Is this circuit risky for an Arduino Uno?

Question

I will show a connection diagram between my Arduino Uno and a DSC HS2032 panel (alarm system).

The DSC panel uses 12V and I don't know the voltage fluctuation.

The yellow and green are RX/TX ports.

Github file: https://github.com/taligentx/dscKeybusInterface/blob/master/examples/Arduino/KeybusReader/KeybusReader.ino

DIAGRAM (I assume the vertical "+--+" means a simple "OR" connection):

  DSC Aux(+) --- Arduino Vin pin

  DSC Aux(-) --- Arduino Ground

                                 +--- dscClockPin (Arduino Uno: 2,3)
  DSC Yellow --- 15k ohm res ----|
                                 +--- 10k ohm resistor --- Ground

                                 +--- dscReadPin (Arduino Uno: 2-12)
  DSC Green ---- 15k ohm res ----|
                                 +--- 10k ohm resistor --- Ground

I need to make sure this diagram is SAFE, and will not overheat or do something risky to my Arduino.

Why is this circuit not going to burn my Arduino if it is using 12V?

Answer 1

That circuit is fine as long as the input signals don't go above 12.5V. You can protect it further by adding a 5.2V zener diode across each of the signals as they enter the Arduino:

^{simulate this circuit – Schematic created using CircuitLab}

Why is this circuit not going to burn my Arduino if it is using 12V?

Because it uses a voltage divider to reduce the voltage to 4.8V.