implement sampling math

firmware/Makefile

@@ -108,6 +108,7 @@ include $(CHIBIOS)/os/common/ports/ARMv6-M/compilers/GCC/mk/port.mk
 # Auto-build files in ./source recursively.
 include $(CHIBIOS)/tools/mk/autobuild.mk
 # Other files (optional).
+include $(CHIBIOS)/os/hal/lib/streams/streams.mk
 
 # Define linker script file here
 LDSCRIPT= $(STARTUPLD)/STM32F042x6.ld
@@ -125,6 +126,7 @@ CPPSRC = $(ALLCPPSRC) \
           lambda_lookup.cpp \
           pwm.cpp \
           pump_dac.cpp \
+          sampling.cpp \
           main.cpp
 
 # List ASM source files here.
@@ -151,7 +153,8 @@ CPPWARN = -Wall -Wextra -Wundef
 #
 
 # List all user C define here, like -D_DEBUG=1
-UDEFS =
+UDEFS = -DCHPRINTF_USE_FLOAT=1
+
 
 # Define ASM defines here
 UADEFS =

firmware/analog_input.cpp

@@ -3,7 +3,7 @@
 #include "hal.h"
 
 #define ADC_CHANNEL_COUNT 3
-#define ADC_OVERSAMPLE 4
+#define ADC_OVERSAMPLE 16
 
 static adcsample_t adcBuffer[ADC_CHANNEL_COUNT * ADC_OVERSAMPLE];
 
@@ -38,9 +38,11 @@ AnalogResult AnalogSample()
 {
     adcConvert(&ADCD1, &convGroup, adcBuffer, ADC_OVERSAMPLE);
 
+    constexpr float nernstInputGain = 1 / 2.7f;
+
     return
     {
-        .NernstVoltage = AverageSamples(adcBuffer, 0),
+        .NernstVoltage = AverageSamples(adcBuffer, 0) * nernstInputGain,
         .VirtualGroundVoltage = AverageSamples(adcBuffer, 1),
         .PumpCurrentVoltage = AverageSamples(adcBuffer, 2),
     };

firmware/main.cpp

@@ -1,10 +1,11 @@
 #include "ch.h"
 #include "hal.h"
+#include "chprintf.h"
 
-#include "analog_input.h"
 #include "can.h"
 #include "pwm.h"
 #include "pump_dac.h"
+#include "sampling.h"
 
 // 400khz / 1024 = 390hz PWM
 // TODO: this is wired to an inverted output, what do?
@@ -20,12 +21,14 @@ static const UARTConfig uartCfg =
     .timeout_cb = nullptr,
 
     .timeout = 0,
-    .speed = 230400,
+    .speed = 500000,
     .cr1 = 0,
     .cr2 = 0,
     .cr3 = 0,
 };
 
+char strBuffer[200];
+
 /*
  * Application entry point.
  */
@@ -33,35 +36,36 @@ int main() {
     halInit();
     chSysInit();
 
+    StartSampling();
+
     InitPumpDac();
 
     InitCan();
 
     uartStart(&UARTD1, &uartCfg);
 
-    adcStart(&ADCD1, nullptr);
-
     heaterPwm.Start();
 
     heaterPwm.SetDuty(0.2f);
 
-     while (true) {
-//         auto result = AnalogSample();
 
-//         // dummy data
-//         SendCanData(0.5f, 300);
+    /*for (int i = 0; i < 500; i++) {
+        SetPumpCurrentTarget(current);
+        chThdSleepMilliseconds(50);
 
-//         uartStartSend(&UARTD1, 13, "Hello, world!");
-//         chThdSleepMilliseconds(10);
+        auto result = AnalogSample();
 
+        //size_t writeCount = chsnprintf(strBuffer, 200, "I: %d\t\tVM: %.3f\tIp: %.3f\n", current, result.VirtualGroundVoltage, result.PumpCurrentVoltage);
+        size_t writeCount = chsnprintf(strBuffer, 200, "%d\t%.4f\n", current, result.PumpCurrentVoltage);
+        uartStartSend(&UARTD1, writeCount, strBuffer);
 
-        SetPumpCurrentTarget(-1000);
-        chThdSleepMilliseconds(10);
-        
-        SetPumpCurrentTarget(0);
-        chThdSleepMilliseconds(10);
+        //current += 10;
+    }*/
 
-        SetPumpCurrentTarget(1000);
-        chThdSleepMilliseconds(10);
+    while(1) {
+        size_t writeCount = chsnprintf(strBuffer, 200, "%.4f\t%.2f\n", GetNernstDc() * 1000, GetSensorInternalResistance());
+        uartStartSend(&UARTD1, writeCount, strBuffer);
+
+        chThdSleepMilliseconds(5);
     }
 }

firmware/sampling.cpp

@@ -0,0 +1,81 @@
+#include "sampling.h"
+
+#include "ch.h"
+#include "hal.h"
+
+#include "analog_input.h"
+
+// Stored results
+float nernstAc = 0;
+float nernstDc = 0;
+volatile float pumpCurrentSenseVoltage = 0;
+
+constexpr float f_abs(float x)
+{
+    return x > 0 ? x : -x;
+}
+
+static THD_WORKING_AREA(waSamplingThread, 256);
+
+static void SamplingThread(void*)
+{
+    float r_2 = 0;
+    float r_3 = 0;
+
+    while(true)
+    {
+        // First toggle the pin
+        palTogglePad(GPIOB, 8);
+        auto result = AnalogSample();
+
+        float r_1 = result.NernstVoltage;
+
+        // Compute results
+
+        // r2_opposite_phase estimates where the previous sample would be had we not been toggling
+        // AKA the absolute value of the difference between r2_opposite_phase and r2 is the amplitude
+        // of the AC component on the nernst voltage.  We have to pull this trick so as to use the past 3
+        // samples to cancel out any slope in the DC (aka actual nernst cell output) from the AC measurement
+        float r2_opposite_phase = (r_1 + r_3) / 2;
+
+        nernstAc = f_abs(r2_opposite_phase - r_2);
+        nernstDc = (r2_opposite_phase + r_2) / 2;
+
+        pumpCurrentSenseVoltage = 0.8f * pumpCurrentSenseVoltage + 0.2f * (result.PumpCurrentVoltage - 1.65f);
+
+        // Shift history over by one
+        r_3 = r_2;
+        r_2 = r_1;
+    }
+}
+
+void StartSampling()
+{
+    adcStart(&ADCD1, nullptr);
+    chThdCreateStatic(waSamplingThread, sizeof(waSamplingThread), NORMALPRIO + 5, SamplingThread, nullptr);
+}
+
+float GetNernstAc()
+{
+    return nernstAc;
+}
+
+float GetSensorInternalResistance()
+{
+    // Sensor is the lowside of a divider, top side is 22k, and 3.3v AC pk-pk is injected
+    return 22000 / (3.3f / GetNernstAc() - 1);
+}
+
+float GetNernstDc()
+{
+    return nernstDc;
+}
+
+float GetPumpNominalCurrent()
+{
+    // Gain is 10x, then a 61.9 ohm resistor
+    // Effective resistance with the gain is 619 ohms
+    // 1000 is to convert to milliamperes
+    constexpr float ratio = 1000 / 619.0f;
+    return pumpCurrentSenseVoltage * ratio;
+}

firmware/sampling.h

@@ -0,0 +1,9 @@
+#pragma once
+
+void StartSampling();
+
+float GetNernstAc();
+float GetSensorInternalResistance();
+float GetNernstDc();
+
+float GetPumpNominalCurrent();