Instructables
Some time ago my girlfriend asked me if I would make her one of those telephone microphones like the kind that all of those hipster bands have. So, I of course told her I would. Much time passed... and then I made this.

This is designed to work with the old-style handsets with the carbon mics inside (see picture). It probably won't work with most newer handsets.

I'm sure twelve year olds in 1994 used to call this a "purple polk-a-dot box." I apologize for my |33t h@><0r ignorance.
 
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Step 1: Go get stuff.

Picture of Go get stuff.
What you will need:

1. Terminal-Block Cover (Radioshack Part #279-455)
2. AA battery holder (Radioshack Part #270-401A)
3. Micromini Toggle Switch (Radioshack Part #275-624)
4. 1/8" Mono Jack (Radioshack Part #274-251)
5. 1 AA battery
6. 2-5/8" x 2-1/4" cover (aluminum, plastic, cardboard, etc...)
7. 3/16 x 1" nuts and bolts (or one size shorter)

Optional:

1. 1 roll black gaffers tape
2. 1 roll white gaffers tape

Tools:

1. Soldering iron
2. Hot glue gun
3. Drill (3/16 and 15/16 drill bits)
4. Flathead screwdriver
5. Needle nose pliers
6. Wire stripper

Step 2: Prepare the case.

With your pliers, break out the little tabs on the bottom of the case so that the battery holder can lay flat on the bottom.

Once the plastic tabs are removed, drill a 3/16" hole in the side of the case at a right angle from the phone jack. This will be for the toggle switch (see picture)

Next drill a 15/64" hole in the bottom of the case opposite the phone jack. This hole will be for the 1/8" mono plug (again, see picture).

Take the 2-5/8" x 2-1/4" piece of material. This will be the lid to your case. Drill a 3/16" hole in your lid approximately 1-1/4" inch in from each side (see picture). Measure your material for better measurements and better results.
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Gigeanyesterday
I'm having trouble tracking down a phone like this-- anyone have any suggestions?
kerikino3 years ago
performance:

http://vimeo.com/18294184
5209680989_77fc60ac6f_b.jpg
beautiful
Great project. A definite improvement of one of my attempts with retrofitting old phones. Have you tried using a three/four pin jack connector and wired the speakers up as well. It would make a completed usable phone. It seems a waste to have the speakers not in use. Keep up the good work!
Well a big Hello to you, Mr. Sarafan. I want to wire my telephone handset to a phone input. The colors on the phone wire are Red, Black, Yellow, and Green. The wires on the 3.5mm cellphone input are colored Red and Gold, and the other set of wires is White and Gold. Do you know which wires to connect? Thanks. Here is a bit of a description on what I'm trying to do. http://www.i-hacked.com/content/view/205/47/
Oops, it is a 2.5mm plug.
how would this be different if i wanted to wire the mic instead of the receiver? 
randofo (author)  comradebrandon4 years ago
What do you mean?
ryguy94 years ago
howdy, thanks for this :D
i can't hear anything except for static when i blow into it, which i find kinda strange...
any pointers?
thanks :D
randofo (author)  ryguy94 years ago
This is going to sound kind of strange, but try bashing your mouthpiece against a hard surface a few times (this loosens the crystals - or something of the sort). If that doesn't help, perhaps try another handset. If that doesn't work, perhaps you accidentally wired it wrong? Or the connection with the jack is bad? Maybe the signal is too hot (high voltage) for your amp? Do you have a picture of it? 
Logan D4 years ago
 This looks like it has some potential to become a DIY (and pretty shotty) bullet mic for harmonica playing
Yeah, I looked up line level, it is hard to understand. Indeed mysterious.
If the mic on these old phones stops working, you can take it out and slam the edge against someting solid a couple of times and then shake it real hard... ... lots of times it will work when you put it back into the handset. I have no idea why this works, just that I have resurrected dozens of phones with this trick, which was taught to me by a 4th grade kid about40 years ago. Only works with those old phones, don't try it with the new "hi tech" phones .
That's because sometimes the carbon granules in the "cup" essentially get clumped. Banging the element around loosens them back up.
Right, 'cos the new 'high tech' phones have what are called piezo condenser microphones.
Hey there, I really like your project! I seem to be picking up an FM signal along with my voice. Did this happen to you? What can I do about it?
If you're getting FM signals, a temporary solution is to touch the ground connections. You won't get shocked, trust me. However, if you're running your circuit on something higher than 12 volts, then ignore what I just said.
randofo (author)  oatmealfight7 years ago
errrr.... nope. Try checking your solder connections to see if any of the connections might accidentally be touching. It's hard to tell what the problem might be without being able to see it.
stratcat6 years ago
You're definately on the right track. Adding a resistor will prevent smoking the carbon element in case of a short (yes, I've done it!). And a capacitor will keep DC out of your amplifier. The resistor can be 680R-3K3 and the cap can be .01 to 1uF. Neither are critical Drawing included.
Phone2Audio.png
doog6 years ago
I, too, would like more explanation of this part.
randofo (author)  doog6 years ago
What in particular is confusing you?
doog randofo6 years ago
personally, I've never dealt with building circuits before, but I've read up some and have gotten a better understanding of this diagram. But, a picture of your circuit would be helpful.
Check mine out.. Quite a bit different than yours, but principally the same thing. I added a few tweaks on the inside.
mwintner16 years ago
is there any way i could skip the box thing and directly connect the wires from the phone to a "guitar cable"?
you can. it's seems simple enough. we did it. splice the guitar cord, they're will be a bunch of bare wires surrounding another wire in the middle. the inside is in is the "hot" or, when it comes to the telephones mic "hi" it should be labeled somewhere. just take the phone's mic out (it should be a speaker with some kind of incasement) pop the speaker out and there we'll be 2 flat metal ehhh, "things" on the incasement sticking up towards where the speaker was before you removed it. just solder the "hot"(inside) guitar cord wire to the "hi" "metal thing" on the phone's speaker's casing. snap it back together and your done. no battery needed! **make sure to test the hot to hi before soldering by wrapping the wires around the metal connectors and snapping it back together and testing it through an amp** I don't know what happened to ours but for some reason the cord went out and it wont work anymore. BUT IT WORKED WELL WHILE IT DID!! another way to try is soldering the wires directly to the mic (hot to middle, ground to outside like this (picture) www.ece.rice.edu/~jdw/241/exp3.1.html let me know how it all works out. message me at: myspace.com/boltofficial if you have any questions.
my phone never had a wall plug or battery, so i'm not sure where the voltage was coming from. anyway i was wondering if i can do this project without a battery (or pots/resistors)
Nope. The carbon mic is a variable resistor. A modern phone would have an electret mic, which actually produces a signal on its own without a power supply. Telephones were always powered by the phone company over the phone line. A simple enough phone can still manage that, by the way . . .
luck6 years ago
what voltage resister will i need and were do i wire it
luck6 years ago
I also found out that the phone has a 9 volt cord. would I be able to wire the 9 volt cord to the wirering diagram and the phone if I were to wire the power in the loop or do I still need to use a separate battery. Another question I have is if instead of tapping into the speaker if I could use your original plans but instead of wirering directly into the microphone I could wire to the microphone receiver and use the regular power cord to power the phone and a battery for the microphone signal, or will I not need a battery if this wirering idea is possible.
randofo (author)  luck6 years ago
If you connect 9V, to the power cord going into the phone, you shouldn't need any other power sources or batteries. The phone should operate fully (except for ringing). If you need to get audio from the speaker, you just need to connect the speaker wires to an audio out jack (or so I'm guessing). However, you might need to add a resistor in series to decrease the voltage of the signal.
luck6 years ago
What do you mean tap into the speaker? Could you explain.
luck6 years ago
is it possible to use a wireless phone. If so then what do i do? do i just wire it the same way and keep the power cord to the phone pluged in so that it will work. Or will the battery alone work. your help would be greatly apreciated. This mic will help me to record my invention ideas before i foget them.
randofo (author)  luck6 years ago
You would just have to power up the phone completely with a 9V battery and then tap into the speaker to get audio out.
luck6 years ago
is it possible to use an LED that will use enought voltage when your mic is on so that u can get the voltage closer to the line level without having to build a totally different circuit.
randofo (author)  luck6 years ago
You might be able to find some low-voltage (1.5v) LEDs, but they are somewhat rare. Try using octopart.com to search for that.
tk421dan6 years ago
Randofo, (I hadn't seen this before I posted mine) ah, your's is prettier then mine to boot, oh well , good job and thanks for the link to your Instructable!
cimz6 years ago
hey guys i've followed this wiring diagram shown except i have replaced the 1/8 jack with a 1/4 jack. I am using a carbon microphone from a rotary phone. i've tried using the exact box created here and i have also wired the speaker directly into the circuit bypassing the need for the phone chord and i am still unable to get any sound from the mic. i am completely new at this and i have not wired the capacitor or the potentiometer into the circuit. is that the reason why i am not getting any sound? and if that is not the reason does anyone have any idea how i can get this to work? any help would be greatly appreciated. this mic would be amazing for my band's live show. thanks!
try my 'bang it on the floor trick" above if the carbon mic doesn't work...
randofo (author)  cimz6 years ago
I have not installed the capacitor in any of the versions that I have made, but I have added it based on some of the feedback that I have gotten and it is probably a good idea to have it. The potentiometer is needed and that may very well be your problem. My original version didn't use a potentiometer, but had a 100K resistor instead. I added the pot to give a little more control over the fine tuning. Then again, I've built one without any resistors or capacitors at all, but it didn't work on all amps since the signal was kind of high. Maybe you just wired it backwards or you have a bad connection somewhere, perhaps? However, I would try adding a 100K resistor in place of the pot and seeing what happens. Just having a 33K resistor might be confusing the device.
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