Diff: MAX31865.cpp

Revision:

2:b42b7148fbe0

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MAX31865.cpp	Fri Mar 29 14:09:06 2019 +0000
@@ -0,0 +1,179 @@
+#include "MAX31865.h"
+
+MAX31865::MAX31865(SPI &_spi, PinName _ncs)
+    : spi(_spi), ncs(_ncs, 1), sensorPresent(false)
+{
+}
+
+bool MAX31865::begin(max31865_numwires_t wires)
+{
+    setWires(wires);
+    enableBias(true);
+    autoConvert(true);
+    clearFault();
+
+    return true;
+}
+
+uint8_t MAX31865::readFault(void)
+{
+    return readRegister8(MAX31865_FAULTSTAT_REG);
+}
+
+void MAX31865::clearFault(void)
+{
+    volatile uint8_t t = readRegister8(MAX31865_CONFIG_REG);
+    t &= ~0x2C;
+    t |= MAX31865_CONFIG_FAULTSTAT;
+    writeRegister8(MAX31865_CONFIG_REG, t);
+}
+
+void MAX31865::enableBias(bool b)
+{
+    volatile uint8_t t = readRegister8(MAX31865_CONFIG_REG);
+    if (b)
+    {
+        t |= MAX31865_CONFIG_BIAS; // enable bias
+    }
+    else
+    {
+        t &= ~MAX31865_CONFIG_BIAS; // disable bias
+    }
+    writeRegister8(MAX31865_CONFIG_REG, t);
+}
+
+void MAX31865::autoConvert(bool b)
+{
+    uint8_t t = readRegister8(MAX31865_CONFIG_REG);
+    if (b)
+    {
+        t |= MAX31865_CONFIG_MODEAUTO; // enable autoconvert
+    }
+    else
+    {
+        t &= ~MAX31865_CONFIG_MODEAUTO; // disable autoconvert
+    }
+    writeRegister8(MAX31865_CONFIG_REG, t);
+}
+
+void MAX31865::setWires(max31865_numwires_t wires)
+{
+    uint8_t t = readRegister8(MAX31865_CONFIG_REG);
+    if (wires == MAX31865_3WIRE)
+    {
+        t |= MAX31865_CONFIG_3WIRE;
+    }
+    else
+    {
+        // 2 or 4 wire
+        t &= ~MAX31865_CONFIG_3WIRE;
+    }
+    writeRegister8(MAX31865_CONFIG_REG, t);
+}
+
+float MAX31865::temperature(float RTDnominal, float refResistor, uint16_t rtdVal)
+{
+    // http://www.analog.com/media/en/technical-documentation/application-notes/AN709_0.pdf
+
+    float Z1, Z2, Z3, Z4, Rt, temp;
+
+    if (rtdVal == 0)
+    {
+        Rt = readRTD();
+
+        if (!sensorPresent)
+        {
+            return 0.0f;
+        }
+    }
+    else
+    {
+        Rt = rtdVal;
+    }
+    Rt /= 32768;
+    Rt *= refResistor;
+
+    Z1 = -RTD_A;
+    Z2 = RTD_A * RTD_A - (4 * RTD_B);
+    Z3 = (4 * RTD_B) / RTDnominal;
+    Z4 = 2 * RTD_B;
+
+    temp = Z2 + (Z3 * Rt);
+    temp = (sqrt(temp) + Z1) / Z4;
+
+    if (temp >= 0)
+        return temp;
+
+    // ugh.
+    float rpoly = Rt;
+
+    temp = -242.02f;
+    temp += 2.2228f * rpoly;
+    rpoly *= Rt; // square
+    temp += (float)2.5859e-3 * rpoly;
+    rpoly *= Rt; // ^3
+    temp -= (float)4.8260e-6 * rpoly;
+    rpoly *= Rt; // ^4
+    temp -= (float)2.8183e-8 * rpoly;
+    rpoly *= Rt; // ^5
+    temp += (float)1.5243e-10 * rpoly;
+
+    return temp;
+}
+
+uint16_t MAX31865::readRTD(void)
+{
+    uint16_t rtd = readRegister16(MAX31865_RTDMSB_REG);
+    sensorPresent = readFault() == 0;
+    clearFault();
+
+    rtd >>= 1;
+
+    return rtd;
+}
+
+/**********************************************/
+
+uint8_t MAX31865::readRegister8(uint8_t addr)
+{
+    uint8_t ret[] = {0};
+    readRegisterN(addr, ret, 1);
+    return ret[0];
+}
+
+uint16_t MAX31865::readRegister16(uint8_t addr)
+{
+    uint8_t buffer[2] = {0, 0};
+    readRegisterN(addr, buffer, 2);
+
+    uint16_t ret = buffer[0];
+    ret <<= 8;
+    ret |= buffer[1];
+
+    return ret;
+}
+
+void MAX31865::writeRegister8(uint8_t addr, uint8_t data)
+{
+    ncs = 0;                //select chip
+    spi.write(addr | 0x80); // make sure top bit is set
+    spi.write(data);
+    ncs = 1;
+}
+
+void MAX31865::readRegisterN(uint8_t address, uint8_t buffer[], uint8_t n)
+{
+    address &= 0x7F; // make sure top bit is not set
+
+    ncs = 0;
+
+    spi.write(address);
+
+    for (uint8_t i = 0; i < n; i++)
+    {
+        buffer[i] = spi.write(0x00);
+    }
+
+    ncs = 1;
+}
+