Reiko Randoja / MCP3021

MCP3021

Dependents:   Telliskivi2_2014

MCP3021.cpp@0:423652b49d07, 2014-09-02 (annotated)

Committer:
Reiko
Date:
Tue Sep 02 15:34:15 2014 +0000
Revision:
0:423652b49d07
Initial commit

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Reiko 0:423652b49d07 1 #include "MCP3021.h"
Reiko 0:423652b49d07 2
Reiko 0:423652b49d07 3 //Create instance
Reiko 0:423652b49d07 4 MCP3021::MCP3021(PinName sda, PinName scl, float supplyVoltage) : i2c(sda, scl), _supplyVoltage(supplyVoltage) {
Reiko 0:423652b49d07 5 }
Reiko 0:423652b49d07 6
Reiko 0:423652b49d07 7 //destroy instance
Reiko 0:423652b49d07 8 MCP3021::~MCP3021() {
Reiko 0:423652b49d07 9 }
Reiko 0:423652b49d07 10
Reiko 0:423652b49d07 11 float MCP3021::read() {
Reiko 0:423652b49d07 12
Reiko 0:423652b49d07 13 //You cannot write to an MCP3021, it has no writable registers.
Reiko 0:423652b49d07 14 //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.
Reiko 0:423652b49d07 15 //It also needs an (NOT) ACKnowledge after the second byte or it will keep sending bytes (continuous sampling)
Reiko 0:423652b49d07 16 //
Reiko 0:423652b49d07 17 //From the datasheet.
Reiko 0:423652b49d07 18 //
Reiko 0:423652b49d07 19 //I2C.START
Reiko 0:423652b49d07 20 //Send 8 bit device/ part address to open conversation. (See .h file for part explanation)
Reiko 0:423652b49d07 21 //read a byte (with ACK)
Reiko 0:423652b49d07 22 //read a byte (with NAK)
Reiko 0:423652b49d07 23 //I2C.STOP
Reiko 0:423652b49d07 24
Reiko 0:423652b49d07 25
Reiko 0:423652b49d07 26 // char data[2];
Reiko 0:423652b49d07 27
Reiko 0:423652b49d07 28 i2c.start();
Reiko 0:423652b49d07 29 int acknowledged = i2c.write(MCP3021_CONVERSE); //send a byte to start the conversation. It should be acknowledged.
Reiko 0:423652b49d07 30 _data[0] = i2c.read(1); //read a byte. acknowledge when we have it.
Reiko 0:423652b49d07 31 _data[1] = i2c.read(0); //read the second byte. (n)acknowledge when we have it to stop the flow.
Reiko 0:423652b49d07 32 i2c.stop();
Reiko 0:423652b49d07 33
Reiko 0:423652b49d07 34 //convert to 12 bit.
Reiko 0:423652b49d07 35 short res;
Reiko 0:423652b49d07 36 int _10_bit_var; // 2 bytes
Reiko 0:423652b49d07 37 char _4_bit_MSnibble = _data[0]; // 1 byte, example 0000 1000
Reiko 0:423652b49d07 38 char _6_bit_LSByte = _data[1]; // 1 byte, example 1111 0000
Reiko 0:423652b49d07 39
Reiko 0:423652b49d07 40 _10_bit_var = ((0x0F & _4_bit_MSnibble) << 6) | _6_bit_LSByte >> 2; //example 100011110000
Reiko 0:423652b49d07 41 res = _10_bit_var;
Reiko 0:423652b49d07 42
Reiko 0:423652b49d07 43 return (_supplyVoltage / 1024) * res;
Reiko 0:423652b49d07 44
Reiko 0:423652b49d07 45 }