diff --git a/src/channel.rs b/src/channel.rs
index 86480f1..c0b72a2 100644
--- a/src/channel.rs
+++ b/src/channel.rs
@@ -19,6 +19,7 @@ pub struct Channel<C: ChannelPins> {
     pub shdn: C::Shdn,
     /// stm32f4 integrated adc
     pub adc: C::Adc,
+    pub vref_pin: C::VRefPin,
     pub itec_pin: C::ItecPin,
     /// feedback from `dac` output
     pub dac_feedback_pin: C::DacFeedbackPin,
@@ -36,6 +37,7 @@ impl<C: ChannelPins> Channel<C> {
             dac,
             shdn: pins.shdn,
             adc: pins.adc,
+            vref_pin: pins.vref_pin,
             itec_pin: pins.itec_pin,
             dac_feedback_pin: pins.dac_feedback_pin,
             tec_u_meas_pin: pins.tec_u_meas_pin,
diff --git a/src/channels.rs b/src/channels.rs
index dd84442..459c5cf 100644
--- a/src/channels.rs
+++ b/src/channels.rs
@@ -142,6 +142,28 @@ impl Channels {
         }
     }
 
+    pub fn read_vref(&mut self, channel: usize) -> Volts {
+        match channel {
+            0 => {
+                let sample = self.channel0.adc.convert(
+                    &self.channel0.vref_pin,
+                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                );
+                let mv = self.channel0.adc.sample_to_millivolts(sample);
+                Volts(mv as f64 / 1000.0)
+            }
+            1 => {
+                let sample = self.channel1.adc.convert(
+                    &self.channel1.vref_pin,
+                    stm32f4xx_hal::adc::config::SampleTime::Cycles_480
+                );
+                let mv = self.channel1.adc.sample_to_millivolts(sample);
+                Volts(mv as f64 / 1000.0)
+            }
+            _ => unreachable!(),
+        }
+    }
+
     pub fn read_tec_u_meas(&mut self, channel: usize) -> Volts {
         match channel {
             0 => {
diff --git a/src/main.rs b/src/main.rs
index a51602e..d70b68a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -43,7 +43,7 @@ mod command_parser;
 use command_parser::{Command, ShowCommand, PwmPin};
 mod timer;
 mod units;
-use units::{Amps, Ohms, Volts};
+use units::{Ohms, Volts};
 mod pid;
 mod steinhart_hart;
 mod channels;
@@ -143,19 +143,19 @@ fn main() -> ! {
                                 Command::Show(ShowCommand::Input) => {
                                     for channel in 0..CHANNELS {
                                         if let Some(adc_data) = channels.channel_state(channel).adc_data {
+                                            let vref = channels.read_vref(channel);
                                             let dac_feedback = channels.read_dac_feedback(channel);
-                                            let dac_i = dac_feedback / Ohms(5.0);
 
                                             let itec = channels.read_itec(channel);
-                                            let tec_i = (itec - Volts(1.5)) / Ohms(0.4);
+                                            let tec_i = -(itec - Volts(1.5)) / Ohms(0.4);
 
                                             let tec_u_meas = channels.read_tec_u_meas(channel);
 
