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Basics of 74HC595
3
Technopreneur :P

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November 4, 2019 13:45

Hi, does the connection require exactly 8 leds? Can I achieve same results with say 7 leds? If yes, how do I wire them to the 595 ic seeing they are short 1 to make the 8?

0 Votes

November 5, 2019 08:22

@BayandaZikode, BradLevy is totally correct, do not use the HC595 for driving LEDs except as indicators or toys like an LED dice. RS supply some of the purpose designed chips for this purpose which are often used in car displays where you require dim for night driving and bright for daylight. The often have similar sounding part numbers presubably as the shift register is similar to the logic parts but the output circuitry is completely different designed for powering LEDs at high currents. The TPIC6B596N is an 8 bit example (but they also produce 12 bit). https://uk.rs-online.com/web/p/counter-ics/6608004/ Look up the TI datasheet for the full spec. I used an older version of these dedicated power shift registers to drive reed relay contacts to provide instrumentation control some time back and they did make life (design) simple and compact.

November 5, 2019 08:22

@BayandaZikode No, you don't have to have 8 LEDs. The unused outputs can be left open. Also be aware that the 74HC595 is not a good choice if you need to output more than about 5ma to each LED. (You should use a resistor in series with each LED to limit the current.) If you need higher output current to your LEDs, or to drive motors or relays, you can add transistor or IC driver circuits between the outputs of the 74HC595 and your loads. Or you can use different chips designed to drive higher loads directly. The 74HC595 is designed primarily for digital logic use, not as an output driver. But if you just need to drive some status LEDs, it can suffice.

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