PWM　spike signal ???

Hi ,,,, i just program my mcu in order to generate the PWM signal ... But when i test the pin output at the o-scope, the signal waveform is spike-like form, The time width between the low and high is just as expected...

i am not sure this is a pwm signal..., and i plan to generate the Edge-aligned pwm signal

So do i need to add a converter something to turn it to Squrewave forms??

I appreciate for anyhelp ....

thanks

Output of a microcontroller is always a square wave. To what are you connecting the output? You may have transmission line noise which can usually be suppressed with a simple pullup resistor.

Are you using a compensated 'scope probe?

If not, then you will see ringing and distortion due to reflections in the unmatched co-axial cable.

Hero999 said:

Are you using a compensated 'scope probe?

If not, then you will see ringing and distortion due to reflections in the unmatched co-axial cable.

Click to expand...

Hi, thanks for replying, i will ask our school staff to confirm the probe type.
Hope it will work when i change the probe.

i will post the result when i switch the probe and test it again

It's not a question of 'changing' the probe, it's a question of adjusting it to work correctly - and you should really test and adjust it every time you use it.

Nigel Goodwin said:

It's not a question of 'changing' the probe, it's a question of adjusting it to work correctly - and you should really test and adjust it every time you use it.

Click to expand...

yeah , but i think i should confirm the type of the probe, if that's not a big matter, then i can remove that possible reason, and seraching for other solutions.

ps: I dont know the probe type is really a big matter on displaying that signal waveform

I think you are not adjusting the Duty Cycle correctly.

The point everbody is making: 'spikes' are due to capacitance & inductance in the signal path, sometimes called 'ringing'. It can be caused with a badly adjusted scope probe, but I've never seen this effect fror such a low frequency. You have not told us what load is attached to the micro output pin. I suggest the following diagnostic test.

Disconnect the output circuit and replace with a 2k pullup resistor connected to the regulated power (probably +5V). If the spike disappears then you may have a circuit loading problem. If the spike remains you need to replace or adjust the scope probe. This test is quite reliable and easy to do.

Has anyone else used the oscilloscope recently. Have they seen a proper square wave?

umliu37 said:

yeah , but i think i should confirm the type of the probe, if that's not a big matter, then i can remove that possible reason, and seraching for other solutions.

ps: I dont know the probe type is really a big matter on displaying that signal waveform

Click to expand...

It's absolutely crucial, which is why all scopes have a built-in probe calibration signal - if you're using a x1 probe it doesn't matter (nothing to adjust) but a x10 probe wrongly adjusted will give EXACTLY what you're getting. Other things could as well, but if you don't know what your probe is, then that's the first place to look - don't look for faults until you know there is one. All you need to do is clip your probe on the calibration pin of the scope, you should see a perfect squarewave.