New project - MSFS C++ USB interface

[richard]

you sketch is incorrect , with button pressed v test == 0.45 v

[Demon]

you sketch is incorrect...

I used this guys design.

https://hackaday.com/wp-content/uplo...uncing-sch.png


His explanation is here:

https://hackaday.com/2015/12/09/embe...uttons-part-i/


I've seen this design in other places. The 3rd resistor is to prevent the input pin from floating.

[richard]

i see , you need to know the leakage current from the ST gate input to calculate the voltages . after the rc time constant is allowed for of course
seems messy to me , at 100k the button may never work depending on ST characteristics

[Demon]

..., at 100k the button may never work depending on ST characteristics

That's why I tested using a pushbutton and checked the voltage out the RC circuit.

The reading did fall to 0V for all configurations.

[Ioannis]

Better be on the safe side. Richards #91 is the one I would use.

But then you can ditch all that stuff if your ports support internal pull up and just read them in software as described in #86.

Ioannis

[richard]

the pull down resistor is a bad idea, the hackaday article [if you wish to trust it] does not have one and does not suggest one.
biasing cmos inputs to values inbetween logic high and logic low thresholds is a proven method for making oscillators , i would not recommend it as a debounce cct. the input pin in the article is never in a floating state regardless of button state, unused cmos input pins cannot be left to float, a completely different thing

[Ioannis]

I guess you refer to post #89. There are no pull downs. It was a graphic design error that meant to be a capacitor, as designated by the letter C.

Ioannis

[Demon]

the pull down resistor is a bad idea, ...

Thanks for keeping an eye open for me. It's now removed.

"Wat waz messa tinking." - Jar Jar