MCP3221.cpp

00001 
00002 #include "MCP3221.h"
00003 
00004 //Create instance
00005 MCP3221::MCP3221(PinName sda, PinName scl, float supplyVoltage) : i2c(sda, scl), _supplyVoltage(supplyVoltage)
00006 {
00007 }
00008 
00009 //destroy instance
00010 MCP3221::~MCP3221()
00011 {
00012 }
00013 
00014 float MCP3221::read()
00015 {
00016 
00017 //You cannot write to an MCP3221, it has no writable registers.
00018 //MCP3221 also requires an ACKnowledge between each byte sent, before it will send the next byte. So we need to be a bit manual with how we talk to it.
00019 //It also needs an (NOT) ACKnowledge after the second byte or it will keep sending bytes (continuous sampling)
00020 //
00021 //From the datasheet.
00022 //
00023 //I2C.START
00024 //Send 8 bit device/ part address to open conversation.   (See .h file for part explanation)
00025 //read a byte (with ACK)
00026 //read a byte (with NAK)
00027 //I2C.STOP
00028 
00029 
00030   //  char data[2];
00031 
00032     i2c.start();
00033     int acknowledged = i2c.write(MCP3221_CONVERSE); //send a byte to start the conversation. It should be acknowledged.
00034     _data[0] = i2c.read(1);  //read a byte. acknowledge when we have it.
00035     _data[1] = i2c.read(0);  //read the second byte. (n)acknowledge when we have it to stop the flow.
00036     i2c.stop();
00037  
00038     //convert to 12 bit.
00039     short res;
00040     int _12_bit_var; // 2 bytes
00041     char _4_bit_MSnibble = _data[0]; // 1 byte, example 0000 1000
00042     char _8_bit_LSByte = _data[1];   // 1 byte, example 1111 0000
00043 
00044     _12_bit_var = ((0x0F & _4_bit_MSnibble) << 8) | _8_bit_LSByte;   //example 100011110000
00045     res=_12_bit_var;
00046 
00047     return  (_supplyVoltage/4096) * res;
00048 
00049 }
00050