured as an activity LED indicator
14	ADKEY	I	GPIO pin configured as an ADC pin for button operation
15	MUTE	O	GPIO pin configured as an output pin when mute (mute=0, operate=1)
16	UART_RX	I	UART data input (default baud rate = 9600bps, 8-n-1)
17	UART_TX	O	UART data output (default baud rate = 9600bps, 8-n-1)
18	VBAT	Power	Power input (2.2V - 5.5V)
19	BT_AVDD	Power	Analog power (1.3V). Bypass this pin with a 1uF ceramic capacitor.
20	BT_RF	I/O	RF antenna feed line for Bluetooth
21	FM_IP	I/O	RF antenna feed line for FM radio
22	VSSIO	Power	Digital ground
23	BT_OSCI	I	24MHz crystal oscillator input (accuracy +/-10ppm or better)
24	BT_OSCO	O	24MHz crystal oscillator output (accuracy +/-10ppm or better)

Electrical Characteristics

Pin Name	Parameter	Min	Typ	Max	Unit	Test Conditions
DACVDD	DAC voltage	-	3.1	-	V	VBAT = 5V, DACVDD loading=10mA
VCOM	DAC voltage	-	1.5	-	V	-
VDDIO	Voltage output	-	3.3	-	V	VBAT = 5V, VDDIO loading = 150mA
VBAT	Voltage input	2.2	3.7	5.5	V	-
BT_AVDD	Analog voltage	-	1.3	-	V	VBAT = 5V

Digital Terminal Characteristics

Test conditions: VDDIO = 3.3V

Terminals	Symbol	Min	Typ	Max	Unit
Input logic level low	VIL	-0.3	-	0.3*VDDIO	V
Input logic level high	VIH	0.7*VDDIO	-	VDDIO+0.3	V
Output logic level low	VOL	-	-	0.33	V
Output logic level high	VOH	2.7	-	-	V

DAC Characteristics

Test conditions: 1kHz/0dB @10k Ohm loading

Parameter	Min	Typ	Max	Unit
Frequency response	20	-	20k	Hz
THD+N	-	-69	-	dB
S/N	-	95	-	dB
Output swing		1		Vrms
Dynamic range		90		dB
DAC output power (@ 32Ohm loading)	11		-	mW

Bluetooth Characteristics

Parameter	Min	Typ	Max	Unit
RF frequency range	2.40	-	2.48	GHz
RF transmit power		0	4	dBm
RF receive sensitivity		-89		dBm
Transmission range	-	-	10	m
Power Class	-	2	-

FM Receiver Characteristics

Parameter	Min	Typ	Max	Unit	Test Conditions
Input frequency	87.5		108.0	MHz
Sensitivity	3	4	8	dBuV EMF	(S+N)/N=26dB
Audio output voltage	0		3	V	Empty loading
Audio frequency response	20		20k	Hz	DAC test
Audio (S+N)/N		52		dB
Audio total harmonic distortion (THD)		0.4		%

Package Information

SOP24 (0.65mm pitch)

Communication Protocol

HSC025A communicates with an external system (e.g. an MCU) by UART (Universal Asynchronous Receive/Transmit) via UART_TX and UART_RX pins in 3.3V (VDDIO) level. The default baud rate is 9600bps of 8-bit data, no parity with 1 stop bit with a command format shown below.

Command format (0x7E len cmd param1 param2 0xEF)

Byte to send	Description
0x7E	Start of transmission (STX).
len	Byte count of the command string excluding STX and ETX bytes
cmd	This is the command byte to send
param1	1st parameter (optional)
param2	2nd parameter (optional)
0xEF	End of transmission (ETX)

The communication is a bidirectional data flow with equal priority: that means it is possible for you to program the MCU to transmit a command to HSC025A and get replies from it or, HSC025A initiates the communication by sending over its status and parameters to the MCU on an external trigger.

Example 1: The MCU sets HSC025A to Bluetooth mode

Command: 7E 03 0D 04 EF

Explanation:

MCU sending	Description
0x7E	STX
0x03	Byte count with STX and ETX excluded
0x0D	Command to switch operation mode
0x04	Bluetooth mode (param1=0x04 for Bluetooth, no param2 required)
0xEF	ETX

Sequence diagram:

Sequence above may keep rolling if there are more activities coming up. For example, an incoming call during music playback will trigger HSC025A to send 7E 03 50 29 EF to indicate a phone call with param1=0x29 followed by 7E 03 50 2A EF to resume music playback (param1=0x2A) when the call ends.

