How to use an arduino to replicate a button push on an external circuit

I have an old drone with a RF camera. When powered (12v drone battery) it turns on and transmits the video to a paired First Person View monitor, it also starts recording onto an SD card (on the drone), works fine. My problem is that when I disconnect the power, the SD card does not save the recorded file. I have to push a momentary button on the pcb to stop the recording, allowing it time to save before I can remove the power.
I want an Arduino to "push" that button form me. I could use a relay, but it's big and bulky, unless anyone knows of something really small?? I thought about an optocoupler (but previous failed attempts on other devices have put me off trying to understand those things, am i using it wrong?), and just using a 2n2222 transistor and connect the grounds, but I don't want to fry the circuit "experimenting". I figure you guys would need to know something about the circuit the where the button is pushed but all I have is this:
https://www.eachine.com/Eachine-Novice-III-135mm-2-3S-FPV-Racing-Drone-Spare-Part-5_8G-40CH-Pegasus-25~400mW-VTX-DVR-3_3V-5_5V-p-1893.html

There is a picture of the main PCB i'm talking about, the 3 cables go the camera, the 5 cables go to another part of the RF transmitter PCB and where the 12v supplies. It says 5V is powering the PCB with the button (Start/Stop Record). The SD card is on the underside of this PCB.

What do I do??

I don't think you have looked very far for a relay. I recently completed a remote control project for a friend using a receiver and a fob from Ebay. The receiver has a SPST relay the size of the "reply" box at the bottom of this reply, and about 1/4 inch thick. It could run continuously at 6-12 volts, or just a single transfer for your button switch replacement.
Paul

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Off to EBay we go!!!

I hope you are not thinking I bought the relay, itself, on Ebay. I bought the whole package, FOB and receiver.
Paul

link?

Hello

I made something similar (controlling the on/off switch of a computer monitor) with a CD4066

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This is the link to what I used. Different seller. My remote control..

I popped the receiver out of the case and superglued it into my enclosure.
Paul

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This looks like exactly what I need! I didn't realize it could be that simple either?! i'm intrigued. Thanks :slight_smile:

Good. Uncoil the antenna wire for greater distance.
Good luck with the project.
Paul

Ahh! Awesome!! I could do it remotely now! :slight_smile:

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