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Electronics for dummies - McComb G.

McComb G., Boes E. Electronics for dummies - Wiley publishing, 2005. - 433 p.
ISBN: 0-7645-7660-7
Download (direct link): electronicsfordummies2005.pdf
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The output of the 555 chip on the left, which produces a slower rising and falling tone, connects into pin 5 of the 555 chip on the right in the figure. You connect the speaker to the output of the 555 chip on the right.
Adjust the two potentiometers, R2 and R4, to change the pitch and speed of the siren. You can produce all sorts of siren and other weird sound effects by adjusting these two potentiometers. You can operate this circuit at any voltage between 5 and about 15 volts.
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Chapter 14: Great Projects You Can Build in 30 Minutes or Less 311
Scoping out the 555 siren parts list
To start alarming your friends, gather these parts together to build the circuit:
^ IC1, IC2: 555 Timer IC R1, R3: 2.2K ohm resistor R2: 50 Kohm potentiometer R4: 100 Kohm potentiometer C1: 47-|iF electrolytic (polarized) capacitor C2: 0.01-|iF disc (non-polarized) capacitor C3: 0.1-|iF disc (non-polarized) capacitor C4: 1-|iF electrolytic or tantalum (polarized) capacitor Speaker: 8-ohm, 1-watt speaker
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312 Part V: A Plethora of Projects
Get Lost___or Found, with the Electronic Compass
Discover where in the world you are with this very cool electronic compass! This magnetic compass uses the same technology that manufacturers build into many cars to show you your direction electronically. Four LEDs light up to show you the four cardinal points on the map: N (north), S (south), E (east), and W (west). The circuit illuminates adjacent LEDs to show the in-between directions, SW, SE, NW, and NE.
Peeking under the compass hood
At the heart of this project is a special compass module, the Dinsmore 1490. This module isn’t a common, everyday part. You have to special order it, but you can have a lot of fun with the project, making it worth the $13 to $15 that you pay for the compass module. Check out the manufacturer’s representative at for the compass module, and don’t forget to try other possible sources by doing a Google or Yahoo! search. Try the search phrase “dinsmore compass.”
The 1490 compass module is about the size of a small thimble. The bottom of the sensor has a series of 12 tiny pins, as you can see in the pinout drawing in Figure 14-8. The pins are arranged in groups of four and consist of the following connection types:
^ Power ^ Ground
^ Output (or signal)
You can see the schematic for the electronic compass in Figure 14-9. By doing some careful soldering, you can build a nice portable, electronic compass that you can take anywhere. Put it in a small enclosure, with the LEDs arranged in typical clockwise N, E, S, W circular orientation. You can buy enclosures at RadioShack and other electronics stores. They come in a variety of sizes, starting from about two inches square. Select an enclosure large enough to contain the circuit board and batteries.
You can power the compass by using a 9-volt battery. Add a switch from the + (positive) terminal of the battery to turn the unit on or off, or simply remove the battery from its clip to cut the juice and turn off your compass.
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Chapter 14: Great Projects You Can Build in 30 Minutes or Less 313
1 2 3
Figure 14-8:
A pinout drawing of the Dinsmore compass module.
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314 Part V: A Plethora of Projects
Checking your electronic compass parts
To point you in the right direction, here are the parts that you need to gather to build your compass:
COMPASS: Dinsmore 1490 magnetic electronic compass (see the section “Peeking under the compass hood” earlier in this chapter)
^ R1-R4: 1 Kohm
C1: 10-|iF electrolytic (polarized) capacitor
^ LED1-LED4: Light-emitting diode (any color)
^ MISC: Project box, switch, battery clip (all optional)
When There’s Light, You Hear This Noise...
Figure 14-10 shows you a schematic of a light alarm. The idea of this project is simple: if a light comes on, the alarm goes off. You build the alarm around an LM555 timer chip, which acts as a tone generator. When light hits the photoresistor, the change in resistance triggers transistor Q1. This response turns the 555 on, and it squeals its little heart out. You can adjust the sensitivity of the alarm by turning R1, which is a variable resistor (potentiometer).
Making your alarm Work for you
Does it seem a little nuts to create an alarm that goes off whenever it senses light? Surprise! You can apply this handy light alarm in several practical ways. Here are just a few of ‘em:
Put the light alarm inside a pantry so that it goes off whenever someone raids the Oreo cookies. Keep your significant other out of your stash — or keep yourself on that diet! When the pantry door opens, light comes in and the alarm goes off.
Do you have a complex electronics project in progress in the garage that you don’t want anybody to disturb? Place the alarm inside the garage, near the door. If someone opens the garage door during the day, light comes through and the alarm sounds.
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