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@dariosalvi78
Created May 2, 2017 19:24
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Simple library for ADS1256 to be used by Arduino. It does not implement the whole set of features, but can be used as a starting point.
/* ADS1256 simple library for Arduino
ADS1256, datasheet: http://www.ti.com/lit/ds/sbas288j/sbas288j.pdf
connections to Atmega328 (UNO)
CLK - pin 13
DIN - pin 11 (MOSI)
DOUT - pin 12 (MISO)
CS - pin 10
DRDY - pin 9
RESET- pin 8 (or tie HIGH?)
DVDD - 3V3
DGND - GND
*/
#define ADS_SPISPEED 1250000
#define ADS_RST_PIN 8 //ADS1256 reset pin
#define ADS_RDY_PIN 9 //ADS1256 data ready
#define ADS_CS_PIN 10 //ADS1256 chip select
// 11, 12 and 13 are taken by the SPI
void initADS(){
pinMode(ADS_CS_PIN, OUTPUT);
pinMode(ADS_RDY_PIN, INPUT);
pinMode(ADS_RST_PIN, OUTPUT);
digitalWrite(ADS_RST_PIN, LOW);
delay(1); // LOW at least 4 clock cycles of onboard clock. 100 microsecons is enough
digitalWrite(ADS_RST_PIN, HIGH); // now reset to deafult values
delay(150);
digitalWrite(ADS_CS_PIN, LOW); // select ADS
delayMicroseconds(50);
while (digitalRead(ADS_RDY_PIN)) {} // wait for ready_line to go low
SPI.beginTransaction(SPISettings(ADS_SPISPEED, MSBFIRST, SPI_MODE1));
delayMicroseconds(10);
//Reset to Power-Up Values (FEh)
SPI.transfer(0xFE);
delayMicroseconds(100);
byte status_reg = 0 ; // address (datasheet p. 30)
byte status_data = 0x01; //status: Most Significant Bit First, Auto-Calibration Disabled, Analog Input Buffer Disabled
//0x03; //to activate buffer
SPI.transfer(0x50 | status_reg);
SPI.transfer(0x00); // 2nd command byte, write one register only
SPI.transfer(status_data); // write the databyte to the register
delayMicroseconds(10);
//PGA SETTING
//1 ±5V 000 (1)
//2 ±2.5V 001 (2)
//4 ±1.25V 010 (3)
//8 ±0.625V 011 (4)
//16 ±312.5mV 100 (5)
//32 ±156.25mV 101 (6)
//64 ±78.125mV 110 (7) OR 111 (8)
byte adcon_reg = 2; //A/D Control Register (Address 02h)
byte adcon_data = 0x20; // 0 01 00 000 => Clock Out Frequency = fCLKIN, Sensor Detect OFF, gain 1
//0x25 for setting gain to 32, 0x27 to 64
SPI.transfer(0x50 | adcon_reg);
SPI.transfer(0x00); // 2nd command byte, write one register only
SPI.transfer(adcon_data); // write the databyte to the register
delayMicroseconds(10);
digitalWrite(ADS_CS_PIN, HIGH); //unselect ADS
delayMicroseconds(50);
Serial.println("ADS1256 configured");
}
long readADS(byte channel) {
long adc_val = 0; // unsigned long is on 32 bits
digitalWrite(ADS_CS_PIN, LOW);
delayMicroseconds(50);
SPI.beginTransaction(SPISettings(ADS_SPISPEED, MSBFIRST, SPI_MODE1)); // start SPI
delayMicroseconds(10);
//The most efficient way to cycle through the inputs is to
//change the multiplexer setting (using a WREG command
//to the multiplexer register MUX) immediately after DRDY
//goes low. Then, after changing the multiplexer, restart the
//conversion process by issuing the SYNC and WAKEUP
//commands, and retrieve the data with the RDATA
//command.
while (digitalRead(ADS_RDY_PIN)) {} ;
byte data = (channel << 4) | (1 << 3); //AIN-channel and AINCOM
SPI.transfer(0x50 | 1); // write (0x50) MUX register (0x01)
SPI.transfer(0x00); // number of registers to be read/written − 1, write one register only
SPI.transfer(data); // write the databyte to the register
delayMicroseconds(10);
//SYNC command 1111 1100
SPI.transfer(0xFC);
delayMicroseconds(10);
//WAKEUP 0000 0000
SPI.transfer(0x00);
delayMicroseconds(10);
SPI.transfer(0x01); // Read Data 0000 0001 (01h)
delayMicroseconds(10);
adc_val = SPI.transfer(0);
adc_val <<= 8; //shift to left
adc_val |= SPI.transfer(0);
adc_val <<= 8;
adc_val |= SPI.transfer(0);
//The ADS1255/6 output 24 bits of data in Binary Two’s
//Complement format. The LSB has a weight of
//2VREF/(PGA(223 − 1)). A positive full-scale input produces
//an output code of 7FFFFFh and the negative full-scale
//input produces an output code of 800000h.
if (adc_val > 0x7fffff) { //if MSB == 1
adc_val = 16777216ul - adc_val; //do 2's complement, discard sign
}
delayMicroseconds(10);
digitalWrite(ADS_CS_PIN, HIGH);
delayMicroseconds(50);
SPI.endTransaction();
Serial.print("Got measurement from ADS ");
Serial.println(adc_val);
return adc_val;
}
long readADSDiff(byte positiveCh, byte negativeCh) {
long adc_val = 0; // unsigned long is on 32 bits
digitalWrite(ADS_CS_PIN, LOW);
delayMicroseconds(50);
SPI.beginTransaction(SPISettings(ADS_SPISPEED, MSBFIRST, SPI_MODE1));
delayMicroseconds(10);
while (digitalRead(ADS_RDY_PIN)) {} ;
byte data = (positiveCh << 4) | negativeCh; //xxxx1000 - AINp = positiveCh, AINn = negativeCh
SPI.transfer(0x50 | 1); // write (0x50) MUX register (0x01)
SPI.transfer(0x00); // number of registers to be read/written − 1, write one register only
SPI.transfer(data); // write the databyte to the register
delayMicroseconds(10);
//SYNC command 1111 1100
SPI.transfer(0xFC);
delayMicroseconds(10);
//WAKEUP 0000 0000
SPI.transfer(0x00);
delayMicroseconds(10);
SPI.transfer(0x01); // Read Data 0000 0001 (01h)
delayMicroseconds(10);
adc_val = SPI.transfer(0);
adc_val <<= 8; //shift to left
adc_val |= SPI.transfer(0);
adc_val <<= 8;
adc_val |= SPI.transfer(0);
delayMicroseconds(10);
digitalWrite(ADS_CS_PIN, HIGH);
delayMicroseconds(50);
if (adc_val > 0x7fffff) { //if MSB == 1
adc_val = adc_val - 16777216; //do 2's complement, keep the sign this time!
}
Serial.print("Got diff measurement from ADS ");
Serial.println(adc_val);
return adc_val;
}
@dariosalvi78
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I developed this code ages ago so I can't be of help. All I can say is that it worked.
I would invite you to get some understanding of C and particularly bitwise operators which is what is used that line.

@massic76
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massic76 commented Jun 8, 2021

Hi Dario,
Thank you very much. I will try to investigate this on my own and to refresh my memory about the bitwise operators in C.

I am sure it worked and I am thankful you shared it with us.

Best, Massimo

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