DIY: Keyless Entry from Access Cards

How to upgrade access cards to a keyless network version?

If your residential building requires an access card for entry, but there are times when you forget or don't want to carry it, what should you do? You might suggest switching to NFC format, but NFC can't replicate ID cards. So, let's take a look at the video intercom system.

With the indoor unit of the Ryantong video intercom, you can open the unit door even if no one is pressing the room number downstairs. Just press the second button to activate the video, then press the third button to unlock, and you're good to go.

Open up the casing and see if there's a place to modify the buttons.

The button interface is quite handy, even has a 5V power supply. Just connect a GND and you've solved the power problem. But here's the thing, the board with the buttons doesn't connect the 5V to anywhere, there are only 3 wires for the 4 buttons, and none of them connect to GND. Look at the diagram, there are two small solder points next to the four feet of the buttons, seems to be 1N4148 diodes. So, changing the button to connect to GND requires a different approach.

You can't connect it directly to GND or to the plug. Instead, you can try adding an optocoupler, directly connected to the button's feet. When it's activated, it means the button is pressed, and no other modifications are needed.

On the perforated board, use the ESP8266, flash the program, use the light-up app to trigger the buttons 0 and 2, connect two optocouplers, and the door will open successfully.

After testing, it's very effective and doesn't affect manual door opening or intercom downstairs.