MAX6675 K-type thermocouple module
MAX6675 thermocouple amplifier pinout (SO, CS, SCK, VCC, GND), 0–1024 °C K-type readings, polarity, the 220 ms conversion time and NaN fixes.
Community draft — report a mistake
3.3 V or 5 V? The MAX6675 runs from 3.0–5.5 V and its SO output follows VCC. Power it from 3.3 V on ESP32 and Pico, 5 V on Uno — then every pin matches your board.
A thermocouple is two different metals welded together; heating the joint produces a tiny voltage (about 41 µV/°C for K-type). The MAX6675 amplifies that, compensates for the temperature of the screw terminals (the “cold junction”) and hands you a 12-bit reading from 0 to 1024 °C in 0.25 °C steps. It’s used for ovens, kilns, 3D-printer hot ends, tandoors and solar cookers.
It’s read-only SPI: pull CS low, clock out 16 bits on SO, done. You can use any three GPIOs. Each conversion takes up to 220 ms, and it can’t read below 0 °C — for that, use the MAX31855.
Gotchas: the thermocouple tip must not touch a grounded metal part (the MAX6675 needs a floating probe), extending the probe needs K-type extension wire (not copper), and accuracy is about ±2–3 °C at best — fine for ovens, not for body temperature.
Prices are indicative (Nov 2026) and vary by seller.
Pinout
| Pin | What it does |
|---|---|
GND | Ground |
VCC | 3.0–5.5 V supply (about 1.5 mA) |
SCK | Serial clock from the board (any GPIO — the library bit-bangs it) |
CS | Chip select — pull LOW to read, HIGH starts the next conversion |
SO | Serial data out to the board (read-only chip — there is no data-in pin) |
T+ | Thermocouple + (the non-magnetic leg; yellow on ANSI-coded probes — colours vary by seller) |
T- | Thermocouple − (the leg a magnet sticks to; red on ANSI-coded probes) |
Library
MAX6675 library by Adafruit
Arduino IDE → Library Manager → search the name above. Each guide lists the exact version we compile against.
Use it with
Common errors
Reads NaN or 0 °C
The chip reports an open thermocouple. Tighten both screw terminals, check the probe isn’t broken, and confirm SO/SCK/CS match the pin numbers in your sketch.
Temperature goes down when you heat the probe
The thermocouple legs are reversed. Swap the wires on T+ and T−.
Value never changes or repeats the same number
You are reading faster than the 220 ms conversion time. Wait at least 250 ms between reads.
Readings jump by tens of degrees near a motor or heater
Thermocouple wires pick up noise. Twist the leads, keep them away from mains wiring, and add a 10 nF capacitor across T+ and T−.