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.
Step 1: 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)
1. 1 roll black gaffers tape
2. 1 roll white gaffers tape
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.
Step 3: Solder!
Solder the circuit as shown in the picture.
If you do not like looking at pictures, then follow these simple instructions:
The red wire on the battery holder goes to the toggle switch. The black wire from the phone jack also goes to the toggle switch.
The black wire from the battery holder goes to the ground terminal on the 1/8" mono jack. The yellow wire from the phone jack goes to the other terminal on the 1/8" mono jack.
Step 4: Debug.
Put in a battery. Plug in a phone handset. Connect it with an audio cable to a speaker and make sure it works (don't forget that the toggle switch might be in the off position).
If it does not work, check your wiring. Make sure the connections are good and the connections are right. If both of those are good, then check to see if your phone handset works and looks like the one shown below. If you still can't figure out the problem then put in a new battery. If that is a no go, check to see if your speaker is turned on, the volume is up and you plugged the mic in to the right jack. If none of that works, you may have an audio device that requires a 1.2V line-level input. Try using a different audio device or see Step 8. If you have tried everything and you still can not get it to work, get someone else to do it for you.
Step 5: Install the Components.
With your hot glue gun, glue the battery holder to the inside of the case opposite from the holes for the switch and the jack. Take the nuts off your switch and jack, put the two components through the holes you made for them and screw the nuts back on, fastening them in place. Clip the unused red and green wire.
Step 6: I Lied About the Circuitry!
My initial design has no voltage protection (the thing that you were building up until now).
So, realizing that this lack of voltage regulation is a problem, I built the circuit pictured below to kick down the output voltage from 1.5 to 1.2 volts (because rumor had it that this was line level). Line level is still a bit myserious to me, but thanks to a comment posted on the main page by Phatso I can now tell you that line level is probably more around 1v. However, the circuit below should still work fine.
Put together the circuit shown below and shove it inside your case (so that your mic works right and doesn't harm any other devices that you plug it into).
You can also try just using a 100K potentiometer and a 10uF electrolytic capacitor between the telephone jack and the mono jack. This, in theory, will provide volume control and protection from bad voltages. However, I'm not really sure how or even if this will work. This is mere speculation on my part (based on what someone told me once in passing).
Also, a low voltage LED to indicate whether the device is on or off may be nice.
Step 7: Optional Beautification.
If you are like myself and cut out an aluminum cover out of a much larger sheet of aluminum, then you have a small piece of conductive metal with some nasty edges. You are going to want to both cover and insulate this to prevent injury or the rare crossed wire. More importantly, you are going to want to cover it so that it does not look ugly.
To solve all of these problems at once I wove a checker board pattern out of thin strips of black and white gaffers tape.
I started with the tape stuck to the back side and folded it over and under until the whole front side of the lid was covered. Going in one direction were all of the white pieces of tape, one next to another, and in the other, the black. The pictures below might help you understand better.
This whole weaving process can be maddening. Figure out what works for you. There is no right answer. You can make any pattern you want. Just make sure that both sides and especially the edges of the lid are covered.
If you are working with a material that does not have sharp edges and is non-conductive, you may want to consider decorating your case in some manner any which way.
Step 8: Closing the Case.
Now your box should be more or less done.
If you covered over the 3/16" hole in your lid, now would be the time to poke through the covering.
If you have not removed the screw that came with the case, now would be the time to do that.
Taking the 1" bolt, screw on a nut all the way to the bottom and then insert it into your case. Put the bolt through the hole in the lid. Fasten the lid to the to the case with a nut, tightening it with your pliers if need be.
Step 9: Perform "Sweet Jane" (words and Music by the Velvet Underground)
The only way to complete your telephone handset microphone is to perform "Sweet Jane" with your new microphone and the instrument of your choice.
Words and chords can be found here:
You can view my performance here:
(Be warned! My video camera broke and I had to resort to a really bad stop motion animation.)
Please post a link to your performance.