increase protection of port

Hi,
Which one is better?
is The diode in second circuit effect to reduce noise?
and the switch is connected with 20 meter wire.

Use ceramic & polaroid capacitor with high value just beside the microcontroller pin to reduce noise.

Hi GelecG
Which one is better?
is The diode in second circuit effect to reduce noise?
and the switch is connected with 20 meter wire.

Click to expand...

Hi
Figure one is better ! however you can use figure two too . because diodes will need a voltage to being conducted and if you're using it's ADC pin it will destroy the precision .
And if you just need to use that key in on or off state then you don't need to use any diode !
Best Wishes
Goldsmith

thanks.
someone protecting port with optocoupler.
why we must isolation with optocoupler?

someone protecting port with optocoupler.
why we must isolation with optocoupler?

Click to expand...

Hi GelecG
It is simple ! because that someone , used an unsafe ground , perhaps , so he/she wanted to make an isolation between grounds to prevent some problems and hazards .
Best Wishes
Goldsmith

Hello goldsmith,
can you tell me more about "some problems and hazards"?

can you tell me more about "some problems and hazards"?

Click to expand...

Hi GelecG
Of course . if you want measure something from the main power line , which is not isolated , if you touch one of the wires which is the main one , then your body will complete the loop from the mail line till the ground . so your hairs will be stubby , ha ha ! besides the kidding , it can kill a human . it means your micro controller ground won't be safe too . so you will consider every pin in the controller side is with low voltage , but if you touch it something interesting as i've told before , would be happened ha ha !
It is one of the reasons behind why we would use an opto isolator . if you didn't understand this section i can draw something for you to clarify it .

Another problem is , if an spike from the power line came , then your MCU won't be survived and it might be destructed because it can't operate in voltages more than 5 volts ion it's pins . MUC is more expensive than a simple opto isolator and you can't easily replace it with an intact one . because you need to program the new one . but an opto isolator can be easily replaced with low cost and without any inconvenience . so thus we can protect our MCU with a simple opto isolator . and sometimes an opto isolator can play role of a level shifter section . and many issues more than this ...

You need further explanations ?

Best Wishes
Goldsmith

I know, you describe very well.
I think about elevator circuit.
the power supply is 24 volt DC. and it is isolated from main power line.
but the button isolated with MCU. why???
for example key of the door isolated with MCU.

I know, you describe very well.
I think about elevator circuit.
the power supply is 24 volt DC. and it is isolated from main power line.
but the button isolated with MCU. why???
for example key of the door isolated with MCU.

Click to expand...

Hi Gelec
Ok , i think you need to be precise on what kind of key you have for the door ? is that inductive ?
Of course when we are talking about an elevator the problem is it should be very safe because we are working on humans safety and their life . so we should think about everything .
Just consider if the door key is something like inductive keys or there is an inductive circuit in it's path . so it will deliver an spike while it is going to be turned on or off . so these spikes can suffer the MCU . so if MCU be noisy or perhaps destructed by that spike , then human's safety and life will be in danger . ok ? so most of the times we prefer to sue such and isolation to be sure . because we don't want if someone will be suffered our conscience suffer us .

Best Wishes
Goldsmith