Megaphone, symbol of loud sound, siren, protesting and communication, and this is why we are going to hack it so add a 3.5mm jack plug into it as a feature to give the possibility to send sound from any device with a audio output.
There are new models with expensive high tech wireless or bluetooth connections, but we don't want that, we want cheap hackable stuff, so let's do this.
Step 1: Adquire the Megaphone
The megaphone we adquired was a LP DH-12 megaphone, that works at 12V.
It has an embedded siren and a diferential mike, to reduce noise in the voice signal and on/off switch.
You can find a lot of these around, for a good price/quality. It's handy to have the mike around because we can use the sound and add voice at the same time without any problem.
Step 2: Understand How It Works
We start by opening the mike, remove the 3 screws in the back, careful not to pull wires from the mike and we analysed that the signal is sent to the main board through the yellow wire and somehow they change the colours and the red is ground, so just a reminder:
DON'T TRUST THE WIRING COLOURS!!!
Step 3: Get to the Main Board
Then open the battery lid, remove the screw in the top cap and have access to the board. Be carefull when you pull, there is quite a few wires comming from diferent locations, big mess.
At this fase, if you want, you can carefully remove some connectors to work more freely but first if you want, you have to leave it like that to confirm wire from the mike. Don't forget were you disconnected them.
After that in the bottom, there are 2 screws that hold's the board to the protection you just removed. Remove them and you'll have access to the circuit board connections.
Step 4: Hacking the Signal
We followed the wires up until the board, thats why i didn't disconnected before and found out that the two indicated tracks are the signal from the mike that goes to a filter and ground, so once again be carefull, somehow (in our megaphone) the colours are mixed and in the bottom, where the batteries connect, the positive is the black one and negative the red one.
We connected the white wire in the signal and black one the ground, this is a mono connection, not stereo.
For new PCB's with SMD components, we have to check where the microphone signal goes and connect our signal in the right place or it will short circuit your sound jack (happened to me), you can see the second photo the yellow and white wire, where white is ground and yellow the signal.
We soldered it to the board to have a good connection, these are large tracks i suppose it won't be a problem.
Step 5: Making It Functional and Pretty
As a connection we used mini XLR connectors to 3.5mm 3 poles sound jack, but we only used 2 pins, the back one to ground and the front one to signal and since it's mono the middle stayed disconnected.
We drilled 2 holes at the side of the megaphone, one for a 10K potentiometer and 1 for the wire to come out.
The potentiometer in series was to reduce the power comming to the amplifier, since usually cellphones have a stronger signal to power up the headphones, but you can try with a low resistor, like 1 or 2.2 ohms in series. You can also adjust a little bit the volume here.
Get the potentiometer in place and the wire just give a knot so that he won't be pulled from the board.
Get the board screwed in place and start connecting and closing everything.
Step 6: Testing
To start testing, even if you don't have it closed, you can plug it in with a 12V transformer and use in the existing DC jack in the back, then connect the sound jack to the testing device and after you turn on, press the megaphone switch and we would start soon.
You can adjust the sound in your device.
To make it stay always on, you can just eliminate the switch or place a relay to control it.
HAVE FUN ANNOYING NEIGHBORS!!!