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Topic: [SOLVED] Problem with Serial to Parallel Shifting-Out with a 74HC595 (Read 920 times) previous topic - next topic


Jun 12, 2012, 09:43 pm Last Edit: Jun 13, 2012, 12:44 am by AndyMcCall Reason: 1
Hi Folks!

I've been working through some of the examples getting ready for my own project and I've stumbled upon a problem when doing the Serial to Parallel Shifting-Out with a 74HC595 example.  I'm using a 74HC595N and I've ripped the example apart around 4 times, and everytime I seem to get the same problem.

My LEDs seem to go "wrong" at around binary 5 or 6.  Then they just seem messed up until I can see the counter starts again.  I'm pretty sure I've got something wrong as they are also dipping in power on some numbers, as if there is a bad ground or something, but I've checked for shorts bad connections and can't see anything.

I was wondering if anyone could help me with some ideas on what could be wrong.  I've posted a video of the problem and a picture of my project on my Google+ page here and I've attached the picture to this post.  I'm sorry for the yellow wires I realise this may make tracing the cables difficult, I'm waiting for a delivery of jumper cables - I knocked these home made tinned ones up myself so I could get on with playing :)

Thank you in advance!



Do you have that 1uF cap on the latch pin? If so remove it.

Rob Gray aka the GRAYnomad www.robgray.com


I did have it on the latch pin as the tutorial said to have it on to iron out any flickering.  I removed it as you suggested.and the problem seemed to get worse, so I replaced it.  When I replaced it I accidently put the right hand leg of the capacitor - what was on the breadboard hole 18 - back to 5V, rather than GND like the tutorial says.  This has actually fixed the problem. The binary sequence is perfect now, although I don't understand why.  I'm still getting every other number a bit dimmer though...


Are the grounds connected between the Arduino and the other circuitry?

Rob Gray aka the GRAYnomad www.robgray.com


Jun 13, 2012, 12:43 am Last Edit: Jun 13, 2012, 12:51 am by AndyMcCall Reason: 1
Excellent - got it working!  The grounds were connected, but the breadboard has two +5 rails that are not connected (I'm a newbie to electronics, but not programming so didn't realise this!).  I've connected them just under the first green LED in my picture, and I've now got a perfect binary sequence with the cap returning to GND and rock solid LED's with no dimming.

Thank you very much for your help!  Next up is moving on to driving a 1602 LCD instead of LED's :) Thank ou once again!

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