Example 2: User clicks and holds on the Volume-up key (via a resistor network wired to ADKEY pin) on HSC025A, in music playback mode

Commands: 7E 03 0E 06 EF 7E 03 0E 07 EF 7E 03 0E 08 EF

Explanation:

HSC025A sending	Description
0x7E	STX
0x03	Byte count
0x0E	Get current volume
param1	param1 = 0x06, 0x07, 0x08 as volume increases
0xEF	ETX

Sequence diagram:

Command Table

Public Commands

cmd (command byte in hex)	Function	MCU transmits in hex	HSC025A returns in hex
0x00	Mode switch in a round robin manner (Standby:0 USB:1 SD:2 Bluetooth:4 FM:5 REC:7 (REC not implemented)) Remarks: Device goes into standby mode (0) on power up.	7E 02 00 EF	The target mode to switch, e.g. 7E 03 0C 05 EF if FM radio is the target mode. Byte 0x0C is the command to get the current mode of operation with 0x05 as the parameter for FM radio. See command 0x0C below.
0x01	Playback from the location paused or restart from beginning Remark: (1) If audio was paused with a command 0x02 (see below), this command continues playback from the last location (2) If audio was stopped with a command 0x0A (see below), this command restarts playback from the beginning (3) MUTE pin set high on this command (4) EDR status also changed on this command	7E 02 01 EF	EDR status if Bluetooth is connected (see command 0x50 below)
0x02	Pause (during playback) Remark: (1) MUTE pin set low on this command (2) EDR status also changed on this command	7E 02 02 EF	EDR status if Bluetooth is connected (see command 0x50 below)
0x03	Next title/episode/FM station number	7E 02 03 EF	Return the target title for USB/SD or FM station number for radio. No return for Bluetooth.
0x04	Previous title/episode/FM station number	7E 02 04 EF	Return the target title for USB/SD or FM station number for radio. No return for Bluetooth.
0x05	Set volume up (0 - 30 in decimal)	7E 02 05 EF	Return the target volume after increment, e.g. 7E 03 0E 07 EF with 0x0E as the command to get current volume and 0x07 as the volume level (max 0x1E).
0x06	Set volume down (0 - 30 in decimal)	7E 02 06 EF	Return the target volume after decrement, e.g. 7E 03 0E 0F EF with 0x0E as the command to get current volume and 0x0F as the volume level (min 0x00).
0x07	Go to sleep (consumes less than 10mA). All commands disabled after this command except a wakeup command 0x08 Remarks: Sleep is not standby mode. In sleep mode, HSC025A does not accept new command except Wakeup 0x08, but in standby mode all new commands are accepted. Standby mode is the default state after power up.	7E 02 07 EF	7E 03 07 00 EF
0x08	Wakeup from sleep	7E 02 08 EF	7E 03 08 01 EF followed by the results of current mode request with automatic issuing of command 0x0C
0x09	Toggle between pause/play	7E 02 09 EF	-
0x0A	Stop playing and restart if it is followed by the playback command (0x01)	7E 02 0A EF	-
0x0B	Request if USB/SD card is available	7E 02 0B EF	7E 03 0B param1 EF param1 is the bitwise combination of USB:bit(0) and SD:bit(1) param1=1 if only USB mass storage is available param1=2 if only SD card is available param1=3 if both USB mass storage and a SD card are available
0x0C	Get the current mode of operation (Standby:0 USB:1 SD:2 Bluetooth:4 FM:5 REC:7)	7E 02 0C EF	7E 03 0C param1 EF param1=0 Standby param1=1 USB mode param1=2 SD card mode param1=4 Bluetooth mode param1=5 FM radio mode param1=7 Recorder mode (not implemented yet)
0x0D	Set a target operation mode (Standby:0 USB:1 SD:2 Bluetooth:4 FM:5 REC:7(not implemented))	7E 03 0D param1 EF (param1=0 for standby, 1 for USB, 4 for Bluetooth etc.)	Return the target mode of operation, e.g. 1) 7E 03 0C param1 EF param1=0 Standby param1=1 USB mode param1=2 SD card mode param1=4 Bluetooth mode param1=5 FM radio mode 2) optional: 7E 03 0C 04 EF + EDR status if the target mode is Bluetooth. See description below on command 0x50 for EDR status request
0x0E	Get current volume (0 - 30 in decimal)	7E 02 0E EF	7E 03 0E param1 EF to return the current volume level param1 = volume (0 - 30 in decimal), e.g. 7E 03 0E 0B EF to indicate a volume of 11 in decimal.
