[SOLVED] Problem with Serial to Parallel Shifting-Out with a 74HC595

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 :slight_smile:

Thank you in advance!


12 - 1.jpg

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


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?


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 :slight_smile: Thank ou once again!