#522 Remote Doorbell

A simple doorbell using a 433MHz transmitter/receiver pair for remote signalling, and an HS-088 sound chip for a doorbell effect.

Build

Here’s a quick demo..

Notes

I can’t hear my doorbell when I’m in the workshop, which often means an extra trip to the post office when I miss a bulky aliexpress delivery.

This is a quick build of a wireless doorbell using:

a cheap 433Mhz RF transmitter and receiver kit
and an HS-088 ding-dong sound chip

I decided not to use any encoding over the wireless link, so I’m using it more like a spark-gap transmitter. So far in my experiements, I’m not seeing enough interference to get false positives ringing the doorbell. If that changes, I’d probably add an ATtiny and run a simple ASK signal over the connection. We’ll see how this goes..

RF Module Specs

Receiver:

Model MX-05V
Working voltage : DC5V
Quiescent current : 4MA
Receiving frequency : 433MHZ
Receiver sensitivity : -105DB
Size : 30147mm external antenna : 32CM single core wire , wound into a spiral shape

Transmitter:

Product number : MX-FS-03V
Transmission distance : 20-200 meter ( different voltage , the effect is different )
Operating voltage : 3.5-12V
Dimensions : 19*19mm

Incoming Signals

The incoming signal (DATA pin output) looks like this when the doorbell is pressed. The positive pulse is a fixed-width signal on incoming data. The pulse goes to 0V and stays low for the full duration of the incoming signal.

scope_inbound_pulse

Circuit

The transmitter is configured to power up and send a signal when the doorbell is pressed.

The transmitter uses an opamp to perform a peak-detection on the incoming signal to identify a doorbell press, and then fire the HS-088 module.

A speaker is connected with R2 selected between say 0-47Ω depending on the desired volume.

Breadboard

Schematic

Testing on a breadboard:

RFDoorbell_bb_build

Antenna

For good reception over about 30m with a few blocking walls and doors, I found the following antennas worked just fine:

Receiver: 32cm of 0.55mm copper wire wound ø5mm air coil
Transmitter: 25cm of 0.55mm copper wire wound ø5mm air coil

Construction

I put the receiver circuit on a small piece of protoboard and mounted in a probject box with a speaker and a micro-USB adapter (for power only)

build_rx_1

build_rx_2

The transmitter is powered by a 9V battery. I put a mini-pushbutton on the board for testing, and a JST connector for the doorbell wiring.

build_tx_1

Project Notes