PIC driven transistor - smoothed signal edge - why?

[dhouston]

What kind of o'scope is this?

It looks like a Protek 220 ISA bus scope card which has very high sampling rates. If I'm right, the scope is not a limiting factor.

And 21 cycles at 38kHz is ~550uS which is a typical burst duration for several IR protocols.

[Acetronics2]

Hi, Dave

This scope ... has already shown its limits with Flotul :

We were offered a wonderful sample of demodulated "HF" ( LoL ... better to say Mid Freq ) signal, some posts ago ...


Now, this waveform is perfectly correct and true ... and shows bipolar switching limits with unipolar supplies ...

I also have samples of that ( but taken on an ... analog scope !

Alain

[flotulopex]

My scope is a "cheap" HANTEK DSO-220 USB modell

I couldn't try Alain's suggestions up to now; don't have any Schottky diodes neither 1nF capacitors... will be bought and tested by tomorrow evening.

My initial question was more about to understand the difference between both transistors since nothing else changes in the circuit.

so, might we say it is a " Flatul Hence " ???

I wish this was true: I would bother you All again with a methane powered PIC project

[dhouston]

My scope is a "cheap" HANTEK DSO-220 USB modell

Interesting. It looks like it was copied from the Protek 220 which was an ISA card DSO capable of 20 million samples per second. Of course, the sampling rate will be much slower using USB. The GUI is identical to Protek's with the exception of the colored knobs.

[Acetronics2]

My scope is a "cheap" HANTEK DSO-220 USB modell

Let's be honest ... and use the tools for what they are intended to do ...

I couldn't try Alain's suggestions up to now; don't have any Schottky diodes neither 1nF capacitors... will be bought and tested by tomorrow evening.

Amateur ...

My initial question was more about to understand the difference between both transistors since nothing else changes in the circuit.

This is exactly the same feature : junction capacities to discharge ... a strong cut off is obtained by polarizing the base to - 2 to 3 volts ...
just look at old "logic" schemes !!!

I wish this was true: I would bother you All again with a methane powered PIC project

Ah, la vache !!! ...

have a Good evening ...

Regards

Alain

[flotulopex]

Amateur, amateur...

In the early 1900's, the very best professionals & engineers built the Titanic