Your sketchpad: a breadboard.

And these are your drawing instruments: jumper wires.

The great thing about them: they are easily removeable. So you can quickly sketch another idea if your first one doesn't work out.

Below, a sketch in action. Don't like it? Pull the jumper wires out and start over.

On the Internet:

• Breadboards for Absolute Beginners (from Instructables)
• How to Use a Breadboard (from Sparkfun)