Could you please advise me about oscope results? I have fashioned the BPW34 with the rezistor as posted by @KM .
I am measuring my camera display which is a source of pain. In the first image, the brightness is set on +3 out of a range -5 to +5. It clearly shows PWM on the graph, but it doesnt show the frequency.
On the second image, the brightness is +2, there it shows PWM and freq as well (20 Khz).
Am I doing something wrong? The ***** symbol instead of the freq number also shows with brightness below -3, so -4 and -5 show no freq. Is it because the display then is too dim and the diode cant pick it up? It obviously must have PWM at lower levels as well, if it has PWM at -3. Could it apply for the too bright setting as well?
I am confused as then I do not know how well to trust the measurements I make with this. When I measure with the soundcard oscope, it shows PWM at all brightness levels of 15Khz.
Also there is a red switch on the probe, either to 1x or 10x. When its set on 10x it doesnt show any readings, so I leave it at 1x.