1

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?

3
  • There is a schematic editor built in to the question editor, you know... No need for dodgy ASCII art...
    – Majenko
    Jul 19 '20 at 15:45
  • The vertical +-+ is not an or, but an and. You need to connect both. These are pulldown resistors
    – chrisl
    Jul 19 '20 at 16:12
  • @Majenko I also think that dodgy ASCII art is disgusting, but I took it "as it is" from the Github file which I don't own.
    – J. Francis
    Jul 19 '20 at 21:05
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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:

schematic

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.

6
  • This is perfect. May I connect the grounds into the Arduino's ground? Sorry about my lack of knowledge and thank you.
    – J. Francis
    Jul 19 '20 at 21:12
  • Not only "may" you - you must. majenko.co.uk/blog/importance-sharing-grounds
    – Majenko
    Jul 19 '20 at 21:25
  • Yes, adding a zener diode will offer further protection to your Arduino, and is a very good idea. (Voted). If I read the specs right that 1N4733A diode can dissipate a watt of power? (jameco.com/Jameco/Products/ProdDS/36097VIS.pdf)
    – Duncan C
    Jul 20 '20 at 12:52
  • No idea, that's just the default in the editor.
    – Majenko
    Jul 20 '20 at 13:00
  • The Arduino also has clamping diodes inside the MCU, that will clamp the voltage to VCC (+0.6V).
    – Gerben
    Jul 20 '20 at 18:57

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