New project - MSFS C++ USB interface

[Ioannis]

Why is the PWR_FLAG necessary to be added? Isn't +5V enough?

Ioannis

[tumbleweed]

You shouldn't leave the inputs of the HC14 floating... the outputs will be unknown.

Also, an ST gate really won't debounce anything if that's what you're trying to do.

[Ioannis]

Yes, inputs should not be in the air.

Also despite being ST inputs, the resistor and a cap should still be added. Tubleweed is very right about that.

Ioannis

[Demon]

You shouldn't leave the inputs of the HC14 floating... the outputs will be unknown.
....

I wish I had seen that before sending that order to JLCPCB. I'm gonna have a resistor jumper on my brand spanking new circuit (only printed 5 to test).

...
Also, an ST gate really won't debounce anything if that's what you're trying to do.

I'm trying to get a cleaner signal like he explains here at "Hysteresis: The Full Fix".

Are you saying this doesn't work as he explained?

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

[Ioannis]

It will work if you included the RC network also. But NOT as in your post #69, where switch go directly to the HC14 input.

Ioannis

[Demon]

I really shouldn't work until the wee hours in the morning. That rotary switch circuit was totally not finished.

I've updated my pushbutton circuit.




And my rotary switch circuit. (CORRECTED VERSION IN NEXT POST)




1. Do you see any other mistakes?

2. Do I still need a cap at the MCU pin when it's a signal from a 74HC14?


EDIT: Hmmm, just noticed my pull-ups on the rotary switch are between the 10K and 74HC14. Gonna go change that.

Thanks!

[Demon]

Here's my corrected rotary switch with corrected pull-ups.

[Ioannis]

Well, better but not perfect I suspect.

The HC14 inputs are at High (~5V) level when not triggerd by the switch/encoder.

When the switch is at ground, the HC14 sees the voltage divider of two 10K resistors, so the voltage is at 2.5Volts.

According to the datasheet, this will lead to not clearly defined state of low or high. Will depend on the HC14 type, brand and temperature.

I would strongly recommend to increase the 10K pull up to 100K.

Ioannis

[Demon]

You shouldn't leave the inputs of the HC14 floating... the outputs will be unknown.

...

Oooops. I've since added a pull-down for the input I was using.


I'm seeing several comments on google about connecting the unused pins to ground. If I'm not using their output, can a floating input disturb the other circuits?


EDIT: I've googled some more and found this explanation:

"...random charges accumulating there can/will cause unpredictable internal behavior in the chip, including oscillation and high power dissipation."

https://electronics.stackexchange.co...-inputs-outpus

[Demon]

Why is the PWR_FLAG necessary to be added? Isn't +5V enough?

Ioannis

In order for KiCad to be able to test the circuit, it has to know where the current is coming from. I just noticed how one dude uses a tiny legend to connect the flag with VDD and GND. You only need to connect the flag on each once.

https://forum.kicad.info/t/erc-error...nd-gnd/39364/5