mattmiller wrote:Im looking to help automate my garage door and from what I can tell, it sits at 3.8V normally, but when the door button is pushed, it changes to 1-1.5V and when the light button is pushed it changes to 2v.
What people are telling you is that those voltages are most probably the EFFECT of your existing control system and not the CAUSE of getting the door to operate.
That is why you are being advised to connect relays to directly emulate actually pushing the buttons.
Note: This is 99% the best way to interface to ANY low voltage existing control systems such as your garage door.
Exactly this. Lemme put it this way - if you are interfacing a microcontroller to detect when a switch/button is pressed, one common way would be to tie the pin you are reading to 5 volts (or whatever the controller runs on) through a resistor. You would then run your ground (or negative terminal from your power supply - which is generally just zero volts) through a smaller resistor to your switch and then to the same pin you are already feeding 5 volts. The effect would be that you would normally measure 5 volts at one of the switch terminals and 0v at the other. If you press the button, those two terminals are simply connected together and would measure something in between 0 and 5 volts (closer to 0 than 5) because you two resistors that are just there for circuit protection create a voltage divider. Every microcontroller has a threshold where it interprets the incoming voltage as a high or low signal...say...2.5 volts in this example. As long as we feed 5 volts to the pin that we're reading, the controller reads "HIGH" and does nothing because the switch is not pressed. If the voltage drops below 2.5 volts, the controller reads the pin as "LOW" and thinks "Oh, the button is pressed - Better move the door!" Note that the remote button doesn't do anything to "change voltage" all it does is open or close and the pullup/pulldown resistors at the microcontroller (inside your garage door) do the actual voltage dividing. Again though - it's not so tightly controlled as "1 volt to open the door...2 volts to close it...3 volts turn on the light...etc," It's just a matter of whether the two wires are connected momentarily down at the button to not. The fact is you can trigger your door the same from the two terminals on the back of the opener itself with just a screwdriver - This is how I opened and closed my garage from the inside before I set up my wifi enable pi-controller for it because my house didn't come with a button inside and a normal button is boring. You will only be able to send a "trigger" command (same as pressing your button) and unless you are watching the door yourself will not be able to know if it's opening or closing unless you add an end switch. That is how mine is set up - I have a button on my phone for "open" and one set for "close" - it reads the end switch then either tells me it's already closed or it triggers the door, waits 15 seconds and reads the switch again to confirm it did the right thing (because if the door is ever in the middle position, the controller has no way of knowing if it will open or close upon triggering)