This project started as an instrument for ['http://dorkbot.org/dorkbotcolumbus/Sched.htm#musicevent Sonic Tooth], our local Dorkbot music event. I was looking for something where you could put any sound into the mix.

As an instrument, it's basically a mash-up of an answering machine and a megaphone. It ends up being a small package with a loud punch, so you could use it to play the same sample over and over (and over...). It uses a solid-state recorder with a 120 second capacity (Winbond's ISD25120)

The really cool potential that I didn't explore in this project is the ability to control the recorder via a microcontroller. It looks like the recorder's memory is addressable via a 10-bit address setting. With that, you could have the resulting playback be driven by any number of environmental stimuli. I was looking at using an Amtel ATiny13 to drive it, because I only really needed a 4-bit address space, leaving 4 ADC lines for input. But, that's all to come still.

Step 1: The Design

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....

Step 2: If It's Too Loud, You're Too....

The output side of this thing is a cheap megaphone from Harbor Freight. Watch their sales, I see it come up every couple months for about $5 US (Normally in the $15-$30 range). The things I really like about this unit are a) the handle comes off easily, and b) the amp board both easy to get at and is completely self-contained. There's no remote switch in the handle like some other designs.

For a modification, I simply de-soldered the on-board microphone (you could reuse it in the design, if you want!) and soldered in a short piece of 24gauge CAT-5 wire. I soldered that to the RCA plug, enlarged the mic hole a bit with a utility knife (note, safety first!), and hot-glued it in place. Again, I'd use a smaller connector format next time.

Also, I'd secure it with cyanoacrylate (thin super-glue - check your hobby store and be sure to get Thin) and baking soda. It's amazingly strong - like concrete. To use it, put down a thin bead of glue, sprinkle in baking soda. When it's dry, repeat. Add a couple layers and it'll never come apart.

Step 3: Second Skin

I put this together in a hurry, so I grabbed a box that I got a replacement iPod shipped in. It actually worked out really well - the circuit board is exactly the right size for the pre-cut foam. I just cut a hole for the 9v battery and a couple holes for switched.

I would have liked to mount the CE switch (lower right), but I ran out of time. As it was, it actually worked better. It made the device easier to handle while moving toward an audio source. In the next design, I'd add a 1/8-inch microphone port to use a PC-style mic, I think.
<p>Does anyone know how I can connect a 'cox box' to a portable speaker? It has a cable that plugs into a boat frame but to make it portable what would I need? And what store would have the adapter ports? thanks.</p>
Good progect but use a different case there only like 5 bucks at radio shack, or just buy it online and suffer shipping it because radioshack is a ripoff.
Cool but i'd add a 3.5 mm mic jack or something OR a 2.5mm one and buy one of those old bluetooth adapters and speak through bluetooth to it having it stuck on your car roof lol
I'm also currently hacking 'round a ISD25XX, but, unfortunately, Winbond consider the <a rel="nofollow" href="http://www.winbond-usa.com/mambo/content/view/153/283/">25XX series to be obsolete</a>... :-(<br/><br/>S, tig<br/>
Yeah, I saw that. I was looking around and the ISD4002 series looks like a replacement (ISD4002-120 has 120s recording at 8KHz). Even cooler, it support a 4-wire SPI interface to be driven by a microcontroller. However, it doesn't look like it supports a standalone mode. I need to dig into the app notes more. What type of applications are you looking at building for? M
I'm building a stomp-box looper. I've done a proof-of-concept (lovely, beautiful, lo-fidelity sound), but I'm yet to do the final build. (BTW, my approach was slightly different from yours in that I took a an existing PCB/kit and modified that.)&lt;br/&gt;As far as possible alternatives to the ISD25XX, I was looking at the &lt;a rel=&quot;nofollow&quot; href=&quot;http://www.winbond-usa.com/en/content/view/160/290/&quot;&gt;ISD17XX&lt;/a&gt;. Interestingly, unlike the 25XX, the internal clock on the 17XX is set by an external resistor which might means realtime pitch/time stretching by wiring a pot up to the chip.&lt;br/&gt;&lt;br/&gt;tig&lt;br/&gt;<br/>
i like this, would i be able to just attach a 1/4in. socket instead of the the mic?
Yep, it's just a question of playing with the input filter. For a mic, the data sheet calls for an external capacitor/resistor filter (which I think gives you the ability to limit the frequency sensitivty ). That's what's in this design. <br/><br/>However, it also says:<br/><pre>If the desired input is derived from a source other than a microphone, the signal can be fed, capacitively coupled, in the ANA IN pin directly.</pre><br/>Also, if you need more capacity, you can daisy-chain multiple chips together and they will automatically cascade over to each other.<br/><br/>M<br/>

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