Limit i_set within range of MAX1968 chip

The REF pin of the MAX1968 on hardware revisions v2.x is missing a
buffer, loading the pin on every CPU ADC read. Avoid reading from it and
leave the pin floating on affected hardware revisions, and return the
nominal 1.5V instead.

README.md

@@ -271,18 +271,19 @@ with the following keys.
 | `tec_u_meas`   | Volts           | Measurement of the voltage across the TEC            |
 | `pid_output`   | Amperes         | PID control output                                   |
 
+Note: With Thermostat v2 and below, the voltage and current readouts `i_tec` and `tec_i` are disabled and null due to faulty hardware that introduces a lot of noise in the signal.
+
 ## PID Tuning
 
 The thermostat implements a PID control loop for each of the TEC channels, more details on setting up the PID control loop can be found [here](./doc/PID%20tuning.md).
 
 ## Fan control
 
-Fan control is available for the thermostat revisions with integrated fan system. For this purpose four commands are available:
+Fan control commands are available for thermostat revisions with an integrated fan system:
 1. `fan` - show fan stats: `fan_pwm`, `abs_max_tec_i`, `auto_mode`, `k_a`, `k_b`, `k_c`.
-2. `fan auto` - enable auto speed controller mode, which correlates with fan curve `fcurve`.
-3. `fan <value>` - set the fan power with the value from `1` to `100` and disable auto mode. There is no way to disable the fan.
+2. `fan auto` - enable auto speed controller mode, where fan speed is controlled by the fan curve `fcurve`.
+3. `fan <value>` - set the fan power with the value from `1` to `100` and disable auto mode. There is no way to completely disable the fan.
 Please note that power doesn't correlate with the actual speed linearly.
-4. `fcurve <a> <b> <c>` - set coefficients of the controlling curve `a*x^2 + b*x + c`, where `x` is `abs_max_tec_i/MAX_TEC_I`, 
-i.e. receives values from 0 to 1 linearly tied to the maximum current. The controlling curve should produce values from 0 to 1,
-as below and beyond values would be substituted by 0 and 1 respectively.
-5. `fcurve default` - restore fan curve settings to defaults: `a = 1.0, b = 0.0, c = 0.0`.
+4. `fcurve <a> <b> <c>` - set coefficients of the controlling curve `a*x^2 + b*x + c`, where `x` is `abs_max_tec_i/MAX_TEC_I`, a normalized value in range [0,1],
+i.e. the (linear) proportion of current output capacity used, on the channel with the largest current flow. The controlling curve is also clamped to [0,1].
+5. `fcurve default` - restore fan curve coefficients to defaults: `a = 1.0, b = 0.0, c = 0.0`.

src/channel_state.rs

@@ -2,11 +2,13 @@ use smoltcp::time::{Duration, Instant};
 use uom::si::{
     f64::{
         ElectricPotential,
+        ElectricCurrent,
         ElectricalResistance,
         ThermodynamicTemperature,
         Time,
     },
     electric_potential::volt,
+    electric_current::ampere,
     electrical_resistance::ohm,
     thermodynamic_temperature::degree_celsius,
     time::millisecond,
@@ -29,6 +31,7 @@ pub struct ChannelState {
     /// i_set 0A center point
     pub center: CenterPoint,
     pub dac_value: ElectricPotential,
+    pub i_set: ElectricCurrent,
     pub pid_engaged: bool,
     pub pid: pid::Controller,
     pub sh: sh::Parameters,
@@ -44,6 +47,7 @@ impl ChannelState {
             adc_interval: Duration::from_millis(100),
             center: CenterPoint::Vref,
             dac_value: ElectricPotential::new::<volt>(0.0),
+            i_set: ElectricCurrent::new::<ampere>(0.0),
             pid_engaged: false,
             pid: pid::Controller::new(pid::Parameters::default()),
             sh: sh::Parameters::default(),

src/channels.rs

@@ -18,27 +18,33 @@ use crate::{
     channel_state::ChannelState,
     command_parser::{CenterPoint, PwmPin},
     command_handler::JsonBuffer,
-    pins,
+    pins::{self, Channel0VRef, Channel1VRef},
     steinhart_hart,
+    hw_rev,
 };
 
 pub const CHANNELS: usize = 2;
 pub const R_SENSE: f64 = 0.05;
+
+// as stated in the MAX1968 datasheet
+pub const MAX_TEC_I: f64 = 3.0;
+
 // DAC chip outputs 0-5v, which is then passed through a resistor dividor to provide 0-3v range
 const DAC_OUT_V_MAX: f64 = 3.0;
 
