There are a variety of boards that can play MP3 (or .WAV) files from a uSD, but I’ve come up with a possible need to be able to record to a uSD, preferably in stereo from a pair of (off board) microphones. Are there any such boards out there?
Background on why: For several years, I’ve had contact with a group that periodically launches high-altitude (“near space”) balloons to over 90,000 feet. I know that the speed of sound changes with altitude (this has been known since the early 1960s). I’ve discussed with that group from time to time the idea of building a payload to actually measure the speed of sound, and at least “on paper” have come up with a way of doing so with a fairly light weight payload. It will involve two microphones and at least one speaker. It occurred to me a few days ago that rather than build an audio frequency synthesizer, I could “pre-record” the requiired audio for the measurements onto a uSD and use one of the available player boards to get the sounds. (Actually, I’d “pre-record” these by mathematically generating the files.) Since I’m going to be including two microphones anyway, it has occurred to me that recording the sounds of the flight might be interesting – it might be interesting to hear the balloon bursting and other sounds, plus the recording could be “post processed” to verify “real-time” results for the speed of sound.
You might be able to use something like this https://www.sparkfun.com/products/16400 , along with a processor like https://www.sparkfun.com/products/16402 (but you could choose among several micromod processor options) (could even use the 2 MEMs microphones on the board for an extra data signal) integrating the playing boards into your carrier board’s pinouts
Depending on the data, you may be able to record multiple streams on one card; but it might be simpler to just run 2 boards.
Although I appreciate the reply TS-Russell, I think you may have mis-understood the question. I’m not worried about the microphones – there are issues in the basic project that dictate where they can be physically located, and I am well capable of dealing with the electronics to support them, and indeed they make up a relatively minor portion of the “electronics design and build” to get the basic project to work. What I’m looking for is a board that has “audio in” connectors (preferably “stereo”) that I can feed (likely through isolation amplifiers) and has the capability to digitize and RECORD the audio to a microSD, probably a CODEC and a supporting microprocessor. One other wrinkle is that the MINIMUM viable record time is about 3 hours, preferably more.
Unfortunately we don’t carry a board that records audio, but a Teensy paired with a I2S ADC and a bit of code should be able to record at least WAV. Don’t know if it’s fast enough to encode to MP3 but you should be able to find a chip that does the encoding for you.