This was inside the bill of a baseball cap with the word "MARINES" on the front. I tried changing the batteries, but it doesn't seem to be doing anything. Does anyone know what this is?
It has a button on one side. But new batteries didn't reveal it's purpose. I'm thinking it's too corroded now to work. I know that round thing is a simple speaker or buzzer, but I don't know (a) what sound it's intended to make and (b) why it was sewn into the bill of a baseball cap.
Internals, image 1:
Internals, image 2:
External, backside:
Cap pictures:
Edit: added images of the internals.
Edit 2: added a small description of the button, and why I didn't just test it with new batteries (I did, but it doesn't work). So, basically, all I know.
Edit 3: added a picture of the backside of the casing.
Edit 4: Adding pictures of the cap itself.
Thank you, everyone, for all of your input. If I'm ever able to get this thing working, I'll add a video of the device and it's audio.
I've designed similar devices.
The epoxy blob likely plays factory-set chiptunes out the piezo element.
It's unlikely to play voices, just tones. The ones that record arbitrary audio use specific ICs from China, none of which I see there. Also those work with small but standard speakers, not generally piezo elements.
As a small window into how these are designed, a lot of the engineering goes into reducing power consumption and parts count. The button might for example drop the pin of an MCU low to trigger an interrupt that wakes it from deep sleep. Then it plays a tune stored in eeprom (more common) or internal flash (less common). Usually the chips are one-time-programmable and cost under 0.10$!
That makes perfect sense. Thank you!!