Thing Innovations / MCP342x

Microchip MCP342x ADC library

mcp342x.cpp@3:03911aa07029, 2017-07-18 (annotated)

Committer:
antoniogonzalez
Date:
Tue Jul 18 09:43:27 2017 +0000
Revision:
3:03911aa07029
Parent:
1:c4da9889ff85
Child:
4:9480edf3926d
Typo fixed

Who changed what in which revision?

UserRevisionLine numberNew contents of line
antoniogonzalez 0:7dbf7356da6b 1 #include "mcp342x.h"
antoniogonzalez 0:7dbf7356da6b 2
antoniogonzalez 0:7dbf7356da6b 3 #define LEN_ONE_BYTE 1
antoniogonzalez 0:7dbf7356da6b 4
antoniogonzalez 0:7dbf7356da6b 5 MCP342x::MCP342x(I2C *i2c, uint8_t device_address)
antoniogonzalez 0:7dbf7356da6b 6 {
antoniogonzalez 1:c4da9889ff85 7 _i2c = i2c;
antoniogonzalez 1:c4da9889ff85 8
antoniogonzalez 0:7dbf7356da6b 9 // The address byte is the device code (4 bits, hardcoded in
antoniogonzalez 0:7dbf7356da6b 10 // factory) and the device address (3 bits). These are shifted one
antoniogonzalez 0:7dbf7356da6b 11 // bit to the left because mbed uses 8-bit addresses.
antoniogonzalez 0:7dbf7356da6b 12 _address = (_device_code << 4) | (device_address << 1);
antoniogonzalez 1:c4da9889ff85 13
antoniogonzalez 1:c4da9889ff85 14 // Initialise to default settings: channel 1, gain 1x, 12 bits.
antoniogonzalez 1:c4da9889ff85 15 // It is necessary to do this to ensure that the variables
antoniogonzalez 1:c4da9889ff85 16 // _resolution and _pga are properly set.
antoniogonzalez 1:c4da9889ff85 17 _configuration = 0x10;
antoniogonzalez 0:7dbf7356da6b 18 set_channel(CHANNEL_1);
antoniogonzalez 0:7dbf7356da6b 19 set_resolution(RESOLUTION_12);
antoniogonzalez 0:7dbf7356da6b 20 set_pga(PGA_1);
antoniogonzalez 0:7dbf7356da6b 21 }
antoniogonzalez 0:7dbf7356da6b 22
antoniogonzalez 0:7dbf7356da6b 23 void MCP342x::set_channel(mcp342x_channel_t channel)
antoniogonzalez 0:7dbf7356da6b 24 {
antoniogonzalez 1:c4da9889ff85 25 _configuration &= REG_CHANNEL_Clear;
antoniogonzalez 1:c4da9889ff85 26 _configuration |= channel << REG_CHANNEL_Pos;
antoniogonzalez 0:7dbf7356da6b 27 _write_configuration();
antoniogonzalez 0:7dbf7356da6b 28 }
antoniogonzalez 0:7dbf7356da6b 29
antoniogonzalez 0:7dbf7356da6b 30 void MCP342x::set_conversion_mode(mcp342x_conversion_mode_t mode)
antoniogonzalez 0:7dbf7356da6b 31 {
antoniogonzalez 1:c4da9889ff85 32 _configuration &= REG_MODE_Clear;
antoniogonzalez 1:c4da9889ff85 33 _configuration |= mode << REG_MODE_Pos;
antoniogonzalez 0:7dbf7356da6b 34 _write_configuration();
antoniogonzalez 0:7dbf7356da6b 35 }
antoniogonzalez 0:7dbf7356da6b 36
antoniogonzalez 0:7dbf7356da6b 37 void MCP342x::set_resolution(mcp342x_resolution_t resolution)
antoniogonzalez 0:7dbf7356da6b 38 {
antoniogonzalez 1:c4da9889ff85 39 _resolution = resolution;
antoniogonzalez 1:c4da9889ff85 40
antoniogonzalez 1:c4da9889ff85 41 // _lsb and _max_code are variables required for converting the ADC
antoniogonzalez 1:c4da9889ff85 42 // data into volts; see Section 4.9 of the MCP342x datasheet. Their
antoniogonzalez 1:c4da9889ff85 43 // value depends on the resolution chosen, so it is useful to
antoniogonzalez 1:c4da9889ff85 44 // calculate these values here, whenever the resolution setting is
antoniogonzalez 1:c4da9889ff85 45 // changed.
antoniogonzalez 1:c4da9889ff85 46 //
antoniogonzalez 1:c4da9889ff85 47 // _lsb is the magnitude (in volts) of the last significant byte,
