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  • Sandeep V Menon commented on Syst3mX's instructable Make a 24X6 LED Matrix4 weeks ago
    Make a 24X6 LED Matrix

    No, that is not the case. The Decade Counters (so called as they "count" 10 digits, usually 0 to 9), aid in the display of a given letter. (I shall explain)Consider a 5x5 LED matrix, it would have 25 LEDs. Let us assume that the anodes (+ve terminals) of all the LEDs are connected to rows and the cathodes (-ve terminals) are connected to columns via switches to a battery (as illustrated in image).> Now, if say LED L13 needs to be lit. We press switch SW3 and SW8. If we hold SW3 while pressing sequentially SW6 to SW10, we will see that L11 to L15 lights up as the switches are pressed (and turns OFF as soon as the switch is released)> If we were to somehow repeatedly press the switches SW6 to SW10 at, say, 120 times a minute, our eyes will perceive that the line remains li...

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    No, that is not the case. The Decade Counters (so called as they "count" 10 digits, usually 0 to 9), aid in the display of a given letter. (I shall explain)Consider a 5x5 LED matrix, it would have 25 LEDs. Let us assume that the anodes (+ve terminals) of all the LEDs are connected to rows and the cathodes (-ve terminals) are connected to columns via switches to a battery (as illustrated in image).> Now, if say LED L13 needs to be lit. We press switch SW3 and SW8. If we hold SW3 while pressing sequentially SW6 to SW10, we will see that L11 to L15 lights up as the switches are pressed (and turns OFF as soon as the switch is released)> If we were to somehow repeatedly press the switches SW6 to SW10 at, say, 120 times a minute, our eyes will perceive that the line remains lit.> Now, continuing as in the previous step, we press the switches SW1 to SW5 one-by-one. We will be able to see/perceive that LEDs L1 to L5 lights up when SW1 is pressed, L6 to L10 lights up when SW2 is pressed and so on.>If we need to light up the entire matrix in the above mentioned way, we need to press switches on both the row and column in the same manner as we were pressing SW6 to SW10.>An alphabet is displayed in this manner. Let us consider displaying the alphabet 'A' in our 5x5 LED matrix. We can see that we need to light up L3, followed by L7 and L9, then L11 and L15, L16 to L20 and finally both L21 and L25. If this light up occurs at very fast rate, we will perceive the letter 'A' on the matrix.This switching without errors is not physically possible. To make error free and precise switching, we use the switching circuits(example - Decade Counter with transistors). To display a word, such ON-OFF patterns (from above example) are required. If we represent ON state by 1 and OFF state 0, for the above example we get a pattern as below :0 0 1 0 00 1 0 1 01 0 0 0 11 1 1 1 11 0 0 0 1Such patterns are called Bit Patterns. Each letters (upper or lower case) symbols are created in this way.PS:- I could not clearly understand your requirement in second half of the comment, hence I'm replying from my understanding of it. I hope this helps.>> The components are named based on the functions, technology with which they are built and so on. For example, and IC AtMEGA328 (which is a microcontroller) is named so due to following reasons - the IC is a microcontroller of the "MEGA" series, from the manufacturer named ATmel Corporation. It has a 32KB flash memory and and 8 bit CPU/ALU

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  • Sandeep V Menon commented on Syst3mX's instructable Make a 24X6 LED Matrix8 weeks ago
    Make a 24X6 LED Matrix

    The resistors before BJTs are called as Bias Resistors. Now, assume that, the supply voltage is 5V and (or, refer datasheet to ensure the exact value) the max current the IC terminal can supply is 5mA. The transistor needs 0.7V to "turn ON". Rest needs to be dropped across some device. This is where the resistor plays it's part On the assumption that the voltage at IC terminals is the supply voltage, 5V, we use Ohm's Law (R = V/I ) to get R = (5 - 0.7)V/5m = 820 OhmTo be on safe side, the current from the IC terminals need to be less than the maximum value hence the value is approximated to 1K Ohm.

    This is something that crossed my mind. I thing you will have to update/modify the circuit to accommodate as well as drive the 192 LEDs. If this has been done then the program will need be updated, ie, search and find out all the instances where there is a call to drive the 28 pins and modify it to 32.Ps:- I too am going through the program myself as I type this. Please consider the reply/answer as more of a comment rather than an answer. Thanks

    The short answer is the transistors are used to turn ON/OFF a particular row at a very fast rate so that there is persistence of vision. The long answer is - the transistors act as a switch that gets triggered by the input of the decade counter. The decade counter's out put is a positive pulse. As it can be seen, the LED matrix is composed of Coumns made up of anodes and Rows made up of cathodes if the LEDs, connecting the rows ( even via resistor) will damage the IC (due to currents flowing beyond permissible range). Also there would be no persistence of vision as any one of the row may light up or entire matrix not lighting up at all.

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