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Maxim / Analog Devices · Integrated circuit

MAX6675 Thermocouple Converter

Reads a type-K thermocouple to 1024 C and hands back a 12-bit number over SPI, with cold-junction compensation already done.

Cheat sheet (SVG)
Logic level
3-5.5 V
Package
SO-8

1.Pinout diagram

Highlight a signalhover to preview, click to keep

Pins 1-4

MAX6675

Pins 5-8

Pin detail

Hover a pin for its mappings and gotchas. Click to keep it here.

Logic level
3-5.5 V
Package
SO-8

Fig. 1. MAX6675 Thermocouple Converter, SO-8. Hover or tap a signal to light up every pin that carries it.

2.Watch out

  • The hot junction reads 0 to 1023.75 C in 0.25 C steps. Below zero it cannot go: the MAX6675 has no negative range at all, which is the usual reason to reach for the MAX31855 instead.
  • The cold end, meaning the board the chip is sitting on, has to stay between -20 and +85 C. Compensation works by measuring the chip's own temperature, so putting the chip near the thing you are heating breaks the measurement rather than just the chip.
  • T- must be grounded externally. The datasheet says so plainly, and it is the connection people leave out because a thermocouple looks like a floating pair.
  • It is read-only SPI: there is no MOSI and nothing to configure. Drop CS low and clock out 16 bits. Bit 2 of that word is the open-thermocouple flag, which reads high when the probe is disconnected, and is worth checking because a missing probe otherwise looks like a plausible temperature.
  • Type-K only. The linearization is built for that alloy pair, so a J, T or N probe will read, and will read wrong.
  • Conversion takes about 0.2 s. Reading faster than that just returns the same number.
  • Pin 8 is not connected. Modules usually bring it out anyway.

3.Minimum circuit

What has to go around the chip before it will run.

VCCGNDMAX66750.1 uF ceramic between VCC (4) and GND0.1 uFceramicGround link between T- (2) and GNDGroundlinkGND (1) to GNDVCC (4) to VCCType-K thermocouple between T+ (3) and T- (2)Type-K thermocoupleGND 1T- 2T- 2T+ 3VCC 4VCC 4
Fig. 2. Minimum circuit, drawn from Table 1. Crossing wires are not connected.
Table 1. External parts, and why each one is there.
PartBetween
0.1 uF ceramicVCC (4) to GND
Ground linkT- (2) to GND
Type-K thermocoupleT+ (3) to T- (2)

Nothing else is needed. CS, SCK and SO go straight to the microcontroller, and the chip has no registers to set up. For long probe leads a 10 nF across T+ and T- is the usual noise fix.

4.Full pin reference

Every pin, alias and mapping. This is the table that prints.

Table 2. Pin assignments.

Complete pin reference for MAX6675 Thermocouple Converter
PinNameFunctions

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Primary sources

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