On 8/6/11 4:49 AM, jb-electronics wrote:
I was trying to include a DCF77 module to turn it into a radio clock,
but it never worked, so I put the board away. Just for fun, I checked
the board again today with my 25MHz scope, and I think discovered the
culprit:
PWMing the Numitrons causes about 1V ripple on the supply. The DCF board
(designed for operation between 3.3V..5V) - probably can't manage the
supply voltage of unstable 4 to 5V. The noise on U_supply has the same
frequency as the PWM, and when turning PWM on 1 or 0 continuously, the
problem vanishes, and the DCF module works fine.
A long text, but the main question is: How do I resolve that issue?
The short answer: Don't use PWM next to a radio receiver.
You are introducing an interfering radio signal.
Dim the lights using a variable DC supply with a regulator IC. It will
get warmer, but your radio will work.
--
David Forbes, Tucson AZ
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