antoniogonzalez 1:c4da9889ff85 48 // and it is calculated as 2 * 2.048 / (2^N), where N is the
antoniogonzalez 1:c4da9889ff85 49 // resolution (datasheet Eq. 4-3).
antoniogonzalez 1:c4da9889ff85 50 //
antoniogonzalez 1:c4da9889ff85 51 // _max_code is the maximum output code, and it is equal to
antoniogonzalez 1:c4da9889ff85 52 // 2^(N-1) - 1 (datasheet Table 4-3).
antoniogonzalez 1:c4da9889ff85 53 switch(_resolution){
antoniogonzalez 0:7dbf7356da6b 54 case RESOLUTION_12:
antoniogonzalez 1:c4da9889ff85 55 _lsb = 2 * 2.048 / 4096;
antoniogonzalez 1:c4da9889ff85 56 _max_code = 2047;
antoniogonzalez 0:7dbf7356da6b 57 break;
antoniogonzalez 0:7dbf7356da6b 58 case RESOLUTION_14:
antoniogonzalez 1:c4da9889ff85 59 _lsb = 2 * 2.048 / 16384;
antoniogonzalez 1:c4da9889ff85 60 _max_code = 8191;
antoniogonzalez 0:7dbf7356da6b 61 break;
antoniogonzalez 0:7dbf7356da6b 62 case RESOLUTION_16:
antoniogonzalez 1:c4da9889ff85 63 _lsb = 2 * 2.048 / 65536;
antoniogonzalez 1:c4da9889ff85 64 _max_code = 32767;
antoniogonzalez 0:7dbf7356da6b 65 break;
antoniogonzalez 0:7dbf7356da6b 66 case RESOLUTION_18:
antoniogonzalez 1:c4da9889ff85 67 _lsb = 2 * 2.048 / 262144;
antoniogonzalez 1:c4da9889ff85 68 _max_code = 131071;
antoniogonzalez 0:7dbf7356da6b 69 break;
antoniogonzalez 1:c4da9889ff85 70 }
antoniogonzalez 1:c4da9889ff85 71
antoniogonzalez 1:c4da9889ff85 72 _configuration &= REG_RESOLUTION_Clear;
antoniogonzalez 1:c4da9889ff85 73 _configuration |= _resolution << REG_RESOLUTION_Pos;
antoniogonzalez 0:7dbf7356da6b 74 _write_configuration();
antoniogonzalez 0:7dbf7356da6b 75 }
antoniogonzalez 0:7dbf7356da6b 76
antoniogonzalez 0:7dbf7356da6b 77 void MCP342x::set_pga(mcp342x_pga_t pga)
antoniogonzalez 0:7dbf7356da6b 78 {
antoniogonzalez 1:c4da9889ff85 79 // The gain value (1, 2, 4 or 8) is required for converting digital
antoniogonzalez 1:c4da9889ff85 80 // output codes to voltage. For this purpose the actual PGA value is
antoniogonzalez 1:c4da9889ff85 81 // kept in the variable _pga, instead of keeping the *position* in
antoniogonzalez 1:c4da9889ff85 82 // the register of PGA, which is what the variable type
antoniogonzalez 1:c4da9889ff85 83 // mcp342x_pga_t represents.
antoniogonzalez 1:c4da9889ff85 84 switch (pga) {
antoniogonzalez 0:7dbf7356da6b 85 case PGA_1:
antoniogonzalez 0:7dbf7356da6b 86 _pga = 1;
antoniogonzalez 0:7dbf7356da6b 87 break;
antoniogonzalez 0:7dbf7356da6b 88 case PGA_2:
antoniogonzalez 0:7dbf7356da6b 89 _pga = 2;
antoniogonzalez 0:7dbf7356da6b 90 break;
antoniogonzalez 0:7dbf7356da6b 91 case PGA_4:
antoniogonzalez 0:7dbf7356da6b 92 _pga = 4;
antoniogonzalez 0:7dbf7356da6b 93 break;
antoniogonzalez 0:7dbf7356da6b 94 case PGA_8:
antoniogonzalez 0:7dbf7356da6b 95 _pga = 8;
antoniogonzalez 0:7dbf7356da6b 96 break;
antoniogonzalez 1:c4da9889ff85 97 }
antoniogonzalez 1:c4da9889ff85 98
antoniogonzalez 1:c4da9889ff85 99 _configuration &= REG_PGA_Clear;
antoniogonzalez 1:c4da9889ff85 100 _configuration |= pga << REG_PGA_Pos;
antoniogonzalez 0:7dbf7356da6b 101 _write_configuration();
antoniogonzalez 0:7dbf7356da6b 102 }
antoniogonzalez 0:7dbf7356da6b 103
antoniogonzalez 0:7dbf7356da6b 104 void MCP342x::_write_configuration()
antoniogonzalez 0:7dbf7356da6b 105 {
antoniogonzalez 1:c4da9889ff85 106 _i2c_command[0] = _configuration;
antoniogonzalez 1:c4da9889ff85 107 _i2c->write(_address, _i2c_command, LEN_ONE_BYTE);
