The Connector Detector: Fraunhofer Uses Sound to Verify Electrical Assembly

April 19, 2023 by Seth Price

Fraunhofer has developed a system that listens for a signature ‘click’ of a connector to ensure proper fastening of electrical assemblies, particularly designed for automotive applications.

The modern automobile is completely loaded with sensors, wiring harnesses, microcontrollers, and all manner of electronics. The function of the vehicle relies on data from numerous sources, including wheel speed sensors, throttle position sensors, camshaft position sensors, oxygen sensors, and many others. Every one of these sensor packages, as well as the controllers and actuators, is only as good as the solid electrical connection between them.

Who hasn’t pushed together an electrical connector and waited for that satisfying “click” as it locks into place? Fraunhofer did exactly this; they developed an audio sensor and processor package that listens for the distinct click of electrical connectors properly connecting.


Audio contact detection configuration app along with prototype enclosure. Image used courtesy of Fraunhofer IDMT


Fraunhofer’s Audio System

The Fraunhofer Institute for Digital Media Technology (IDMT) has developed a system that uses a microphone and audio processing to determine whether a connector has made proper contact. The idea behind this system is that each connector will make a unique sound when connected. Considering each connector has its own number of pins, housing, size, and shape, the processor maintains a library of sound signatures for each connector.

This audio system is designed with the manufacturer in mind. Instead of manually inspecting each connection, some of which are in hard-to-see and hard-to-reach places, the system can simply listen and verify contact. This system can integrate with automation systems so that a simple “go” or “no go” signal can be used to control robotic arm force while pushing connectors together.

Control Automation’s own engineering director, Dale Wilson, got a chance to talk with Christian Colmer, Head of Marketing and PR for Hearing, Speech, and Audio Technology, about the genesis of the idea during Hannover Messe 2023. He mentioned that automobile fuel injection assemblies were one of the catalysts that initiated the development of this project. As he explained, many automobile parts assemblies, including the fuel injectors, meet at least two of three challenges:

  1. A blind connection
  2. A connection made early in the process
  3. A connection that is costly to repair if found later in production or, even worse, after delivery

Danilo Hollosi, Head of Acoustic Event Detection, also described how they are planning different methods for providing feedback to the operator. This could be auditory, visual, or haptic feedback in the form of vibration, allowing the process to be implemented in human-only operations as well as robotic.


Fraunhofer’s Head of Marketing and PR for Hearing, Speech, and Audio Technology, Christian Colmer, demonstrates the audio detection at Hannover Messe 2023. Image courtesy of EETech’s Director of Engineering, Dale Wilson.


Audio as a Signal

The basic premise of this system is that a soundwave is a bunch of signals at different frequencies, all combined together. From physics or trigonometry class, it is easy to think of waves in the time domain or how the air vibrates with respect to time. A solid, single-frequency tone produces a nice sine wave that can be easily characterized.

Real sounds are more complex, such as the impulse signal of a connector clicking into place. To characterize this signal, it must be viewed in the frequency domain, where the wave is broken into all of the frequencies present. Typically, this is performed through a Fourier Transform, which looks at the amplitude and frequency. By analyzing the peaks at each frequency, a fingerprint of the sound is developed, which can be used to determine whether the connector is fully engaged.


Original waveform compared to the matching frequency domain graph. Image adapted and used courtesy of Wikipedia


The figure above shows that the red trace is a time-domain waveform with multiple frequencies present. There is a lower frequency component that has a much higher amplitude, which gives the wave its overall form. Several higher frequency, lower amplitude signals are superimposed on this wave, giving the wave little ripples. Below, the blue trace is the frequency domain waveform. The largest vertical line is the low frequency, high amplitude signal, and the other smaller peaks are the higher frequency, low amplitude signals.


Fraunhofer’s test and development platform for the audio connection detection. Image used courtesy of Fraunhofer IDMT


Industrial Audio Inspection

For many technicians, audio inspection technology appears as a solution in search of a problem. However, upon further investigation, it solves a problem many manufacturing engineers likely took for granted. These audio signals are being emitted anyway, Fraunhofer simply found a way to use this information to verify accuracy.

Furthermore, this is not as far-fetched as one might imagine. Using audio signals to determine vibrations in motors, cavitation in pumps, and other such problems has become standard practice. The real question is, why would someone not use these signals to aid in automation?