 // TODO: -pub
-pub struct Channels {
+pub struct Channels<'a> {
     channel0: Channel<Channel0>,
     channel1: Channel<Channel1>,
     pub adc: ad7172::Adc<pins::AdcSpi, pins::AdcNss>,
     /// stm32f4 integrated adc
     pins_adc: pins::PinsAdc,
     pub pwm: pins::PwmPins,
+    hwrev: &'a hw_rev::HWRev,
 }
 
-impl Channels {
-    pub fn new(pins: pins::Pins) -> Self {
+impl<'a> Channels<'a> {
+    pub fn new(pins: pins::Pins, hwrev: &'a hw_rev::HWRev) -> Self {
         let mut adc = ad7172::Adc::new(pins.adc_spi, pins.adc_nss).unwrap();
         // Feature not used
         adc.set_sync_enable(false).unwrap();
@@ -56,7 +62,7 @@ impl Channels {
         let channel1 = Channel::new(pins.channel1, adc_calibration1);
         let pins_adc = pins.pins_adc;
         let pwm = pins.pwm;
-        let mut channels = Channels { channel0, channel1, adc, pins_adc, pwm };
+        let mut channels = Channels { channel0, channel1, adc, pins_adc, pwm, hwrev };
         for channel in 0..CHANNELS {
             channels.calibrate_dac_value(channel);
             channels.set_i(channel, ElectricCurrent::new::<ampere>(0.0));
@@ -111,11 +117,8 @@ impl Channels {
     }
 
     pub fn get_i(&mut self, channel: usize) -> ElectricCurrent {
-        let center_point = self.get_center(channel);
-        let r_sense = ElectricalResistance::new::<ohm>(R_SENSE);
-        let voltage = self.get_dac(channel);
-        let i_tec = (voltage - center_point) / (10.0 * r_sense);
-        i_tec
+        let i_set = self.channel_state(channel).i_set;
+        i_set
     }
 
     /// i_set DAC
@@ -130,7 +133,12 @@ impl Channels {
         voltage
     }
 
-    pub fn set_i(&mut self, channel: usize, i_tec: ElectricCurrent) -> ElectricCurrent {
+    pub fn set_i(&mut self, channel: usize, i_set: ElectricCurrent) -> ElectricCurrent {
+        // Silently clamp i_set
+        let i_ceiling = ElectricCurrent::new::<ampere>(MAX_TEC_I);
+        let i_floor = ElectricCurrent::new::<ampere>(-MAX_TEC_I);
+        let i_set = i_set.min(i_ceiling).max(i_floor);
+
         let vref_meas = match channel.into() {
             0 => self.channel0.vref_meas,
             1 => self.channel1.vref_meas,
@@ -138,10 +146,11 @@ impl Channels {
         };
         let center_point = vref_meas;
         let r_sense = ElectricalResistance::new::<ohm>(R_SENSE);
-        let voltage = i_tec * 10.0 * r_sense + center_point;
+        let voltage = i_set * 10.0 * r_sense + center_point;
         let voltage = self.set_dac(channel, voltage);
-        let i_tec = (voltage - center_point) / (10.0 * r_sense);
-        i_tec
+        let i_set = (voltage - center_point) / (10.0 * r_sense);
+        self.channel_state(channel).i_set = i_set;
+        i_set
     }
 
     pub fn read_dac_feedback(&mut self, channel: usize) -> ElectricPotential {
@@ -203,20 +212,30 @@ impl Channels {
     pub fn read_vref(&mut self, channel: usize) -> ElectricPotential {
         match channel {
             0 => {
-                let sample = self.pins_adc.convert(
-                    &self.channel0.vref_pin,
-                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
-                );
-                let mv = self.pins_adc.sample_to_millivolts(sample);
-                ElectricPotential::new::<millivolt>(mv as f64)
+                match &self.channel0.vref_pin {
+                    Channel0VRef::Analog(vref_pin) => {
+                        let sample = self.pins_adc.convert(
+                            vref_pin,
+                            stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                        );
+                        let mv = self.pins_adc.sample_to_millivolts(sample);
+                        ElectricPotential::new::<millivolt>(mv as f64)
+                    },
+                    Channel0VRef::Disabled(_) => ElectricPotential::new::<volt>(1.5)
+                }
             }
             1 => {
-                let sample = self.pins_adc.convert(
-                    &self.channel1.vref_pin,
-                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
-                );
-                let mv = self.pins_adc.sample_to_millivolts(sample);
-                ElectricPotential::new::<millivolt>(mv as f64)
+                match &self.channel1.vref_pin {
+                    Channel1VRef::Analog(vref_pin) => {
+                        let sample = self.pins_adc.convert(
+                            vref_pin,
+                            stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                        );
+                        let mv = self.pins_adc.sample_to_millivolts(sample);
+                        ElectricPotential::new::<millivolt>(mv as f64)
+                    },
+                    Channel1VRef::Disabled(_) => ElectricPotential::new::<volt>(1.5)
+                }
             }
             _ => unreachable!(),
         }
@@ -429,8 +448,8 @@ impl Channels {
 
