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I am trying to connect to my home alarm panel via it's built in serial port. It is made by Paradox and there is a GitHub project that I want to use to integrate the alarm into a smart home setup such as OpenHab or HomeAssistant.

Some things I've learnt/discovered:

  • The alarm panel's serial port uses 5V TTL for it's serial interface
  • The serial port's power and GND is connected to the panel's AUX rail, which is at 12V.
  • The ESP can survive 12V input, but the onboard regulator gets very hot.
  • The ESP needs 3.3V for it's serial ports.

The ESP32 I'm using is a NodeMCU32-S clone (link to the actual supplier I used).

My initial solution

From the same supplier as above, I got an LM2596 voltage regulator breakout board, and a logic level converter that I plan to use to take care of all the level and voltage conversions.

My Problem

My power source is the 12v rail from the alarm panel - I would like the whole thing to be self contained. I need to convert this 12v to 5v for the serial on the alarm panel's side, and I need a 3.3v source for the ESP32 side of things.

My question

  • Can I use the LM2596 to bring down the 12v to 5V and then power both the HV side of the level converter, and the ESP32 with it?
  • Can I then use the ESP32's onboard regulator to further bring that 5V down to 3.3V, that I can then use on the LV input of the level converter?

I'm asking before I do anything because the alarm panel is expensive and important for my home security. I don't want to do something that might destroy it.

My electronics fu is extremely limited, and I learn as I go along.

Proposed circuit

See below my suggested circuit for this idea:

proposed interface between ESP32 and Paradox alarm panel

Your assistance and expertise will be greatly appreciated!

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1 Answer 1

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Yes, should be fine.

You better also connect the GND of the Paradox to the GND of the rest.

Check the ESP32 regulator current capabilities if that is enough for the other boards. If you want to be sure, get another buck converter 12V -> 3.3V

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    \$\begingroup\$ Thanks for the tip. I connected the paradox panel also to GND. All seems to be working and no magic smoke yet. I'm not worried about power consumption on the 3.3V rail, the voltage is just used to provide the level converter with a reference for the LV side. \$\endgroup\$
    – getack
    Mar 24, 2021 at 7:38

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