Functional Prototyping Series: Adding I/O to Your Prototype


The Functional Prototyping Series is a collection of articles that walk you through the prototyping processs. Read on for key concepts, benefits of prototyping, product choice discussion, and additional technical resources.


The Role of I/O in a Functional Prototype

Adding input and output to your prototype is essential in creating a truly functional system. By adding sensory input and control output, you prove that your design works can be implemented in the real world. Creating a paper design, implementing that design in software, and even simulating the design in a virtual environment are still largely conceptual exercises. To prove the value of your design to skeptical investors, you need a functional design that exists in and interacts with the real world. Data from prototyping operations also helps you refine functional requirements with clients and the rest of the design team based on actual performance.

This document provides an introduction and resources to get you up and running fast and to help you avoid these pitfalls when adding I/O to your prototype.

The Challenges of Adding I/O

Analog or Digital?

Analog sensors basically transmit raw values from a transducer that you then have to condition and digitize. They usually have a greater bit depth and are less expensive than digital sensors but require more components in the acquisition chain. Analog sensor challenges include lining up all the necessary components in the sensor chain, such as appropriate analog-to-digital converter (ADC) and signal conditioning. Often these components are custom-tailored to the specific sensor you choose, and if your sensor choice changes, you need to reconfigure the whole acquisition chain.

Figure 1. Analog Sensor Acquisition Chain


Digital sensors shorten the acquisition chain by combining signal conditioning and digitization at the chip level in an integrated circuit. They have the advantage of a shorter acquisition chain but require a driver that can interface to the specific digital communications protocol used by the sensor.

Figure 2. Digital Sensor Acquisition Chain (SPI Bus Interface)

Integrating chosen sensors into your prototype and Adapting to Changes

The low-level knowledge required to integrate a sensor into a system from scratch and take meaningful data from it represents an often unforeseen sink for time and resources. The custom nature of traditional sensor integration means costly rework for each design change. And design changes do tend to happen, especially when sensors are concerned, as translating specifications to make sure they  match the needs of your prototype can be a challenge in itself.


  • Implementing a communications interface
  • Customizing output signals
  • Finding a common solution

As we’ve just discussed, adding I/O to your prototype can be a daunting task. It’s often the sticking point in the prototyping process because it’s difficult to forsee the total cost in terms of time & resources of constructing a custom I/O solution.

The RIO Solution

Overcoming the traditional difficulties in prototyping with I/O requires a paradigm shift in approach, especially for domain experts who need to be able to efficiently prototype devices, but may not have the specialized resources to overcome low level sensor interface problems.

National Instruments tools help you overcome these roadblocks by providing that paradigm shift in integrated hardware and intuitive graphical software, reconfigurable I/O devices, and the necessary IP and support systems you need to be successful.

  • Hardware Integration with intuitive graphical software
  • Reconfigurable I/O devices
  • IP gets you up and running quickly
    • I2C and SPI bus IP
    • Support Systems

Next Steps

When you begin to receive data back from your sensors and have a plan for how to use that data, you can replace the random or sample code in your user interface prototype with actual real-world data.

Successfully integrating sensor input and control output into a functional prototype is a huge step forward on the path to deployment and mass production. This step proves that you have overcome some of the biggest challenges in the product design process.

To learn more about the technical aspects of adding I/O to your prototype, see the related resources below. To continue on to the next steps in the prototyping process, return to the Functional Prototyping Series.