LED behavior changes when moving hand near or touching

Other Hardware General Electronics
1

This sketch used to work perfectly with no issues. (It is supposed to count 1-255 in binary)

Now it will run.. pause.. run again.. flash random lights.. stop.. run again when I move my hand near the LED's or touch them..

It is the strangest thing.. I've tried replacing the resistors, LED's etc but I get the same result.. Could the breadboard have gone bad?

This is hooked up to a 74HC595 Shift Register also.. But I don't think the register is it works fine in another project I tested..

Anyone idea what might be causing this?

*Sorry for the shaky video!

Link showing it working correctly: http://screencast.com/t/it10pxMwL
Link showing it being strange: http://screencast.com/t/eYK5P98d

2

Interference.

You shouldn't ever use a bare 595.
Be sure to have some capacitors handy (100 nF is widely used for this).
Put them across all power lines of each chip you're using.
Read datasheets of chips before using them.
Your body interferes with the interference, so you'll see some interaction/

3

It sounds to me like a wire has dropped off or is not making a good connection and so you have an input that is floating.

For more on floating inputs see
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

4

Thanks MAS3 and Grumpy_Mike

Both great answers.. It was a bad wire.. I was also using only one capacitor for all 3 shifters..

5

LEDs especially need good decoupling since they carry much larger currents than
most logic level signals but switch just as fast - suggest 0.1uF for every chip, 10uF
for each board, minimum.

6

MAS3:
You shouldn't ever use a bare 595.
Be sure to have some capacitors handy (100 nF is widely used for this)

And make sure they're ceramic capacitors, not electrolytics.