Design of a PV off Grid System with a Tracking Device

The design incorporates a photovoltaic solar panel orientated to face the sun by a dc stepper motor operating at 5 to 30V. The motor is fed off a car battery. The sensor used is a light dependent resistor whose output is fed into Arduino, analogue to digital converter. The sensor is protected by a series resistor R as shown in figure 1. The sensor supply is 5V. The tracking device consists of a sensor that transduces light into an equivalent voltage or current, the ADC, which converts analogue signal to digital signal, the stepper motor fed from the output of the Arduino through motor drives (Luecke 6).

Fig. 1 The sensor circuit

When there is too dim light the LDR acts as a high valued resistor as a result, a negligible current flow through the sensor circuit (Luecke 6). As the intensity of light increases, LDR resistance drops and the current increases accordingly. The main function of the LDR is to sense if there is light or not.

The L293D integrated circuit in figure 2 is a dual H-bridge motor driver. It acts as a current amplifier. The high current output drives the motor. For the motor to operate, pins 1and 9 must be high. Once input enabled is high, the corresponding driver is enabled. Consequently, activating the output allows for the working in phase of the inputs. In the same manner, low input disables the driver keeping off the output in high impedance state (Maini 172).

The integrated circuit can drive two motors simultaneously in the onward and reverse route. The operations of the two motors are controlled from by the logics at input pins 2 and 7, and 10 and 15. The logics 00 and 11 at the input stop the associated motor. The logics 01 and 10 at the input make the motor to rotate in clockwise and counterclockwise directions respectively.

In figure 2 the microcontroller and the sensors are connected in parallel. The figure shows the pin connections and terminal devices. For instance, the two motors form the terminal devices for the pins 3 and 7, and 11 and 14. Grounds for the integrated circuit, L293D, and the motors are connected to pins 4 and 5, and 12 and 13.

Figure 2 Motor, microcontroller and sensor connection to L293D integrated circuit.

Alternatively, for a small solar panel use of ULN2003 or ULN2004 and single unipolar stepper motor can be employed. Figure 3 shows the connections. The motor controls come from outputs 2, 3, 4 and 5, which are internally connected to their corresponding inputs.

Figure 3 Pin connection of ULN2003 integrated circuit to drive stepper motor

Data sheets

Pin Diagram:

Pin Diagram:

Pin Description:

Pin No Function Name 1 Input for 1st channel Input 1 2 Input for 2nd channel Input 2 3 Input for 3rd channel Input 3 4 Input for 4th channel Input 4 5 Input for 5th channel Input 5 6 Input for 6th channel Input 6 7 Input for 7th channel Input 7 8 Ground (0V) Ground 9 Common free wheeling diodes Common 10 Output for 7th channel Output 7 11 Output for 6th channel Output 6 12 Output for 5th channel Output 5 13 Output for 4th channel Output 4 14 Output for 3rd channel Output 3 15 Output for 2nd channel Output 2 16 Output for 1st channel Output 1

Work cited

Maini, Anil K. Digital Electronics: Principles, Devices and Applications. Chichester, England:          John Wiley &    Sons, 2007. Print.

Luecke, Gerald. Analog and Digital Circuits for Electronic Control System Applications: Using     the Ti    Msp430 Microcontroller. Oxford: Newnes, 2004. Print.