RTD 2 Click is a compact add-on board used for applications with resistive elements that change resistance over temperature. This board features the ADS1247, 24-bit analog-to-digital converter with a programmable gain amplifier (PGA) for sensor measurement applications from Texas Instruments. It features a precision delta-sigma (ΔΣ) ADC with a single-cycle settling digital filter, and an internal oscillator, but also provides a low-drift voltage reference, and two matched programmable excitation current sources (IDACs). It also integrates sensor burn-out detection, voltage bias for thermocouples, system monitoring, and digital GPIOs. This Click board™ is suitable for temperature sensor measurements such as RTDs, thermocouples and thermistors, for pressure measurements, process control, and many more.

RTD 2 Click is supported by a mikroSDK compliant library, which includes functions that simplify software development.

RTD 2 Click is based on the ADS1247, a highly integrated 24-bit data converters with a programmable gain amplifier (PGA) for sensor measurement applications from Texas Instruments. The ADS1247 includes a delta-sigma (ΔΣ) ADC with an adjustable single-cycle settling digital filter, an internal oscillator, and an SPI-compatible serial interface. It also has a flexible input multiplexer with system monitoring capability and general-purpose I/O settings, a very low-drift voltage reference, and two matched current sources for sensor excitation. The ADS1247 provides a system monitor function. This function can measure the analog power supply, digital power supply, external voltage reference, or ambient temperature. Note that the system monitor function provides a coarse result. When the system monitor is enabled, the analog inputs are disconnected.

The two IDAC current sources integrated in the ADS1247 are used to implement the lead-wire compensation. One IDAC current source (IDAC1) provides excitation to the RTD element. The other current source (IDAC2) has the same current setting, providing cancellation of lead-wire resistance by generating a voltage drop across lead-wire resistance R2 equal to the voltage drop across R1 resistor (9.09k). Because the voltage across the RTD is measured differentially at ADC pins AIN1 and AIN2 of the ADS1247, the voltages across the lead-wire resistances cancel. The ADC reference voltage (pins REFP0 and REFN0) is derived from the voltage across R5 resistor with the currents from IDAC1 and IDAC2, providing ratiometric cancellation of current-source drift. R5 also level shifts the RTD signal to within the ADC specified common-mode input range.

The RTD 2 Click communicates with MCU using the standard SPI serial interface with additional data ready signal routed on the INT pin of the mikroBUS™ socket labeled as RDY. Data Ready signal is used to indicate when a new conversion is complete, and the conversion result is stored in the conversion result buffer. It also has an active-low Reset signal routed on the RST pin of the mikroBUS™ used to reset the device, and precise conversion control signal routed on the AN pin of the mikroBUS™ socket labeled as STR. The ADS1247 stays in Reset Mode as long as the RST pin stays low. When the RST pin goes high, the ADC comes out of Reset Mode and can convert data.

This Click board™ can work only with 3-wire probe types, a type of RTD probe used to measure temperatures up to 250°C.

This Click board™ is designed to be operated only with a 3.3V logic voltage level. A proper logic voltage level conversion should be performed before the Click board™ is used with MCUs with different logic levels. However, the Click board™ comes equipped with a library that contains easy to use functions and an example code that can be used as a reference for further development.

• Interface: SPI
• Compatibility: mikroBUS™
• Dimensions: 42.9 x 25.4mm
• Input Voltage: 3.3V
• Supply Voltage: Min. -0.3V, Typ. 3.3V, Max. 5.5V
• Power Consumption: 2.3mW
• Sample Rate: 2 kSPS
• Resolution: 24 bit
• Operating Temperature Range: Min. -40°C, Max. +105°C

• Schematic
• ADS1247 Datasheet
• mikroSDK
• GitHub