Introduction: Sponge Sensor for Scratch

(I am re-editing this Instructable to use the Micro:Bit! as Scratch 3.0 does not support it and it does support the Micro:Bit)

The sponge sensor works like a variable resister- electricity 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 2.0 program and either make your own project or use this one (this will be soon be updated to work with the Micro:Bit extension) 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 (these are still produced - you can find them here) along with the Scratch program.

You can use the Arduino with Scratch as well - look on the Scratch forums for great programs that connect 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.


You need:
Utility knife
Hole punch ( with long neck if you can find one)
Wire stripper

If available:
Awl ( for punching starter holes )
metal ruler or yardstick (for guiding straigh cuts in plastic)

Step 2:

Cut a piece of the plastic cardboard about 3-4 inches by 8-10 inches

Step 3:

You might want to clean any dirt off the piece - the flashing tape will stick better.

Step 4:

Cut a piece of the metal tape that overhangs both sides of the sheet by enough to wrap around to the back

Step 5:

Line it up and snip it in half.

Step 6:

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.

Step 7:

Stick this down...

Step 8:

and wrap it around as well.

Step 9:

Okay punch a hole in the center of the metal tape near the edge ( about a 1/2 inch in)

Step 10:

Its not that easy, so you'll have to force the hole punch.
Try not to bend your hole punch handles. (like I did)

Step 11:

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.

Step 12:

Okay - So you'll end up with 4 holes each near (at least 1/2 inch) to each end of the metal tape pieces

Step 13:

Snip your sponge in half.

Step 14:

Punch a hole near one side (short side if its not a square)

Step 15:

Push one brass fastener through the hole and...

Step 16:

.. put it through one of the middle holes in the sheet.
Bend the legs so it stays.

Step 17:

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.

Step 18:

Bend the other legs so they look similar to this.

Step 19:

The sponge should be in place. You'll want it pushed down, tight against the sheet.

Step 20:

Get your brass fasteners and washers together and add them to each side.

Step 21:

Bend legs - but not too much, we're going to wrap the wires around them.

Step 22:

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.

Step 23:

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.