Haptic Noise Interference | Test for Design Validation, Part 1

Haptic Noise Interference

We don’t think about the engineering complexities of haptic noise interference when our smartphones vibrate or game controllers rumble. We are rarely conscious of the sensory roles that haptics and sensors play in our everyday lives. Yet, as the complexity of our connection to technology continues to evolve rapidly, so does the demand for biofeedback microelectronics.

Systems integration with multiple haptics and sensors presents unique engineering challenges within a small form factor, such as preventing or solving unwanted interactions between components in such close proximity.

Overall performance must be seamless with nearly imperceptible haptic noise interference and feedback – in other words, a product that functions optimally without calling attention to the functionality of the components that produce the feedback to the user.

Consumer Electronics and Haptic Noise

This kind of “imperceptible” sensory experience may seem strangely contradictory, but it’s how humans interact with our physical world: our subconscious continually processes infinitely complex perceptions without our awareness. With VR technology, engineering the right experience is even more crucial for users to become fully immersed in a virtual or augmented reality.

Test for Design Validation

Because hitting the perfect balance of performance and sensory experience is so subjective, we work closely with our clients to define their vision of the perfect user experience. Then we move quickly to design and produce testable samples to narrow in on the perfect prototype. Success requires efficient testing and data analysis when functional or performance roadblocks surface.

Over the years, AC engineers have tackled countless product development design challenges. In today’s blog, let’s explore how our teams troubleshoot the challenges of haptic noise interference in design through testing and validation.

Solving Audible Noise Generated by Haptic Force Motors

When we asked Aaron Young, a Senior EE with AC Product Development, about engineering challenges with devices that rely heavily on haptics and sensors, such as gaming controllers, he described the unwanted interactions of those components:

Aaron Young | Senior EE
AC Product Development

“From an electrical engineering perspective, the design of haptics often involves reducing noise levels produced by certain types of haptic force generators that are necessary to deliver a robust sensory experience.”

Aaron recalls one such project:

“On the haptic side of performance, we had a really strong product, but it was generating quite a bit of audible noise during validation. We had to find a solution to resolve the excessive noise while retaining the haptic response we needed.”

Noise Characterization to Identify Frequency Issue

RF channel measurement with spectrum analyzer - haptic noise

Aaron knew he needed to first characterize the noise before he could identify the best solution.

“We started with audio analysis of noise spikes generated by the device at various distances and measured in decibels. But we also had to think about the changes to the position of the device in relation to audio coming from other sensory input devices worn by the user. Rather than assume the noise spikes were coming only from the haptic motor, we needed to understand if there were contributing factors, such as noise coming from the device making contact with the user.”

Once the characterization data was analyzed, Aaron was able to identify that the noise was tied to the type of frequency wave recommended for the algorithm used with the haptic drive integrated circuit.

For example, the algorithms that drive the haptic response of a device may use a square wave frequency which offers fast on/off transitions that deliver strong haptic pulses. However, square waves also result in odd harmonics and higher levels of noise than the smoother but less intense pulse frequency of sine waves.

“Haptics perform best when you hit a precise resonance frequency to drive the haptic motor, but when you’re off by just a couple of hertz, the performance dips. The product’s algorithm required a strong haptic response using a square wave frequency. We considered using only sine waves, but the algorithm couldn’t calibrate the haptic motor resonance frequency this way. We also knew there would be a high level of use, wear and tear, and environmental factors that could alter the optimal resonance frequency. So, hitting the right resonance every time was like hitting a moving target.”

Square Waveform

Square waveform - Haptic Noise Interference

Sine Waveform

Sine Waveform - Haptic Noise Interference

Developing a New Algorithm for Haptic Noise Interference

With millions of devices scheduled to ship worldwide, the product needed a solution that would preserve its robust performance but ensure that the moving target resonance frequency was hit each and every time the device was activated over the life of the product. While brainstorming ways to solve the challenge, Aaron and the team considered:

“What if we find the precise resonant frequency each time the device wakes or powers on using a square wave pulse, then switch to sine wave to drive the haptic motor based on that resonance?”

This insight, however, would require Aaron to write a new calibration algorithm for the device firmware to enable the acquired square wave resonance frequency to be used for the sine wave operation. Even with his experience designing low power systems, radio-frequency engineering, and mixed haptics integrations, there was no predicate code to leverage – this solution would stretch his understanding of firmware algorithms.

“To develop a new algorithm, I had to use a lot of bit manipulation in order to design an efficient transaction. After completing and validating the new algorithm, the team’s talented coders reviewed and perfected it for deployment in the next firmware build. It worked as planned – all the noise complaints were resolved.”

When we asked Aaron about the joy of solving complex problems that translate to real-world products enjoyed by millions of consumers around the world, he smiled and reflected:

“Yeah, even though we proved the solution out with solid testing, when the improved product was manufactured and out in the wild, I watched the Reddit boards closely for feedback or criticism of the performance. But no, the boards were all quiet. Everyone is happy with the product. It feels amazing.”

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AC Test Engineering provides a full range of custom hardware testing services, at our test lab or yours, to ensure successful product design, verification and validation, and failure analysis.

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