RC2 Decoder sound / voice playback
What is it?
It’s an very simple, only 2 resistors and 1 condensator, sound playback. And it sounds amazing good, check the TheFinalResult.mp3 file.This is based on an article by Mariano Barron in the Circuit Cellar #180 July 2005. Due the copyright I can’t publish the article here. You can buy your copy at the Circuit Cellar website.
The software we need to encode the WAV files is free available from the Circuit cellar ftp server, in this file there is also a short description how it works.With the Rc Sound Encoder software we compress the WAV to RC2 coding. This coding will be stored in eeprom and played back with this simple “Soundcard” Every sample requires only 1 bit, so for 1 second 44,1kHz sound we need 2726 Bytes storage space. It’s not much but for most MCU too much to store in the flash or internal eeprom. Therefore we store the sound samples in an external i2c eeprom.
Schematic is very simple. I’m using a Mega128 running on 16MHz. I2c eeprom (24c256) is connected with the hardware i2c (scl/sda). Software i2c will not work, this is to slow, maybe it will work with 22050hz samples but I didn’t try that.In the upper right corner we have the Rc2 decoder and optional an low pass filter and a simple amplifier.
Even the timer isr calculation is simple Crystal/prescaler/sample rate = 16000000/1/44100 = 362 = &H016A .
If you like to use an other sample rate or crystal you need to recalculate the timer.
The document RC2-Howto.pdf describes how to make your own Eeprom file with your sound or speech, this document can be found in the Zip file. The zip contains also the used WAV files, the ready to run demo Eeprom hex file and some ASM files.
In all the routines are 16bits addressing used, therefore it’s not possible to use Eeprom’s larger then 512KB. If you change the routines you can use more then one 512KB i2c eeprom (you can hook up 4 to 1 i2c bus), but the RC-coder software uses also 16bits addresses and that’s something that we cannot change.
- Sound edit software, Windows sound recorder will do, but there’s always better
- RC Sound encoder ftp://ftp.circuitcellar.com/pub/Circuit_Cellar/2005/180/Barron180.zip
- Atmel Avr studio 4 www.atmel.com
- I2C Eeprom programmer including software or my programmer written in Bascom
- DIY Do it yourself package incl. Bascom source code, used WAV samples and DIY.pdf
Code is written and tested in Bascom 220.127.116.11.001 license.
'------------------------------------------------------------------ ' R2C Decoder voice playback ' Playback sound and voice with very simple hardware 2xR 1xC ' By Evert Dekker 2008 R2CDecoder@Evertdekker dotje com ' Created with Bascom-Avr: 18.104.22.168.100 '------------------------------------------------------------------ $regfile = "m128def.DAT" $crystal = 16000000 $baud = 19200 $hwstack = 50 $swstack = 50 $framesize = 40 $lib "I2C_TWI.LBX" 'Setting up i2c hardware bus Config Twi = 400000 'Hardware i2c bus speed Config Scl = Portd.0 'TWI (i2c) ports on the Mega128 Config Sda = Portd.1 Const Addressw = &B10100000 'slave write address eeprom Const Addressr = &B10100001 'slave read address eeprom Vp1 Alias Porta.1 'Voice pin 1 Vp2 Alias Porta.2 'Voice pin 2 Config Porta.1 = Output Config Porta.2 = Output Config Timer1 = Timer , Prescale = 1 , Compare A = Set , Clear Timer = 1 'Setting up the timer Compare1a = &H016A 'Timer1 comparator Enable Interrupts Enable Compare1a On Compare1a Timer1_int Stop Timer1 'Stop the timer, not yet needed '==== Declaration Declare Sub Read_eeprom_word(byval Adress As Word , Valueword As Word) Declare Sub Playsample(byval Sample As Byte) Declare Sub Read_eeprom_index Dim Samples As Word , Start_byte(10) As Word , Lenght(10) As Word 'If you have more then 10 voices programmed, then incr this here. Dim Bytetodo As Word , Outbyte As Byte Dim Temp As Byte , Tempw As Word , Lus As Byte Dim Bitcount As Byte , Tempadress2 As Byte '=== Main === Do Read_eeprom_index 'Read the eeprom index because we need to know number of samples, startadress and lenght Print Samples ; " Samples present in the eeprom" For Lus = 1 To Samples Print Lus ; "e sample start at eeprom adress: &H" ; Hex(start_byte(lus)) ; " is &H" ; Hex(lenght(lus)) ; " bytes long." Next For Wait 3 For Lus = 1 To Samples Playsample Lus Wait 1 Next Lus Loop End '=== Sub routines === Sub Playsample(byval Sample As Byte) Bytetodo = Lenght(sample) 'Number of bytes to be processed Tempw = Start_byte(sample) * 2 'Index is in word, need now bytes so *2 I2cstart 'Generate start I2cwbyte Addressw Tempadress2 = High(tempw) 'High(adress) I2cwbyte Tempadress2 'highbyte adress of EEPROM Tempadress2 = Low(tempw) I2cwbyte Tempadress2 'lowbyte adress of EEPROM I2cstart 'repeated start I2cwbyte Addressr Start Timer1 'Start the timer and therefore the playback Do If Bitcount = 7 Then '1 byte processed I2crbyte Outbyte , Ack 'Read byte from eeprom Decr Bytetodo '1 byte less todo Bitcount = 0 'Reset bits processed End If Loop Until Bytetodo = 0 'Do until all the bytes from the sample are processed Stop Timer1 'Ready stop the timer I2crbyte Temp , Nack 'read extra byte with Nack to finish the i2c bus I2cstop 'Stop i2c Vp2 = 0 : Vp1 = 0 'Silence the voice pins End Sub Timer1_int: Vp2 = Vp1 'Voice pin2 is the previous setting of voice pin1 If Bitcount > 0 Then Shift Outbyte , Right , 1 'shift the bits out Vp1 = Outbyte.0 'Set voice pin1 Incr Bitcount 'Next bit Return Sub Read_eeprom_index 'Find the start adresse of each Voice. Adress is stored as word Read_eeprom_word 0 , Samples '1e Byte in the eeprom contens the number of programmed samples and is the low byte of the first sample Temp = Low(samples) : Temp = Temp -1 ' For Lus = 0 To Temp 'Loop the number of Samples found Tempw = Lus * 2 'Reading words, so steps 2 Read_eeprom_word Tempw , Start_byte(lus + 1) 'Read the start adres of the samples Tempw = Start_byte(lus + 1) Tempw = Tempw * 2 'Reading words, so steps 2 Read_eeprom_word Tempw , Lenght(lus + 1) 'Read the lenght of the sample from the eeprom Rotate Lenght(lus + 1) , Left , 8 'Msb and Lsb are inverted so swap them Next Lus End Sub Sub Read_eeprom_word(byval Adress As Word , Valueword As Word) Local Tempadress As Byte , Valueh As Byte , Valuel As Byte, I2cstart 'generate start I2cwbyte Addressw 'slave adsress Tempadress = High(adress) I2cwbyte Tempadress 'highbyte adress of EEPROM Tempadress = Low(adress) I2cwbyte Tempadress 'lowbyte adress of EEPROM I2cstart 'repeated start I2cwbyte Addressr 'slave address (read) I2crbyte Valuel , Ack 'read byte I2crbyte Valueh , Nack I2cstop 'generate stop Valueword = Makeint(valuel , Valueh) End Sub