arduino making 7805 output noisy

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please see images setup use. mega powered 7812 , generating pwm wave @ pin 7 (10us on time , 100us offtime) using delaymicroseconds , toggling pin.

i took measurements across 7805 output arduino disconnected 7812. has 15mv p-p noise (see image, on 20mv scale). took measurements mega connected 7812 , generating pwm. 7805 output has become noisy (even @ 10 times scale of 200mv).. how avoid/suppress this. 7805 supposed power dac , noise causing issues. both regulators have output caps @ 0.1uf. cap bank @ trafo output 140kuf.

if have noise need more / better decoupling , better layout circuit.
are caps ceramic? have got big ones? have got caps on devices?

how getting ground scope probe, might artifact.


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