Freescale Semi

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Company Logo Freescale

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  • Created: Sep 17, 2015

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A window blind is a type of window covering that is used to manage the sunlight intensity, provide additional weatherproofing, ensure privacy and sometimes security, or used for purely decorative purposes. Some of the window blinds nowadays are automated and function according to how it was programmed by the user. In this reference design, the window blind opens or closes based on the intensity of light the circuit light sensor detects.

The circuit in this reference design is comprised of a microcontroller, a light sensor, a motor driver and a power supply. The microcontroller used in this circuit is the Freescale MC9RS08KB12CFK 8-bit microcontroller designed for consumer and industrial applications. In this circuit design, the microcontroller reads the analog signal from the light sensor and converts it to a digital value. The wind blind opens or closes depending on how the user wants it to operate. The microcontroller will just send a PWM signal to the motor driver to close or open the window blind if the intensity of the light passes a certain analog value. The light sensor uses a phototransistor to alter the voltage level at the non-inverting terminal of the operational amplifier. The operational amplifier will amplify the analog signal and sends it to the analog to digital converter pin of the microcontroller to read the value.

The motor driver in this circuit is composed of four transistors, two PNP and two NPN transistors arranged in an H-bridge configuration. The base terminals of these transistors (Q1-Q3 and Q2-Q4) are connected to the PTB4 and PTB5 pin of the microcontroller respectively. The motor driver will just wait for a PWM signal from the PTB4 or PTB5 pin of the microcontroller to rotate the motor in forward or reverse direction. The motor in this reference design is attached to a part that opens or closes the window blind. The whole circuit except for the motor driver is powered by a 5VDC power supply.