SparkFun's Thing Plus Dual-Port Data Logging Shield Provides SPI and USB Access to a Single microSD
Providing switchable access to a single microSD over USB or SPI as required, the Dual-Port Logging Shield means never ejecting a card.
SparkFun has launched a new add-on board designed for those who have a Thing Plus and want easy data logging without the need to eject memory cards, with a microSD slot accessible over both SPI and the board's USB Type-C port: the Thing Plus Dual-Port Logging Shield.
"We carry several data logging products which have microSD sockets on them," the company explains of its latest launch. "They're great for logging data to a microSD card, but when it comes to reading the logged data quickly you usually have to pop out the microSD card and plug it into your computer. But what if you're developing an embedded system and you don't want to or aren't able to eject the microSD card. Enter the SparkFun Thing Plus Dual-Port Logging Shield!"
As the name implies, the add-on board features two ports. The first is a USB Type-C port to one end, which can be connected to any device support USB Mass Storage connectivity and that will display the contents of the microSD card for both reading and writing — at speeds, the company claims, of up to 35MB/s theoretical and 20MB/s real-world.
The second port, meanwhile, is an SPI bus connected to the host Thing Plus microcontroller board. A Microchip ATtiny841 decides which port should be connected to the microSD at any given time: If the host Thing Plus is powered it gets exclusive access to the microSD via the SPI bus; if you connect a USB cable to the shield instead, you get the "thumb drive" mode. If both are powered on simultaneously, you can flip between the two using I2C commands.
There are a couple of caveats to the logger's use, however, both stemming from the USB chip used: Only FAT32, exFAT, and NTFS filesystems are supported; and it's not able to use cards larger than 32GB. Given that it's designed for capturing data from a microcontroller, though, 32GB represents a considerable amount of space.
The Thing Plus Dual-Port Data Logging Shield is now available on the SparkFun website for $29.95 before volume discounts; additional information is available in the board's hookup guide.