Date of this Version
Moran, Riddock. Design of Hardware to Aid Smartphone-based Oscilloscope App. Undergraduate Honors Thesis. University of Nebraska-Lincoln. May 2022.
A smartphone-based oscilloscope improves on traditional lab oscilloscopes in accessibility and portability but faces several performance limitations compared to traditional oscilloscopes. Among these, an oscilloscope app that uses the phone’s audio to read voltage signals will have a sampling rate and voltage bottlenecked by the capabilities of the audio codec, which will rarely exceed a rate of 48 kHz and 1 volt, respectively. Additionally, smartphones lack the ability to read line-in audio, allowing only one channel input through the microphone. Direct connections to an audio source may not be possible due to requiring an audio jack connection, and different poles being used for voltage output and input.
These limitations can be remedied with the use of external hardware to aid the oscilloscope app. An adapter can be used to connect voltage output from the left or right channels to the microphone channel, and a channel switch on the adapter can be used to partially alleviate the lack of two-channel input. A digital signal processor external from the phones audio codec can be utilized to process signals higher than 20 kHz that would otherwise be unreadable based on a 48 kHz sampling rate. This processor can send samples digitally to the app, which allows for input of as many channels as the external process has physical connections for.
Copyright Riddock Moran 2022.