0x0F	Set volume to a target level (0 - 30 in decimal)	7E 03 0F param1 EF (param1= volume level from 0 to 30 in decimal)	7E 03 0E param1 EF to return the target volume, e.g. MCU sends 7E 03 0F 0D EF HSC025A returns 7E 03 0E 0D EF
0x10	Get firmware version	7E 02 10 EF	7E 03 10 12 EF for firmware version 1.2
0x11	Enable/disable ADKEY function for push button operation	7E 03 11 param1 EF (param1=0 to disable, 1 to enable) Default: 1	Echo the same command sent to HSC025A as an acknowledgement
0x15	Mute / Unmute audio Remarks: (1) Use this command with care in conjunction with pause/playback commands. This command works independent of the pause 0x02 and playback 0x01 commands. You may have forgot to unmute an audio before sending over a playback command with no audio output. This may lead to a playback malfunction confusion. (2) Send 7E 03 15 01 EF first to use this command (erratic)	7E 03 15 param1 EF (param1=0 mute, 1 to unmute)	Echo the same command sent to HSC025A with param1 negated, i.e. return 7E 03 15 01 EF when 7E 03 15 00 EF is sent to HSC025A and vice versa
0x16	System restart	7E 02 16 EF	7E 02 08 EF to indicate a normal operation status
0x17	System restore to factory settings (need system restart by power removal to take effect)	7E 02 17 EF	7E 02 08 EF to indicate a normal operation followed by 7E 03 0C 00 EF to indicate HSC025A in standby mode if there is no USB/SD media in slots
0x18	Set baud rate according to 0:9600, 1:19200, 2:38400, 3:115200, 4:256000 (need system restart by power removal to take effect)	7E 03 18 param1 EF (param1=0,1,2,3,4)	Echo the same command sent to HSC025A as an acknowledgement
0x19	Enable (1) / disable (0) priority playback from USB/SD card	7E 03 19 param1 EF (param1=0 to disable, 1 to enable) Default: 1	Echo the same command sent to HSC025A as an acknowledgement
0x1A	Enable (1) / disable (0) playback time return in an 1 sec interval. Only valid for USB/SD card playback	7E 03 1A param1 EF (param1=0 to disable, 1 to enable) Default: 0	Echo 7E 03 1A 00 EF as an acknowledgement when disable. Echo 7E 03 1A 01 EF followed by 7E 04 35 msb lsb EF with [msb:lsb] the higher byte and lower byte to indicate the playback time in seconds. This command is useful if a playback timer GUI is required.
0x1B	Enable (1) / disable (0) key press beep	7E 03 1B param1 EF (param1=0 to disable, 1 to enable) Default: 1	Echo the same command as an acknowledgement
0x1C	Enable (1) / disable (0) FM radio presence, i.e. no FM radio mode if param1 = 0	7E 03 1C param1 EF (param1=0 to disable, 1 to enable) Default: 1	Echo the same command as an acknowledgement
0x46	(USB/SD card mode only) Enable/disable automatic advance playback to the next title	7E 03 46 param1 EF (param1=0 to enable automatic advance, param1=1 disable ) Default: 0	Echo the same command as an acknowledgement
0x50	Get EDR Bluetooth status (valid in Bluetooth mode only)	7E 02 50 EF	7E 03 50 param1 EF param1=0x25 to indicate initialization in progress param1=0x26 waiting for connection param1=0x27 connecting param1=0x28 connected and waiting for phone call or music param1=0x29 in a phone call param1=0x2A in music playback
0x52	Return the MAC address of your HSC025A (valid in Bluetooth mode only)	7E 02 52 EF	MAC address in format 7E 08 52 xx xx xx xx xx xx EF (6 bytes)
0x54	Return the MAC address of the connected Bluetooth host (valid in Bluetooth mode only)	7E 02 54 EF	MAC address in format 7E 08 54 xx xx xx xx xx xx EF (6 bytes)
0x55	Return the name of Bluetooth device (valid in Bluetooth mode only)	7E 02 55 EF	7E 09 UHSC025A EF with UHSC025A being the ASCII representation
0x56	Return the name of Bluetooth host (e.g. your smart phone) connected (valid in Bluetooth mode only)	7E 02 56 EF	Echo the same command if no Bluetooth host is connected. Return the name of Bluetooth host connected in ASCII 7E len name EF if any with name being the ASCII representation
Invalid	Any invalid command	7E 02 xx EF Remark: xx is an invalid command	Any invalid command returns 7E 02 EE EF

