Connecting the NI sbRIO Adapter to the Texas Instruments Electrocardiogram (ECG) Analog Front End Module

This tutorial explains how to build an adapter printed circuit board (PCB) to enable direct connection of the NI CompactRIO Single-Board Controller (sbRIO) to the Texas Instruments TMDXMDKEK1258 Electrocardiogram (ECG) Analog Front End Module. All design files are available for the NI suite of design tools: NI Multisim capture and simulation, and NI Ultiboard layout and routing.

Overview to the Adapter for the TI ECG Medical Development Kit

Figure 1 below shows the three-dimensional views of the completed circuit board built using NI Ultiboard.  The components to build this board include:
 

• Qnty: 2 of VOLTAGE_REGULATOR LM317LZ

• Qnty: 2 of CAP_ELECTROLIT 1µF

• Qnty: 2 of CAPACITOR .1F

• Qnty; 1 of RESISTOR 361Ω

• Qnty: 1 of RESISTOR 220Ω

• Qnty: 1 of RESISTOR 119Ω

• Qnty: 1 of RESISTOR 270Ω

• Qnty 2 of Connector 

• Qnty 52 .1in Headers Pins
   

PCB fabrication files are included with this application note and can be directly loaded within the product order site of Sunstone Circuits.
 

Figure 1. NI Ultiboard 3D View
 

CompactRIO Single-Board Controller for OEM Embedded Deployment

CompactRIO Single-Board Controller products are low-cost embedded deployment solutions based on NI CompactRIO. 


Each CompactRIO Single-Board Controller integrates an embedded real-time processor, a high-performance FPGA, and onboard analog and digital I/O onto a single board. All I/O is connected directly to the FPGA, providing low-level customization of timing and I/O signal processing. The FPGA is connected to the embedded real-time processor via a high-speed PCI bus. LabVIEW contains built-in data transfer mechanisms to pass data from the I/O to the FPGA and also from the FPGA to the embedded processor for real-time analysis, post-processing, data logging, or communication to a networked host computer.

Figure 2. Example NI sbRIO with integrated analog, digital and 24V relay control
 

Board Layout Software to Simplify PCB Adapter Board Design

The NI Ultiboard interface enables layout and routing of PCB designs. Integration with NI Multisim allows transfer of schematics to layout. Ultiboard exports and produces industry standard format such as Gerber and DXF to take a final, optimized board to prototype and manufacture.

You can also refer to sbRIO Daughter Board Reference Design for Multisim & Ultiboard.

Figure 3. NI Ultiboard layout of the sbRIO to TI ECG analog front end adapter
 

Texas Instruments TMDXMDKEK1258 Electrocardiogram (ECG) Analog Front End (AFE) module 

The TMDXMDKEK1258 Electrocardiogram (ECG) Analog Front End (AFE) module from Texas Instruments delivers a complete signal chain to enable ECG developers to build a ECG analog front end for evaluation and get to production faster. Connected together with the NI sbRIO, designers have a rapid prototyping platform to allow for rapid algorithm engineering and product design interaction.
 

AFE module components include:
 

1. ADS1258 – 16 channel, 24-bit sigma delta analog-to-digital converter (ADC)

2. INA 128 - precision, low power instrumentation amplifier

3. PCA9535 - remote 16-bit I²C and SMBus low-power I/O expander

4. TLV3404 - nanopower open drain output comparator

5. REF5025 - low-noise, very low drift precision voltage reference
    

The ADS1258 ADC is one of 27 components on the TMDXMDKEK1258 ECG AFE module. The input signals are processed by the ADS1258, which provides for 24 bits of resolution. Additionally, the ADS1258 provides low latency and noise performance, as well as a low power consumption level.
 

A high-quality reference voltage is for achieving the best performance from the ADS1258. The REF5025 precision voltage reference provides  temperature drift (3ppm/°C), low noise of 3uVpp/V and 0.05% accuracy. The INA128 provides high common mode rejection required for noise rejection when used in conjunction with low pass filters.


Below is the signal chain schematic of the TMDXMDKEK1258 ECG AFE module.

Figure 4. Signal Chain Diagram of the TMDXMDKEK1258 ECG AFE module
 

Fabricating the sbRIO to TI Analog EVM Adapter

There are a number of different ports available on the sbRIO to define custom I/O in order to better interface to real world measurements. Contained upon the CompactRIO Single-Board Controller are four, 50 pin digital connectors which in total are comprised of 10 digital ports. Specific versions of the sbRIO include a 50 pin connector with analog I/O capabilities. The sbRIO to TI analog EVM adapter will use one digital connector P5 and the sbRIO analog connector for future expansion to other medical starter kit EVMs.
 

Figure 5. NI sbRIO Digital I/O connectors

NI Ultiboard provides a complete symbolically defined drawing of each CompactRIO Single-Board Controller product port. An example of this connector is shown below.
 

Figure 6. NI Ultiboard Symbol for sbRIO
 

The signals which need to be connected between the sbRIO and the TI EVM can be found in the TI TMDXMDKEK1258 user manual. Below are the signals required:

 

Figure 7. TMDXMDKEK1258 ECG AFE module to sbRIO Pin Assignment

Figure 8. sbRIO Pin Assignment
 

Fabricating a Board Prototype

From Ultiboard, it is simple to export the various Gerber files, industry standard files used to fabricate PCBs, that need to be sent to a board manufacturer for production. In general, there are ultimately six important files that are required for manufacture:
 

1. Copper Bottom

2. Copper Top (with Board Outline)

3. Silkscreen Top

4. Solder Mask Bottom

5. Solder Mask Top
    

The above is suitable for a simple 2 layer design. As you define inner copper layers, additional Gerber files must be generated.
 

For designs upon which through-hole components are placed, a drill file is required to explain the appropriate areas upon which the fabricator must make holes for components. For this an additional file to export is:
 

• Copper Top to Copper Bottom Drill File
   

Board Manufacturers

There are a number of different board manufacturers who can quickly prototype designs. One reputable fabricator is Sunstone Circuits. Sunstone provide very quick turn around on designs. For CompactRIO Single-Board Controller daughter cards, Sunstone can be provided the above Gerber and drill files for design fabrication. Place a board order at Sunstone.com
 

Related Documentation

Refer to the following documents to learn more about ECG measurements and using the sbRIO with the MDXMDKEK1258 Electrocardiogram (ECG) Analog Front End (AFE) module:
 

• NI Biomedical Startup Kit

• Biomedical User Group Forums

Disclamer

Not for Diagnostic Use: For Feasibility Evaluation Only in Laboratory/Development Environments

• The adapter along with the sbRIO and TI Analog EVM front end must not be used for diagnostic purposes.

• The adapter along with the sbRIO and TI Analog EVM front must not be used with other equipment that produces high voltages

• This adapter along with the sbRIO and TI Analog EVM front are intended solely for evaluation and development purposes. They are not intended for use and may not be used as all or part of an end equipment product.

• This adapter along with the sbRIO and TI Analog EVM front should be used solely by qualified engineers and technicians who are familiar with the risks associated with handling electrical and mechanical components, systems and subsystems.

• Use only the proper power supplies for the adapter along with the sbRIO and TI Analog EVM front module.