CWatters said:
Is this the same problem - noise spikes on the digital signal?
http://www.muzique.com/schem/filter.htm
thanks again for the link, It looks like I need 5R with 0.1UF, I was using
100R with 0.1UF, even so I couldn't even get a few hz though it, it seems to
short out my signal generator. 100R with 0.005UF I will try shortly...
It is the same problem as I posted before, I've been on google all day
trying to find a possible cure, the only thing which is closest is the
74LS14, Schmitt device with 0.8 Hysteresis , if that could be like 2V
Hysteresis then that might work. A schmitt sure does help cut down the
problem but far from a cure.
The problem is a just like it is here
http://www.ee.ttu.edu/lab/robot/hyster.htm
Its hard to say how large the spike is, but I know its between 1V and 2V, it
could be a rail to rail spike I know ive had that on the fall). Though its a
bit to fast for my CRT scope to see, the spike seems to be 0.1US, its
filtering that out so its not bounceing on and off when its not supposed to.
I've been playing around with duty cycle, now its a bit hard to explain but
I will try, at say 50:50 ratio the spike is on the rise of the cycle, now
if you adjust the duty either + or - about 10% then you can see the spike
move onto the ground level, OR, onto the high level... When the spike is at
12V it really does not matter since the wave is going via some buffer's
which are ON at about 2.5V so the spike there does not matter really.... On
the LOW spike, the spike Can't be more than 2.5V else the problem wouldn't
go away. But when you adjust the duty you can see the spike moving across
the low level, then slowly moving up the rise and across the high level..
Like I say when the spike is on the low or high its not efecting the
circuit, but when its inbetween (on the rise) its causing false turn
on/off's.
I found a artice on adding Hysteresis to a comparitor, though the values I
worked out I doubt would work without overdriving the comparitor, actually I
am not sure if they even will work at 200khz... probably not....
Cheers,
Chris