                                             let state = channels.channel_state(channel);
                                             let _ = writeln!(
-                                                socket, "t={} raw{}=0x{:06X} dac_feedback={}/{} itec={} tec={} tec_u_meas={}",
+                                                socket, "t={} adc_raw{}=0x{:06X} vref={} dac_feedback={} itec={} tec={} tec_u_meas={}",
                                                 state.adc_time, channel, adc_data,
-                                                dac_feedback, dac_i,
+                                                vref, dac_feedback,
                                                 itec, tec_i,
                                                 tec_u_meas,
                                             );
diff --git a/src/pins.rs b/src/pins.rs
index c46e70f..ff4545f 100644
--- a/src/pins.rs
+++ b/src/pins.rs
@@ -27,6 +27,7 @@ pub trait ChannelPins {
     type DacSync: OutputPin;
     type Shdn: OutputPin;
     type Adc;
+    type VRefPin;
     type ItecPin;
     type DacFeedbackPin;
     type TecUMeasPin;
@@ -37,6 +38,7 @@ impl ChannelPins for Channel0 {
     type DacSync = PE4<Output<PushPull>>;
     type Shdn = PE10<Output<PushPull>>;
     type Adc = Adc<ADC1>;
+    type VRefPin = PA0<Analog>;
     type ItecPin = PA6<Analog>;
     type DacFeedbackPin = PA4<Analog>;
     type TecUMeasPin = PC2<Analog>;
@@ -47,6 +49,7 @@ impl ChannelPins for Channel1 {
     type DacSync = PF6<Output<PushPull>>;
     type Shdn = PE15<Output<PushPull>>;
     type Adc = Adc<ADC2>;
+    type VRefPin = PA3<Analog>;
     type ItecPin = PB0<Analog>;
     type DacFeedbackPin = PA5<Analog>;
     type TecUMeasPin = PC3<Analog>;
@@ -65,6 +68,7 @@ pub struct ChannelPinSet<C: ChannelPins> {
     pub dac_sync: C::DacSync,
     pub shdn: C::Shdn,
     pub adc: C::Adc,
+    pub vref_pin: C::VRefPin,
     pub itec_pin: C::ItecPin,
     pub dac_feedback_pin: C::DacFeedbackPin,
     pub tec_u_meas_pin: C::TecUMeasPin,
@@ -120,6 +124,7 @@ impl Pins {
         let _ = shdn0.set_low();
         let mut adc0 = Adc::adc1(adc1, true, Default::default());
         adc0.enable();
+        let vref0_pin = gpioa.pa0.into_analog();
         let itec0_pin = gpioa.pa6.into_analog();
         let dac_feedback0_pin = gpioa.pa4.into_analog();
         let tec_u_meas0_pin = gpioc.pc2.into_analog();
@@ -128,6 +133,7 @@ impl Pins {
             dac_sync: dac0_sync,
             shdn: shdn0,
             adc: adc0,
+            vref_pin: vref0_pin,
             itec_pin: itec0_pin,
             dac_feedback_pin: dac_feedback0_pin,
             tec_u_meas_pin: tec_u_meas0_pin,
@@ -141,6 +147,7 @@ impl Pins {
         let _ = shdn1.set_low();
         let mut adc1 = Adc::adc2(adc2, true, Default::default());
         adc1.enable();
+        let vref1_pin = gpioa.pa3.into_analog();
         let itec1_pin = gpiob.pb0.into_analog();
         let dac_feedback1_pin = gpioa.pa5.into_analog();
         let tec_u_meas1_pin = gpioc.pc3.into_analog();
@@ -149,6 +156,7 @@ impl Pins {
             dac_sync: dac1_sync,
             shdn: shdn1,
             adc: adc1,
+            vref_pin: vref1_pin,
             itec_pin: itec1_pin,
             dac_feedback_pin: dac_feedback1_pin,
             tec_u_meas_pin: tec_u_meas1_pin,
diff --git a/src/units.rs b/src/units.rs
index 1bf8ea2..a52e07e 100644
--- a/src/units.rs
+++ b/src/units.rs
@@ -1,6 +1,6 @@
 use core::{
     fmt,
-    ops::{Add, Div, Sub},
+    ops::{Add, Div, Neg, Sub},
 };
 
 macro_rules! impl_add_sub {
@@ -18,6 +18,13 @@ macro_rules! impl_add_sub {
                 $Type(self.0 - rhs.0)
             }
         }
+
+        impl Neg for $Type {
+            type Output = $Type;
+            fn neg(self) -> $Type {
+                $Type(-self.0)
+            }
+        }
     }
 }