EYE on NPI – Maxim MAX31888 ±0.25°C Accurate, 1-Wire Temperature Sensor #EyeOnNPI #DigiKey @DigiKey @Adafruit

This week’s EYE ON NPI (video) comes in right under the wire…the one wire! It’s Maxim’s MAX31888 high-accuracy 1-Wire sensor with 0.25ºC degree accuracy.

This is a lovely little upgrade to the extremely popular DS18B20 series of 1-Wire temperature sensors, but with a smaller body and better accuracy – the DS18B20 has at best ±0.5ºC in comparison.

What Is Special About 1-Wire?

1-Wire is a voltage-based digital system that works with two contacts, data and ground, for half- duplex bidirectional communication. Compared to other serial communication systems such as I2C or SPI, 1-Wire devices are designed for use in a momentary contact environment. Either disconnecting from the 1-Wire bus or a loss of contact puts the 1-Wire slaves into a defined reset state. When the voltage returns, the slaves wake up and signal their presence. With only one contact to protect, the built-in ESD protection of 1-Wire devices is extremely high. With two contacts, 1-Wire devices are the most economical way to add electronic functionality to nonelectronic objects for identification, authentication, and delivery of calibration data or manufacturing information.

We don’t tend to cover 1-Wire products on EYE ON NPI, although there’s not a lot of new products in the family, these chips are used very often in industry for low-pinout interfaces. For example batteries or power adapters can use 1-Wire devices for authentication or LED control.

With temperature, basic authentication, multiple GPIO and 1-wire parasitic power, this chip would also be great for embedded sensors that are used for authentication and temperature tracking. For example cold-chain storage, a specialized logging and tracing use case that prior to 2020 was not something we all knew about. 1-wire is cheaper and simpler for hot-plug detection than I2C, also it can work well when you have a large box and say you want to log or track the temperature in 6 corners + center.

With I2C you would need a chip that can handle 7 different addresses and you’d need 4 wires traced to each section. With 1-Wire you only need 2 wires and you can have a near-infinite number of sensors, each with guaranteed unique IDs for logging and ultra low power usage during measurement.

1-Wire is also specifically designed for long wire drops, where-as I2C and SPI are not:

Network weight is limited by the ability of the cable to be charged and discharged quickly enough to satisfy the 1-Wire protocol. A simple resistor pullup has a weight limitation of about 200m. Sophisticated 1-Wire master designs have overcome this limitation by using active pullups, that provide higher currents under logic control and have extended the maximum supportable weight to over 500m. See application note 244, “Advanced 1-Wire Network Driver.”

Yep, you read that right: simple pullup-style controllers are good for up to 200 meters – compare that with I2C which wasn’t recommend over 200mm! There’s I2C to 1-Wire converters available or you can find drivers for 1-Wire controllers on most board-support-packages – it’s not significantly hard to bit bang 1-Wire in C/C++.

The MAX31888 temperature sensors will keep your temperature logging system fresh and secure, and best of all… They’re in stock right now at Digi-Key! Order both MAX31888 sensors and the eval board for immediate shipment, you could have them in your hot li’l hands tomorrow afternoon!

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