Samsung SmartThings / ALEXA to control Arduino

Sorry for the long post, but I’ve tried to include everything I discovered on this project.

I’ve had the SmartThings ecosystem for about a year and now have quite a lot of Zigbee and Zwave sensors. I’m very impressed with the plug and play ability. Also, Samsung keep the system up to date with firmware upgrades. One limitation is that to control devices, I’m locked into using the proprietary mains voltage outlet. I haven’t seen anything with low/no voltage outputs that can be controlled by SmartThings. I could go down the route of the ESP8266 etc, but then I’d be diverging from the Samsung App for the rest of my house. I’ve also read that sometimes the ESP8266 locks up, which means you have a problem if you are not at the location.

So, I decided to open one of the mains outlets to see what was inside and if I could find a way to make it work with an Arduino. This would allow me to control an Arduino remotely from the SmartThings App. The control would only be on/off. I guess Alexa control is possible, but I haven’t started using that yet.
Inside the outlet unit I found two PCBs; mains voltage controller, and the rf controller. These are linked together with a fixed 6 pin connector. I split the connector and found there is just a VCC/GND/Control Out. The connectors are SMD, so very easy to damage when desoldering. As this is connecting to the Arduino, I’m only using the rf controller. The rf controller functions ok off the 3.3v supply from the Arduino. I found that the floating output needs to be connected between two resistors which bridge to 3.3v and GND. Then I get 1.6 volts with the outlet turned off and 0.02 volts when the outlet is turned on. I used two 320kohm resistors to tie the floating output.

I connected the Control Out to an Arduino ADC input and wrote a simple program to detect the two levels and turn on/off the relay as appropriate.

Overall, this is a very expensive way to integrate SmartThings to an external controller and I really just wanted to see if it could be done. The surgery is pretty much one way, but I understood that from the start.

Integrates an Arduino/other controller to the SmartThings ecosystem
Fit and forget. The RF side is very reliable.
There feasibility for two way control. (But not possible using this surgery method)
Expensive for just an RF interface
Precision soldering skills required to remove the rf controller from the outlet
Only two state operation
Unsure if VCC is 5v tolerant
Samsung sell just the rf module for the Maker community.
Proportional control ability
Tri-state operation (eg for curtains; open, close, off)
Nicer 4 pin interface (VCC, GND, Control Output, Switch input)
Operation off 3.3v or 5v
Ability to change labels of swich states in the App.

sketch_smart_output.ino (1.53 KB)