8 Thermocouples 16 Open-drain Outputs for Raspberry Pi I/O Back Panel

The 8 Thermocouples 16 Open-drain Outputs Card adds eight thermocouple inputs and sixteen open-drain (OD) outputs to your Raspberry Pi Back Panel for precise temperature monitoring and simple alarm/control actions. The card integrates cold-junction compensation and noise filtering for stable readings, routes all wiring cleanly through the Back Panel, and works with CLI/Python or RS485/MODBUS—so you can stack it alongside other HOP cards and scale your system with ease FEATURES 8 Thermocouple Inputs Eight software selectable inputs can read thermocouple types J, K, T, N, E, B, R and S 16 Open-Drain Outputs Sixteen open-drain outputs can drive loads up to 2A and 24VDC. Loads power must be provided by the user. Seamless Raspberry Pi Integration Plugs directly into the Raspberry Pi Back Panel — no additional wiring or hardware needed. Expandable Stack Design Stack up to 8 identical modules horizontally for larger projects. MODBUS Support via RS485 Integrated RS485 port allows MODBUS RTU communication for easy industrial integration. CAN Support via CANopen Integrated CAN interface enables reliable CANopen communication for seamless industrial networking and real-time device control. Real-Time Status LEDs Input and output LED indicators provide immediate visual feedback. Built-in OLED Display 128×32 dot matrix screen for displaying system status, messages, or sensor values. Cross-Platform Software Support Includes Python library and command-line tools for rapid development. OpenPLC & CODESYS Compatible Industrial-grade compatibility with both OpenPLC and CODESYS environments. No Export Restrictions ECCN classification EAR99 — freely exportable under U.S. regulations. DESCRIPTION Part of the HOP (Hardware On Panel) family developed by Sequent Microsystems, the 8 Thermocouples 16 Open-drain Outputs Card is designed to integrate seamlessly with the Raspberry Pi Back Panel. Up to eight HOP cards—of any type—can be installed on a single Back Panel, offering maximum flexibility for industrial automation applications. The card features: Eight software selectable thermocouple inputs reading type J, K, T, N, E, B, R and S thermocouples Sixteen open-drain outputs driving loads up to 2A and 24VDC Sixteen onboard LEDs display the real-time status of each input and output. Additional indicators show board power and signal any error condition. An RS485 port enables external PLC or industrial controller communication using the industry-standard MODBUS RTU protocol. Power Requirements The 8 Thermocouples 16 Open-drain Outputs Card is powered via the Back Panel power connector. The local processor is powered from the 5V rail through a 3.3V LDO regulator and consumes 10 mA. The open-drain outputs require additional 25mA from the 5V supply and 100mA from the 24V supply. Error Processing One pin on the spring-loaded terminal block of the Back Panel is reserved for signaling an error condition. The user can connect this pin to an external contact of their choice. When the error signal is activated, the 8 Thermocouples 16 Open-drain Outputs Card automatically resets all outputs to a predefined default state. WATCHDOG: If the watchdog is enabled and the Raspberry Pi fails to access the 8 Thermocouples 16 Open-drain Outputs Card within the preset time, the card signals the Back Panel, which performs a hard reset of the Raspberry Pi by turning the power off for 10 seconds. STACK LEVEL: The stack level is automatically determined by the slot into which the card is inserted on the Back Panel. It is shown on the OLED display after power up. Up to eight cards of the same type can be connected to a single Back Panel installation. INTERRUPT: Any HOP card can be programmed to interrupt the Raspberry Pi. The interrupt handler running on Raspberry Pi needs to monitor pin 37 on the GPIO interface. Thermocouple Connectors Pinout The eight thermocouples are routed to individual, dedicated screw mount thermocouple connectors. Thermictors mounted next to each connector measure the local connector temperature. BACK PANEL TERMINAL BLOCK PINOUT Each slot on the Back Panel has alocated three 6-pin spring-loaded terminal blocks for IO wiring. The pinout is shown in the following picture: The open-drain outputs are routed to the Back Panel as follows: IO01: OD1 IO02: OD2 IO03: OD3 IO04: OD4 IO05: OD5 IO06: OD6 IO07: OD7 IO08: OD8 IO09: OD9 IO10: OD10 IO11: OD11 IO12: OD12 IO13: OD13 IO14: OD14 IO15: OD15 IO16: OD16 IO17: ERROR IO18: PANIC IO17 is an open drain output triggered by a predefined error condition on an out of bounds input. It can be used to activate an external alarm, or can be routed back to IO18 to reset the outputs to a predefined state. IO18 is a dry contact to ground input and can be activated by an external contact wired to the Back Panel terminal block. When triggered, it resets all outputs to a predefined state. DOT MATRIX DISPLAY The card includes a 128 × 32 dot-matrix display driven by the on-board processor. It can show status information, self-test results, and error messages. At power up it displays the card name, the I2C address, the slot position and the value of the 24V supply. ELECTRICAL SPECIFICATIONS Power Supply: Back Panel provided 5V 35mA 24V 100mA MECHANICAL SPECIFICATIONS DOWNLOADS 2D DXF Mechanical 3D STEP Model 3D Printable Enclosure SOFTWARE Command Line Drivers Python Libraries CODESYS Driver OpenPLC Module QUICK START Plug the 8 Thermocouples 16 Open-drain Outputs Card on the Back Panel for Raspberry Pi and power up the system. Enable I2C communication on Raspberry Pi using raspi-config. Install the software from github.com: git clone https://github.com/SequentMicrosystems/sequent-cli.git cd /home/pi/sequent-cli sudo make install sequent-cli 8thermo -h The program will respond with a list of available commands. FAQ Q: What Raspberry Pi models are compatible with this card? A: The card is compatible with all 40-pin Raspberry Pi models, including Pi 4, Pi 3, Pi 2, and Pi Zero. Q: How is the stack level determined? A: Stack level is automatically assigned based on the slot the card is plugged into on the Back Panel via ID0–ID2 pins. Q: What does the watchdog function do? A: If the Raspberry Pi fails to communicate over I²C in a set time, the watchdog cuts power for 10 seconds to trigger a system reset. Q: What is the purpose of the Panic function? A: The Panic input resets all outputs to their predefined default states for emergency shutdown or fail-safe scenarios. Q: Can multiple cards be used together? A: Yes, up to 8 cards can be stacked using the Back Panel. Each card auto-assigns its ID for seamless expansion. Q: Is there a display on the card? A: Yes, it features a 128×32 dot-matrix display for status, self-test, and error messages. Q: How is communication with the Pi handled? A: Communication is via I²C using SDA and SCL lines on the 2×20 GPIO connector.