     fn report(&mut self, channel: usize) -> Report {
         let i_set = self.get_i(channel);
-        let i_tec = self.read_itec(channel);
-        let tec_i = self.get_tec_i(channel);
+        let i_tec = if self.hwrev.major > 2 {Some(self.read_itec(channel))} else {None};
+        let tec_i = if self.hwrev.major > 2 {Some(self.get_tec_i(channel))} else {None};
         let dac_value = self.get_dac(channel);
         let state = self.channel_state(channel);
         let pid_output = ElectricCurrent::new::<ampere>(state.pid.y1);
@@ -524,9 +543,9 @@ impl Channels {
         serde_json_core::to_vec(&summaries)
     }
 
-    pub fn current_abs_max_tec_i(&mut self) -> f64 {
-        max_by(self.get_tec_i(0).abs().get::<ampere>(),
-               self.get_tec_i(1).abs().get::<ampere>(),
+    pub fn current_abs_max_tec_i(&mut self) -> ElectricCurrent {
+        max_by(self.get_tec_i(0).abs(),
+               self.get_tec_i(1).abs(),
                |a, b| a.partial_cmp(b).unwrap_or(core::cmp::Ordering::Equal))
     }
 }
@@ -543,8 +562,8 @@ pub struct Report {
     i_set: ElectricCurrent,
     dac_value: ElectricPotential,
     dac_feedback: ElectricPotential,
-    i_tec: ElectricPotential,
-    tec_i: ElectricCurrent,
+    i_tec: Option<ElectricPotential>,
+    tec_i: Option<ElectricCurrent>,
     tec_u_meas: ElectricPotential,
     pid_output: ElectricCurrent,
 }

src/command_handler.rs

@@ -207,11 +207,11 @@ impl Handler {
     }
 
     fn set_center_point(socket: &mut TcpSocket, channels: &mut Channels, channel: usize, center: CenterPoint) -> Result<Handler, Error> {
-        let i_tec = channels.get_i(channel);
+        let i_set = channels.get_i(channel);
         let state = channels.channel_state(channel);
         state.center = center;
         if !state.pid_engaged {
-            channels.set_i(channel, i_tec);
+            channels.set_i(channel, i_set);
         }
         send_line(socket, b"{}");
         Ok(Handler::Handled)

src/fan_ctrl.rs

@@ -4,17 +4,18 @@ use stm32f4xx_hal::{
     pwm::{self, PwmChannels},
     pac::TIM8,
 };
-
+use uom::si::{
+    f64::ElectricCurrent,
+    electric_current::ampere,
+};
 use crate::{
     hw_rev::HWSettings,
     command_handler::JsonBuffer,
+    channels::MAX_TEC_I,
 };
 
 pub type FanPin = PwmChannels<TIM8, pwm::C4>;
 
-// as stated in the schematics
-const MAX_TEC_I: f32 = 3.0;
-
 const MAX_USER_FAN_PWM: f32 = 100.0;
 const MIN_USER_FAN_PWM: f32 = 1.0;
 
@@ -50,10 +51,10 @@ impl FanCtrl {
         fan_ctrl
     }
 
-    pub fn cycle(&mut self, abs_max_tec_i: f32) {
-        self.abs_max_tec_i = abs_max_tec_i;
+    pub fn cycle(&mut self, abs_max_tec_i: ElectricCurrent) {
+        self.abs_max_tec_i = abs_max_tec_i.get::<ampere>() as f32;
         if self.fan_auto && self.hw_settings.fan_available {
-            let scaled_current = self.abs_max_tec_i / MAX_TEC_I;
+            let scaled_current = self.abs_max_tec_i / MAX_TEC_I as f32;
             // do not limit upper bound, as it will be limited in the set_pwm()
             let pwm = (MAX_USER_FAN_PWM * (scaled_current * (scaled_current * self.k_a + self.k_b) + self.k_c)) as u32;
             self.set_pwm(pwm);

src/main.rs

@@ -138,7 +138,7 @@ fn main() -> ! {
 
     let mut store = flash_store::store(dp.FLASH);
 