Commands valid in mode of USB Mass Storage / SD card only

1. Automatic playback from an USB/SD media when it is slot in, in the order of the files in FAT/FAT32's file table. How files are sorted in a file system is more complex than we have thought. Interested readers may visit https://www.codeproject.com/Articles/95721/FAT-32-Sorter or https://superuser.com/questions/376577/how-to-reorder-the-files-of-a-fat32-file-system for further information
   
2. Format media in FAT or FAT32. No NTFS is allowed.
   
3. Supported file formats: MP3/WAV/WMA/FLAC/APE
   
4. Filenames in both ASCII and Unicode formats are supported
   
5. Both short and long filenames are supported
   
6. Comply with the following folder and filename conventions if you want to play designated audio files with UART commands:
   

• append a 4-digit prefix, e.g. 0001, 0002, 4678 say, for files in the root directory
  
• use a 3-digit folder name, e.g. 002, 232

• append a 3-digit prefix in the range of 000 - 255 for files in all folders

7. Sequential command is allowed, e.g. it is allowed to send over 7E 04 42 02 08 EF 7E 04 42 02 09 EF to preemptive playback two voice files 008.wav and 009.wav from the folder /002
   

cmd (command byte in hex)	Function	MCU transmits in hex	HSC025A returns in hex
0x30	Get playback status	7E 02 30 EF	7E 03 0C param1 EF param1=0 (Stop) param1=1 (Play) param1=2 (Pause) param1=3 (FF) param1=4 (FR)
0x31	Get current playback mode	7E 02 31 EF	7E 03 31 param1 EF param1=0 (all files in root and all folders are played repeatedly) param1=1 (reserve) param1=2 (repeat playing the current file) param1=3 (shuffle play) param1=4 (playback from root/current folder only)
0x32	Set playback mode	7E 03 32 param1 EF param1 = 0 (all files in root/all folders are played repeatedly) param1 = 1 (reserve) param1 = 2 (repeat playing the current file) param1 = 3 (shuffle play) param1 = 4 (playback from root/current folder only) Default: 0	Echo the same command as an acknowledgement
0x33	Get the order of the files in FAT/FAT32 file system, which is also the order of copying the files to a storage media Remarks: 1) order of files in FAT/FAT32 filesystem is not the number prefix in the filename as mentioned in point 5 above (filename conventions) 2) you may use a simple program, e.g. FAT Reader (http://public.bplaced.net/) to sort the FAT/FAT32 file order	7E 02 33 EF	7E 04 33 msb lsb EF [msb:lsb] returns the FAT/FAT32 order number (0x0001 - 0xFFFF) with msb the higher byte, lsb the lower byte
0x34	Get total number of audio files in the media Remark: only compatible audio files are counted	7E 02 34 EF	7E 04 34 msb lsb EF [msb:lsb] returns the total number of audio files in the media (all directories) in range 0x0001-0xFFFF with msb the higher byte, lsb the lower byte
0x35	Get current playback location in seconds	7E 02 35 EF	7E 04 35 msb lsb EF [msb:lsb] returns the current playback location in seconds with msb the higher byte, lsb the lower byte
0x36	Get the length of the current title in seconds	7E 02 36 EF	7E 04 36 msb lsb EF [msb:lsb] returns the length in seconds with msb the higher byte, lsb the lower byte Example: [msb:lsb] returns 0x02 0x58 to indicate a length of 600 seconds, i.e. 10 minutes
0x37	Return short filename in ASCII	7E 02 37 EF	7E len 37 ASCII EF Example: 7E 0E 37 2F 30 30 30 37 7E 31 20 20 4D 50 33 EF 0E = length of command, in this example the length is 14 bytes = len + cmd + ASCII length 37 = original command ASCII = 2F 30 30 30 37 7E 31 20 20 4D 50 33 = /0007~1 MP3
