All-weather solar automatic tracking controller

There are two types of existing solar automatic tracking controllers: one is to use a photosensitive sensor and a Schmitt trigger or a monostable trigger to form a light-controlled Schmitt trigger or a light-controlled monostable trigger to control the stop and start of the motor; the other is to use two photosensitive sensors and two comparators to form two light-controlled comparators to control the forward and reverse rotation of the motor. Since the intensity of ambient light and sunlight varies greatly throughout the year, morning, evening and noon, it is difficult for the above two controllers to make the solar receiving device track the sun all year round. The control circuit introduced here also includes two voltage comparators, but the photosensitive sensors at its input end are respectively composed of two photoresistors connected in series and cross-combined. One of the two photoresistors in each group is the upper bias resistor of the comparator, and the other is the lower bias resistor; one detects sunlight and the other detects ambient light, and the comparison level sent to the input end of the comparator is always the difference between the two light. Therefore, this controller can make the solar receiving device track the sun all year round, and the debugging is very simple and the cost is relatively low.

Circuit Principle

The circuit schematic is shown in Figure 1 (click to download the schematic). The dual op amp LM358 and R1, R2 form two voltage comparators, and the reference voltage is 1/2 of VDD (+12V). Photoresistors RT1, RT2 and potentiometer RP1 and photoresistors RT3, RT4 and potentiometer RP2 respectively form a photosensitive sensing circuit. The special feature of this circuit is that it can automatically compensate according to the intensity of ambient light. As shown in Figure 2, RT1 and RT3 are installed on one side of the vertical sunshade, and RT4 and RT2 are installed on the other side. When RT1, RT2, RT3 and RT4 are simultaneously exposed to ambient natural light, the center point voltage of RP1 and RP2 remains unchanged. If only RT1 and RT3 are exposed to sunlight, the internal resistance of RT1 decreases, the potential of pin 3 of LM358 increases, pin 1 outputs a high level, transistor VT1 is saturated and turned on, relay K1 is turned on, and its conversion contact 3 is closed with contact 1. At the same time, the internal resistance of RT3 decreases, the potential of LM358's pin ⑤ decreases, K2 does not work, its conversion contact 3 and static contact 2 are closed, and the motor M rotates forward; similarly, if only RT2 and RT4 are exposed to sunlight, relay K2 is turned on, K1 is turned off, and the motor M rotates reversely. When the illumination on both sides of the vertical sunshade is the same, relays K1 and K2 are both turned on, and the motor M stops rotating. During the continuous shift of the sun, the intensity of the illumination on both sides of the vertical sunshade changes alternately, and the motor M rotates-stops, rotates-stops, so that the solar energy receiving device always faces the sun. The advantages of the cross-arrangement of the four photoresistors are: (1) When the potential of LM358's pin ③ increases, the potential of pin ⑤ decreases, and when the potential of LM358's pin ⑤ increases, the potential of pin ③ decreases, which can make the forward and reverse rotation of the motor both clean and reliable; (2) The housing of the circuit board can be directly used as a vertical sunshade to avoid the trouble of leading the photoresistors RT2 and RT3 to a shaded place.

When using the device, there is no need to worry about whether it can automatically retract the next morning. When the sun rises in the morning, the illumination on both sides of the vertical sunshade cannot be exactly equal, so the control circuit will control the motor to drive the receiving device to rotate eastward until the solar receiving device is aligned with the sun.

Installation and Debugging

The structure of the entire solar receiving device is shown in Figure 2. The shell that also serves as the vertical sunshade is preferably made of non-reflective dark-colored material. The parameters of the four photoresistors are required to be consistent, that is, the light and dark resistances are equal and change linearly. When installing, the four photoresistors should not protrude from the surface of the shell, but should be recessed a little to avoid interference from scattered sunlight; the vertical sunshade (i.e., the control box) is installed on the edge of the receiving device, which can rotate with it and is not strongly irradiated by its reflected light. During the test, first prevent the sun from shining directly on the four photoresistors, and then adjust RP1 and RI2 so that the potentials of the two forward input ends of LM358 are equal and higher than the reverse input end by 0.5V-1V. After debugging, let the sun shine on the vertical sunshade, and the receiving device can automatically track the sun.