LONG LIFE BATTERY-Debugging Steps
The variable resistor is held in the full counterclockwise position, the switch is turned to the on position, then the photosensitive resistor is aligned with the power supply, and then the variable resistor is slowly rotated clockwise until a reading appears on the meter head.Put your hand between the light source and the photoresistor. When you move your hand back and forth, the pointer on the meter also swings left and right. If the pointer on the meter does not read on the positive plate, but swings in the direction below the zero scale of the scale, there may be two reasons why the connection is reversed D: one is that the terminal of the meter is reversed, and the other is that the polarity of the power supply is reversed.Other possible problems, such as faulty wiring, broken wires, and discharged batteries, must be noted: in this chapter, all exposure meter circuits are designed with specific photoelectric components.For example, the output current of photovoltaic cells is about IO milliamperes, and other photovoltaic cells can also be used.However, if the output current value of the adopted element deviates too far, the resistance value of the variable resistor must be corrected accordingly.If the pointer changes from zero to full scale during adjustment, the resistance value of the variable resistor should be properly reduced.If the variable resistance is adjusted counterclockwise and the pointer on the meter still cannot return to zero at the end of the silk knot, the variable resistance value must be increased.This is probably not necessary unless the solar cells used are extremely powerful.
4 - 6 compound exposure meter
Some readers who are willing to make a slightly more complicated electronic circuit can refer to Figure 4 - 5.The picture is a slightly more complicated circuit, but it can still be made into a real object within an hour.
The circuit of fig. 4 5 makes use of the advantages of solar cells and photoresists, which are sensitive to changes in light.But also retains the simple structure of the circuit and does not need battery power.
It must be noted that the polarities of the solar cell and the meter head should be consistent, the photoresistor and the variable resistor have no polarities, and they can be connected at will.
Figure 4 - 3 shows a plastic or metal box for this circuit.
Gui.0?50 microampere PC, - rectangular solar cell
PCa?Photosensitive Resistance RI - 75 KQL / 2 \ V Variable Resistance
Fig. 4 - 5 circuit diagram of combined exposure meter
In order to pass through the leads of the photoelectric elements, four holes need to be drilled in the box.The two photoelectric devices are then firmly fixed to the top of the box with epoxy resin.
The positive electrode of the solar cell is connected to the positive electrode of the 50 microampere ammeter, and the negative electrode is connected to any terminal of the photoresistor. The wire between the photoresistor and the solar cell is fixed by welding, while the other terminal of the photoresistor is welded together with the middle terminal of the variable resistor.If installed in an aluminum box, the two wires must be insulated.Before welding the last wire to the right end terminal of 1, it is necessary to turn the resistance of the resistor to the terminal counterclockwise, and the other end of this wire is connected to the negative terminal of the microampere meter.Now that the circuit has been completed, you can cover the box.
4 - 7 Debugging Steps
As with the power adjustment method above, a light source with medium light intensity is used to irradiate the photoresistor and adjust the variable resistance until a reading appears on the meter head.If the reading on the meter head decreases, the circuit will work normally.When the exposure meter is not in use, the variable resistor must be turned counterclockwise to the terminal to protect the ammeter.In addition, a metal sleeve or cup-shaped cover can also be used to shield the photoresistor to protect the ammeter.When such a cover is covered, the photoresistance will increase to 5,000,000 ohms, and the meter will never turn even if there is more intense light.
The ammeter used in the three types of exposure meters described above can sometimes have some changes in their specifications without necessarily changing the parameters of other electronic components.If you happen to have other specifications of milliammeters or microamperes at hand, they are also applicable.When the ammeter has a range of more than 5 milliamperes and a small solar cell is used, its sensitivity will decrease. Such an exposure meter is not very useful.However, in the battery-powered circuit, even if a milliammeter with a large range is used, it can still work normally.If you have a ready-made ammeter at hand, you can try it.If necessary, the resistance value of the variable resistor RI can be changed accordingly.