The Thermal Stability Regulatory Control Tool (TSRCT-PCB-01) is an Arduino Nano Every-based temperature-control board for experimental thermal management. It connects one Pt100 and one Pt1000 resistance temperature detector (RTD) to independent 5 V digital solid-state-relay (SSR) control outputs, with controller power and host communication through a single USB connection. External SSRs switch a separately powered heater circuit.

Basic functions

• Two MAX31865 RTD acquisition channels with independent temperature set points.
• Pt100 operation on channel 1 and Pt1000 operation on channel 2, with matching component population and firmware settings; configurable 2-, 3-, or 4-wire connections.
• PI/PID control, manual operation, set-point ramping, and anti-windup.
• Windowed SSR actuation, with nominal 1 s control and actuation windows.
• Open-loop step-response acquisition and FOPDT-based analytical SIMC PI / iSIMC PID tuning tools.
• USB serial telemetry and companion Python logging and analysis.
• RTD fault handling, stale-measurement detection, and over-temperature alarms that disable both heater commands.
• Connections for an I²C display, push button, and audible alarm.

Assembly variant: Pt100 on channel 1, Pt1000 on channel 2

The BOM and centroid file on this page populate channel 1 for Pt100 sensor operation: Rref-1 = 430 Ω 0.1 % (ERA-6AEB431V) and C-CH1 = 100 nF (CL21B104KBCNNNC); and channel 2 for Pt1000 sensor operation: Rref-2 = 4.3 kΩ 0.1 % (ERA-6AEB432V) and C-CH2 = 10 nF (CL21B103KBANNNC). Each channel reads correctly only with its matching sensor type.

All three variants share the same PCB and Gerber files; only the reference-resistor and channel-capacitor values differ:

• Pt100 version (both channels):

https://www.pcbway.com/project/shareproject/TSRCT_PT100_SSR_PID_Temperature_Controller_67959e58.html

• Pt1000 version (both channels): https://www.pcbway.com/project/shareproject/TSRCT_PT1000_SSR_PID_Temperature_Controller_ba38c86e.html

For straightforward ordering, use the listing matching your sensors. Alternatively, modify this BOM before ordering: a Pt100 channel uses a 430 Ω, 0.1% reference resistor (ERA-6AEB431V) and a 100 nF channel capacitor (CL21B104KBCNNNC); a Pt1000 channel uses 4.3 kΩ, 0.1% (ERA-6AEB432V) and 10 nF (CL21B103KBANNNC).

BOM and centroid files for all three variants are in the GitHub repository.

The Arduino Nano Every is supplied unprogrammed -- the firmware is available within the GitHub repository.

Adafruit design attribution and changes

The RTD front ends are based on the Adafruit MAX31865 breakout design by Limor Fried/Ladyada for Adafruit Industries. The MAX31865 interface software is derived from Adafruit's Arduino library.

The original projects are:

• Adafruit MAX31865 hardware: https://github.com/adafruit/Adafruit-MAX31865-PCB
• Adafruit MAX31865 Arduino library: https://github.com/adafruit/Adafruit_MAX31865

Hardware changes: TSRCT-PCB-01 integrates two RTD front ends into one control PCB with the Nano Every, SSR command connections, and display, button, and alarm interfaces. The layout consolidates the measurement and control wiring while retaining configurable RTD connections. Reference resistors and input-filter capacitors are populated per channel for the selected sensor type.

Firmware changes: RTD acquisition has been changed to a non-blocking state machine. Bias settling, conversion waiting, and readout are scheduled as separate stages so acquisition does not hold up the main loop during the sensor waiting periods. The application adds independent control loops, timer-scheduled SSR windows, analytical tuning support, fault handling, and host telemetry. The V1.1 timer implementation uses the Nano Every's ATmega4809 TCB2 peripheral; another microcontroller requires timer adaptation.

RTD wiring configuration

Assembled boards are ready for 4-wire RTD operation with no soldering required. For 2-wire or 3-wire sensors, the solder jumpers for each MAX31865 are configured by hand soldering after assembly -- they are not part of the BOM. The procedure follows the original Adafruit MAX31865 documentation, linked in the GitHub repository. Wire configuration and firmware settings must match -- published firmware uses 3-wire operation.

Further information is available within the GitHub repository: https://github.com/hefinn-lab/TSRCT-PT100-SSR-PID-Temperature-Controller