On 11/6/21 10:13 AM, Mont Pierce KM6WT
On Tue, Nov 2, 2021 at 10:45 AM, Mont Pierce KM6WT wrote (click here):
I think the noise may be
from a ground loop
on further testing I found that the low noise on the
signals is only present when I power the board from 12V source.
If I pull the 12V power, and instead power the board from the 5V
line on the ISP programmer, the noise is gone.
Actually, powering the ATtiny PCB from the ISP port is NOT
a good idea...
Let me confirm...not a good
Looking over the schematic (click here,
see bottom right), I could not logically figure out how the 3v3
regulator was being powered....
It appears to me: After trying this on three
different boards, it appears on my first board there was enough voltage leaking
back through the 7805 to power the 78L33, and thus power the
onboard 3v3 Si5351. Relying on voltage leak back through the 7805
is not reliable. I don't think it's designed
for this, and the amount of current leaked back varies from
component to component.
Diz: what about powering the 78L33 from the 5V rail
instead of from 12V rail ?
Not needed if the above
Just a thought...
Interestingly, Hans powers the QCX's Si5351a from 5V through two
diodes to drop the voltage down from 5V to 3.6V (just within