Books
in black and white
Main menu
Share a book About us Home
Books
Biology Business Chemistry Computers Culture Economics Fiction Games Guide History Management Mathematical Medicine Mental Fitnes Physics Psychology Scince Sport Technics
Ads

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
Previous << 1 .. 82 83 84 85 86 87 < 88 > 89 90 91 92 93 94 .. 149 >> Next

11. Adjust the Horizontal Position knob until the beam is more or less centered on the screen.
You donít need to worry about making this setting exact.
12. If your scope has a Signal Clamp switch, set it to DC. If you donít have a Signal Clamp switch, move the test probe from its ground connection to the calibration test point.
Many oscilloscopes use a test signal that appears as a relatively low-frequency square wave. (Forgot what a square wave looks like? Review Chapter 1 for details.) Consult the manual that came with your scope to see what voltage and frequency your scope produces with its built-in test calibration circuit.
For example, say that the signal should be 0.5 volts peak-to-peak (indicated as 0.5v p-p) at 1000 Hz. Because you set the Volts per Division knob to 0.5 volts and the test signal has amplitude of 0.5 volts, the waveform spans one division on the screen.
TERM LinG - Live, informative, Non-cost and Genuine !
226 Part IV: Getting Your Hands Dirty
Figure 10-11:
Adjust the Vertical Position knob so that the beam sits on the bottom of the grid.
By decreasing the Volts Per Division setting, you can make the waveform larger. Do this adjustment when you need more accuracy. For example, if you set the Volts Per Division knob to 0.1 volts, a 0.5 volt test signal spans five divisions.
Does your battery have any juice ?
Admit it. You have a drawer full of spare batteries, and you sure would like to know just how much voltage the darn things have to give, right? A rudimentary test that you can perform using the oscilloscope is measuring voltage. A battery produces a DC voltage, so the sweep setting on the scope is irrelevant in this test. You just want to know what voltage the scope displays on the screen.
For this demonstration, you test the voltage of a 9-volt battery: So, first, dig around in your drawer and pull out a 9-volt battery; then, follow these steps:
1. Follow the basic setup and initial testing procedure outlined in the previous section.
2. Set the Volts Per Division knob to 2 volts.
3. Attach the ground clip of the test probe to the - (negative) terminal of the battery.
term LinG - live, informative, Non-cost and Genuine !
Chapter 10: Getting Down with Logic Probes and Oscilloscopes 227
4. Attach the center of the test probe to the + (positive) terminal of the battery.
The line on the screen should fall approximately mid-way between the fourth and fifth divisions. Because you have the Volts per Division knob set at 2 volts, this line placement indicates that your battery has 9 volts, or 4.5 divisions times 2.
Dissecting your radio to display an audio waveform
You can have a lot of fun with this test because you get to take apart a gadget to run the test. Oscilloscopes can visually represent the AC waveform, which is the electrical signal that drives a speaker. The AC waveform is complex because itís made up of constantly changing frequencies. These changing frequencies are what you hear as singing, talking, or the sound of musical instruments.
For this test, pry off the back of an ordinary battery-powered radio so that you can reach the two terminals on the speaker. Then, follow these steps:
1. Follow the setup-and-testing procedure outlined in the section ďBasic setup and initial testing,Ē earlier in this chapter.
2. Set the Volts Per Division knob to 1 volt.
3. Set the Sweep/Time Per Division knob to 100 microseconds.
4. Attach the ground clip of the test probe to one of the speaker terminals.
5. Attach the center of the test probe to the other speaker terminal.
6. Turn on the radio and watch the display.
7. If at first you donít get much of a reading, try, try again by decreasing the Volts Per Division setting.
Here are some things to watch for when you perform this test:
^ The amplitude of the waveform increases and decreases as you change the volume on the radio. This change happens because the volume control alters the signal voltage that you apply to the speaker.
^ By turning the Sweep/Time -Per Division knob, you can see finer detailís of the signal. A slower sweep of, say, 0.1 milliseconds displays frequencies of up to 1000 Hz per division. A faster sweep of, say, 100 microseconds displays frequencies of up to 10,000 Hz per division.
If you have access to a signal test generator that can produce a single tone, you can use this same technique to take a look at its waveform. Rather than a mish-mash of squiggly lines, you see a distinct sine wave.
TERM LinG - Live, informative, Non-cost and Genuine !
228 Part IV: Getting Your Hands Dirty
Testing the frequency of an AC circuit
You can determine the frequency of an AC signal by using an oscilloscope. Now, although you can plug the test probe of the scope into a wall socket to display the 60 Hz (50 Hz in some parts of the world) alternating current coming out of it, DONíT! This poses a significant safety hazard so donít even think about it. Instead, test the frequency of your household current indirectly (and more safely), using a phototransistor.
Previous << 1 .. 82 83 84 85 86 87 < 88 > 89 90 91 92 93 94 .. 149 >> Next