This is, essentially, two mono audio breakout boards on one FeatherWing. With this board, any of these functions (and sometimes more than one at the same time) can be either turned into or integrated into a Feather project:
- Voice changer (primarily for cosplay, Halloween costumes, and similar projects; fit the device inside a helmet, or in your pocket!)
- Voice amplifier for teachers and other small-room speakers, or those with certain medical conditions (such as some forms of muscular dystrohy) that result in an unusually quiet voice
- Two-way communicator (over wires, or whatever wireless protocol you deem best -- LoRa, XBee, Bluetooth, etc.)
- Effects processor for musical instruments (generally but not necessarily acoustic instruments on mikes)
- Smart speaker (or interface with an existing smart speaker system)
- Hearing aid (probably with some extra features that can't be found in commercial hearing aids, since those can fit inside your ear)
- Boom mike operator's sound unit (in a film/TV setting)
- Parabolic microphone
- Myriad things I haven't thought of yet! (If you have an idea, please put it in the Comments below!)
Obligatory Tech Info:
The microphone pre-amplifier chip takes audio from a microphone input and sends it out to a speaker, in both cases connecting through the I2C bus.
The microphone input is an MAX4468 from Maxim, while the speaker output comes from an ON Semiconductor NCS2211D. Both are 8-pin SOIC chips, which can make breadboarding and freehand soldering a serious challenge but goes a long way toward freeing up space on the board.
In each case the application, other than connecting directly to two of the Feather's Analog pins, follows the suggested application on the respective chip's data sheet (page 9 in both cases).
The actual connections for the mike and speaker are next to each other, using wire-to-board terminals. This is probably the cleanest solution, since the overall device will probably be kept in an enclosure that includes either mounts or jacks for these parts. You may, of course, replace them with whatever type of connector that you find appropriate (though you may need to edit the .fzz file, depending on what you choose).
The MAX4468 has a Shutdown pin which may be connected to D12. It normally is set to Low; set it to High, and the chip enters a power-saving Shutdown mode (supply current drops to 5nA, output enters a high impedance state, and bias current is switched off). In case you don't want to use it, a jumper is available to connect it to Ground full-time; it should not be left unconnected. (This is my preferred way of running an on-board selection for something that might change after installation, but not often.)
The input and output are connected to the I2C bus using a Microchip Technologies MCP3424 and a Texas Instruments DAC8571, respectively. These are also given passive components in the manner suggested by their data sheets. The MCP3424 has two possible I2C addresses, selectable with a solder jumper on the board's underside.
Besides the optional D12 connection for the Shutdown and the Analog Reference for the DAC8571, the only other connections on the board are for the 3.3V and Ground.
The MAX4468 is explicitly designed for an electret microphone; I don't know for sure whether it would work with a piezoelectric mike, but I think it should. (I hope it does; one of my own designs calls for it!)
I'm open to just about any input on these questions. I've divided them into those calling for a bit of expertise that I don't have, and those calling for opinions from a prospective user's perspective. On any of these, if nobody says anything, I'll just assume I got it right, at least until any breadboarding or other real-world attempt on my part shows otherwise.
- I'm pretty sure -- but not 100% -- that...