Eight Thermocouples DAQ 8-Layer Stackable HAT for Raspberry Pi

Compatible with all Raspberry Pi models from the Raspberry Pi Zero to Raspberry Pi 5, the Eight Thermocouples Card provides a compact and cost-effective solution for monitoring and logging temperature data from up to 64 thermocouple sensors.
The card uses high-resolution 24-bit delta-sigma analog-to-digital converters, each supporting four input channels, to deliver measurement accuracy better than 0.1%. When calibrated in the field using a precision 100 Ω reference resistor, measurement accuracy can be improved to better than 0.01%.
Communication with the Raspberry Pi is accomplished over the I²C bus, requiring only two GPIO pins regardless of the number of installed cards. Up to eight cards can share the same bus, leaving the remaining Raspberry Pi GPIO pins available for user applications.
An integrated RS485/MODBUS RTU interface provides virtually unlimited expansion capabilities. The interface can operate in slave mode under Raspberry Pi control or allow the card to function as a standalone MODBUS device connected directly to a PLC or other industrial controller, eliminating the need for a Raspberry Pi.
For increased system reliability, the card includes an onboard hardware watchdog that can monitor Raspberry Pi activity and automatically cycle power to the computer in the event of a software lockup or system failure.
A programmable tactile pushbutton enables safe Raspberry Pi shutdown without requiring a keyboard, monitor, or remote login. A status LED indicates proper operation of the onboard processor, while eight user-programmable LEDs can be configured to illuminate when the corresponding temperature channel exceeds a predefined threshold.

COMPATIBILITY

The Eight Thermocouples card is compatible with all Raspberry Pi versions from Zero to 5. It shares the I2C bus using only two of the Raspberry Pi’s GPIO pins to manage all eight cards.  This feature leaves the remaining 24 GPIOs available for the user. 

POWER REQUIREMENTS

The Eight Thermocouples DAQ Card needs 5V to operate and can be powered from Raspberry Pi or from it's own pluggable connector. The cards needs 50mA to operate.

DIP SWITCH CONFIGURATION

A six position DIP switch is used to select the source of the RS485 port and the position of the card in the stack, if multiple cards are used. 

RS485/MODBUS PORT

The card includes a standard RS485 transceiver that can be accessed either by the onboard processor or directly by the Raspberry Pi. The desired operating mode is selected using two configuration switches on the onboard DIP switch.

When the corresponding DIP switches are ON, the Raspberry Pi has direct access to the RS485 interface and can communicate with any RS485-compatible device. In this mode, the card functions as a passive hardware bridge, providing only the electrical interface required by the RS485 standard. To enable this configuration, the onboard processor must be instructed to release control of the RS485 bus:

~$ smtc [0] wcfgmb 0 0 0 0

When the DIP switches are OFF, the onboard processor takes control of the RS485 interface and the card operates as a MODBUS RTU slave. In this mode, any MODBUS master can read all input values and control all outputs using standard MODBUS RTU commands. A complete description of the implemented MODBUS registers and commands is available on GitHub:

https://github.com/SequentMicrosystems/smtc-rpi/blob/main/MODBUS.md

In both operating modes, the onboard processor must be configured to either release control of the RS485 interface (DIP switches ON) or manage the RS485 communications (DIP switches OFF). Refer to the command-line online help for detailed configuration instructions.

RS485 TERMINATOR

The first position on the DIP switch is the RS485 line terminator. Set it to ON if the card is last on the RS485 chain.

CARD LAYOUT

MECHANICAL SPECIFICATIONS

SOFTWARE INTERFACES

You can write your own Data Acquisition system in C, C++, PERL or the language of your choice using the Command Line functions or the Python Library. A browser interface can easily be deployed using Node-Red. 

FIELD CALIBRATION

Field calibration to 0.01% precision can be achieved using an external high precision voltage reference. Software commands permit the user to calibrate the card in two points (the 2 points must be as far as possible but inside the measurement range). 

RS485/MODBUS Communication

The card includes a standard RS485 transceiver that can be accessed either by the onboard processor or directly by the Raspberry Pi. The desired operating mode is selected using two configuration switches on the onboard DIP switch.

When the corresponding DIP switches are ON, the Raspberry Pi has direct access to the RS485 interface and can communicate with any RS485-compatible device. In this mode, the card functions as a passive hardware bridge, providing only the electrical interface required by the RS485 standard. To enable this configuration, the onboard processor must be instructed to release control of the RS485 bus:

~$ smtc [0] wcfgmb 0 0 0 0

When the DIP switches are OFF, the onboard processor takes control of the RS485 interface and the card operates as a MODBUS RTU slave. In this mode, any MODBUS master can read all input values and control all outputs using standard MODBUS RTU commands. A complete description of the implemented MODBUS registers and commands is available on GitHub:

https://github.com/SequentMicrosystems/smtc-rpi/blob/main/MODBUS.md

In both operating modes, the onboard processor must be configured to either release control of the RS485 interface (DIP switches ON) or manage the RS485 communications (DIP switches OFF). Refer to the command-line online help for detailed configuration instructions.

FIRMWARE UPDATE

The card firmware can be updated in the field by running a command. The update is made with the latest firmware version located on our servers. More instructions about the process can be found on GitHub. Please make sure there is no process, like Node-Red or python scripts, that tries to access the card during the update process.

DIN-RAIL MOUNTING

The 8-Thermocouples DAQ card can be installed parallel on a DIN-Rail using the DIN-Rail Kit Type 1, or perpendicular using the DIN-Rail Kit Type 2.

1. 8-Thermocouples DAQ HAT for Raspberry Pi

2. Mounting hardware

4. All female connector plugs