New project - MSFS C++ USB interface

[Demon]

Wow from me too!

You got all that in a few days? Well, KiCAD will be my next try on PCB software then!...

Ioannis

I can't say enough good about KiCad. It even has SPICE, but I never got to learning exactly how to use that.

I can generate all the files for a new circuit within a few hours. I can't imagine not working with it now. I love the Electrical Rules Checker; that saves a ton of time, money and effort.

It takes a while to get used to some of its way of doing things. There's a LOT of information on the web for any error I encountered; like having to add a PWR_FLAG to VDD and GND lines, and how symbols can be divided into units).

Units are essentially individual layers for components with multiple functions, like a 74HC14 chip with 6 circuits and the power circuit. In this example, I use only 4 of the 6 circuits. I'm putting the decoupling caps near the pin on the MCU (it's a separate circuit).



And best of all, it's free.

[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.

[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