Dear all,
Iām new to PCB design and wonder though if termination resistors ( R1, R2, R7 and R8) for the in- and outputs are needed for speeds bellow MHz (probably only 50kHz).
Best,
Hilma
If rise time is well below the propagation time on the cable, missing termination will have minimal effect on the signal. Provide a footprint on the board. but start without populating those footprint. If you can see no problem, good, otherwise add the resistores later.
1 Like
Hello Hilma,
First of all, where is R1 connected to?
If R1 is not connected it is useless. (Except you want to optionally solder a wire to it)
The same goes for R2, C2, C1, R7 and R8.
Secondly, what Uwe said is correct, but let me explain it a bit different.
Important is not only the frequency, but also the rising time.
That is the time the signal needs to go from low to high.
E.g. if you get a 50 KHz Sine Wave you have a very long rising time and you should be fine.
But if you get a 50KHz Square Wave it will cause reflections.
The edge of the Square wave has very high frequencies and will be reflected and/or distorted.
If a reflected part of the signal edge arrives a second time on your electronics it can cause your electronics to see multiple signal edges where only should be one.
For some electronics it looks like a bouncing switch.