March 04, 2008
by: jovial_cynic
As a kid, I had a habit of sticking amped audio wires into my mouth, so I could feel the way the audio waves changed the feel of the voltage going through it. I later discovered that you could take those same wires and connect them to a small motor and cause the motor to vibrate at the frequency of the music. I would then take the motor and mount it to a cabinet and cause the whole cabinet to resonate with sound.

Editor's note: You probably shouldn't stick wires with any amount of electricity going through it into your mouth

Lately, I've taken an interest in wireless technology. I love the idea that one can take raw audio signals and send them through the air and pick them up in a remote location. Having several small children, I happen to have a wireless device handy: a baby monitor. It's a simple device; it simply has a microphone on one box and a speaker on the other. It's just a remote listening device.

Today, I decided to hack the baby monitor to see if I could cut the microphone out of system and run wires from my electric mandolin in its place.

Here's the speaker end of the monitor.

My first step was to connect some wires to the plug coming from the mandolin. I didn't have a spare jack handy, so I just used some electrical tape to secure the wires in place.

Here's the back of the sending unit; I've got the wires going to the spot where the microphone wires are soldered into place.

If you take a look at the red wire, you can see where I cut it. I needed to leave the microphone in place, as we still need to use the baby monitor for the baby. This is all just a proof of concept. I've ordered another $5 baby monitor from eBay so I can fully take it apart.

I'm not 100% positive, but I believe this is the business end of the sending unit. The antennae is wired into the cylinder at T2, so I have to assume that it's the actual wireless sender.

Anyhow, patching the audio output jack directly to the microphone wire worked just fine. Here's a video my 4-year old daughter made of me playing my mandolin through the hacked baby monitor:

Pretty steady for a 4-year old. And pretty decent sound coming through the wireless amp.

Fun fact: This post got picked up by boingboing and by Make. Neat!


Joelle said:
Wow! What a cool trick! Good photography by Hayden too!!
March 04, 2008

Kendra said:
I sure get a kick out of you in such a "girly" room. :) I love the Hello Kitty in your picture.

Thanks for putting the baby monitor back together so I could use it. ;)

March 05, 2008

Lisa said:
How the heck did u figue this out????? It is amazing!!!! Please let me know my email is
March 05, 2008

Dan said:
I suggest that you connect (2nd pix of wires taped to plug) the shield to the sleeve of the plug and the white wire to the tip. You will have less hum.
March 05, 2008

Austin said:
Nice concept. I might try something like that myself for my violin since I don't want to actually buy an amp. Of course, I'll have to learn HOW to play it at some point ;)
March 05, 2008

Omyword! said:
Found you through BoingBoing. You your pink room. :-) I added you to my RSS feed. Now maybe I can play my Mandolin badly, but loudly. Love your political and corporate stuff too.
March 06, 2008

Max Hyland said:
Cool- hacked yourself a makeshift amp. lol

Tried putting an amping circuit together with a power supply and a 3.5mm audio plug? headphones would rock.

March 06, 2008

Old Fart said:
"I love the idea that one can take raw audio signals and send them through the air and pick them up in a remote location."

Yeah, it's called RADIO. LOL. It was discovered by Herr Doktor Hertz more than one hundred years ago.

PS: Just kidding.

March 06, 2008

jovial_cynic said:
ha! Thanks, Old Fart. It's true, but I think that while most people listen to the radio, there are significantly fewer people who are doing the sending. And my fascination was really about the sending part. :)
March 06, 2008

Becky said:
An Internet Shower for Kristen
Date: 3/18/08
Place: Why on your blog of course . . .
What: This shower is to celebrate Kristen and the new life of Alyssa Star. To do that you might post a song, a quote, a poem, a piece of art that reminds you of the spirit of Kristen. Also, along with something inspired by Kristen, you might post a piece of wisdom or caring for Kristen to hold on her new journey into motherhood. Of course, in addition, you may also buy a traditional baby gift. If you do, we want to see a pic on your blog!!!
How: Post your gift on 3/18/08. I will create a link to everyone participating and post it on The Meantime.
Who: Anyone who loves Ms. Kristen. If you would like to participate but don’t have a blog, leave your email address in the comments below. The Meantime will be happy to post for anyone

March 06, 2008

levi betz said:
wow nice filming for a 4 year old!!! i tried to do a similar thing except with a old wireless phone, but now it won't go into "talk" mode.
April 08, 2008

Randy said:
I did this a long one while ago. On the first try I blew out the baby monitor transmitter sending line level audio into the microphone terminals. On the second transmitter I stuck a 20K resistor (I think) in series and no more problems.
June 26, 2008

Annette said:
I've been being harrassed by amplified breath sounds for almost a year now. I couldn't figure out what the person was using. I called geek squad and the guy suggested it might be a altered baby monitor. If that's what it is, is there anyway to stop him besides staying up all night?
December 28, 2008

jovial_cynic said:
Annette - I'm not exactly sure what you're describing. Are you hearing the sound on one of your baby monitors? Baby monitors often have multiple channels, so if you're receiving unwanted interference on your monitor, perhaps you can change the monitor channel?
December 28, 2008

pango said:
Great explanation of the baby monitor wireless amp!

You can do something similar with old cordless phones that you can find for about 5 bucks at thrift stores. Just find one that has a "page" or "intercom" feature. They work by allowing you to push the button and hear yourself (or allow someone else to hear you) on the base station speaker (which is used ordinarily for the speaker phone).

It's also possible to de-wire the cheap little speaker and run those wires to, say, a computer speaker (still cheap and little, but better). Sound quality is increased, but you really have to experiment around to get one that doesn't chop off a lot of your guitar's frequencies.

February 22, 2009

jovial_cynic said:
pango -

I've actually thought about doing this, and I periodically stop by the local goodwill to see if I can find any of those cordless phones. I've also thought about making my own little AM or FM transmitter, which would play my music through nearby radios...

February 23, 2009

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November 30, 2009

Jason said:
"I love the idea that one can take raw audio signals and send them through the air and pick them up in a remote location."

You should consider getting your Amateur Radio License (i.e., ham radio). With that, you can build your own radio transmitters, use high power transmitters, and buy equipment typically not available to the general public.

April 26, 2010

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