antoniogonzalez 0:7dbf7356da6b 108 }
antoniogonzalez 0:7dbf7356da6b 109
antoniogonzalez 1:c4da9889ff85 110 uint32_t MCP342x::read()
antoniogonzalez 0:7dbf7356da6b 111 {
antoniogonzalez 1:c4da9889ff85 112 uint32_t adc_value = 0;
antoniogonzalez 1:c4da9889ff85 113 _i2c->read(_address, _i2c_command, COMMAND_N_BYTES);
antoniogonzalez 0:7dbf7356da6b 114
antoniogonzalez 0:7dbf7356da6b 115 switch (_resolution) {
antoniogonzalez 1:c4da9889ff85 116 case RESOLUTION_12:
antoniogonzalez 1:c4da9889ff85 117 adc_value = (_i2c_command[0] << 8) | _i2c_command[1];
antoniogonzalez 0:7dbf7356da6b 118 adc_value &= 0xfff;
antoniogonzalez 0:7dbf7356da6b 119 break;
antoniogonzalez 0:7dbf7356da6b 120
antoniogonzalez 1:c4da9889ff85 121 case RESOLUTION_14:
antoniogonzalez 1:c4da9889ff85 122 adc_value = (_i2c_command[0] << 8) | _i2c_command[1];
antoniogonzalez 0:7dbf7356da6b 123 adc_value &= 0x3fff;
antoniogonzalez 0:7dbf7356da6b 124 break;
antoniogonzalez 0:7dbf7356da6b 125
antoniogonzalez 1:c4da9889ff85 126 case RESOLUTION_16:
antoniogonzalez 1:c4da9889ff85 127 adc_value = (_i2c_command[0] << 8) | _i2c_command[1];
antoniogonzalez 0:7dbf7356da6b 128 adc_value &= 0xffff;
antoniogonzalez 0:7dbf7356da6b 129 break;
antoniogonzalez 0:7dbf7356da6b 130
antoniogonzalez 1:c4da9889ff85 131 case RESOLUTION_18:
antoniogonzalez 1:c4da9889ff85 132 adc_value = (_i2c_command[0] << 16) |
antoniogonzalez 1:c4da9889ff85 133 (_i2c_command[1] << 8) | _i2c_command[2];
antoniogonzalez 0:7dbf7356da6b 134 adc_value &= 0x3ffff;
antoniogonzalez 0:7dbf7356da6b 135 break;
antoniogonzalez 0:7dbf7356da6b 136 }
antoniogonzalez 0:7dbf7356da6b 137 return adc_value;
antoniogonzalez 0:7dbf7356da6b 138 }
antoniogonzalez 1:c4da9889ff85 139
antoniogonzalez 1:c4da9889ff85 140 float MCP342x::read_volts(){
antoniogonzalez 1:c4da9889ff85 141 float volts = 0.0;
antoniogonzalez 1:c4da9889ff85 142 uint32_t adc_value = read();
antoniogonzalez 1:c4da9889ff85 143
antoniogonzalez 1:c4da9889ff85 144 // The digital output of the MCP342x is in two's complement format;
antoniogonzalez 1:c4da9889ff85 145 // see datasheet Section 4.9. This 'if... else' construction
antoniogonzalez 1:c4da9889ff85 146 // determines whether the digital code is negative or positive; if
antoniogonzalez 3:03911aa07029 147 // it is the former, its two's complement is calculated.
antoniogonzalez 1:c4da9889ff85 148 if (adc_value > _max_code) {
antoniogonzalez 1:c4da9889ff85 149 // if the output code is negative...
antoniogonzalez 1:c4da9889ff85 150 volts = (~adc_value & _max_code) + 1;
antoniogonzalez 1:c4da9889ff85 151 volts *= -1;
antoniogonzalez 1:c4da9889ff85 152 } else {
antoniogonzalez 1:c4da9889ff85 153 // if the output code is positive...
antoniogonzalez 1:c4da9889ff85 154 volts = (float)adc_value;
antoniogonzalez 1:c4da9889ff85 155 }
antoniogonzalez 1:c4da9889ff85 156
antoniogonzalez 1:c4da9889ff85 157 // The actual voltage is proportional to the resolution and PGA
antoniogonzalez 1:c4da9889ff85 158 // settings. This equation corresponds to Equation 4-4 in the
antoniogonzalez 1:c4da9889ff85 159 // datasheet. The variables _lsb and _pga are calculated whenever
antoniogonzalez 1:c4da9889ff85 160 // the user changes the resolution or PGA parameters.
antoniogonzalez 1:c4da9889ff85 161 return volts * _lsb / _pga;
antoniogonzalez 1:c4da9889ff85 162 }