Ask MAKE: Playing back a recorded sound

Ask MAKE is a weekly column where we answer reader questions, like yours. Write them in to mattm@makezine.comor drop us a line on Twitter. We can’t wait to tackle your conundrums!


George writes in:

I’ve been wanting to make a prank project, that I can leave somewhere to play back a recorded sound and flash some lights. I’ll use LEDs for the lights, but don’t know how to play back sound. Do you have any suggestions?

Aha, this sounds like it could be a fun project. I’m going to assume you are using a microcontroller to monitor an input (sound? light? time? vibration?), and then initiate a sequenced event. It’s a bit late for Halloween, but this would be a good way to make lawn props that react when someone comes near your house.

Because playing back sound takes a reasonable amount of memory and speed, it’s not something that can be done easily with a standard microcontroller. Instead, the best way to handle this would be to hook up another device, that can be started by the micro and then do the heavy lifting of actually playing back a sound. At least three possibilities come to mind: using a Wave Shield, hacking an MP3 player, or hacking a cheap toy with a sound recorder.

If you are using an Arduino, the Wave Shield might be an ideal solution to your problem. It is an expansion module that allows you to play sounds off of an SD card, and there is a nice library to control it as well. It runs in at about $22 bucks, which seems pretty reasonable for what you get.

If you aren’t using an Arduino, or already have an old MP3 player and don’t want to spend the bucks on a project you will only use once, then you can try to use that. The best way to do this is probably to wire an optocoupler to the play button on the MP3 player, and then trigger that with your microcontroller. If you have more than one sound track that you want to trigger, you could also wire up the next button, but that might get tricky. The bonus for going this way is that you could recycle some electronics junk that would otherwise go to the scrap heap.

Either of the two above solutions are great if you are only thinking of making one or two of the devices, but what if you want to make a bunch of them? In that case, it might be more economical to try hacking a cheap toy, such as this one. Somehow these are still available, and are less than $2 in quantity. The sound quality probably won’t be anywhere as good, but hey, the’re cheap! If you are in a rush, you could also try hacking a voice recording card that you can pick up at a local store. Good luck!

In the Maker Shed:



Arduino WaveShield Kit