Arduino PWM signal acquisition dubt

Other Hardware General Electronics
1

I'm doing a little project in order to learn to use Arduino.
In the attached image it's shown the circuit.
3 phototransistors with 3 colored filters let a RGB LED shine accordingly to che color of the light that hit the three sensors.
I have connected my probes to the pins 11 (RED), 10 (BLUE) and 9 (GREEN).
Those are the 3 traces displayed on the oscilloscope screen. I change light conditions sequentially (RED light then GREEN light then BLUE light) and I can see that the duty cycle of the 3 signals (RED, GREEN, BLUE) change accordingly.
The red trace (PIN 11) is the one the trigger of the scope is referred to.
Its rising edge is fixed on the screen while its falling edge moves accordingly to the power supplied by the probed PIN.
When the power delivered to the PIN 10 and 9 changes looking at the GREEN and BLUE traces I notice that not only the corresponding falling edge move on the screen but even the rising edges move.
In another moment I have set the trigger for the GREEN trace: in this case only the GREE trace rising edge is fixed.
I have even set the trigger for the BLUE trace and I have noticed that only the BLUE trace rising edge is fixed.
Can sonmeone tell me what's going on?
I was expecting to see all the three rising edges traces in fixed positions on the screen.
I have to say that I'm still learning to use the scope so maybe I haven't understood something related to the settings.
Cheers
I'm doing a little project in order to learn to use Arduino.
In the attached image it's shown the circuit.
3 phototransistors with 3 colored filters let a RGB LED shine accordingly to che color of the light that hit the three sensors.
I have connected my probes to the pins 11 (RED), 10 (BLUE) and 9 (GREEN).
Those are the 3 traces displayed on the oscilloscope screen. I change light conditions sequentially (RED light then GREEN light then BLUE light) and I can see that the duty cycle of the 3 signals (RED, GREEN, BLUE) change accordingly.
The red trace (PIN 11) is the one the trigger of the scope is referred to.
Its rising edge is fixed on the screen while its falling edge moves accordingly to the power supplied by the probed PIN.
When the power delivered to the PIN 10 and 9 changes looking at the GREEN and BLUE traces I notice that not only the corresponding falling edge move on the screen but even the rising edges move.
In another moment I have set the trigger for the GREEN trace: in this case only the GREE trace rising edge is fixed.
I have even set the trigger for the BLUE trace and I have noticed that only the BLUE trace rising edge is fixed.
Can sonmeone tell me what's going on?
I was expecting to see all the three rising edges traces in fixed positions on the screen.
I have to say that I'm still learning to use the scope so maybe I haven't understood something related to its settings.
Cheers

pwm.png
pwm.png742×551 69.9 KB

2

Pin 11 uses a different timer for PWM than pin 9 and 10.

3

aarg:
Pin 11 uses a different timer for PWM than pin 9 and 10.

In the attached pic it's shown what happens when the blue signal is triggered and I use blue light.
The duty cycle of the blue trace increases while both the green and red traces just shift to the right.
If pin 9 (GREEN) and pin 10 (BLUE) refer to the same timer shouldn't those traces have the same position for the rising edges?
Cheers

pwm2.png
pwm2.png516×619 424 KB

4

Maybe you have your pins mixed up.