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Project #197
OBJECTIVE: To sound an alarm when
water is detected, tone will vary with salt
Build the circuit at left and connect the two (2) jumpers
to it, place the loose ends of the jumpers into an empty
cup (without them touching each other). Press the
press switch (S2) - nothing happens. Add some water
to the cup and an alarm sound will sound. Add salt to
the water and the tone changes.
You can also test different liquids and see what tone
they produce.
Water Alarm
Project #198
Use the circuit from Project 197, but replace the press switch (S2) with the slide switch (S1) and you don’t
need the cup of water. There is one more part that you need and you are going to draw it. Take a pencil
(No. 2 lead is best but other types will also work). SHARPEN IT, and fill in the shape below. You will get
better results if you place a hard, flat surface directly beneath this page while you are drawing. Press hard
(but don’t rip the paper), and fill in the shape several times to be sure you have a thick, even layer of
pencil lead.
Turn on the switch and take the loose ends of the jumpers, press them to the shape and move them around
over the drawing. The tone of the sound should have a higher pitch if the ends are farther apart in the
shape. If you don’t hear any sound then move the ends closer together and move over the drawing, add
another layer of pencil lead, or put a drop of water on the jumper ends to get better contact.
Now you can draw your own shapes and see what kinds of sounds you can make!
Drawing Resistors
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