0x38	Return long filename in Unicode	7E 02 38 EF	7E len 38 Unicode EF Example: 7E 20 38 30 00 30 00 30 00 31 00 4B 00 61 00 6C 00 69 00 6D 00 62 00 61 00 2E 00 6D 00 70 00 33 00 EF 20= length of command, in this example the length is 32 bytes in decimal 38 = original command Unicode = 001Kalimba.mp3 = 30 00 30 00 30 00 31 00 4B 00 61 00 6C 00 69 00 6D 00 62 00 61 00 2E 00 6D 00 70 00 33 00 Remark: lower byte of 16-bit Unicode is sent first
0x3A	Navigate up/down a folder	7E 03 3A param1 EF (param1 = 00 to go up, param1 = 01 to go down)	1) 7E 03 0C param1 EF to return the current playback mode, USB (param1=01) or SD (param1=02) 2) 7E 04 33 msb lsb EF to return the target FAT/FAT32 file order number 3) 7E 03 0B param1 EF to return if USB/SD card is available, USB (param1=01), SD (02), or both (03)
0x3C	Get the number of folders in media	7E 02 3C EF	7E 04 3C msb lsb EF [msb:lsb] return the number of folders in media with msb the higher byte, lsb lower byte. Example: 7E 04 3C 00 02 EF indicates two folders in media
0x3D	Get the current folder number to play from	7E 02 3D EF	7E 04 3D msb lsb EF [msb:lsb] returns the current folder number to play from, with msb the higher byte, lsb lower byte
0x3F	Set which file to play with a FAT/FAT32 file order number	7E 04 3F msb lsb EF [msb:lsb] indicates the FAT/FAT32 file order number with msb the higher byte, lsb the lower byte	1) 7E 03 0C param1 EFto return the current playback mode, USB (param1=01) or SD (02) 2) 7E 04 33 msb lsb EFto return the target FAT/FAT32 file order number 3) 7E 03 0B param1 EF to return if USB/SD card is available, USB (param1=01), SD (02), or both (03)
0x40	Set which file to play with a number prefix in filename (if any)	7E 04 40 msb lsb EF [msb:lsb] indicates the number prefix in the filename with msb the higher byte, lsb the lower byte Example: 7E 04 40 12 46 EF to play the file "4678Sleep Away.mp3" with the 4-digit 4678 represented by its hex format1246 in command string Remark: (1) Need to set a 4-digit prefix (0001-9999) for files in the root directory if designated playback is required	1) 7E 03 0C param1 EF to return the current playback mode, USB (param1=01) or SD (02) 2) 7E 04 33 msb lsb EF to return the target FAT/FAT32 file order number 3) 7E 03 0B param1 EF to return if USB/SD card is available, USB (param1=01), SD (02), or both (03)
0x41	Set which file to play from a folder with a designated folder number and file number prefix (if any)	7E 04 41 folder# file# EF Remarks: 1) folder# ranges 0x00 - 0xFF (0-255 decimal) 2) file# ranges 0x00 - 0xFF (0-255 decimal) indicates the 3-digit prefix Example: 7E 04 41 02 06 EF to play the file ./002/006nombre.mp3	1) 7E 03 0C param1 EF to return the current playback mode, USB (param1=01) or SD (02) 2) 7E 04 33 msb lsb EF to return the target FAT/FAT32 file order number 3) 7E 03 0B param1 EF to return if USB/SD card is available, USB (param1=01), SD (02), or both (03)
0x42	Preemptive file playback from a folder. Resume playing the original file after preemptive playback.	7E 04 42 folder# file# EF Remark: folder# and file# follow the same definition in command 0x41 above	1) 7E 03 0C param1 EF to return the current playback mode, USB (param1=01) or SD (02) 2) 7E 04 33 msb lsb EF to return the target FAT/FAT32 file order number 3) 7E 03 0B param1 EF to return if USB/SD card is available, USB (param1=01), SD (02), or both (03)
0x43	Fast forward	7E 02 43 EF	7E 04 35 msb lsb EF Return location in seconds [msb:lsb] after fast forward
0x44	Fast rewind	7E 02 44 EF	7E 04 35 msb lsb EF Return location in seconds [msb:lsb] after fast rewind
0x45	Delete current file followed by playback next file Caution: Use this command with care!	7E 02 45 EF	7E 03 0C param1 EF to return current playback mode, USB (param1=01) or SD (02) 7E 04 33 msb lsb EF to return next playback order number 7E 03 0B param1 EF to return if USB/SD card is available

