Hi all, my first post here and appreciate any help you can provide. I'm not completely new to all of this as I have experience coding, but am definitely new to the electronics aspect so please be gentle. I have searched all over but the only results I can find on this question relate to supplying power to DC motors which is not what this is about.
I'm in an apartment building and would like to control my garage opener via Alexa and/or iPhone/Apple Watch. It automatically closes after a moment, so I just need the remote to send the "Open" command when needed.
Obviously because it's an apartment building I cannot modify the garage door opener in any way. What I can do is wire my existing remote control (300MHz non-rolling code, operates on a 9V battery) into an Arduino board to trigger a "button press" that activates the transmitter. The Arduino and transmitter would stay in my apartment, which is in range of the garage opener. To me it makes the most sense to just use the existing remote instead of buying an RF transmitter and trying to replicate the signal.
My question is what strategy you would recommend for supplying the 9V power to the remote, and what parts apart from the Arduino board I would need. I'm looking for the simplest and preferably cheapest of options:
1) Solder the remote button contacts so that the button is always "pressed." Remove the 9V battery from the remote and instead use a 5V output from the Arduino and increase it to 9V (would a transistor be best for this?) Use a digital pin to allow power to the remote for about 3-4 seconds on command then revert to LOW when done. I am unsure of how to determine the level of current the remote would actually draw. It can't be much but obviously I don't want to fry it by supplying it with too much power from the Arduino.
2) Leave the remote battery in tact and connect the Arduino pin to the button contacts on the remote to make it think the button is pressed and simply draw on the internal 9V remote battery. I am unsure how to do this without frying either device—would I need a relay for this or would the digital pin be able to function to simply close the circuit without supplying too much power?
Again, thanks for your help. I feel like this should be a very simple project and that's what I'm looking for. I will probably get an Uno with an ethernet shield unless there is an even easier way to enable Internet connectivity so I can use either an IFTTT recipe or other way to control via Alexa or an app.