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Port TEC DAC calibration procedure from Thermostat

- Needs clean up
- To be evaluated and rethink the calibration procedure
This commit is contained in:
linuswck 2023-12-22 17:09:45 +08:00
parent d3f3608136
commit 23ee568ea7
3 changed files with 77 additions and 8 deletions

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@ -35,7 +35,7 @@ pub const R_SENSE: ElectricalResistance = ElectricalResistance {
// Rev 0_2: DAC Chip connects 3V3 reference voltage and thus provide 0-3.3V output range
// TODO: Rev 0_3: DAC Chip connects 3V3 reference voltage,
// which is then passed through a resistor divider to provide 0-3V output range
const DAC_OUT_V_MAX: f64 = 3.3;
pub const DAC_OUT_V_MAX: f64 = 3.3;
const TEC_VSEC_BIAS_V: ElectricPotential = ElectricPotential {
dimension: PhantomData,
units: PhantomData,
@ -258,17 +258,15 @@ impl MAX1968 {
}
pub fn set_i(&mut self, i_tec: ElectricCurrent) -> ElectricCurrent {
let center_point = self.phy.center_pt;
let r_sense = R_SENSE;
let voltage = i_tec * 10.0 * r_sense + center_point;
let voltage = i_tec * 10.0 * R_SENSE + self.phy.center_pt;
let voltage = self.set_dac(voltage);
let i_tec = (voltage - center_point) / (10.0 * r_sense);
let i_tec = (voltage - self.phy.center_pt) / (10.0 * R_SENSE);
i_tec
}
// AN4073: ADC Reading Dispersion can be reduced through Averaging
// Upon test, 16 Point Averaging = +-3 LSB Dispersion
fn adc_read(&mut self, adc_read_target: AdcReadTarget, avg_pt: u16) -> ElectricPotential {
pub fn adc_read(&mut self, adc_read_target: AdcReadTarget, avg_pt: u16) -> ElectricPotential {
let mut sample: u32 = 0;
sample = match adc_read_target {
AdcReadTarget::VREF => {
@ -317,7 +315,7 @@ impl MAX1968 {
}
pub fn get_dac_vfb(&mut self) -> ElectricPotential {
self.adc_read(AdcReadTarget:: DacVfb, 1)
self.adc_read(AdcReadTarget:: DacVfb, 16)
}
pub fn get_tec_i(&mut self) -> ElectricCurrent {

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@ -1,2 +1,3 @@
pub mod ad5680;
pub mod max1968;
pub mod thermostat;

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@ -1,5 +1,14 @@
use crate::sys_timer;
use crate::thermostat::ad5680;
use crate::thermostat::MAX1968;
use crate::thermostat::max1968::{MAX1968, AdcReadTarget, DAC_OUT_V_MAX};
use log::info;
use uom::si::{
electric_current::ampere,
electric_potential::{millivolt, volt},
electrical_resistance::ohm,
f64::{ElectricCurrent, ElectricPotential, ElectricalResistance},
ratio::ratio,
};
pub struct Thermostat {
max1968: MAX1968,
@ -15,4 +24,65 @@ impl Thermostat{
pub fn setup(&mut self){
self.max1968.setup();
}
/// Calibrates the DAC output to match vref of the MAX driver to reduce zero-current offset of the MAX driver output.
///
/// The thermostat DAC applies a control voltage signal to the CTLI pin of MAX driver chip to control its output current.
/// The CTLI input signal is centered around VREF of the MAX chip. Applying VREF to CTLI sets the output current to 0.
///
/// This calibration routine measures the VREF voltage and the DAC output with the STM32 ADC, and uses a breadth-first
/// search to find the DAC setting that will produce a DAC output voltage closest to VREF. This DAC output voltage will
/// be stored and used in subsequent i_set routines to bias the current control signal to the measured VREF, reducing
/// the offset error of the current control signal.
///
/// The input offset of the STM32 ADC is eliminated by using the same ADC for the measurements, and by only using the
/// difference in VREF and DAC output for the calibration.
///
/// This routine should be called only once after boot, repeated reading of the vref signal and changing of the stored
/// VREF measurement can introduce significant noise at the current output, degrading the stabilily performance of the
/// thermostat.
pub fn calibrate_dac_value(&mut self) {
let samples = 50;
let mut target_voltage = ElectricPotential::new::<volt>(0.0);
for _ in 0..samples {
target_voltage = target_voltage + self.max1968.adc_read(AdcReadTarget::VREF, 1);
}
target_voltage = target_voltage / samples as f64;
let mut start_value = 1;
let mut best_error = ElectricPotential::new::<volt>(100.0);
let before_cal = self.max1968.phy.center_pt;
for step in (0..18).rev() {
info!("Step: {} Calibrating", step);
let mut prev_value = start_value;
for value in (start_value..=ad5680::MAX_VALUE).step_by(1 << step) {
//info!("Calibrating");
self.max1968.phy.dac.set(value).unwrap();
sys_timer::sleep(5);
let dac_feedback = self.max1968.adc_read(AdcReadTarget::DacVfb, 64);
let error = target_voltage - dac_feedback;
if error < ElectricPotential::new::<volt>(0.0) {
break;
} else if error < best_error {
best_error = error;
start_value = prev_value;
let vref = (value as f64 / ad5680::MAX_VALUE as f64) * ElectricPotential::new::<volt>(DAC_OUT_V_MAX);
self.max1968.set_center_point(vref);
}
prev_value = value;
}
}
loop {
info!("Before Calibration, VREF = {:?}", before_cal);
info!("After Calibration, VREF = {:?}", self.max1968.phy.center_pt);
self.max1968.set_i(ElectricCurrent::new::<ampere>(0.0));
info!("VREF Value {:?}", self.max1968.adc_read(AdcReadTarget::VREF, 64));
info!("DAC VFB Value {:?}", self.max1968.adc_read(AdcReadTarget::DacVfb, 64));
sys_timer::sleep(100);
}
}
}