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Oct 27, 2023
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Better document the resistor divider and the ADC ID value #723

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117 changes: 74 additions & 43 deletions Firmware/RTK_Surveyor/Begin.ino
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Original file line number Diff line number Diff line change
@@ -1,62 +1,93 @@
// Initial startup functions for GNSS, SD, display, radio, etc
/*------------------------------------------------------------------------------
Begin.ino

void identifyBoard()
This module implements the initial startup functions for GNSS, SD, display,
radio, etc.
------------------------------------------------------------------------------*/

//----------------------------------------
// Constants
//----------------------------------------

#define MAX_ADC_VOLTAGE 3300 // Millivolts

// Testing shows the combined ADC+resistors is under a 1% window
#define TOLERANCE 4.75 // Percent: 95.25% - 104.75%

//----------------------------------------
// Macros
//----------------------------------------

// ADC input
// Ra KOhms | Rb KOhms
// MAX_ADC_VOLTAGE -----/\/\/\/\-----+-----/\/\/\/\----- Ground
//
#define ADC_ID_mV(RaK, RbK) ((uint16_t)(MAX_ADC_VOLTAGE * RbK / (RaK + RbK)))

//----------------------------------------
// Hardware initialization functions
//----------------------------------------

// Determine if the measured value matches the product ID value
bool idWithAdc(uint16_t mvMeasured, uint16_t mvProduct)
{
// Use ADC to check resistor divider
// Express: 10/3.3
// Express+: 3.3/10
// Facet: 10/10
// Facet L-Band: 10/20
// Reference Station: 20/10
// Facet L-Band Direct: 10/100
// Surveyor: ID resistors do not exist

const float rtkExpressID = 3.3 / (10 + 3.3) * 3300; // 819mV
const float rtkExressPlusID = 10.0 / (10 + 3.3) * 3300; // 2481mV
const float rtkFacetID = 10.0 / (10 + 10) * 3300; // 1650mV
const float rtkFacetLbandID = 20.0 / (20 + 10) * 3300; // 2200mV
const float rtkReferenceStationID = 10.0 / (10 + 20) * 3300; // 1100mV
const float rtkFacetLbandDirectID = 1.0 / (4.7 + 1) * 3300; // 579mV

const float tolerance = 0.0475; // 4.75% Testing shows the combined ADC+resistors is under a 1% window
const float upperThreshold = 1 + tolerance; // 104.75%
const float lowerThreshold = 1 - tolerance; // 95.25%
uint16_t lowerThreshold;
uint16_t upperThreshold;

// Return true if the mvMeasured value is within the tolerance range
// of the mvProduct value
upperThreshold = (1.0 + (TOLERANCE / 100.)) * mvProduct;
lowerThreshold = (1.0 - (TOLERANCE / 100.)) * mvProduct;
return (upperThreshold > mvMeasured) && (mvMeasured > lowerThreshold);
}

// Use a pair of resistors on pin 35 to ID the board type
// If the ID resistors are not available then use a variety of other methods
// (I2C, GPIO test, etc) to ID the board.
// Assume no hardware interfaces have been started so we need to start/stop any hardware
// used in tests accordingly.
void identifyBoard()
{
// Use ADC to check the resistor divider
int pin_deviceID = 35;
uint16_t idValue = analogReadMilliVolts(pin_deviceID);
log_d("Board ADC ID (mV): %d", idValue);

if (idValue > (rtkFacetID * lowerThreshold) && idValue < (rtkFacetID * upperThreshold))
{
productVariant = RTK_FACET;
}
else if (idValue > (rtkFacetLbandID * lowerThreshold) && idValue < (rtkFacetLbandID * upperThreshold))
{
productVariant = RTK_FACET_LBAND;
}
else if (idValue > (rtkExpressID * lowerThreshold) && idValue < (rtkExpressID * upperThreshold))
{
// Order checks by millivolt values high to low

// Facet L-Band Direct: 4.7/1 --> 551mV < 579mV < 607mV
if (idWithAdc(idValue, ADC_ID_mV(4.7, 1)))
productVariant = RTK_FACET_LBAND_DIRECT;

// Express: 10/3.3 --> 779mV < 819mV < 858mV
else if (idWithAdc(idValue, ADC_ID_mV(10, 3.3)))
productVariant = RTK_EXPRESS;
}
else if (idValue > (rtkExressPlusID * lowerThreshold) && idValue < (rtkExressPlusID * upperThreshold))
{
productVariant = RTK_EXPRESS_PLUS;
}
else if (idValue > (rtkReferenceStationID * lowerThreshold) && idValue < (rtkReferenceStationID * upperThreshold))

// Reference Station: 20/10 --> 1047mV < 1100mV < 1153mV
else if (idWithAdc(idValue, ADC_ID_mV(20, 10)))
{
productVariant = REFERENCE_STATION;
// We can't auto-detect the ZED version if the firmware is in configViaEthernet mode,
// so fake it here - otherwise messageSupported always returns false
zedFirmwareVersionInt = 112;
}
else if (idValue > (rtkFacetLbandDirectID * lowerThreshold) && idValue < (rtkFacetLbandDirectID * upperThreshold))
{
productVariant = RTK_FACET_LBAND_DIRECT;
}
// Facet: 10/10 --> 1571mV < 1650mV < 1729mV
else if (idWithAdc(idValue, ADC_ID_mV(10, 10)))
productVariant = RTK_FACET;

// Facet L-Band: 10/20 --> 2095mV < 2200mV < 2305mV
else if (idWithAdc(idValue, ADC_ID_mV(10, 20)))
productVariant = RTK_FACET_LBAND;

// Express+: 3.3/10 --> 2363mV < 2481mV < 2600mV
else if (idWithAdc(idValue, ADC_ID_mV(3.3, 10)))
productVariant = RTK_EXPRESS_PLUS;

// ID resistors do not exist for the following:
// Surveyor
// Unknown
else
{
productVariant = RTK_UNKNOWN; // Need to wait until the GNSS and Accel have been initialized
}
}

// Setup any essential power pins
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