I have a fairly general question, but cannot seem to find an answer to confirm my thoughts.

I have a garage motor door, and on the top has 4 terminals - 1 and 2 for a switch button to open and close, 3 is COM, and 4 is +24VDC.

enter image description here

I want to add a little module that will allow me to connect to the garage door and control it. Most modules I can find are 5VDC, and there are some that are 12VDC.

My question is, the garage door states it is +24VDC, does that mean I cannot use a DC converter to change it to 12/5VDC as there is no negative?

I was intending to use something like this: https://www.andymark.com/products/power-converter-12-24vdc-to-5vdc to do the conversion, but the lack of both poles is throwing me especially when the output will be to a USB powered 5V.

This is a diagram from the manual of the circuit board: enter image description here

  • 1
    I suspect that com is the ground reference terminal ... it is negative in relation to the 24Vdc terminal
    – jsotola
    May 20 '19 at 0:01
  • "Com" (short for "common") is a better term than "Ground" in many cases - with much electronic equipment, "Ground" does not actually imply a connection ot the earth - it is just used to indicate the point in the circuit that the designer intended to use as "Zero Volts" May 20 '19 at 0:07

"COM" is short for "common". It means ground, or, in this case, negative.

  • Awesome! Thanks Tim :) Everything I read stated it was ground, which to me is Earth and was throwing me out
    – Ahhhhhhhhhhhhhdfgbv
    May 19 '19 at 23:59
  • Since this is also an AC mains powered device, the DC electronics guy's friend "COM/GND/Vss/Earth" (normal DC current return) must be distinguished from equipment safety ground (never a mains current return except during a fault, and safety shield only). There would be no, um, earthly reason to connect Vss/COM/GND to mains safety ground, because there are things that can go wrong with mains ground that may throw 230V onto it. Your DC stuff would not like that. May 20 '19 at 0:40

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