This is a simple electronic gadget you can build for yourself using old electronics and cheap kits. Connect the components, protect them with polyurethane foam and install them in the street. Record a message and let others record their own message.

//// Vox Populi is an open source project based in DIY interaction designs to fight advertisement and corporate branding in our streets.////

Step 1: Connect the Components

This is what you need:
ELECTRONICS
_Voice synthesizer type Cebek ref. C9701 or similar. (Basically a 20seg voice rec+play)
_Speaker (as big as you want, consider 4 cm /1.6inch diameter minimum)
_Switch
_Infrared sensor (I used CROW ref. SPR-100, but any alarm infrared sensor should work also tiny like cebek ref.7288)
_5V Relay
_Batteries (depending of synthesizer and infrared)

PROTECTION
_Polyurethane foam, sold in spray avaliable in any drugsore
_Half plastic bottle

TOOLS:
_soldering iron
_Silicone mould (optional)
_Cutter
_Gluegun

Step 2: Change Speaker and Rec Button

Usually voice synthesizer are provided with tiny speakers, change the original one and connect a bigger one to obtain louder sound. (I used one as big as my bottle screw top as they have to fit together)

Change also the rec button for a lamp switch to make an easier interaction.
The switch is going to work better if you stick it to a piece of wood or plastic as a lever.

At the end, secure the connections with the gluegun to make sure it's going to work.

Step 3: Change Play Button

Change now the play button for the infrared sensor. That means that the gadget is going to play the recorded message when pedestians walk close to it. That makes a much more interesting interaction that through buttons.

Follow the connections of the original play button and exchange them for the infrared. Remember to use the Relay.

Step 4: Protect

Before putting it al into foam, protect the sensible/mechanic parts to avoid foam disables them. Protect the speaker, microphone, sensor and switch. (follow the sketch)

Step 5: It's Foam Time

Now that the electronics are done make sure they work as planned.

If everything it's ok, then find a silicone mould (any pastry-mould should work) or any other PP / PE packaging (foam is not going to stick to it). You can also work without mould, by putting trhe foam directly on the electronics.

*Foam is not only going to keep things together but to protect them from weather

Wait util the foam is completely dry (also inside) - usually takes from 6 to 12 hours (see foam spray instructions)

Step 6: Battery Location

When the foam is completely dry it's easy to shape simply by cutting it with a blade (cutter).

Step 7: It's Done!

Now do a hundred of them and spread them away!
(stick them to the walls with some more foam)

*depending on the batteries should work for a week at least