Introduction: 555 Capacitor Tester
这个is something I built from a published schematic late in the 1980s. It works very well. I gave away the magazine with the schematic because I believed I would never need it again and we were downsizing.
这张照片显示了我的测试。我钻洞1/8 inch Plexiglas to make a circuit board. Just decide where each component should be located and mark the location for the holes. Drill with a small drill. I place the component on top of the Plexiglass and connect leads below the Plexiglass. There is a selector for different resistance arrays. I tapped the Plexiglass for 8-32 brass screws. I soldered leads to the screw heads under the Plexiglass and I attach an alligator clip to the appropriate screw for the desired resistance range on each test. I used hot glue to fasten components to the Plexiglass where necessary. The battery holder is fastened to the Plexiglass with a screw.
Step 1: Removing the Mystery
I know just a little about electronics, but not a lot. For a long time I was in awe of the genius who used a 555 Timer chip to make a capacitor tester. Then I began reading a little more about 555 Timer circuits. According to my rudimentary understanding, they can be configured in different ways, including astable, monostable, and bi-stable. Each works a bit differently with different results for different purposes. After reading about each of these just a little, I decided the capacitor tester I built is a very common monostable multivibrator or “one-shot” configuration.
A monostable multivibrator turns “on” when a momentary contact switch is depressed and released. The multivibrator produces a continuous pulse that lasts until the capacitor in a resistance/capacitance bridge charges up to a particular percentage of a full charge. When that happens, it signals the 555 Timer chip to stop the pulse. In this case, that means an LED came “on” when the momentary contact switch was depressed and released. It continued to be lit until the capacitor charged to its threshold level. Then the 555 Timer turned the LED “off.” If the resistance has been carefully chosen, counting the number of seconds the LED was “on” indicates the value of the capacitor multiplied by 1 or by 10 or by 100 according to the selected test range.
这个link在电路摘要中，使用555定时器芯片讨论单稳态多谐振荡器电路中的电阻/电容桥，它给出了用于计算LED在秒内的标准公式，基于指定的电阻和指定的电容。它还提供了用于使用555个定时器芯片的配置的示意图。如上所述，R1和C1是变量。在我的测试仪上，如果R1为900,000欧姆，则乘法因子是1.如果R1为90,000欧姆，则乘法系数为10.如果R1为9000欧姆，则乘法系数为100.在我用来推出100微米时的照片中的照片在观察极性的同时，电解电容器到测试鳄鱼夹。LED在10秒内出去了。选择器设置在10x选项上。10 x 10 = 100.电容器的值非常接近其指定值。（该测试仪不表示其他东西，如电容器的内部电阻。）
The image is a monostable multivibrator circuit from the link above to Circuit Digest. You could build the circuit as shown. R1 and C1 are conveniently marked. I would add a three-position selector for the resistances mentioned in the paragraph above. It would make the tester easier to use.
As I mentioned, I did not save the magazine with the schematic that I built, but gave it away. I have looked, but not found anything exactly like it on the Internet. I believe any monostable multivibrator circuit would work. They seem to vary just a little.
I did try to trace the circuit from my actual tester. It can be viewed in the photo with this step. I viewed my circuit board from the bottom and tried to trace the connections accurately. There is always the possibility I made an error, although I checked it a few times.
I am accustomed to pin out diagrams on IC chips that begin with #1 in the upper left corner and progress to pin #2 and so on. See the circuit diagram in the image from the previous step. Pin #1 is on the bottom at the center. What you see in that diagram is now the standard way to show the pin out for a 555 Timer chip. My diagram of what I built is further complicated because the pin out is from the back side of the circuit board.
Step 3: How to Use the Tester
1. Always discharge the capacitor first.
2. Select the appropriate resistance range. (If you are testing a 4700 microfarad capacitor counting 47 seconds makes more sense than counting 4700 seconds to arrive at the approximate value of the capacitor.)
3. Attach the positive (+) and negative (-) test leads to the capacitor. Be careful to observe the correct polarity.
4. Depress the momentary contact switch and release it.
Good capacitor—The LED stays “on” for the appropriate number of seconds before turning “off.”
Range set too high—The LED turns “off” as soon as the momentary contact switch is depressed and released.
Capacitor is “open” and must be replaced—The LED turns “off” as soon as the momentary contact switch is depressed and released.
LED stays “on”—The capacitor’s connection to the tester is the wrong polarity, or the capacitor is shorted and needs to be replaced.
关于我发现用电容器测试仪电路的杂志我买了一个40岁的Zenith Trans-Oceanic AM-Shortwave Radio，用真空管构建。当我开始使用收音机时，电解电容器开始吹一个，并且当时使用它很有一点。测试可疑电容器而不是仅在无线电时刻在无线电时抛出金钱和新电容器是有帮助的。该测试仪帮助我识别出故障的电容并改变它。我不再拥有那个收音机，但偶尔我发现当我尝试再次工作时检查电容非常有用。我不经常使用这个测试员，但是当我需要它时非常有用。我现在确实具有多米的电容秤，但米经常不涵盖所需的范围。我通常建造的测试仪。
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