LCD Tv Keyboard (S.W Button)

UNDERSTANDING THE BUTTON INTERFACE PANEL (KEYBOARD)

Keyboard / button is used to complete the interface between the user and CPU / processor / program so that users can interact. On TV consists of a few buttons include CH +, CH-, VOL +, VOL-, MENU and others. 
Method key input into cpu frequently encountered are:

1. ADC
   ADC stands for Analog to Digital Converter. Means cpu will read the voltage difference on the analog inputs, and then translate it so that the CPU knows which buttons to push. The advantages of this method are summarily lane (usually only consists of one line for a lot of buttons up to 7 or more buttons in one track. The drawback is easily affected by outside signals, noise, damp and when swit damaged will be read other than its function (eg pressing VOL + that exit even MENU.
   buttons compose a voltage divider that produces a voltage is different for each button. for example 1V to CH +, 1V2 to CH-, 1V8 for Power and others. These methods include pull-up resistor, the value pull-up resistor this change in value, then the voltage of key / swith also changed so that readings are also changing. Example scheme that uses the ADC input for the keyboard / keypad (keys arranged in series and set / menswit resistor voltage divider so that the output voltage can be changed depending on the button pressed):
   
   
2. Bit or Parallel
   main characteristic of this type is one key 1 cable / port. IC read voltage / logic on the push button cable, if Hi (no voltage) or 0V.Advantages of this method is high accuracy. The drawback is the sum of many cable and inefficient. This method is also equipped with R pull-up when the value of the enlarged / end, the voltage track buttons will be recognized as Low (usually less than half VDD), which means no buttons pressed despite the fact no one pressured at all.
   When R pull-up still good, whereas the keys are unsuitable or if they are depressed button then the damage is likely in the IC / cpu. Otherwise need replacement cpu / ic but if the "forced" pin the key can dijumper directly to 3V3 (so that the key can not be used), provided that the remote can still be used.
   Examples scheme buttons with the parallel method, note the pull-up resistors are mounted in each track buttons.
   
   
3. Matrix
   When required a lot of buttons, while cable / pin cpu is very limited, then the method can answer the manufacture of matrix keyboard interface. The keys are arranged based matrix, for example, wanted to create 32 buttons, the buttons can be arranged into 4 rows x 8 column of buttons, so it only requires 12 wires / lines only.
   Readout method by the CPU begins with choosing the line first, and then read paths button , then choose the line to 2, then read buttons and so on (called scanning). If no key is pressed, the CPU will store the key keberapa row and column is how the button, and then translated into a number button by cpu.
   Examples of using matrix method as in the following series of Remote Control:
   
   

Examples mainboard LCD TVs are often damaged keys, buttons Channel or Volume Often their own way. This mainboard using bits or parallel, the most common damage to the chipset / icnya, when there is no substitute then forced dijumper to 3V3 to disable button to hang around.