Introduction
The ThermokUSB-RTD2 is a small module that plugs into your USB port and provides two precision RTD inputs. Versions are available for PT100 or PT1000 RTDs. 2 wire, 3 wire, and 4 wire RTDs are supported. Communications with the computer is via Modbus RTU format. The ThermokUSB-RTD2 is a Serial CDC device, so no drivers are needed with modern operating systems.
Internally the ThermokUSB-RTD2 uses two of Maxim Integrated's MAX31865 RTD to digital converters. These converters are high resolution (0.03125°C nominal resolution) and high accuracy (0.5°C across all operating conditions). Built-in fault detection allows shows open RTD elements, RTD shorted to out-of-range voltage, and shorts across RTD. +-50V input protection is provided. The inputs are not isolated from the computer. A Microchip PIC18F14K50 is used to provide Modbus communications and USB interface.
The ThermokUSB-RTD2 is open source hardware and software. Schematic and PCB files are available in open formats. Firmware source code is open source, however it requires CCS's PCH compiler to compile.
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