JNTU B.Tech III INTRODUCTION TO MECHATRONICS Previous Question Paper (November/December - 2020 - R16)

An automatic camera functions by integrating optical, mechanical, and electronic systems to achieve optimal exposure and focus without manual intervention. The process begins when light enters through the lens, passes through an aperture, and reaches the image sensor. The camera's control system continuously monitors the scene's light intensity and distance to adjust settings in real-time.

Key components include:

• Lens System: Focuses light onto the sensor.
• Aperture: An adjustable opening that controls the amount of light entering the camera.
• Shutter: A mechanism that determines the duration for which the sensor is exposed to light.
• Image Sensor (CCD/CMOS): Converts optical images into digital signals.
• Microcontroller/Processor: The brain of the system that processes input from light meters and autofocus sensors to calculate and execute the correct exposure and focus.

The working sequence is as follows: When the shutter button is pressed halfway, the autofocus sensor detects the distance to the subject using infrared or phase detection, and the lens motor adjusts the focal length. Simultaneously, the light meter measures the ambient light levels. The microcontroller then calculates the required aperture and shutter speed based on the ISO setting. Upon full depression of the shutter button, the aperture closes to the calculated value, the shutter opens for the precise duration, and the image is captured and stored in memory.

A labeled diagram would show the light path entering the lens, the mechanical shutter/aperture assembly located between the lens and the sensor, and the feedback loop connecting the sensor and light meter to the central processing unit, which in turn controls the focus motor and exposure settings.

Analog-to-Digital Converters (ADC) and Digital-to-Analog Converters (DAC) are essential components for interfacing digital controllers with physical systems. Two common hardware implementations for each are described below.

ADC Implementations:

1. Flash ADC: This is the fastest type of ADC. It uses a series of comparators connected to a voltage divider network. The input signal is compared simultaneously against multiple reference voltages. The outputs of the comparators are fed into a priority encoder to produce a digital binary output. While extremely fast, it requires 2^n - 1 comparators for an n-bit resolution, making it hardware-intensive for high resolutions.
2. Successive Approximation ADC: This type uses a comparator, a DAC, and a Successive Approximation Register (SAR). It determines the digital value bit-by-bit, starting from the Most Significant Bit (MSB). The SAR sets a bit, the DAC converts it to an analog voltage, and the comparator checks if it is higher or lower than the input. This process repeats for each bit, making it a balanced choice between speed and hardware complexity.

DAC Implementations:

1. Weighted Resistor DAC: This implementation uses an operational amplifier in a summing configuration with a set of binary-weighted resistors (R, 2R, 4R, 8R, etc.). Each digital bit controls a switch that connects the corresponding resistor to a reference voltage. The output voltage is the weighted sum of these inputs, proportional to the binary value. It is simple but becomes impractical for high resolutions due to the wide range of resistor values required.
2. R-2R Ladder DAC: This is the most common DAC architecture. It uses only two resistor values, R and 2R, arranged in a ladder network. This eliminates the need for high-precision resistors across a wide range of values, as required in the weighted resistor method. It provides high accuracy and is easier to manufacture in integrated circuits, as it relies on the ratio of resistances rather than absolute values.