09/07/2025 6:10 am
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I'm trying to cascade multiple 74HC595 shift registers to expand the number of digital outputs in my project. While one shift register works perfectly on its own, as soon as I add the second (and especially the third), I start getting strange or inconsistent output—some LEDs don’t light up correctly, or they shift out of order.
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Is there a timing issue I might be overlooking?
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Do I need to delay between latching and shifting?
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Could signal integrity or voltage drop be the issue when chaining several ICs?
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12/07/2025 6:55 am
This kind of issue is quite common when cascading multiple 74HC595 shift registers. First, make sure you're shifting out the correct number of bits—8 bits per chip—before pulsing the latch pin.
Timing can also be a factor, so try adding a small delay (like delayMicroseconds(1)) after the latch pulse. Signal integrity often becomes a problem as more ICs are added, especially with long wires or breadboards—keep connections short, use 100nF decoupling capacitors near each chip, and consider adding 100Ω series resistors on data and clock lines.
Also, check that all chips share a common ground and that your power supply can handle the total current draw. Lastly, ensure your shiftOut() direction (MSBFIRST or LSBFIRST) matches your wiring. These steps usually solve most inconsistent behavior when chaining multiple 74HC595s.
