LONG LIFE BATTERY-If only the two outer terminals of the potentiometer are used
If only the two outer terminals of the potentiometer are used
If only the two outer terminals of the potentiometer are used, the resistance value will not be changed no matter how the rotating shaft is rotated, and the resistance value between the two outer terminals will always be 50,000 ohms of the resistance value of the component.Therefore, when the potentiometer is used as a variable resistor, its center terminal is always connected to the circuit and the other terminal is selected according to the actual application.
Fig. 4 - 2 is an assembly diagram for mounting such a circuit in a small box made of plastic or aluminum.The solar cell and the meter and the variable resistance need to be connected by wires, and the insulation treatment can be eliminated by using plastic boxes as the bottom plate for installation.The solar cell is mounted on the top of the rectangular box and fixed in place with one or two epoxy resins.The meter is embedded in the upper part of the panel.Drill another half-inch figure 4 - 2 exposure meter on the panel for installation in an aluminum or plastic box
An inch hole for mounting a variable resistor.The variable resistor is fixed with a screw cap and washer.Two small holes are drilled in the top of the box to pass through the connection line between the solar cell and the components inside the box.The positive electrode of the solar cell is connected to the positive electrode of the meter, and the negative electrode is connected to the middle terminal of the variable resistor.Using a stranded wire, one end of which is welded to the right terminal of the variable resistor *;The other end is connected to the negative electrode of the meter.This completes the installation.
4 - 3 Debugging Steps
Debugging is very simple.When the last wire is connected, there will be a reading on the meter head.First turn the potentiometer counterclockwise to the terminal, then aim the solar cell at a nearby light bulb, then slowly adjust the variable resistor R clockwise until a reading appears on the meter head.Cover the light with your hand, the pointer reading on the meter head should be greatly reduced, and the inspection is over.
The device is then corrected with an adjustable light source of known light intensity.The way is to install a knob with a pointed end on the shaft of the variable resistor and mark the circumference of the winding.Alternatively, the variable resistor may be fixed to a device.Read the meter readings and note the corresponding light intensity, and finally record these readings in a small table and paste them on the back of the box.
4 - 4 Photosensitive Resistance Exposure Meter
Fig. 4 - 3 is another type of exposure meter, its function is the same as that of the exposure meter described above.In this electronic circuit, a 1.5V No. 1 battery is used as the power source, and a photosensitive resistor is used as a light source indicator. After being irradiated by light, its resistance value is changed, and the current value flowing through the DC ammeter is controlled accordingly. The intensity of the light can be seen from the reading of the ammeter.The range of ammeter is 1mA.The specification requirement of the photoresistor is not strict, as long as it meets the requirement that the resistance value presented under bright light is less than 500 ohms.The minimum value of the photoresistor used in the circuit of fig. 4 - 3 is about 100 ohms, while the maximum value of the photoresistor in the dark ranges from 5,000,000 ohms.This element is sensitive to light and exhibits high sensitivity over a wide power range.
M, - 0 - 1 milliampere meter PQ - photoresistor
R, - 50kql / 2w potential thin * s - single pole single throw small switch
Figure 4 - 3 Photosensitive Resistance Exposure Meter
The 1.5V No. 1 battery provides a constant current to the electronic circuit.This circuit is also the same as that shown in the figure. It also uses series variable resistors to regulate the current.A single pole single throw switch is used to turn on and off the power supply.This switch is not needed in the circuit of fig. 4 - 1, because the power supply is completely cut off when the potentiometer is rotated counterclockwise to the bottom, and there are no energy storage components in the circuit.When the ammeter is not in use, the switch should be turned to the off position.This is to protect the ammeter from being accidentally exposed to extreme light during handling: excessive current will be generated to damage the ammeter.
The structure of the box is almost the same as that of the box described above, with two additional components to be installed.Under the installation of the variable resistor, drill another half-inch hole to install the switch.If a small switch is used, it is usually enough to drill a quarter inch hole, of course, the diameter of the installation hole should be determined according to the specifications of the small switch.Inside the metal or plastic box, there should be a battery holder for the No. 1 battery.This bracket is mounted on the back of the box and is fixed with epoxy resin or other adhesive, but it should be noted that the adhesive cannot drip onto the battery because the adhesive will stick the electric oil and cannot be replaced.
Figs. 4 - 4 show front and side views of the box in which this circuit is installed.Photosensitive resistor is installed at the top of the box, and its connection mode is clearly shown in the figure.If an aluminum box is used, two rubber washers must be embedded in the hole through which the photosensitive resistance leads pass for insulation.The purpose of this is to protect the insulation layer of the lead wire from being scratched by aluminum burrs in the drill hole. Rubber pads are very cheap.
After all the components are installed, carefully check the wiring before connecting the battery, turn the switch to the off position, and turn the variable resistor counterclockwise to the terminal.This is to prevent the current generated when the photoresistor is exposed to strong light from burning out the meter head.After the battery is loaded and the box cover is covered, the manufacturing process is completed.