Hi Guys,
I'm trying the 74HC595 in Tinkercad and when all led are ON I got the chip burned.
Can you tel me why? What I did wrong?
Almost certainly because you exceeded the total current rating for the chip. The individual pins have a current rating but you can't run the whole chip with each pin sticking to the maximum current output because this exceeds the maximum for the chip.
Also the ceramic decoupling capacitor needs to be as close to the chip power and ground pins as possible, not way out on the Arduino.
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I followed this tutorial and like we can see on the gif image all led was ON at some point.
If they should not be ON at the same time what would I do? Use more resistors? I already use 470 Ohm.
Yes.
Oh OK with 1k Ohm it's works. Usually 330 ohm is good for led right, why they did not think about that.
Thanks
Who are "they"?
The manufacturers did tell you in the data sheet. The people who produced the circuit did not know as much as they thought they did. There is a lot of useless designs on the web these days, and most people are not as clever as they think they are.
Hello kamoba
Take a view here to gain the knowledge.
I just taught if they (the manufacturers) made 8 outputs they should think we may use them all in same time.
Thanks paulpaulson I should read more datasheet.
Ah no. There are a lot of chips where that does not happen, in fact it is more common than not. Even the processor chips in the Arduino have combined limits as well as individual limits on the output pin current.
You see that allowing all the pins to output there full limits means that the chip has to be made to have a much greater rating. This is expensive and it causes problems with heat dissipation, so often the solution is to have a combined limit.
This is the individual versus combination limits on the Arduino's Uno processor.
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They did think of that. They tell you in the data sheet the maximum current can be shared between all the outputs that are used, so that you would not exceed that maximum. If you do not design your circuit to use less than the maximum, the chip can be burned.
74HC595 was not designed for driving LEDs. It was designed as a logic chip to drive other logic chips. The inputs of logic chips need only a very small current compared to a LED. 74HC595 can be used to drive LEDs, but the maximum current is not enough to drive 8 LEDs at the maximum current that the LEDs can take. So if using 8 LEDs, the current must be reduced down to less than the maximum current of 74HC595 by using higher value resistors.
If you want to drive 8 LEDs at the maximum current of the LEDs (usually around 20~30mA for most "normal" LEDs) you can use TPIC6B595 instead of 74HC595. These chips work in almost the same way as 74HC595, so only small code changes would be required. One difference between the chips is that with TPIC6B595, the output pins can only sink current, they cannot source current. So the LEDs and series resistors must be connected between +V and the output pin, not between the output pin and ground.
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