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Build your own electronic rooster that wakes you up at daybreak. (Who needs an alarm clock?)
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Chapter 14: Great Projects You Can Build in 30 Minutes or Less 315
Assembling a light alarm parts list
Hereís the shopping list for the light alarm project:
^ IC1: LM555 Timer IC Q1: 2N3906 PNP transistor R1: 100K potentiometer R2: 3.9 Kohm resistor R3: 10 Kohm resistor R4: 47 Kohm resistor
C1, C3: 0.01-|iF disc (non-polarized) capacitor
C2: 1.0-|iF electrolytic or tantalum (polarized) capacitor
Speaker: 8-ohm, 0.5-watt speaker
Photoresistor: experiment with different sizes; for example, a larger photoresistor will make the circuit a little more sensitive.
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316 Part V: A Plethora of Projects_
'Lit Amp, Big Sound
Schematic of the little amplifier.
Give your electronics projects a big mouth with this little amplifier designed around parts that are inexpensive and easy-to-find at most electronics suppliers. LM386 power amplifier IC ó this amp boosts the volume from microphones, tone generators, and many other signal sources.
The ins and outs of'Lit Amp
Figure 14-11 shows the schematic for this project, which consists of just six parts, including the speaker. You can operate the amplifier at voltages between 5 and about 15 volts. A 9-volt battery does the trick.
To use the amplifier, connect a signal source, such as a microphone, to pin 3 of the LM386. Be sure to also connect the ground of the signal source to the common ground of the amplifier circuit.
Depending on the source signal, you may find that you get better sound if you place a 0.1-|iF to 10-|iF capacitor between the source and pin 3 of the LM386. For smaller values (less than about 0.47-|iF), use a disc capacitor; for larger values (1-|iF or higher), use a tantalum capacitor. When you use a polarized capacitor, orient the + (positive) side of the component toward the signal source.
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Chapter 14: Great Projects You Can Build in 30 Minutes or Less 317
This little amp doesnít come with a volume control, and the sound quality can take you back to your days listening to the high school PA system. But this simple circuit puts out a whole lotta sound in a small and portable package.
Sounding the roll call for little amplifier's parts
Hereís a rundown of the parts that you have to gather for this project:
IC1: LM386 Amplifier R1: 10-ohm resistor
C1: 10-|iF electrolytic (polarized) capacitor C2: 220-|iF electrolytic (polarized) capacitor C3: 0.047-|iF disc (non-polarized) capacitor Speaker: 8-ohm, 0.5-watt speaker
The better the microphone and speaker, the better the sound!
Building the Handy-Dandy Water Tester
You may not be able to divine underground water with the water tester circuit in Figure 14-12, but it can help you check for moisture in plants or find water trapped under wall-to-wall carpet.
How the water tester works
The Handy-Dandy Water Tester is deceptively simple. It works under the principle of electrical conductivity of water (this is the principle that says you donít take a bath with a plugged-in toaster in your lap). The tester contains two small metal probes. When you place the probes in water, the conductivity of the water completes a circuit. This completed circuit drives current to a transistor. When the transistor turns on, it lights an LED. When the probes arenít in contact with water (or some other conductive body), your tester has a broken circuit, and the LED doesnít light up.
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318 Part V: A Plethora of Projects
You make the two probes with small nails, say 4d (four penny). Place the nails about a half-inch apart on a piece of plastic (but not wood or metal). The nails should be parallel to one another. File down the tips of the nails to make sharp points. These points help you drive the probes deep into the material that youíre testing. For example, you can drive the probes into a carpet and pad to determine if water has seeped under the carpeting after a pipe in the next room bursts.
You can adjust the sensitivity of the tester by turning potentiometer R2. Start with the potentiometer in its middle position and turn one way or another, depending on the amount of moisture or water in the object that youíre testing.
Power the water tester by using 5 to 12 volts. A 9-volt battery works well.
Gathering Water tester parts
Go out and get the following parts to build your water tester project:
^ Q1: 2N2222 NPN transistor ^ R1: 470-ohm resistor ^ R2: 50 Kohm potentiometer ^ LED: Light-emitting diode (any color)
^ Probes: Two small nails (4d, also called four penny)
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Creating a Very Cool Lighting Effects Generator
If you were a fan of the Knight Rider television series that aired back in the í80s, you remember the sequential light chaser that the Kitt Car sported. You can easily build your own (light chaser setup, not car) in the garage in under an hour.