VoltLog's Voltlogger Packs 10 K-Type Temperature Probe Inputs Into a Single ESP32-Powered Board
Built to help debug a faulty reflow oven, the Voltlogger can track temperatures across up to 10 K-type probes at once.
Florin "VoltLog" C. has released an open source Espressif ESP32-based thermocouple data logger boasting an impressive 10 channels, originally designed as a debugging tool for a faulty reflow oven.
"After discovering that my T-962 reflow oven had uneven heating inside the oven I wanted to investigate this further and I needed a way of measuring & logging the temperature inside the oven in multiple points at the same time," Florin explains. "I designed the Voltlogger to be capable of recording 10 simultaneous thermocouple measurements."
"An ESP32 is the processor for this board which means you not only get lots of processing power but also a Wi-Fi/BT interface. There are 10x MAX31855 (K-Type) thermocouple interface chips which feature built-in cold junction compensation and each MAX31855 features input filtering circuitry to improve noise immunity."
The surprisingly compact multi-channel board includes a microSD slot for data storage, a CP2104 USB to serial adapter, and a USB Type-C connector which serves as both programming port and power input — or, alternatively, the board can be fed using an on-board pin header. The microcontroller also offers 2.4GHz Wi-Fi and Bluetooth connectivity for wireless monitoring.
"You can write code in pretty much any development environment that supports the ESP32 but you can checkout the example code which is written in Arduino using PlatformIO and Visual Studio," Florin writes. "This is just an example code and is provided AS IS without warranty of any kind."
There's another warning, too: "Depending on what type of thermocouples you plan to use (shielded or not) and depending on where you are performing the measurement, the effect of ground loops or floating voltages needs to be considered," Florin notes. "Having the board connected to a computer while doing the measurements means that any potentially dangerous voltages travelling through the shield of the thermocouples could travel through the GND connection up to your computer."
"These issues can be avoided by powering the board from an isolated 5V external supply like a power bank or 1S lithium-ion battery and keeping the board disconnected from the computer while performing the measurements. If you need live broadcasting of the measured values, the Wi-Fi connectivity could be used instead."
Revision A boards, which include a fix for a minor design flaw, are available to buy for $99.99 on the VoltLog Tindie store. The design files and source code, meanwhile, can be found on GitHub under the reciprocal GNU Public License 3.