Raspberry Pi expansion specialist Sequent Microsystems has launched a crowdfunding campaign for its latest design, a Resistance Temperature Detector (RTD) driver add-on expandable to 64 channels.
Based on the changing resistance value of a material as the temperature shifts, RTDs are a popular component where precise measurements are required — easily hitting ±0.1°C accuracy. "RTD data acquisition systems are readily available, but rather pricey," explains Sequent Microsystems' Mihai Beffa. "'OM-CP-OCTRTD' from OMEGA offers 8 channels for $1,060 ($132.5/channel). Lower cost options are available. 'Model DI-718B-U' from DATAQ Instruments has also eight channels for 'only' $595.
"At the low end of the scale, Adafruit offers a single channel RTD sensor for $15 (you solder the connectors). Following in the footsteps of our previous Raspberry Pi IO Boards, we are offering the maximum number of channels in the minimum possible space, at the lowest possible cost."
The result is the Mega-RTD, a HAT add-on board for any Raspberry Pi with a 40-pin general-purpose input/output (GPIO) header. Built around two Texas Instruments ADS1248 24-bit delta-sigma analog to digital converters (ADCs) connected to an STMicro STM32F030, the HAT offers four or eight channels depending on model — but can be stacked to offer a total of 64 channels per Raspberry Pi host.
The HATs communicate with the host Raspberry Pi over I2C, and Sequent Microsystems says it will be providing a command-line interface (CLI) and Python code with each board. No housing is included, though the files to 3D print one are being published.
More information on the boards are available on the project's Kickstarter campaign page, with rewards starting at $30 for the four-channel variant.