My new Guardline Security Alarm can send a 12 volt output signal to an accessory device. I would like to send that signal to my Rashberry pi and have it send an email to my iphone. I bought a SMAKN Dc/dc converter to step down the 12v to 3.3v Can I just direct wire them together? Any help would be appreciated. Don’t want to blow up a $100 alarm. Thanks.
I bought a SMAKN Dc/dc converter to step down the 12v to 3.3v
DO NOT do this!
These devices are for converting power NOT logic levels!
You could use a voltage divider provided the circuits share a common ground.
I would NOT directly connect a foreign voltage source to a Pi (or any other logic circuit) without protection. NOTE you do NOT need 3.3V – indeed an engineer would use a circuit designed to safely exceed the logic threshold. (I normally aim to supply 2.2V to a Pi GPIO input). I wouldn’t even connect the Pi 3.3V power to a GPIO without protection.
See https://raspberrypi.stackexchange.com/a/105246/8697 which is an answer to a similar question.
If you know the voltage (is it always 12V or is it sometimes 14V) you could have used a pair of suitable resistors as a voltage divider.
As long a your DC converter or whatever circuit you end up using constrains the voltage at the Pi to 3V3 or less you will be fine.
In any case I don’t see how you could damage your alarm by tapping its 12V output (unless you chose to be deliberately inept).