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Topic: Noisy latch line on 74HC595? (Read 1 time) previous topic - next topic

rj77

Being neat in your wiring using  shortened wires isn't just for aesthetics.


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Wow - that's a pretty amazing layout!

larryd

#31
Jun 23, 2016, 01:26 am Last Edit: Jun 23, 2016, 01:27 am by LarryD
Make your own wire lengths, use 24AWG wire.  solid wire, not stranded as shown.

No technical PMs.
The last thing you did is where you should start looking.

rogbigras

I had lots of issues with a similar circuit, Every time I'd press a button on my board, it would go flaky. then I transferred the circuit to a solder prototype board, and it's been working perfectly. I find consistent troubles with the cheaper bread boards. Using the Jumper wires from kits they sell seems to work better, The 24AWG wire found in telphone cable works better then 26AWG Cat5E wire 
If your not learning, your wasting time :)

hakanArduino

Just want to share my experience and the solution I found. I have three 74HC595 shift registers daisy chained and they drive LEDs directly through current limiting resistors.

My setup is terrible with around 30 hair thin magnet wires all mixed together and shoved under a protoboard. I assume due to tons of noise the outputs were acting up; flickering randomly or not turning on at all. Especially if I try to light up all or majority of them. I tried 0.1 uF ceramic caps on each IC across Vcc and GND but they didn't help at all. Tried all kinds of stupid things like putting caps across latch, clock, and data to ground (individually), as expected didn't help at all. Also tried putting large electrolytic caps across power lines - yep, you guessed it: didn't work.

What worked rock solid was putting a 0.1 uF cap across latch and data output on the last stage (last IC, between RCLK&QH or pins 12&9). I believe it is as stupid as it looks but it works like a charm. I have no idea why it works.

Hope this helps..

Grumpy_Mike

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What worked rock solid was putting a 0.1 uF cap across latch and data output on the last stage (last IC, between RCLK&QH or pins 12&9). I believe it is as stupid as it looks but it works like a charm.
Yes it is stupid.

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I have no idea why it works.
It is called parasitic decoupling. Your attempts at using decoupling capacitors were probably not done correctly.
Doing this can damage the Arduino outputs by giving a too large current pulse when you switch.

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