433 MHz Power Switches Frontend

This is a simple network front end for a set of wireless remote power switches in my home. It sets up an HTTP server, drives a 433 MHz transmitter and displays the current status of the power sockets. The design is responsive to work on phones as well as desktop computers.

Sockets

I got mine from a large retailer in germany, and they are branded "REV". There's only a few protocols for those radio power outlets, but instead of opening it, looking for the radio chip ID and adapting an existing library, I found it quicker and easier to just reverse engineer the timing of the signals with a receiver (they come together with the transmitter for just 1-2 Euros) and a logic analyzer. If you want to take the other route, however, there's an excellent library that covers most wireless control protocols at RC Switch.

Control sequences

Power up the receiver and connect a logic analyzer to the data line. Then press buttons on the remote and capture the sequence. Take note of the timinig. I only captured three on and three off signals (since I only have three power sockets). The encoding seems to be a return zero code, where a "1" is encoded by the data line being high for 875us and then low for 275us, and the "0" is encoded by a high for 275us and then low for 875us. A command has 25 bit, where the 3rd nibble seems to encode the channel id, and the 6th nibble (counting from left to right) is either on or off.

This is what one command looks like on the analyzer output:

I repeated the process for the other buttons on the remote as well and those are the sequences I measured:

1 ON    1101 0101 1101 0100 0000 1100 0
1 OFF   1101 0101 1101 0100 0000 0011 0

2 ON    1101 0101 0111 0100 0000 1100 0
2 OFF   1101 0101 0111 0100 0000 0011 0

3 ON    1101 0101 0101 1100 0000 1100 0
3 OFF   1101 0101 0101 1100 0000 0011 0

The remote sends each control sequence 5 times in a row, but I went with 10 times, because my transmitter only runs on 3.3V and the signal needs to pass through walls. From what I can tell, this seems to work quite reliably. The transmitter could take up to 12V, if more range is needed.

HTML

The website, including all assets, is built with npm and served from the ESP8266 filesystem. To build the website, go to the html directory and build using npm:

Build step

cd html
npm run build

This is what the whole thing looks like on small device:

And that's what it looks like in a browser:

Building & Flashing Firmware

Your WiFi credentials need to be compiled into the application. Create a file src/credentials.h with the following content:

#ifndef CREDENTIALS_H
#define CREDENTIALS_H

const char *ssid = "YOUR_SSID";
const char *password = "YOUR_PASSWORD";

#endif

Building and flashing is handled by PlatformIO. To flash the code, run:

pio run 

Building and uploading the LittleFS file system is handled separately:

pio run -t uploadfs

If you want to open the serial terminal, run:

pio run -t monitor