Noise on the 3.3 volt line.

[JMazu.1]

I have a photo interrupter attached to an interrupt port powered by the 3.3. volt supply.

Every now and then, there is a burst of activity on the 3,3 volt line which cause havoc on the interrupt line.

img_0933 shows the output of the photo interrupter and the following schmidt trigger stage. Looks good.

img_0936 shows this weird burst activity. Top top trace is the 3.3 volt line and the lower the schmidt trigger output.

Thanks.

[TDK]

How are you connecting the signal ground to the scope? Looks like it may be taken far from the signal source, which can add noise. Custom board? Do you have the appropriate decoupling caps?