Need help understanding a circuit diagram..

Projects General Guidance
1

I'm attempting to use a rotary phone dialer with the GitHub Rotary-Dialer software. Below is what they give for the 'expected circuit', but it's not really clear to me what the circuit should really look like.

Any help or clarification would be appreciated - thanks.

Rotary Dial Arduino

/---------------------- readyPin
/- ready switch (NO) -- pull-up resistor -- VCC
/-- pulse switch (NC) -- pull-up resistor -/
\ ---------------------- pulsePin
------------------------------------------ GND

2

Looks like:

3

Isn't this equivalent to setting readyPin and pulsePin to INPUT_PULLUP? In the source code, the pins are set to INPUT.

Thanks..

4

If you set the pins to input-pullup then you don't need the external resistors.

5

Internal pull-ups are fragile and can be damaged relatively easily. So it's recommended to use an external pull-up resistors if possible.

6

alesam:
Internal pull-ups are fragile and can be damaged relatively easily. So it's recommended to use an external pull-up resistors if possible.

Where is that in the datasheet?
If that recommendation is not in the datasheet, who is making the recommendation and where is it published?

7

"Internal pull-ups are fragile and can be damaged relatively easily."

Nonsense. They are 30-50K and have very little current flow.