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I2C 2 channels digital volume controller IC PT2257 : 

Datasheet

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 /*  
 PT2257 - Electronic Volume Controller IC  
 Datasheet - http://www.princeton.com.tw/Portals/0/Product/PT2257.pdf  
 Pinout  
   |-----_-----|  
 1 -| Lin  Rin |- 8  
 2 -| Lout Rout |- 7  
 3 -| Gnd  V+ |- 6  
 4 -| SDA  SCL |- 5  
   |-----------|  
 The interface protocol consists of the following:  
 • A Start bit  
 • A Chip Address byte=88H 10001000  
 • ACK=Acknowledge bit  
 • A Data byte  
 • A Stop bit  
 Max. clock speed=100K bits/s  
 FUNCTION BITS  
 MSB  2  3  4  5  6  7  LSB Function  
 ----------------------------------------------------------------------------------------  
  1  1  1  1  1  1  1  1  Function OFF (-79dB)  
  1  1  0  1  A3  A2  A1  A0  2-Channel, -1dB/step  
  1  1  1  0  0  B2  B1  B0  2-Channel, -10dB/step  
  1  0  1  0  A3  A2  A1  A0  Left Channel, -1dB/step  
  1  0  1  1  0  B2  B1  B0  Left Channel, -10dB/step  
  0  0  1  0  A3  A2  A1  A0  Right Channel, -1dB/step  
  0  0  1  1  0  B2  B1  B0  Right Channel, -10dB/step  
  0  1  1  1  1  0  0  M  2-Channel MUTE (M=1 -> MUTE=ON / M=0 -> MUTE=OFF)  
 ATTENUATION UNIT BIT  
  A3  AB2 AB1 AB0 ATT(-1) ATT(-10)  
  0  0  0  0   0   0  
  0  0  0  1  -1  -10  
  0  0  1  0  -2  -20  
  0  0  1  1  -3  -30  
  0  1  0  0  -4  -40  
  0  1  0  1  -5  -50  
  0  1  1  0  -6  -60  
  0  1  1  1  -7  -70  
  1  0  0  0  -8  
  1  0  0  1  -9  
 */  
 #include <Wire.h>  
 void setup() {  
  Serial.begin(9600);  
  Serial.println("pt2257 Ampli");  
  Wire.begin();  
  delay(200);  
 }  
 void loop() {  
  Wire.beginTransmission(0x44);  
  Serial.println("Set attenuation");  
  Wire.write(0b011100000);  // set low attenuation  
  delay(200);  
  Wire.endTransmission();  
  delay(5000);  
  Wire.beginTransmission(0x44);  
  Serial.println("Set very attenuation");  
  Wire.write(0b011100001);  // set very low attenuation  
  delay(200);  
  Wire.endTransmission();  
  delay(5000);  
  Wire.beginTransmission(0x44);  
  Serial.println("Set very very attenuation");  
  Wire.write(0b011100011);  // set very low attenuation  
  delay(200);  
  Wire.endTransmission();  
  delay(5000);  
  Wire.beginTransmission(0x44);  
  Serial.println("Set very very very attenuation: ");  
  Wire.write(0b011100111);  // set very low attenuation  
  delay(200);  
  Wire.endTransmission();  
  delay(5000);  
  /*  
  Wire.beginTransmission(0x44);  
  Serial.println("set full attenuation ");  
  Wire.write(0b111111111);  // set very low attenuation  
  delay(200);  
  Wire.endTransmission();  
  delay(5000);  
  */  
 }