The LM324 is unity gain stable at low C loads. See attached response for C = 0
and C = 50 pF. Note the 50 pF load chart shows reduced phase margin, eg. stability.
The V divider, very high Z elements ? Like in the 100K ohms + element values ?
If so you can get stray pickup other signals in your lab.
The second pic, I take it green is output of LM324, violet the input to 324. A 324
should not show that kind of ripple. It does have a slew rate of ~ .5 V/uS so that
limits its step response significantly.
Bypassing critical, supply pins should have a .01 and .1 uF ceramic on them, as
well as a suitable bulk, like tantalum. Figure the tant size based on load driving
impedance and I = C x dV/dT, or C = (I x dT) / dV, what is the droop you want
to live with on supply pin...
Pay attention to any ground loops. That adds L to the ground path, and could be
the cause of unexpected ripple. Grounds, analog, should be single point grounding
system where possible.
Some ap notes on noise -
https://www.dropbox.com/s/2h96beh1fbvz4e2/noise_notes.zip?dl=0https://www.dropbox.com/s/ruaf9booe17jk8n/PCB%20Layout.zip?dl=0Regards, Dana.