هاڻ اچو ته ٽائيمر آ سي 555 جيڪا بازار ۾ عام آهي ان تي ڪم ڪريون اچو ته پهرئين هن آ سي جي ٽنگن تي لڳل نالن کي پڙهون ۽ ڏسون ته هن جو پنهنجو اندريون اسٽرڪچر ڇا آهي پوِ هن آ سي تي تفصيل۔ توهان ڏٺو ته هن آ سي کي سامهون رکي پڙهبو ته هن جي پنن جي نمبرن جي تفصيل کاٻي پاسي مٿان کان ٿيندي پن 4 تي ويندي ۽ وري ساڄي پاسي هيٺان پن 5 کان پڙهبي ۽ مٿان پن 8 تائين ويندي معنيى ته 8 پن آِ سي آهي۔ هن آِ سي جي جوڙ جڪ ۾ هر پاسي هڪ ڪمپيريٽر، هڪ پاسي هڪ فلپ فلاپ ۽ ائوٽ پُٽ اسٽيج ڏنل آهن۔ انهن حصن کي اسان پو اڳتي هلي سمجائينداسو ۽ سيکارينداسون۔
اچو ته هاڻ هن 555 جي گهر ۾ هلون ڏسون تان ۾ ڇا ڇا بند آهي۔ Well here are a couple of schematics from the National Semiconductor datasheet to help explain it. واهه واهه هتي تهاليڪٽرڪ دُنيا ڀري پئي آهي In the first picture we can see that there are two comparators, one on the trigger pin and one on the threshold pin. We can also see that they are connected to a voltage divider. One input of the Threshold comparator is at 2/3 Vcc and one input of the Trigger comparator is at 1/3 Vcc. The outputs of the comparators lead to a flip flop. Although it doesn't say on the image, the flip flop happens to be a SR flip flop. From the flip flop there is the output stage which leads to the output pin and the transistor that controls the discharge.These are the basic parts of the 555 timer.
This is the basic theory of operation: When the trigger voltage goes below 1/3 Vcc (its reference voltage) the comparator Sets the flip flop, which pulls the output high and turns off the discharge. When the threshold swings higher than 2/3 Vcc (its reference voltage) the comparator Resets the flip flop, which pulls the output low and turns the discharge on. This basic operation allows the 555 timer to operate in various ways with various configurations.
If we look at the schematic diagram in the datasheet (second image), we can see what is actually happening inside the chip. The comparators are differential amplifiers, or long tailed pairs with a few added components to increase gain and sensitivity. The differential amplifier is the basis of the comparator, it greatly amplifies the difference in voltage to the point where millivolt differences result in rail to rail swings (voltage swings between 0v and Vcc). What's interesting here is that the threshold comparator uses NPN transistors whereas the trigger comparator uses PNP transistors. I don't know if that has an effect on the operation, but I just kept them like that in my circuit. The threshold comparator also has several extra transistors not present in the trigger comparator, along with a slightly different configuration. They perform the same function though, so I just replicated the trigger comparator but using NPNs instead. The flip flop circuit is rather interesting. There is a lot going on for what is just a SR flip flop with a second force reset. That can be made with 3 transistors so I discarded that circuit and made my own. The output driver is fairly simple. It is composed of two transistors, with the signal to one inverted so that when one is on, the other is off. This allows the output to operate in push-pull mode. This means that the output can source current, the output is shorted to Vcc, when it is high and sink current, the output is shorted to ground, when it is low.
مٿئين ٿيوري سمجهي اسان پنهنجي 555 آ سي ٽائيمر به ٺاهي سگهون ٿا۔ اسان کي بس گهُرجن هي سامان The parts list for this project is fairly small. (Just transistors and resistors, remember?) Of course you will need a breadboard and some connecting wire too. Here is the list: 2 1k ohm resistors 2 10k ohm resistors 11 4k7 ohm resistors (4k7 means 4.7k) 11 2n3904 NPN transistors or similar 9 2n3906 PNP transistors or similar The exact type of transistor isn't necessary. Any small signal NPN or PNP transistor should do. The exact values of the resistors aren't very important either, just so they are close (100 ohms for 1K isn't very close). I just chose common values. *You will also need a large bypass capacitor (100µf) on the supply rails when testing and running the timer. If you plan on making this a permanent you will also need a circuit board to solder everything to.
We are going to start with the trigger comparator. For this step, you will need 4 PNP transistors, 3 NPN transistors, a 10k ohm resistor and a 4k7 ohm resistor. You can build the comparator how you want just by following the schematic, but to make it easier if you don't, here are lots of pictures to help. First, put two PNP transistors on the breadboard so that the left one has the rounded edge facing you and the right has the flat edge facing you. Have their emitters (the two innermost leads) in the same row so that they are connected. Also in this row, add the 10k ohm resistor and connect it to Vcc. Next, add two more PNP transistors on the outsides of the first two. They should have the same orientation. Do NOT connect them to the first two! After that, add jumpers between the emitters of the outer transistors to the bases of the inner transistors. Also add wires from the collectors of the outer transistors to Ground (GND). Then spin the board around and add two NPN transistors exactly how you did it for the first two transistors. The should be in the same rows as the middle two PNPs, but on the other side of the board so they are isolated. Next, add a jumper that connects the collector and base together on the right transistor. It is important to remember which transistor it is because that determines what input is the reference. Then add a jumper between Ground and the emitters, they are the two connected together. Next, add two jumpers across the middle divider from the outside leads of the NPN transistors to the outside leads of the middle PNPs. The picture may be helpful here. Then connect the bases (middle lead) of the NPN transistors together. After that, add the third NPN transistor to the left of the first two. It must be opposite of the transistor with its base and collector connected together. It should have it's flat side facing you and not be connected to the other two in any way. Then add a wire from the leftmost lead, the emitter, to Ground. Also add a jumper between the base of the third transistor and the leftmost wire of the middle transistor. Finally add the 4k7 ohm resistor between Vcc and the collector of the third transistor, the rightmost lead. Finally add the inputs. For this instructable, a yellow wire will indicate an input and blue will indicate an output. The inputs should be on the base, middle lead, of the outer PNP transistors. The output on the side of the third NPN transistor will be the reference input and the other will be the trigger lead input. The output should be connected to the collector of the third transistor, the same lead as the 4k7 ohm resistor. The reference input is on the opposite side of the NPN with its collector and base connected in the schematic. That applies for real too. You have now completed the trigger comparator! Now to test it...
