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Project 201
Pitch (III)
OBJECTIVE:
Project #202
OBJECTIVE: To sound an alarm when water is
Flooding Alarm
Project #199 Pitch
OBJECTIVE: To show
how to change the pitch
Project 200
Pitch (II)
OBJECTIVE:
Remove the 0.1uF capacitor and
replace the 100kΩ resistor (R5)
wth the photoresistor (RP).
Wave your hand up and down
over the photoresistor to change
the sound. Changing the light on
the photoresistor changes the
circuit resistance just like varying
the adjustable resistance does.
Note: If you have the adjustable
resistor set to the right and light
shining on the photoresistor,
then you may not get any sound
because the total resistance is
too low for the circuit to operate.
Build the circuit on the left, turn
it on, and vary the adjustable
resistor (RV). The frequency or
pitch of the sound is changed.
Pitch is the musical profession’s
word for frequency. If you’ve
had music lessons, you may
remember the music scale
using chords such as A3, F5,
and D2 to express the pitch of a
sound. Electronics prefers the
term frequency, as in when you
adjust the frequency on your
radio.
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). Turn on the switch - nothing happens. This circuit is
designed to detect water and there is none in the cup. Add some
water to the cup - an alarm sounds!
You can use longer jumper wires and hang them near your basement
floor or next to your sump pump to give a warning if your basement is
being flooded. Note that if the loose jumper ends accidentally touch
then you will have a false alarm.
Since we’ve seen we can
adjust the frequency by
varying the resistance in the
adjustable resistor, are there
other ways to change
frequency? You can also
change frequency by
changing the capacitance of
the circuit. Place the 0.1µF
capacitor (C2) on top of the
0.02µF capacitor (C1); notice
how the sound has changed.
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