It is always better to use a dedicated controller for touch screens, instead of designing your own. The best option according to me is to use one of the product of MAXIM, MXB7843.
MXB7843 is controller dedicated for 4 wire resistive touch screens. It has a configurable ADC of 8/12 bit resolution. Overall pictorial representation says that to interface a 4 wire resistive touch screen, what you have to have a microcontroller apart from touch screen controller and a touch screen itself. Touch Screen is directly connected to the microcontroller. The microcontroller which is controlling all the affairs gets the coordinates of the touch screen, whenever it is interrupted, via SPI communication. SPI communication is used for high speed synchronous communication. Once the data is received in 8 or 12 bit format, you can play around as you desired.
The schematic of MXB7843 is given below:
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08:03 |
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4 wire resistive touch screen,
Block Diagrams,
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touch screen controller
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The basic building blocks involved in digital communication system can be seen in the figure. Some block shown above might seem strange for the newbies. Source Coding is the process of compressing the data efficiently. In other words, source coding is the process of optimizing the length of data. An example of this can be a surveillance system. It is useless to send the whole background of the image when a motion is detected. Source coding is thereby used to send only that portion of a frame which is being changed and not the useless information in terms of the whole background. Another example of this could be the transmission of English Text. We know that the probability of occurrence of vowels i-e a,e,i,o,u is more than the other alphabets thereby giving a clue to compress the English Text in terms of bits transmitted.
After that comes the Channel Coding. For a layman, it can be referred to as opposite of Source Coding in term of process. Channel coding involves the addition of redundant bits to a message signal that will make up for the errors. This involves the identification and as well as the correction of errors, if any. Hamming code it the best example of Channel Coding. Modulation and Demodulation needs another post for discussion which will be discussed later.
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18:01 |
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Figure shows basic block diagram of PLC (Programmable Logic Controller). The CPU of PLC is programmed using a programming terminal usually through personal computers or dedicated HMIs. Basic Modules associated with the CPU are external modules and i/o modules along with bit, byte, word and double word addressable memory locations.
A PLC is an example of a hard real time system since output results must be produced in response to input conditions within a bounded time.
11:50 |
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What is a Servo Motor? A servo motor comprises of mostly DC motors with feedback for position controlling. Stepper motor is also used for position controlling but without feedback. Mostly Servo Motors are DC because they provide high locking power. The above block diagram depicts the basic block diagram that most of the servo systems are based on. Microcontroller provides PWM signal to the H-Bridge which onwards drive the motor in either direction on the basis of received input PWM signal. Lets say if PWM signal of 50% duty cycle locks the motor, so increasing or decreasing PWM value will drive the motor in CW or CCW direction. The Shaft of the motor is connected to potentiometer thus changing the Vf ( Feedback Voltage) as the motor rotates. User can set the desired position of the motor using another potentio meter. This is the Set-point voltage. Microcontroller takes the difference of both the voltages i-e Feedback and Set-point and generates a PWM signal such that Motor reaches the desired position. When it does do, the difference gets zero and ultimately motor comes into locking position. This is how DC motor servo system operates. More to Follow!
13:08 |
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How Stuff Works?
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