-    let mut channels = Channels::new(pins);
+    let mut channels = Channels::new(pins, &hwrev);
     for c in 0..CHANNELS {
         match store.read_value::<ChannelConfig>(CHANNEL_CONFIG_KEY[c]) {
             Ok(Some(config)) =>
@@ -185,7 +185,7 @@ fn main() -> ! {
                     server.for_each(|_, session| session.set_report_pending(channel.into()));
                 }
 
-                fan_ctrl.cycle(channels.current_abs_max_tec_i() as f32);
+                fan_ctrl.cycle(channels.current_abs_max_tec_i());
 
                 if channels.pid_engaged() {
                     leds.g3.on();

src/pins.rs

@@ -66,21 +66,31 @@ pub trait ChannelPins {
     type TecUMeasPin;
 }
 
+pub enum Channel0VRef {
+    Analog(PA0<Analog>),
+    Disabled(PA0<Input<Floating>>),
+}
+
 impl ChannelPins for Channel0 {
     type DacSpi = Dac0Spi;
     type DacSync = PE4<Output<PushPull>>;
     type Shdn = PE10<Output<PushPull>>;
-    type VRefPin = PA0<Analog>;
+    type VRefPin = Channel0VRef;
     type ItecPin = PA6<Analog>;
     type DacFeedbackPin = PA4<Analog>;
     type TecUMeasPin = PC2<Analog>;
 }
 
+pub enum Channel1VRef {
+    Analog(PA3<Analog>),
+    Disabled(PA3<Input<Floating>>),
+}
+
 impl ChannelPins for Channel1 {
     type DacSpi = Dac1Spi;
     type DacSync = PF6<Output<PushPull>>;
     type Shdn = PE15<Output<PushPull>>;
-    type VRefPin = PA3<Analog>;
+    type VRefPin = Channel1VRef;
     type ItecPin = PB0<Analog>;
     type DacFeedbackPin = PA5<Analog>;
     type TecUMeasPin = PC3<Analog>;
@@ -150,13 +160,17 @@ impl Pins {
             gpioe.pe13, gpioe.pe14
         );
 
+        let hwrev = HWRev::detect_hw_rev(&HWRevPins {hwrev0: gpiod.pd0, hwrev1: gpiod.pd1,
+            hwrev2: gpiod.pd2, hwrev3: gpiod.pd3});
+        let hw_settings = hwrev.settings();
+
         let (dac0_spi, dac0_sync) = Self::setup_dac0(
             clocks, spi4,
             gpioe.pe2, gpioe.pe4, gpioe.pe6
         );
         let mut shdn0 = gpioe.pe10.into_push_pull_output();
         let _ = shdn0.set_low();
-        let vref0_pin = gpioa.pa0.into_analog();
+        let vref0_pin = if hwrev.major > 2 {Channel0VRef::Analog(gpioa.pa0.into_analog())} else {Channel0VRef::Disabled(gpioa.pa0)};
         let itec0_pin = gpioa.pa6.into_analog();
         let dac_feedback0_pin = gpioa.pa4.into_analog();
         let tec_u_meas0_pin = gpioc.pc2.into_analog();
@@ -176,7 +190,7 @@ impl Pins {
         );
         let mut shdn1 = gpioe.pe15.into_push_pull_output();
         let _ = shdn1.set_low();
-        let vref1_pin = gpioa.pa3.into_analog();
+        let vref1_pin = if hwrev.major > 2 {Channel1VRef::Analog(gpioa.pa3.into_analog())} else {Channel1VRef::Disabled(gpioa.pa3)};
         let itec1_pin = gpiob.pb0.into_analog();
         let dac_feedback1_pin = gpioa.pa5.into_analog();
         let tec_u_meas1_pin = gpioc.pc3.into_analog();
@@ -198,10 +212,6 @@ impl Pins {
             channel1,
         };
 
-        let hwrev = HWRev::detect_hw_rev(&HWRevPins {hwrev0: gpiod.pd0, hwrev1: gpiod.pd1,
-            hwrev2: gpiod.pd2, hwrev3: gpiod.pd3});
-        let hw_settings = hwrev.settings();
-
         let leds = Leds::new(gpiod.pd9, gpiod.pd10.into_push_pull_output(), gpiod.pd11.into_push_pull_output());
 
         let eeprom_scl = gpiob.pb8.into_alternate().set_open_drain();