Audio Annunciator over RS485 Network

I felt a need to add annunciating facility to my Home Automation network, so I came up with this solution. The very basic idea is to play an audio segment of choice over RS485 network. For this I made use of a Serially Addressable MP3 playback module –WTM-SD. Audio for annunciation purposes are stored in the On-board SD (up to 2 GB) card which is inserted in this module, in mp3 format.

Features –

1. ·        Single Supply Operation. 8 ~ 12V AC/DC
2. ·        On-board stereo amplifier to drive the speaker directly.
3. ·        PWR ON  BUSY and ACTIVITY/RX Indicator LEDs
4. ·        On-board volume Control POT for adjusting the audio level.
5. ·        On-board 5V regulator to supply regulated Power to the Board.
6. ·        Packet Protocol @ 9600 baud Rate.

Something about the MP3 Module –

The Model number of this module is WTM-SD and has four control modes of operation - Standard mode(mp3 mode), Key mode, Parallel mode, Serial mode.  We would be using the Serial mode for this project. This module safely operates on 5V DC, so there’s no need for a separate power source on the PCB. Standard Serial protocol @ 9600 baud rate applies to control this module. A busy pin Indicator is available , should you wish to use. I have used it , but yet have not found a reason to apply it (make use of it). A total of 9 operating codes are available to control various functions of this module and some, if not all, have been used in this project.

The MP3 module has 3 LED , to indicate if the Module has Supply, a Busy Indicator - when the Module is playing audio and a SD Card Detect indicator to display when a inserted SD Card is recognized / detected by the Module itself. So when Powered on the PWR ON and the SD Card Indicator should light up.

Audio clips (files) are saved on the SD card in folders with specific name like advert01, advert02 and so on. A total of 99 folders are possible for use by the module, limited by the SD card capacity. Files have to be in mp3 format only having file names like 001.mp3, 002.mp3 , so on. A total of 999 files can be stored in each folder, again limited by the capacity of the SD card , used. There’s no limit on the length/duration of the audio clip that could be used. A must, the first folder (minimum) “advert01” must have a configuration file , which decides the Control mode that is used by this module. This is nothing but an ASCII file with the file name – cof.mp3 followed by a configuration number. 1 – Standard Mode, 2 – Key Mode, 3 – Parallel Mode. We use the standard mode. I don’t know why, but Serial Mode does not have a number and can be addressed directly. But without this Config file in Standard mode the module does not operate. Once this file is made and stored on the SD card, it will show up as a audio file , because of its mp3 extension, which is not a worry.

Operation –

This board operate on a similar line protocol followed by its predecessor. A complete protocol summary is listed here.

PROTOCOL SUMMARY SHEET
ADDR	CMD	PARA	RESPONSE
XXX	XXX	XXX	PLAY >  FOLDER NO. + MSG NO.
XXX	100	0	STOP PLAY
XXX	101	0	PAUSE PLAY
XXX	102	0	START PLAY FROM PAUSE
XXX	103	X	CHANGE VOLUME (0-8)
XXX	104	0	QUERRY VOL
XXX	105	0	QUERRY FOLDER
XXX	106	XX	CHANGE MAX. FOLDER - MAX. 99
XXX	107	0	QUERRY BUSY PIN
XXX	110	XXX	PLAY BACKGROUND AUDIO
XXX	111	0	PAUSE BACKGROUND AUDIO PLAY
XXX	112	0	REPLAY FROM PAUSE - BACKGROUND AUDIO
XXX	113	0	STOP PLAY - BACKGROUND AUDIO
XXX	250	XXX	CHANGE NODE ADDRESS
XXX	251	0	Querry Product ID
XXX	252	0	Querry Product Firmware
XXX	253	123	RESET Board to Default Setting
123	254	255	Display Board Details
123	255	255	BOARD RESET/RE-START
PRODUCT ID:		228	MP3 ANNUNCIATOR MODULE

The Node/Slave address of this Board at start is 228. You can change this if you wish like using appropriate command structure shown above. Default Volume Level is 4 and Default Folder is 1 When a Query command is issued , it generates a response which is sent back. Try and avoid it as it could cause a clash on the network. These are used only during configuration of this module , when this module is singly connected with a PC during configuration.

For example if you wish to play a voice clip “002.mp3” in folder “advert01” on the SD Card at address 228, then packet sent , should be  AT228001002<CR> on the network. This information is shown if you want to create an application to address this module on your own. To STOP PLAY, you issue a packet AT228100000<CR> . Please remember that the maximum Folders that can be allowed on the SD card are 99 and each folder can have a maximum of 999 audio clips. I must admit that I have not tried the Background Music option available on the MP3 Module, but I have provided a provision for use, should any of you’ll plan to use. You could try the options individually , by connecting this module separately to a PC and issuing individual commands using a Terminal and the USB <> RS485 Bridge PCB. .Remember the baud rate is @9600.

Power is applied at connector CN3 which should safely be between 8 ~ 12V AC/DC. D1 is the Power On Indicator on the Board. LED D2 is an Activity Indicator and blinks whenever a valid transmission is detected over the Network. D3 LED is a Busy Signal indicator, which lights up when an audio is being played / trigged. RS485 Network cable connects at connector marked CN2 on the PCB. Please remember to insert a jumper at J1 if this node is the last component on your Network. This is the RS485 Termination link jumper. CN1 is a ISP connector which is an optional component. Speakers are connected at connector marked CN4 on the PCB. Any 8 ohm 1W speaker would do. If you want more power, connect this output to your PA system. If assembling , remember there are 5 jumpers on the PCB, assemble them first. CN5 marked on the PCB can be omitted. Always remember to write down the present Node address on the White Band available on the PCB. This will help you answer or address the module with its address information.

Application –

I see a lot of use of this module operated over RS485 network. One such idea was a Remote Call Bell to be fitted in a PANTRY area having customized audio messages. This application would involve 1 Slave unit , which is this PCB and many Masters , encoding required triggering option. Another Application would be a Nurse Call Bell, where by a deserving patient gathers the attention of a Nurse / Maid with Voice. When a Master with an RTC Clock is introduced over a RS485 system, it can be programmed to annunciate different audio messages at a particular time on different SLAVEs of this type. In a Fire/Security Alarm system for Remote Annunciation. It can also be used in Annunciating purposes in Elevator systems. Keep thinking and let me know……………

  

RS485 Aunnunciator Board
Sr.No.	Qty.	Ref.	Value
1	1	BR1	W04M
2	1	CN1	6 pin Bergh Pin (Optional)
3	2	CN2,CN4	3 PIN PBT CONNECTOR
4	1	CN3	2 PIN PBT CONNECTOR
5	1	CN5	7 PIN BERGH PIN (OPTIONAL)
6	7	C1,C2,C5,C7,C10,C14,C16	100N
7	1	C3	1000uF/25V
8	4	C4,C6,C9,C15	100uF/25V
9	2	C8,C13	220uF/25V
10	2	C11,C12	4u7F
11	3	D1,D2,D3	LED
12	1	J1	JUMPER + CLOSER
13	2	R3,R9	10K
14	1	P1	PCB MOUNTED DUAL GANG POT
15	3	R1,R2,R10	470E
16	2	R4,R7	1K
17	2	R5,R6	10E
18	1	R8	120E
19	2	R11,R12	4E7
20	1	U1	12F1840
21	1	U2	7805
22	1	U3	SN75176
23	1	U4	PC817
24	1	U5	WTM-SD + 2Gb SD Card
25	1	U6	TDA2822
26	3		8 PIN IC SOCKET
27	1		11x2 Row Female Connector for MP3 Module