diff --git a/firmware/src/tec.rs b/firmware/src/tec.rs
index 1d58103..643bffe 100644
--- a/firmware/src/tec.rs
+++ b/firmware/src/tec.rs
@@ -35,44 +35,47 @@ impl fmt::Display for TecPin {
     }
 }
 
-fn enable_shdn<G>(gpio: G)
+fn setup_shdn<G>(gpio: G) -> GpioOutput<G>
 where
     G: Gpio,
     GpioOutput<G>: OutputPin,
 {
     let mut pin = gpio.into_output();
-    let _ = pin.set_high();
+    // keep off until first use
+    let _ = pin.set_low();
+    pin
 }
 
 /// Thermo-Electric Cooling device controlled through four PWM
 /// channels
-pub struct Tec<MaxIPos: PwmChannel, MaxINeg: PwmChannel, ISet: PwmChannel, MaxV: PwmChannel> {
+pub struct Tec<MaxIPos: PwmChannel, MaxINeg: PwmChannel, ISet: PwmChannel, MaxV: PwmChannel, SHDN: OutputPin> {
     max_i_pos: MaxIPos,
     max_i_neg: MaxINeg,
     i_set: ISet,
     max_v: MaxV,
+    shdn: SHDN,
 }
 
-impl Tec<pwm::T2CCP0, pwm::T2CCP1, pwm::T3CCP0, pwm::T3CCP1> {
+impl Tec<pwm::T2CCP0, pwm::T2CCP1, pwm::T3CCP0, pwm::T3CCP1, GpioOutput<PP4>> {
     pub fn tec0() -> Self {
         let (max_i_pos, max_i_neg) = tm4c129x::TIMER2::split();
         let (i_set, max_v) = tm4c129x::TIMER3::split();
-        enable_shdn(PP4);
-        Tec { max_i_pos, max_i_neg, i_set, max_v }
+        let shdn = setup_shdn(PP4);
+        Tec { max_i_pos, max_i_neg, i_set, max_v, shdn }
     }
 }
 
-impl Tec<pwm::T4CCP0, pwm::T4CCP1, pwm::T5CCP0, pwm::T5CCP1> {
+impl Tec<pwm::T4CCP0, pwm::T4CCP1, pwm::T5CCP0, pwm::T5CCP1, GpioOutput<PP5>> {
     pub fn tec1() -> Self {
         let (max_i_pos, max_i_neg) = tm4c129x::TIMER4::split();
         let (i_set, max_v) = tm4c129x::TIMER5::split();
-        enable_shdn(PP5);
-        Tec { max_i_pos, max_i_neg, i_set, max_v }
+        let shdn = setup_shdn(PP5);
+        Tec { max_i_pos, max_i_neg, i_set, max_v, shdn }
     }
 }
 
 
-impl<MaxIPos: PwmChannel, MaxINeg: PwmChannel, ISet: PwmChannel, MaxV: PwmChannel> Tec<MaxIPos, MaxINeg, ISet, MaxV> {
+impl<MaxIPos: PwmChannel, MaxINeg: PwmChannel, ISet: PwmChannel, MaxV: PwmChannel, SHDN: OutputPin> Tec<MaxIPos, MaxINeg, ISet, MaxV, SHDN> {
     pub fn setup(mut self, max: u16) -> Self {
         self.max_i_pos.set(max, max);
         self.max_i_neg.set(max, max);
@@ -99,8 +102,11 @@ impl<MaxIPos: PwmChannel, MaxINeg: PwmChannel, ISet: PwmChannel, MaxV: PwmChanne
                 self.max_i_pos.set(width, total),
             TecPin::MaxINeg =>
                 self.max_i_neg.set(width, total),
-            TecPin::ISet =>
-                self.i_set.set(width, total),
+            TecPin::ISet => {
+                self.i_set.set(width, total);
+                // enable on first use
+                let _ = self.shdn.set_high();
+            }
             TecPin::MaxV =>
                 self.max_v.set(width, total),
         }