Today, almost all of us use mobile phones every day and we depend on them for many features that personal computers offered earlier. The major advantages of mobile phones is their mobility, compact form-factor, always networked and untethered to power (except when charging). Moreover, mobile phones are now platforms that support continuous sensing applications.
Although mobile phones nowadays house many sensors such as imagers, gyroscopes and accelerometers, some sensors such as soil moisture, air quality and EKG have not been integrated yet. Many people desire support for such sensors and prefer a limited set of direct-connecting interfaces that make it suitable to power external peripherals for transferring data to and from them. This has resulted into a search for a universal peripheral interface port.
Every mobile phone has a headset port, which is almost standardized. Users can connect physically and electrically a vast range of hands-free and headphone audio devices. Therefore, the mobile phone’s headset port is a suitable candidate for such a peripheral interface. Recently introduced peripherals show that designers and manufacturers have a growing interest in using the mobile phone’s headset port for more than just headsets.
Transferring power and data to peripheral devices via the headset port looks an attractive proposition when considering the cost, simplicity and the ubiquity involved in the process. However, different mobile phones show considerable variance in their power delivery ability, microphone bias voltage and passband characteristics among their headset ports.
Therefore, contrary to recent claims, one is forced to conclude that the headset port is not as universal as it is made out to be. For example, peripherals designed to work with iPhones may fail on other Windows or Android phones and vice versa. Moreover, designs for smartphones may not be suitable for less capable feature phones. Therefore, mobile phone peripherals may have a hard time working with the headset ports of different mobile phones.
A new platform, called the AudioDAQ, makes it easier to acquire data continually via the headset port of a mobile phone. Unlike existing phone peripheral interfaces such as HiJack, AudioDAQ draws all the necessary power from the bias voltage of the microphone. It encodes all data as analog audio while taking advantage of the voice-memo application built into the phone for continuously collecting data.
Therefore, AudioDAQ is not limited only to iOS devices, but works smoothly on smartphones and feature phones as well – no hardware modification is required on the phone. Compared to HiJack, AudioDAQ has extended sampling periods, which is a result of using a power-efficient analog solution, making it suitable for a large class of sensing applications.
The efficient AudioDAQ design draws all its necessary power from the microphone bias voltage. Since this voltage is present on all phones, irrespective of whether it is a smartphone, feature phone, Android or iOS phone. Moreover, the voice memo application is present in almost all mobile phones. That makes AudioDAQ almost universal in its application. Designers of AudioDAQ have demonstrated the viability of their architecture by and end-to-end system that captures EKG signals continuously for several hours and sends the collected data to a cloud for storage, further processing and visualization.
