MAX6675 thermocouple module: specs and pinout
A cold-junction-compensated K-type thermocouple-to-digital converter that outputs a 12-bit reading over a read-only SPI-compatible interface. The store listing mentions a relay; no source documents one, so this page makes no relay claim.
Specs
| Spec | Value | Source |
|---|---|---|
| Supply voltage VCC | 3.0 V to 5.5 V | source Electrical Characteristics (p.2) |
| Resolution | 12-bit, 0.25 degC | source Features (p.1) |
| Hot-junction read range | 0 degC to +1023.75 degC | source Detailed Description, Cold-Junction Compensation (p.4) |
| Thermocouple accuracy | 8 LSB for 0 degC to +700 degC | source General Description (p.1) |
| Cold-junction (board) temperature range | -20 degC to +85 degC | source Detailed Description (p.4); Operating temperature range (p.2) |
| Thermocouple type | K only (T+ is chromel, T- is alumel) | source Pin Description (p.4) |
| Conversion time | 0.17 s typ, 0.22 s max | source Electrical Characteristics (p.2) |
| Supply current ICC | 0.7 mA typ, 1.5 mA max | source Electrical Characteristics (p.2) |
| Serial clock frequency | 4.3 MHz max | source Timing Characteristics (p.3) |
| Serial read length | 16 clock cycles, read on the falling clock edge | source Serial Interface (p.5) |
Power
| Value | Source | |
|---|---|---|
| Supply | 3.0 V to 5.5 V | source Electrical Characteristics (p.2) |
| Current | 0.7 mA typ, 1.5 mA max | source Electrical Characteristics (p.2) |
Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.
The pin table is the bare 8-pin SO chip (GND, T-, T+, VCC, SCK, CS, SO, N.C.), not the module header: do not wire the module from this list. The module board (header order, thermocouple terminal, anything else on it) is not covered by an official document.
| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| GND | Ground | source Pin Description (p.4) | ||
| T- | Alumel lead of the type-K thermocouple | Connect to ground externally | Datasheet: should be connected to ground externally | source Pin Description (p.4) |
| T+ | Chromel lead of the type-K thermocouple | source Pin Description (p.4) | ||
| VCC | Positive supply | 3.0-5.5 V | Bypass with a 0.1 uF capacitor to GND | source Pin Description (p.4); Electrical Characteristics (p.2) |
| SCK | Serial clock input | source Pin Description (p.4) | ||
| CS | Chip select; set low to enable the serial interface | Forcing CS low stops any conversion; forcing CS high starts a new one | source Pin Description (p.4); Serial Interface (p.5) | |
| SO | Serial data output | source Pin Description (p.4) | ||
| N.C. | No connection | source Pin Description (p.4) |
Build with it
Project ideas for the MAX6675 thermocouple module. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.
- MAX6675 SPI link test with open-thermocouple flag: MAX6675 runs from 3.0-5.5 V so a 5 V Uno works. With nothing connected to the thermocouple input, bit D2 of the 16-bit frame is the open-thermocouple flag (p.4-5); the datasheet says T- must be grounded for this detection, and the module's wiring of T- is undocumented, so a high D2 shows the SPI read works, not that the module is wired correctly. A K-type thermocouple is not in the stocked list; bring your own for real temperatures. The module itself needs checking with a meter.
- Raw frame logger over serial: The ESP32 gives SPI at 3.3 V, inside the 3.0-5.5 V supply range; read about 4 times a second at most (0.22 s max conversion). Without a probe the open-thermocouple bit is set; a K-type probe is not in the stocked list. Open-thermocouple detection needs T- grounded (datasheet); check how the module wires T-.
- Pico SPI readout test: The Pico is 3.3 V and the chip accepts 3.0-5.5 V, with a read-only SPI link that needs no data-in line. A K-type probe is not in the stocked list, so this checks the link and the open-thermocouple flag only. Open-thermocouple detection needs T- grounded (datasheet); check how the module wires T-.
Common mistakes
- Using a J-type or other thermocouple: the converter is for type-K only (source)
- Wiring T- to the wrong place: T- should be connected to ground externally, and T+ is the chromel lead (source)
- Reading it faster than it converts: conversion takes 0.22 s max, so poll at about 4 Hz at most; the chip is read-only SPI with no data-in pin (source)
Not covered by the official source
- Only the chip is documented. The listing says Relay Module, but no official sheet describes any relay, its rating, or how it is driven; the page does not publish relay claims.
- Whether a thermocouple probe comes with the module is not stated by any source. No K-type thermocouple is in the stocked list (the stocked thermocouples are J type, which this chip does not support), so the ideas below are SPI link tests, not temperature builds.
- Conversion time and supply current should be checked against the datasheet table.
- Maxim Integrated is now part of Analog Devices.
Sources
- link (Maxim MAX6675 datasheet, 19-2235 Rev 1, 3/02)