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Hobbyists looking to add a sound-bite to a project - whether something hard-wired or micro-controlled such as with an Arduino - sometimes buy a digital voice recorder module like this one costing $11 from Radio Shack.  However you can get almost the same thing by stripping down that ghastly Christmas or birthday card you got from Grandma last year!  (or buy a card for $7).

Step 1: How It Works

Strip the back off the card to get at the circuit and you'll see how it works.  There's a main switch to activate playing the recording which is triggered by a plastic interrupter being slid out from between spring-loaded contacts when the card is opened.  There's a pushbutton which triggers a voice prompt and after the instructions are played, it records as long as the button is down. You can either use the module stand-alone as it is, or hook it up to a PIC and drive it entirely from software.

A variant of the simple recordable card is the musical card which overlays your recording on a music sample. (That's the one I have in the pictures here.)  This is done in a crude analog fashion by playing the sound on the speakers as you talk or sing.  This is actually good for us compared to the alternative of mixing the music with the recording in software, because we can add a switch to disable the speaker during recording and avoid having the music added to your voice.  You can either manually turn off the speaker after the voice prompt completes, or have your Arduino turn it off a fixed time after triggering the recording mode.

Controlling from a PIC is trivial if you use relays, but I suspect that you could also use logic signals on the pins to trigger the functions, possibly with some added pullup resistors.  (If anyone works out the details to do this with say an Arduino please post!)

Step 2: Recording Instructions

  • After purchase, remove pull tab on left.  This disables the preview function and allows you to save your recorded song.
  • Open card.
  • Press and hold preview button.
  • After beep, continue holding and sing along to the music for 10 seconds.  Release button when finished.
  • To hear your new song, close and open card.  Re-record if necessary.

Step 3: Project Ideas?

Post your project ideas.  Here's some to kick it off...
  • Add a piezo sensor and when someone knocks twice on your door, have it say "Who's there?"
  • Build an automated SOS recorder
  • Countdown blastoff timer for model rocket launch

By the way, the circuit is powered by a standard CR2032 button cell.  It's in a holder so it's easy to replace.  You should be able to power the system off an Arduino board.  It can be re-recorded more or less indefinitely.  The vendor claims 400 plays from one CR2032.

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