newam / loadcelloccupany

Home automation occupancy sensor using load cells

Load Cell Occupancy Sensor

What is it?

This project is a occupancy sensor that uses a load cell for couches and beds, transmitting data to my Home Assistant server via MQTT over Ethernet.

Why?

Other bed occupancy sensors that I have used in my home automation setup trigger false negatives when rolling around at night. I use bed occupancy to turn on my lights if I get up at night, and I wanted a faster, more accurate solution.

Why PoE?

Wireless home automation devices often make sense only when they are battery powered, if a power cable needs to be run to the device it can carry data too. Designing a low power wireless device is far more complicated than designing a wired device and running an Ethernet cable.

Overview

Load cells → HX711 (ADC) → ATMega328P (MCU) → W5100 (Ethernet) → MQTT Broker → Home Assistant

This sensor takes input from 4 load cells, each supporting one leg of a bed or couch. The load cells are sampled with a ATMega328P (Arduino) using an HX711 load cell ADC. These samples are then transmitted to an MQTT broker via the Wiznet W5100 (same as Arduino Ethernet shield).

Project Contents

• LoadCell_ArduinoCode - firmware for the ATMega328P
• LoadCell_Case - 3D printable case designed in OpenSCAD
• LoadCell_Holder - 3D printable holder for the load cells designed in OpenSCAD
• LoadCell_HomeAssistant - example Home Assistant configuration
• LoadCell_KiCAD - schematic and PCB

Media

Software Used

• KiCad
• Arduino IDE
• OpenSCAD
• Libre Office
• Home Assistant

Arduino Libraries used

• Sparkfun HX711 Library
• Arduino MQTT Client

Forks

• ESP8266 Load Cell - wireless edition

loadcelloccupany's Issues

I made a ESP8266 fork which include OTA updates

Thanks @newAM for publishing your work. I wouldn't be able to do this project otherwise. Especially the 3D printed case.

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In case someone build it's own version with a ESP8266 you might be interested in my fork. It connects via WiFi (obv) and support Over The Air updates.

It also saves the 'tare'/offset to the EEPROM and doesn't reset on restart/power off. And it only sends MQTT updates if the load has changed. (reduce the load on MQTT broker)

https://github.com/Skaronator/ESP8266-Load-Cell

Can I Make an Adruino Write ESP8266 Firmware?

Can you share your homeassistant automated yaml writing?
I am buying esp8266+HX711+Load Cell Occupancy Sensor but I don't know if it is okay to use Arduino.

W5500 vs W5100

Just curious if you saw any technical reason that the Wiznet W5500 chip couldn't be used instead of the W5100 for this application. I'm thinking the 48-LQFP package of the W5500 would be significantly easier to solder than the 80-LQFP of the W5100. I'd have to redesign the board, but that may also reduce the number of caps needed as well.

W5500 on Digikey

Looking over the datasheets, it looks to me like there are pins on the W5500 that closely match the pins being used on the W5100, but admittedly this isn't my area of expertise. Thoughts?

Strange fluctuations in weight

Hi mate,

For some reason I'm getting some pretty huge random fluctuations in weight & can't really work out why, it seems to work pretty well (other than needing to calibrate it so it's actually accurate).

Have a look at the attached image, what does your homeassistant sensor graph look like?

Compile Error

I'm running into an issue on line 34 when I try to compile the code.

exit status 1
no matching function to call to 'HX711::HX711(int, int)'

I'm using bodge's library here: https://github.com/bogde/HX711

Is there a different library I should be using instead?

As an aside, thanks for publishing this project. I've been hoping to do something similar for quite a while and I've learned a ton of new things by working on it.

Load cell cable length

How did you extend the length of the wires of the load cells, the ones I found have about 30cm of very thin cable, is it an issue to solder some more wire on an extend this or even better somehow replace it with a thicker cable thats a bit more protected?

few questions

The image of the final product looks different from the boards you mention as the hardware. I would like to have the input jacks and PoE but where do i purchase that specific board?

If my bed has 6 legs will that interfere? I have a purple mattress and it is very very heavy so there are 6 large cylinders for the legs. Can i use 6 load cell sensors just to have it all balanced properly?