Dog bed is also a dog scale

Description

Milli is a Bernese mountain dog. When she was younger, I was easily able to lift her up and she would put her head on my shoulder. Then we could step on the scale together. Then I would step on the scale alone. After some complex math, partial differential equations and complex neural networks, I would know here weight. But nowadays, she is too heavy to lift her up without risking serious injury (yes, hips and stuff). But she was still getting bigger and bigger every day. Unless, she is losing density, that would also mean that she would gain mass. But how much?

Therefore, I created a scale mostly from scrap or unused parts to be placed under the dog bed so that we know her current weight.

Details

This project was not about perfectionism but rather using/recycling materials I had with minimal new orders. Here are the items I had and was able to use:

ESP8266 (I am trying to use existing ones to switch to ESP32 or alternatives for more serious projects)
LCD 16x2 display. It is nice for such robust applications but this bulky display takes space in my drawer
A left over 5V power supply
Left over wood screws and bolts from assembled furniture (they include extra pieces)
A piece of acrylic sheet

I had to 3D print case for the electronics, buy

left-over wood from hardware store (they are much cheaper)
50 kg load sensors (a pack of 3x4 for future projects)

These 4 sensors can be hooked to weigh her up to 200 kg! (overkill but these sensors are quite cheap)

The project should fulfill the following requirements (most urgent to least urgent):

Weigh Milli whenever she lies on the bed and display it on the LCD display, without causing discomfort
Easy to use, somewhat requiring almost no manual interaction
Some network connectivity
IoT function to report the weight to a server (e.g. via MQTT to Home Assistant)

I realized that the bed must be as flat as possible. I was scared that she would be easily scared of any wobble or topple. For instance, if the load cells are not at the edge, then she could step on the edge tilt the bed with her weight. This could (and was) enough to scare her. She gets scared very easily. That would mean that she would lie on her bed anymore 😢. Also, if the "ground" under her soft bed would have large gaps, she would not like this either (and she didn't). Imagine stepping on a soft yoga mat without knowing, if the there are pot holes underneath. It would be uncomfortable. Your feet would have to bend in unpredictable ways. Milli had the same issue.

With these in mind I managed to build something which worked!

Files

load_cell_mount.3mf

ms-3mfdocument - 46.72 kB - 05/25/2025 at 23:37

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load_cell_mount_spacer.3mf

ms-3mfdocument - 12.30 kB - 05/25/2025 at 23:37

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display_mount_hinged_head.3mf

ms-3mfdocument - 96.76 kB - 05/25/2025 at 23:35

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ControllerBoxOneSided.3mf

ms-3mfdocument - 92.93 kB - 05/25/2025 at 23:35

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display_mount_hinged_base.3mf

ms-3mfdocument - 52.13 kB - 05/25/2025 at 23:35

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Build Instructions

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Wood assembly

Well, I basically cut wood sticks with rectangular profile at roughly the same size as the dog bed. I also cut the cheapest wood sheets I found as stripes. Then I screwed them together. See pictures below. But try to find type of wood, which is as stiff as possible. These pieces bend easily under the dog's weight! Worst of all if the wood touches the floor, your readings will be inaccurate. I think that also the bending messes up with the load sensors' "measurements". Also, leave enough space at the center for the controller board (see later steps).

(currently there is an issue with image upload)

3D printing parts and heat inserts

Soldering sockets and connections on a perf board

It was possible to use female pins to insert all necessary components. If you scale is lower/slimmer, then you may not be able to use female pins, perhaps even have to design a PCB.

Discussions

Sebastian wrote 06/02/2025 at 06:32

How is LCD backlight controlled? I hope it's off when the dog is sleeping or going to sleep, because I think that light (reflected from near surfaces) could disturb their sleep. Especially that's blue light, so it controls circadian rhytm the most, at least for humans, so probably for dogs it's similar.

Are you sure? yes | no

Saren Tasciyan wrote 06/02/2025 at 06:39

I needed to add an I2C controller (I will add more details about electronics in the future). I can turn on/off the back light in the software. Actually, it is off most of the time and will be turned on once the weight is sensed to save energy.

Are you sure? yes | no

Dog bed is also a dog scale

Description

Details