Homemade LED digital display photovoltaic meter

The author encountered such a problem in a solar street lighting project. There are a batch of solar panels that need to detect short-circuit current and open-circuit voltage. There are many circuits, and they work for several days. Some in the morning, some at noon. The result data varies greatly and it is difficult to draw a conclusion. This is because the amount of sunlight in a day is not constant. Of course, different power generation cannot be comparable. In order to obtain relatively consistent parameters, it is necessary to test under the same light intensity conditions. For this purpose, a photovoltaic meter or lumen meter is urgently needed. In order to deal with the emergency, the author used several electronic components to make an LED digital display, two-speed photovoltaic meter. The field test results are relatively ideal. It can not only detect the intensity of sunlight, but also imitate the lux meter to identify the luminous intensity of LED lamps, fluorescent lamps, and incandescent lamps. The darker the ambient light, the clearer the display, which has a unique advantage over LED display. Its cost is only a few dozen yuan. ,

The photosensitive element can be purchased from the market as a solar photovoltaic cell, which has an area of ​​3.5cm×10cm and very good detection sensitivity. The maximum voltage generated in strong sunlight is up to 3.6V, and 2.5V in rainy days. In the dark night, it can sense 150mV from the light of a match 2 meters away, and has different reactions to various luminous bodies. Due to the wide spectrum reception range and high sensitivity, the pre-amplifier can be eliminated and the LED digital meter can be directly driven.

The display element is a three-and-a-half-digit LED digital display (200mV), and the working power supply is 5V. See the attached figure for the circuit principle.

Three series resistors are connected in parallel between the positive and negative poles of the solar panel output: R1, R2 and R3.

K1 is a double-throw dual-position synchronous transfer switch

When K1-1 is closed, the test range is 0V~20V;

When K1-2 is closed, the decimal point of the digital display is positioned at D2 (tens);

When K1-3 is closed, the test range is 0V~2V;

Similarly, when K1-4 is closed, the decimal point of the digital display is positioned at D1 (units place). The intensity of sunlight can be measured by taking the signal of point A in the first gear, and the weak brightness of LED lights can be measured by taking the signal of point B in the second gear.

The whole machine is powered by four 6V No. 5 batteries with an operating current of about 50mA. As long as the components are correct, it can be assembled successfully in one go.

This photovoltaic meter cannot be used as a standard instrument because different solar cells are different, but it can be used as a tool to identify the intensity of light during work. It is also widely used, such as in dark rooms, breeding greenhouses, flower and bird greenhouses, and other places where light intensity needs to be detected.