#1: using a recorded voice
#2: using a recorded or LIVE voice, modified,
#3: using the remote method, but nearer.
Step 1: Materials and Tools
Since it didn't need to be REAL loud, just audible.
The schematic shows the other parts for the amplifier.
FYI: R1 is a 2.2 K ohm resistor.
One also needs the recorder device (some are sold already soldered together, some need to be built as they are kits),
For my project, I decided to go with a plug in power supply for the amp, rather then using the four AA batteries and holder supplied. So, I found a 6 vdc wall wart (transformer) and soldered a receptacle to the board, and removed the battery holder and soldered in a plug to fit the receptacle.
I also used a switch (dpdt, but a spst is fine)
for the other projects I also needed
2 working but not so useful walkie talkies
a CDS cell
and the misc. solder, iron, and screwdrivers, etc.
Caution should be taken when soldering, it burns like hang on the skin, but in the eyes, it'll definitely blind: wear protection.
Step 2: Putting Together the Recorder Module
I removed the speaker from the voice recorder (digital, BTW), and wired it (the recorder) directly into the input of the amp. then wired the output to the speaker. I had a bit of difficulty as I am much more familiar with the LM386 amp (but not having one handy, I used the LM380-8 instead), so I had to tweak this a bit more then normal to get it to work well.
Wiring in the CDS cell, in series with the switch should give you some control over the mechanism, so you can turn it off manually.
Once all this is wired together, you can choose a box or "setting" that hides the hardware, after recording your message.
Turn on the switch, and have the CDS cell facing a light source.
If all has been constructed properly, someone coming between the light source and the cell, will set off a tremendously funny (just how funny depends on your imagination) pre-recording.
Since it is coming from something the person would never imagine, it should, at very least, startle.
Step 3: Prank #2
I have included a few pictures of what this unit looks like.
Step 4: The Best Is Saved for Last :-)
In the simplest form, I removed the voice "recording" device and inserted one half of a walkie talkie pair's guts.
This allowed me to monitor if someone was near the device from the next room over. When someone entered the room, I could switch on "my side" i.e. my walkie talkie (using the squelch if one is available to keep it from hissing too loud), and then speak TO the person. Your voice (or your modified voice) coming out of an inanimate object is sure to make even the most suspecting person jump a bit.
NOW, if you want to make this a bit more effective, albeit a bit more complicated to construct: you "could" wire the CDS cell across the "send" button of the walkie talkie guts in the music box (or doll, or where ever you put it), and a third portion of guts "to receive" what you send. What this affords you is that you don't NEED to be in the next room, but you can be up to (the sending distance of the device), many times, as far as 1/2 to 1 mile away. This definitely has the most "freak them out" factor of all of these.
I hope you enjoyed this somewhat sketchy outline of my three latest practical jokes.