Starting to play with the ADC

Adding audio capabilities to our instrument is the most challenging (but exciting) part of the project. We need to find an analog to digital converter (ADC) that can record multiple channels simultaneously (4 channels minimum), is inexpensive, and can be used with the Raspberry Pi. After looking at different options, we settled on the TLV320ADC6140 Quad-Channel, 768-kHz, Burr-Brown Audio ADC from Texas Instrument. It can record sounds up to 24 kHz (sampling rate of 48 kHz) when the 4 channels are used, which is high enough to cover the frequency band of fish sounds, but also of many other aquatic sounds (whales, pinnipeds, invertebrates, etc.). A nice thing is that several of these ADCs can be daisy-chained to increase the number of channels. So in the future, if we need to, we will be able to expand our design to 8 channels. Importantly, this ADC uses the Inter-Integrated Circuit protocol (I2S) which the Raspberry Pi supports.

For now, we are using the evaluation board version of the ADC (ADC6140EVM-PDK) along with its TI motherboard. This is not what we will use in the final product, but it helps us to get more familiar with the ADC and it makes it easier to test different configurations.

We don't intend to reinvent the wheel with this project. We plan to built upon work from other amazing projects that used the same (or similar) ADC! One of these projects is the High Performance Audio ADC for Machine Learning Hackaday project from Filip Mulier. Filip used the same ADC with a Raspberry Pi and made a lot of his work open source. This is an amazing starting point! We are also learning a lot from the work that Walter Zimmer did for his microPAM recorder.