Changing the functionality of a foot switch using transistor - Looking for some advice from the pro

[Paul_B]

@bklyn3

1. The way I wired the buttons was based on this article : https://www.arduino.cc/en/Tutorial/BuiltInExamples/Button

Yes, that is what is so truly terrible about the "tutorials" on the Arduino site which "teach" things entirely contrary to good engineering practice.

@bklyn3

What difference would it make if I wire it as you suggested ?

More practical and generally safer. Wiring the power supply line to switches, contacts or in fact anything that you do not need to, carries a risk however slight, of interference with the supply either from picking up impulses from other devices or mechanical damage and being shorted to ground.

In addition, the microcontroller provides a built-in pull-up resistor function of approximately 45k, which may be sufficient to not require an external component.

@bklyn3

2. Knowing the voltage between the tip and sleeve is 3V (not sure about the current but probably very low) , what relay would you recommend using ?

Any, preferably small, a reed relay would probably be very appropriate.

@bklyn3

3. I added a diode after the transistor based on some other article. What's the purpose of that diode? Why is it needed ?

It suppresses a substantial voltage surge when the transistor switches off the current to the coil, called "kickback" and other things.

[Grumpy_Mike]

@bklyn3 yes Paul is correct in what he says.

[bklyn3]

@Paul_B
@Grumpy_Mike

Thanks Paul and Mike. I am truly learning a lot here.

So from what Mike previously suggested, I would have to wire the button as follows (the right 5V wire goes to the relay so ignore it for the sake of the button discussion) :

Is that right ?

I have also seen postings where it is wired without the resistor + 5V connection. Directly to the ground, like this :

Is this second wire diagram acceptable ? If so, why would you favor one vs the other?

[Paul_B]

@bklyn3

Is this second wire diagram acceptable?

It assumes you are using a pinMode of INPUT_PULLUP on that pin to enable the internal pull-up "resistor" of approximately 45k.

[Grumpy_Mike]

@bklyn3

Is this second wire diagram acceptable ?

Yes

@bklyn3

If so, why would you favor one vs the other?

Because:-

1. You don't need an extra component.
2. In the wiring you don't have 5V going round the place which as the potential to cause damage in the case of a wiring mix-up. See my tutorial at Inputs

If you are keen to learn about MIDI and Audio then I do have a book out:-
Arduino Audio Projects

[bklyn3]

@Grumpy_Mike

If you are keen to learn about MIDI and Audio then I do have a book out:-
Arduino Audio Projects

Hi Mike,

Thanks a lot for the link to your tutorial. I should have started there !!!
I will checkout your book.