MCP3021.cpp

00001 #include "MCP3021.h"
00002  
00003 //Create instance
00004 MCP3021::MCP3021(PinName sda, PinName scl, float supplyVoltage) : i2c(sda, scl), _supplyVoltage(supplyVoltage) {
00005 }
00006  
00007 //destroy instance
00008 MCP3021::~MCP3021() {
00009 }
00010  
00011 float MCP3021::read() {
00012  
00013 //You cannot write to an MCP3021, it has no writable registers.
00014 //MCP3021 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.
00015 //It also needs an (NOT) ACKnowledge after the second byte or it will keep sending bytes (continuous sampling)
00016 //
00017 //From the datasheet.
00018 //
00019 //I2C.START
00020 //Send 8 bit device/ part address to open conversation.   (See .h file for part explanation)
00021 //read a byte (with ACK)
00022 //read a byte (with NAK)
00023 //I2C.STOP
00024  
00025  
00026   //  char data[2];
00027  
00028     i2c.start();
00029     int acknowledged = i2c.write(MCP3021_CONVERSE); //send a byte to start the conversation. It should be acknowledged.
00030     _data[0] = i2c.read(1);  //read a byte. acknowledge when we have it.
00031     _data[1] = i2c.read(0);  //read the second byte. (n)acknowledge when we have it to stop the flow.
00032     i2c.stop();
00033  
00034     //convert to 12 bit.
00035     short res;
00036     int _10_bit_var; // 2 bytes
00037     char _4_bit_MSnibble = _data[0]; // 1 byte, example 0000 1000
00038     char _6_bit_LSByte = _data[1];   // 1 byte, example 1111 0000
00039  
00040     _10_bit_var = ((0x0F & _4_bit_MSnibble) << 6) | _6_bit_LSByte >> 2;   //example 100011110000
00041     res = _10_bit_var;
00042  
00043     return  (_supplyVoltage / 1024) * res;
00044  
00045 }