Build a DIY PID Temperature Controller for Sous‑Vide Cooking in 5 Simple Steps

If you’ve ever tried to get that perfect medium‑rare steak at home and ended up with a rubbery mess, you know why precise temperature matters. Sous‑vide takes the guesswork out of cooking, but the pricey commercial units can scare off a hobbyist. Luckily, with a little solder, a cheap microcontroller, and a dash of patience, you can build a PID temperature controller that rivals the big brands. Here’s how I did it, step by step, on a Saturday afternoon in my garage.

Why a PID Controller?

A PID (Proportional‑Integral‑Derivative) controller is just a smart way to keep a temperature steady. Think of it like a thermostat that learns from its mistakes. The “proportional” part reacts to the current error, the “integral” part remembers past errors, and the “derivative” part predicts where the temperature is heading. Together they smooth out the ups and downs that a simple on/off switch would cause. In sous‑vide, even a few degrees off can change a steak from buttery to overcooked, so a PID is worth the effort.

Step 1 – Gather the Parts

You don’t need a PhD in electronics, just a few common components:

Arduino Nano (or any small microcontroller you already have)
Thermocouple (type K is cheap and works well in water)
MAX6675 or MAX31855 board – this reads the thermocouple and talks to the Arduino
Solid‑state relay (SSR) – switches the heating element on and off without sparking
12 V or 24 V heating element – a simple immersion heater works fine
Power supply for the Arduino (USB or 5 V wall wart)
Breadboard and jumper wires for prototyping
Enclosure – a small project box or a 3D‑printed case

All of these can be found on a typical electronics site for under $30. I bought mine from a local hobby shop, and the whole thing fit in a shoebox.

Step 2 – Wire the Sensors and Relay

First, connect the thermocouple to the MAX board. The board has four pins: VCC, GND, SCK, and CS. Hook VCC to 5 V on the Arduino, GND to ground, SCK to pin 13, and CS to pin 10 (you can change these later in code). The thermocouple’s two wires plug directly into the board – no solder needed.

Next, wire the SSR. The SSR has two sides: a low‑voltage control side and a high‑voltage load side. Connect the control side to the Arduino’s digital pin 9 and ground. The load side goes in series with the heating element and the mains (or DC) supply. Safety tip: make sure the SSR’s rating exceeds the voltage and current of your heater. I used a 25 A SSR for a 1500 W element, which gave me a comfortable safety margin.

Step 3 – Write the PID Code

Open the Arduino IDE and install the PID_v1 library (just search “PID” in the Library Manager). The code is short, but let me walk you through the key parts.

#include <PID_v1.h>
#include <SPI.h>
#include "max6675.h"

const int thermoDO = 4;
const int thermoCS = 5;
const int thermoCLK = 6;
MAX6675 thermocouple(thermoCLK, thermoCS, thermoDO);

double Setpoint, Input, Output;
double Kp = 2.0, Ki = 5.0, Kd = 1.0;   // Tune these later
PID myPID(&Input, &Output, &Setpoint, Kp, Ki, Kd, DIRECT);

const int relayPin = 9;

void setup() {
  pinMode(relayPin, OUTPUT);
  Serial.begin(9600);
  Setpoint = 55.0;          // Desired temperature in °C
  myPID.SetMode(AUTOMATIC);
  myPID.SetOutputLimits(0, 255); // PWM range
}

void loop() {
  Input = thermocouple.readCelsius();
  myPID.Compute();
  analogWrite(relayPin, (int)Output);
  Serial.print("Temp: ");
  Serial.print(Input);
  Serial.print("  Output: ");
  Serial.println(Output);
  delay(1000);
}

A few notes:

Setpoint is the temperature you want – 55 °C is a classic sous‑vide spot for steak.
Kp, Ki, Kd are the tuning constants. Start with the values above, then adjust: increase Kp if the temperature reacts too slowly, raise Ki if there’s a steady offset, and tweak Kd to dampen overshoot.
analogWrite on the relay pin uses PWM (pulse‑width modulation) to give the heater a variable power level instead of just on/off.

Upload the sketch, open the Serial Monitor, and you should see the temperature reading rise as the heater turns on.

Step 4 – Tune the PID

Tuning is where the magic happens. I follow a simple “Ziegler‑Nichols” method:

Set Ki and Kd to zero.
Increase Kp until the temperature starts to oscillate steadily.
Note that Kp value (call it Ku) and the oscillation period (Pu).
Apply the formulas: Kp = 0.6 * Ku, Ki = 2 * Kp / Pu, Kd = Kp * Pu / 8.

In practice, I turned the knob a bit lower than the calculated values to avoid aggressive swings. After a few minutes of watching the graph, the temperature settled within ±0.2 °C of the setpoint – perfect for sous‑vide.

Step 5 – Pack It Up and Test

Once the controller is stable on the breadboard, move everything into your enclosure. Drill a small hole for the thermocouple tip, and another for the power cord. Mount the SSR and Arduino on standoffs to keep them from touching the metal case. I added a tiny OLED display (optional) to show the current temperature and setpoint at a glance.

Now fill a large pot with water, drop in the immersion heater, and set the controller to 55 °C. After about 30 minutes the water should be steady. I tested with a ribeye, sealed in a zip‑lock bag, and after 1 hour the meat was exactly the pink I was aiming for. No more guessing, no more burnt edges.

A Few Lessons Learned

Don’t skimp on the SSR rating. A cheap 5 A relay will overheat quickly with a 1500 W heater.
Thermocouple placement matters. Keep the tip away from the heater coil; otherwise you’ll read a hotter temperature than the water actually is.
Cable length can introduce noise. Keep the thermocouple wires short and twisted together to reduce interference.
Safety first. Use a proper waterproof enclosure if you plan to leave the controller near water for long periods.

Building this controller reminded me why I love DIY: you get to understand every part of the system, and you end up with a tool that’s both cheap and customized. If you’re already tinkering with home automation on ThermoCraft, you can even add Wi‑Fi to the Arduino and control the setpoint from your phone. The sky’s the limit, but the basic five‑step build gets you cooking right away.

Happy sous‑vide, and may your steaks always be juicy!