Intro: Sponge Sensor for Scratch
The sponge sensor works like a variable resister- electricty passes through a wet sponge.
As the sponge is squished more or less water lets more or less electricity pass through.
I made this to play with resistance and sound with Scratch and a sensor board...
You need to download the Scratch program and either make your own project or use this one that makes musical notes based on how much resistance there is in the sponge.
To combine Scratch and the sensor you'll also need to get a PICOboard along with the Scratch program.
You can use the Arduino with Scratch as well - look on the Scratch forums for a great program that connects Scratch and Arduinos
Lastly the sponge sensor might be great for circuit bending as well - then all your music making materials can be free and/or recycled
Step 1: Materials
Plastic cardboard - 1 sheet ( or scrap piece at least 5x10 inches) We need plastic because this is going to get wet. Save and recycle those political yard signs!
Telephone wire - 2 pieces about 10 inches each. This is also recycled: old computer cables. It has nice colors as well.
Sponges - 1 ( you'll cut it in half to conserve) I recycle or purchase the synthentic traditional kitchen - sized sponges ( run them through a dishwasher if you want to clean old sponges.
Brass fasteners - 4 of these.
Washers - 4 small washers that just the legs of Brass fasteners can fit through.
Aluminum (metal) flashing tape - about 10 inches. I bought a roll because I use this in all sorts of projects - its great. Find it at big box and small hardware stores.
Hole punch ( with long neck if you can find one)
Awl ( for punching starter holes )
metal ruler or yardstick (for guiding straigh cuts in plastic)
Cut a piece of the plastic cardboard about 3-4 inches by 8-10 inches
You might want to clean any dirt off the piece - the flashing tape will stick better.
Cut a piece of the metal tape that overhangs both sides of the sheet by enough to wrap around to the back
Line it up and snip it in half.
Tape down one side so that it starts near the center and wraps around to the back. Smooth it down.
Start the other piece in the center leaving a gap. 1/4 - 1/2 inch seems to work well.
Stick this down...
and wrap it around as well.
Okay punch a hole in the center of the metal tape near the edge ( about a 1/2 inch in)
Its not that easy, so you'll have to force the hole punch.
Try not to bend your hole punch handles. (like I did)
You'll do this to the other side.
Then get the hole punch as near to the other end of the tape - try to get it near the center. This will depend on the length of the neck of your hole punch.
Okay - So you'll end up with 4 holes each near (at least 1/2 inch) to each end of the metal tape pieces
Snip your sponge in half.
Punch a hole near one side (short side if its not a square)
Push one brass fastener through the hole and...
.. put it through one of the middle holes in the sheet.
Bend the legs so it stays.
Lower the sponge so you can see where to punch a hole in the sponge to line up with the second hole in the plastic (you can use an awl to push a hole through the sponge if that helps you line them up)
Put the other brass fastener through.
Bend the other legs so they look similar to this.
The sponge should be in place. You'll want it pushed down, tight against the sheet.
Get your brass fasteners and washers together and add them to each side.
Bend legs - but not too much, we're going to wrap the wires around them.
Strip the 4 ends of your two wires. Strip off about 3/4 - 1 inch of insulation.
Wrap one ( circle the brass fastener a couple times) end of each around each of the brass fasteners.
Push the brass fasteners down again to keep the wire held tightly and bend the legs to hold them.
Finish the other side....
and you're ready to hook it up to the PICO board.
Go here to look at the Scratch project that shows how to make sponge music.