Getting power from a 24v bus system

Hi everyone,

I’ve got a quick question regarding a door opener bus system. I’m trying to read from this 2 wire (a/b) UART compatible bus running on 24V (with 15v being the power supply). Using the attached schematic, I’m getting 5v signals.

The bus system is also meant to power attached devices, so I also want to run my Arduino on it. What is the easiest way to get regulated 5V or 3.3V power from it, without interfering with the signals?

And since the attached schematic isn’t mine (and is meant for 5v signals), and I wanted to get 3.3v signals from it, what would I need to change? ZF15.1 is dropping away the 15v power supply. Would replacing the 470 Ohm resistor R2 with a 270 Ohm one be enough? If I understand voltage dividers correctly, that should get me a ~3.28V signal – am I right there?

Thank you for your help! :slight_smile:



Drawing any more than a very low current will result in a higher voltage drop across the 1k R, this will likely drop the voltage available at the output of the circuit supplied.


A buck converter can convert 24volt to 5volt very efficently (no heat).


The question is, which part of the circuit do you have access to?


You can easily get a buck converter off eBay for not a lot. And regarding your question on 3.3v signals use a voltage divider on the TX of the bus system. Google it to find out more