Computer/Embedded Technology


Data acquisition HATs for Raspberry Pi

29 September 2021 Computer/Embedded Technology

Raspberry Pi is the most popular single-board computer in use today, but does not have built-in test and measurement capabilities such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs) or conditioned digital inputs and outputs (DIO). However, these capabilities can be added through the Pi’s 40-pin GPIO header. A device that connects directly to the 40-pin header and stacks onto the Raspberry Pi is called a HAT (Hardware Attached on Top).

Over the years, individuals have published open-source designs and small companies have sold low-cost HATs for a variety of tasks, including support for analog and digital I/O. These designs and products are adequate for the education and hobbyist/maker market but have some serious shortcomings for professional test and measurement applications. Most of these devices are provided partially assembled, without specifications or programming support and without performance guarantees that can only be achieved with a thorough device validation process.

To bring professional-quality measurement products to the Raspberry Pi platform, Measurement Computing Corporation (MCC) has developed a series of DAQ HATs that offer similar specifications and accuracy as traditional USB- and Ethernet-based DAQ products from MCC, with resolution up to 24 bits and sample rates up to 100 KSps. This range is now available in South Africa through Osiris Technical Systems.

Product range

MCC offers five products designed for test and measurement applications that conform to the Raspberry Pi HAT standard. These devices provide data acquisition features like analog and digital I/O in a small, stackable format. DAQ HATs can be used in basic applications with just a few voltage input channels, or more sophisticated applications with up 64 channels of multiple signal types.

Voltage measurement

The MCC 118 is an 8-channel voltage measurement HAT which allows users to measure 12-bit data at an overall throughput of 100 KSps. Eight devices can be stacked on a single Raspberry Pi to create a 64-channel device capable of reading data at a combined rate of 320 KSps.

The MCC 128 features 16-bit resolution and includes eight analog inputs with a maximum sample rate of 100 KSps. Multiple gain ranges are also included to give users the ability to make precision measurements.

Voltage output and digital I/O

The MCC 152 provides two 12-bit analog outputs along with eight 5 V or 3,3 V DIO channels, enabling the creation of a full, multifunction Raspberry Pi measurement and control system.

Thermocouple measurement

The MCC 134 is designed for temperature measurement applications and features four thermocouple input channels. A 24-bit ADC and cold junction compensation provide professional-grade accuracy. Multiple thermocouple types are selectable on a per-channel basis.

MCC has a long history of designing and building accurate DAQ devices for measuring thermocouples. Thermocouples provide a low-cost and flexible way to measure temperature, but measuring thermocouples accurately is difficult. Through innovative design and extensive testing, MCC overcame the challenge of measuring thermocouples accurately in the uncontrolled Raspberry Pi environment.

IEPE measurement

MCC 172 is designed for sound and vibration applications and offers two IEPE (integrated electronic piezoelectric) input channels capable of measuring IEPE sensors like accelerometers and microphones without any additional signal conditioning. Inputs can be simultaneously sampled at up to 51,2 KSps per channel.

Software libraries

MCC’s DAQ HATs come with software libraries that support Python and C/C++ to facilitate quick and easy development. Comprehensive API and hardware documentation are also provided. The DAQ HAT software library was created and is supported by MCC. The development repository is located on GitHub where users can find libraries, examples, firmware updates and more: https://github.com/mccdaq/daqhats

Applications

Raspberry Pi is a good fit for many DAQ applications and MCC DAQ HATs have been used in a variety of applications and industries. These applications can be lab-based, remote and IoT solutions and OEM/embedded systems. Some customer applications and industry examples include biomechanics, wind energy, power monitoring, machine condition monitoring and predictive maintenance. The following are a few specific examples.

AC power monitoring IoT solution

A mobile communications company used the MCC 118 to create an IoT solution to monitor and analyse the external city power being supplied to its facilities.

Probe permeameter machine

RO Scientific used the MCC 118 voltage measurement HAT and the MCC 134 thermocouple measurement HAT in the design of a probe permeameter machine used in testing rock samples for the oil and gas industry.

Machinery monitoring and predictive maintenance

The MCC 172 IEPE measurement HAT and MCC 134 thermocouple measurement HAT are used to measure vibration and temperature, respectively and collect the data needed to create accurate measurements, analysis and strategy.

Neuromuscular biomechanics test system

The Raspberry Pi and MCC 172 allowed researchers to create a lightweight and wearable DAQ solution to measure dynamic activity for testing neuromuscular biomechanics.


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