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patroclus said:I'm building this circuit:
**broken link removed**
I need caps C1 to C5, 100pF, for filtering, I suppose.
Can I use a higher capacitance caps?? for example, 10nF?? Is there a higher limit??
This is wrong. The caps work with the output resistance of the 74HC125s, not the 100 ohm resistors. The resistors are there for damping (to minimize ringing on the cable), and also provide a measure of short circuit protection._3iMaJ said:You can change the cap values if you want, but you must change the associated resistances as well.
If they are first order LPF (which they sound like) then 1/(2*pi*R*C) = fc. Where fc is the cutoff frequency of the LPF (or 3db frequency). Simply choose a cap value you like and calculate the associated resistance.
What you say for C5 is true, but probably only within a limited range. I hadn't looked at it because patroclus mentioned 100pF, and C5 is 0.01uF. What I said holds for C1-C4. Perhaps you hadn't looked at them prior to your first post._3iMaJ said:No no, C5 works with the 1k resistor as for C1, that may be the case, however its most likely a HF noise cap. So changing it probably wouldn't be a good idea.
C1 is similar to a coupling cap.
I think the 100pF caps are there simply to slow down the edge rates so that ringing on the far end of the cable is minimized. Note that the DATA line has an LED attached to it. That ain't gonna be very kind to a sample and hold.audioguru said:The output resistance of the 74HC125 buffers is fairly low,except when they go tri-state and the 100pF caps are needed for "sample and hold" (I think). :lol:
Patroclus, does "damped oscillation" translate a little better?patroclus said:What is ringing??
I'm spanish and don't know what this word means (appart from telephone ringing )