Working: To take the photograph of an object with the help of the camera, the switch is pressed which activates the system. The range sensor, senses the distance of the object to be photographed and this data is input to the micro processor. The microprocessor in turn sends on output to motor drive to position the lens for focusing. The position of the lens is input to the micro processor. The light sensor sends the signal of light intensity on the object to the microprocessor. Based on this, signals are sent to control the duration of time the shutter have to be kept open. All these actions and reactions take place with in fraction of a second. Once the film has been exposed, the information is input to the microprocessor which gives output for driving the motor for advancing the film to drive and the camera is ready for the next exposure. Earlier cameras were adjusted for light, focusing and time or duration of operture opening based on the sensitivity of the film including winding all being carried out manually.
Digital cameras: Digital cameras are flooding the market, indicating an era of digital technology. In this case the image of the object taken by the cameras is converted to digital images and stored is memory housed in the camera. As many number of photographs can be shot depending on the memory size. The photos stored in the memory can be seen on the monitor of a computer system and selection can be made. With the help of a good printer and quality paper the photographs can be obtained. The memory chip can be used again and only thing is it is overwritten. Also the contents of the memory chip can be transferred and then printout of selected shot can be made at leisure. Handy cams of magnetic tape, and digital types with separate memory chip for still photographs are available in the market.
Automatic washing machine
This is a sequential controlled system wherein control is exercised based on event, or are time driven i.e., control action will be executed one after another operation. The operations to be carried out in a domestic washing machine are soaking, washing, rinsing and drying. Each of these operations involves number of steps. Soaking involves selection of correct quantity of detergent and water based on the type and amount of cloth. This requires opening of the valve to fill the machine drum to the required level and closing the valve once the required level of water has reached and rotating the drum one/two rotations in either direction for a pre-set amount of time during the soaking operation.
This is followed by washing which is a time event. Then the rinsing event which measures the pH value and compares it with the supply water. This event continues till the pH value of the water in the cloth and the supply water are equal. Finally the drying operation till the minimum percentage of moisture is retained in the cloth.
All these events were earlier controlled with the help of mechanical system which involved a set of cam-operated switches; the contour of the cam operating different switches being proportional to time. The sequence of instruction used was a function of the set of cams used.