Hi everybody,
First of all, excuse my English i’m not a native speaker.
So i’m studying a circuit which uses the internal capacitive module of a PIC 16LF1823 to detect the presence of a finger on a pad, and then, lights up an LED, if the signal reaches 1V at the Vmax.
I wanted to probe the input of the PIC which is connected to the capacitive pad, as you can see on the schematic attached, to watch on the oscilloscope the signal depending on the finger’s touch.
The problem is the following : I’m using two oscilloscopes, a Voltcraft DSO-1062D (which is the same as the Hantek DSO 5062b) and a Rigol DS1054Z. When I probe the signal with the Voltcraft, everything is okay, if my finger is touching the capacitive pad, the LED lights up and the signal on the scope is correct as you can see on the picture attached.
However, with the Rigol in the same conditions, I get a signal completely attenuated (see the picture attached) and the LED doesn’t light up even if my finger is touching the pad.
If I remove the probe while i’m still touching the pad, then the LED lights up.
It’s like the Rigol interferes the capacitive module.
I switched the Voltcraft and Rigol probes and nothing changed. However, the input impedance of these two scopes are nearly the same : 1Mohm // 20pF for the Volcraft VS 1Mohm // 13pF for the Rigol.
Does anybody has the explanation of the Rigol issue ? Since both input impedances are the same, what could make the Rigol worst than the Volcraft for this measurement ?
Thanks in advance and have a good day/night.
François
PS : the pictures show the result with the probe in 1:1 mode. With the probe in 1:10 mode, it’s a bit better for the Rigol but it’s still bad.