Commands valid in Bluetooth mode only

cmd (command byte in hex)	Function	MCU transmits in hex	HSC025A returns in hex
0x51	Set Bluetooth mode	FE 03 51 param1 EF param1 = 03 to disconnect Bluetooth connection 09 to disable Bluetooth discoverable 0A to enable Bluetooth discoverable 0B to disable Bluetooth connectable 0C to enable Bluetooth connectable 17 to pickup an incoming call 18 to hang up the connected phone call 19 to redial the last number called 24 to disconnect current call and pickup a second incoming call 25 to keep current call and pickup a second incoming call or switching between two calls 28 to refuse incoming call Following commands are valid in Bluetooth music playback mode (2A) only: 2C to toggle between playback and pause 2D to pause music 2E to stop playback (need to play from the host if replay is required after this command 2F to play next episode from the playlist (if any) 30 to play previous episode from the playlist (if any) 31 to fast forward 32 to fast rewind 44 to turn off Bluetooth radio 45 to turn on Bluetooth radio	1) Echo the same command as an acknowledgement 2) Optional: return Bluetooth status with public command 0x50 for EDR status
0x5B	Get telephone number of current / last phone call	7E 02 5B EF	7E len cmd [ASCII] EF Example, 7E 0A 5B 39 31 39 30 31 32 33 34 EF 0A = length of command string = len + cmd + sizeof(ASCII) 5B = command byte echo ASCII = phone number in ASCII characters = 91901234 in the example above
0x63	Set telephone number and place call	FE len 63 ASCII EF len = length of command string excluding STX and ETX 0x63 = command byte ASCII = telephone number in ASCII characters, e.g. 91901234	1) Echo the same command as an acknowledgement 2) 7E 03 50 29 EF to indicate an in-progress Bluetooth call

Commands valid in FM Radio only

cmd (command byte in hex)	Function	MCU transmits in hex	HSC025A returns in hex
0x80	Automatic station scan and save in the frequency range 87.5-108.0MHz	7E 02 80 EF	7E 04 8A msb lsb EF [msb:lsb] indicates the number of stations scanned and saved, e.g. 7E 04 8A 00 01 EF 7E 04 8A 00 02 EF ...7E 04 8A 00 07 EF shows a total number of 7 stations saved
0x81	Forward tune (87.5MHz > 108.0MHz) a station and save it if it has not been stored	7E 02 81 EF	-
0x82	Backward tune (108.0MHz > 87.5MHz) a station and save it if it has not been stored	7E 02 82 EF	-
0x85	Set a target frequency in unit of 100000Hz	7E 04 85 msb lsb EF 1) [msb:lsb] indicates the frequency in unit of 100000Hz, e.g. sending over 7E 04 85 03 ED EF to set a frequency of 100.5MHz 2) [msb:lsb] ranges 875 - 1080 (decimal)	Echo the same command as an acknowledgement
0x86	Get current radio frequency in unit of 100000Hz	7E 02 86 EF	7E 04 86 msb lsb EF 1) [msb:lsb] indicates the frequency in unit of 100000Hz, e.g. [msb:lsb] = 03:ED indicates a frequency of 100.5MHz 2) [msb:lsb] ranges 875 - 1080 (decimal)
0x89	Get current station number playing	7E 02 89 EF	7E 04 89 msb lsb EF 1) [msb:lsb] indicates the current station number playing 2) [msb:lsb] ranges 1-255 (decimal)
0x8A	Get the total number of station stored	7E 02 8A EF	7E 04 8A msb lsb EF 1) [msb:lsb] indicates the total number of stations stored 2) [msb:lsb] ranges 1-255 (decimal)
0x8B	Erase current station	7E 02 8B EF	7E 04 8A msb lsb EF 1) [msb:lsb] indicates the remaining number of stations after erase
0x8C	Erase all stations stored	7E 02 8C EF	7E 04 8A 00 00 EF

Evaluation Board

To facilitate the task to test HSC025A, I have designed an evaluation board with the following features:

1. Meandered printed inverted-F antenna with a matching network
2. Connection for FM radio antenna
3. Four push buttons connected in a resistor network to ADKEY pin for full operations
4. Onboard USB-to-UART bridge (CH340N) to test the UART commands
5. USB host type A and microSD card sockets for playing offline music files
6. Electret microphone to test Bluetooth phone call feature
7. Onboard 5W stereo amplifier (PAM8406) with screw terminals for R/L speakers
8. Onboard 4-pole, 3.5mm headphone jack with an automatic cut-off circuit for PAM8406
9. Expansion port in 2.54mm 2x5 pin headers for wiring up an MCU

Using the Evaluation Board

To kickstart, you may connect the board to a pair of speakers by screwing them to terminal J4 (right channel) and J3 (left channel). Since it is a 5W power amplifier on the PCB, the minimum ratings of your speakers should not be lower than 5W to avoid the chance of overloading them.

If there is no speaker yet, you may use a headphone too. The headphone jack is a 3.5mm jack wired in CTIA standard that is adopted by most Android devices and Apple as well.

Power up the board with 5V from a common smartphone charger or simply connect it to your PC through the microUSB socket J2 at the top right corner. UART communication is optional here so there is no need to install the driver for CH340N yet.

On power up the blue LED will turn on. Now click on the MODE button once.

Open your smartphone, rescan the Bluetooth menu and look for a new device HSC025A to start pairing

Congratulation! Now you have a new Bluetooth player.

Testing with UART Commands

To a developer of embedded systems like you and me, perhaps the most exciting experience is to learn and invent new gadgets from the hardware and firmware levels. Up to now, we have got a basic understanding on the hardware aspect. Before we can incorporate the chip in our novel Bluetooth player with a custom firmware, a thorough understanding on the context of UART communication is required. A handy tool is the USB-to-UART bridge (CH340N) on the evaluation board so that you may quickly type in some commands to test it from a keyboard. The procedures to start testing are stated here:

1. Make sure two 2.00mm jumpers are installed to complete the connections between CH340N and HSC025A

   

2. Download and install the driver for CH340N UART bridge from this hyperlink: http://www.wch-ic.com/downloads/category/30.html

   

3. Open Device Manager from your PC to make sure a new COM Port is enumerated. In my case it is COM93.

   

4. Pick your favorite serial communication program. I tried Docklight, TeraTerm, and YAT (Yet Another Terminal) and found Docklight (https://docklight.de/) and YAT (https://sourceforge.net/projects/y-a-terminal/) more applicable because both of them accept transmission of ASCII control characters such as 0x7E, 0xEF, 0x02, etc., that are essential in the command set but they are not typeable from standard keyboards. In my opinion, YAT is more user-friendly because it doesn't require to save every command before sending although it has the intermittent problem of missing incoming data in the terminal window. On the other hand, Docklight is very accurate in showing data flow but it requires every command to have saved before it is sent. By the way, you may toggle between the tools since both of them are free-to-use. From procedures below I will use YAT for illustration.

5. In YAT, open Terminal>Settings and apply settings as shown in screen capture below except the Serial Port number in your case should be different from mine. You need to match the Serial Port number to the enumerated port number in your Device Manager.

6. Continue by clicking on Advanced Settings button, disable ASCII Control Characters replacement option.

   

7. Now, in the Send Text box, try the first command \h (7E 03 0D 04 EF) and click Send Text (F3) button. On the Monitor window you will see the characters you sent (Tx) in blue and commands returned (Rx) in purple like screen capture below (don't forget to click on the 16 button to display characters in hex format.)

   

   Commands returned from HSC025A indicate the following status

   • 7E 03 0C 04 EF : get current operation mode cmd=0C with param1=04 for Bluetooth
   • 7E 03 50 26 EF : get Bluetooth EDR status cmd=50 with param1=26 to indicate that it is waiting for a connection
   • 7E 03 50 28 EF : get Bluetooth EDR status cmd=50 with param1=28 updated to indicate that it is connected and waiting for a call/music. It is automatically connected because in the last operation with buttons you have connected with the module once and the permission to connect has been memorized in your smart phone

What's next?

Add frequency response data and live tests

Schematic of a Reference Design

Footnotes

1. The SD bus allows dynamic configuration of the number of data lines from 1 to 4 bi-directional data signals (Kingston Technology 4900180-001.A00) ↩