433MHz sensors and devices are good value
This page is about integrating older stuff with newer stuff – or how to upcycle old wireless gadgets for home automation. 433MHz sensors are more plentiful than wifi sensors and they are inexpensive too.
see also: 433MHz smarter letterbox
sensors and receiving devices
A wireless doorbell, as you know sends a message to a chime. This is however one of many types of wireless switches and sensors. Others include a door contact; a motion sensor; water leak sensor; push button; wall switch and remote control.
Like the wireless bell push, sensors send their message to ‘something’. As well as sending to a chime they could send a message to turn on an electrical socket or lamp; a relay; sound a siren; open a garage door or office door lock.
types of wireless
Sensors that tell you the room temperature or whether a door is open, can send their on of off status over Bluetooth, Wifi, Z-wave or Zigbee. Yesterday’s sensors and gadgets mostly used 433MHz (also called RF ) for wireless communication. The 433MHz frequency is still used in remote controlled sockets and home security systems.
I unknowingly had a lot of RF technology – the RF remote control for my ceiling LED lights (picture below) uses the 433MHz band. The 433MHz signal can travel the length of the house and sensor batteries last for months or a year. And as the sensors are inexpensive (a few £ each instead of tens of £) here’s something to experiment with. In comparison, a wifi device needs to be near a power outlet and its signals probably wouldn’t travel as far – and if they did I’d need to pay bigger money.
making 433MHz smarter
The 433MHz RF systems unfortunately just work as standalone gadgets. This disadvantage tends to mean that they aren’t part of the smart home automation platforms such as Google or Alexa. For example, if you wanted an alert on your phone when the basement was flooding; or you wanted the heating to respond to temperatures in various rooms, they aren’t connected up to do so. The way forward is to use a bridge – e.g a Sonoff RF bridge – to connect them. This connects your RF devices to home automation platforms like Google Home or Home Assistant (described here). Your RF devices can now talk to the home automation system and you can put its capabilities to work in projects such as this smarter letterbox.
pairing is how 433MHz works in practice
Get yourself a 433MHz push button and the plug-in wireless chime (M2D 300m 433MHz 60 chimes) as shown below. Often they don’t need to be the same brand. Press the chime button to select a tune; press the set button for a couple of seconds. An LED will turn on to show it’s ready to learn a button. Press the white button and the chime will now sound when the doorbell is pressed.
It is common for different 433MHz devices to be compatible with each other. For example, the chime can learn the signal from the door contact sensor above. You can set a different chime sound should the door be opened. You can also teach the chime the signal from a PIR sensor (main picture) so that anyone crossing its path will cause a chime sound.
how it doesn’t work
After experimenting with a lot of devices (and do try everything a few times each) you’ll have a lot of happy surprises as to what works with what. You’ll see that not every 433MHz device is compatible with each other – HomeEasy is it’s own system while a garage door remote will use a more secure ‘rolling code’.
If you also wanted the doorbell button to send an alert to your phone or computer; or turn on a light or boost the water heating or close the blinds, the next step is to integrate the RF system with the wifi system of a home automation platform. So get the Sonoff RF Bridge. The bridge reads many kinds of 433MHz signals so you can use its sensors to trigger events.
make use of a Sonoff RF bridge
- This device is a 433MHz receiver that listens for RF signals such as a press on that white doorbell button above. Install the app Ewelink on your phone and use it to ‘learn’ your sensor’s code.
- The bridge can also send a 433MHz signal to say, a RF socket. You can use the app to set up a time schedule for a socket. For example, if my laptop charger was plugged into an RF controlled socket, I’d make the socket turn off a couple of times a day. That way I can’t overcharge a battery and ruin it as I’ve done several times. I have smart sockets controlling electricity-hungry lights and they’re on a schedule that turns them off every two hours. A motion sensor turns them on as required.
- This Sonoff device is indeed a bridge – it receives 433MHz signals and it can send out RF signals to RF devices and inform you via wifi to your phone. The video below by Csongor Varga illustrates the bridge you’ve now made between different systems.
- There more fun to be had by connecting Ewelink to IFTTT or Amazon Alexa or Google Home.
going further with the Sonoff RF bridge – Tasmota & MQTT
I’ve so far mentioned sensing and sending RF with the bridge and phone app. You may have devices that you need to work in the way you want – for example, I want to know not just the temperature of a room but also to see a graph of how fast the room heats up and cools down. For this I installed different software on the Sonoff RF bridge and connected it to Home Assistant.
There is a choice of software to use on the RF bridge – there’s openmqttgateway which provides a bridge that responds to a variety of 433MHz, Bluetooth and other senders. The software turns received data into MQTT messages which Home Assistant can process. The software I used for my Sonoff RF bridge is called Tasmota which also turns received RF into MQTT messages for Home Assistant. Tasmota can be installed on many modern devices. I went for it because has a web interface that makes it easy to see what’s being sent.
Scarily, what follows involves taking apart your bridge. You’ll need some ‘female headers’, Dupont jumper wires, a 3.3v FTDI unit and some flashing software.
optional: how to flash Tasmota on an RF bridge