screening / glitchy operation - sanity check

[dsc]

I've switched to a 9VDC battery, not much difference, after which I've earthed the driver chassis, which dropped the noise levels significantly. Comparison between a battery supply and plug-in DC supply with the driver chassis earthed:



I'll stick with the plug-in supply and keep everything earthed.

Regards,
dsc.

[Jonathan]

Your code looks like it should be fine.

I've switched to a 9VDC battery, not much difference, after which I've earthed the driver chassis, which dropped the noise levels significantly.

So did it solve the problem? Since using a battery didn't make a difference, that implies the noise is not emanating from the supply. The most likely source is the 'mess of breadboard wires'. You should aim to keep the wires short to minimize stray inductance, keep power wires close together for the same reason and use decoupling capacitors.

For example, you can see in this photo how the breadboard on the right uses much longer wires than necessary and the capacitor is a long way from the IC. My one on the left is neater...



The circuit above still worked as it operated at quite low frequencies (where stray inductance is less of an issue). If it hadn't then it would be worth rearranging it.

[Jonathan]

Oh also, if you want to be able to record logic level signals over a longer period, you could get a logic analyzer like this one:

USB 24M 8CH 24MHz Logic Analyser 1.1.16 | eBay