Just Catching up on my old email reading so someone
may have answered already ....
Yeah ... what happening is the the oscilloscope is
probably set to "AC" coupled instead of "DC" coupled
input. It's a switch... usually near the vertical
volts per division switch.
In "AC" mode, the scope tries to remove the DC
component out of the waveform. And because the 555
output is from 0 to Vcc, the average (DC component) is
1/2 of Vcc.
Hope this helps!!
Curtis
--- verhap@... wrote:
In my class today, I hooked a 555 in astable mode to
an o'scope.
Before powering up the scope, I centered the trace.
After powering
up the 555 I noticed the output from pin 3 was going
from +v to -V (I
didn't check the voltage scale, so I don't know how
large V is). I
don't understand why that happened. I should have
gone from 0V
to +V.
Am I missing something?
Paul
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