You could think of this thing as the guts of a digital answering machine hooked to a portable PA system. However, instead of being limited to the outgoing/incoming messages, we have full access to the capabilities of the chip.
The chip is a Winbond ISD 25120p
. It records up to 120 seconds of audio at a 4KHz sample rate. It's about the quality of an answering machine (surprise!), but coupled with the amp in the megaphone, it produces a very textured sound.
The design here is the reference design shown on page 33 of the chip's datasheet
The only things I really added were a couple of status LED and a 7805 voltage regulator. I drive it off a 9v battery, but you might get longer life out of 4-6 AA cells. YMMV.
The capacitors and resistors above the chip are filters for the mic and speaker, as well as a gain-preset.
I soldered this design together, more as an excuse to practice using a new soldering iron. If you plan on making more than 2 of these things, plan on etching a board. This is a very simple design, and you could probably make a single-sided board. If anyone wants to design one, I'll post it here for you....