Dog Weight Scale Part 8: Electronics, version 2

It’s a good time to recap: This project is a scale that will sit underneath my dog Pippa’s bed, so that I can measure her weight automatically, at night while she sleeps.  The project-in-progress is Open Source, at my CurieBLEWeightMonitor Github repository.  I occasionally tweet about it (among other things) as @bneedhamia.

In my previous post I covered how to choose matching resistors for the Load Sensor to convert the Load Sensor into a Load Cell that can be wired into Sparkfun’s Load Cell Amplifier.  In this post, I nearly finish building the breadboarded circuit and start transferring it to a soldered protoboard.

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Dog Weight Scale Part 7: Choosing Matching Resistors

In my previous post, I worked through the calculations of weight and center of gravity when using four Load Cell Amplifiers instead of one.  In this post, I build the circuit for the first of the four Load Sensor / Load Cell Amplifier combinations I’ll be using.

The Sparkfun Load Cell Amplifier is designed to connect a Load Cell to an Arduino.  A Load Cell contains a full (4 resistor) Wheatstone Bridge, but a Load Sensor contains only half of a Wheatstone bridge.  To connect a Load Sensor to a Load Cell Amplifier, I need to add two resistors: R3 and R4 in the following diagram.  The dotted box represents the Load Sensor. The triangle in the middle of the diagram represents the Load Cell Amplifier.  As the weight on the Load Sensor increases, R1 decreases, which causes the voltage V1 to increase, causing the digitized amplifier output to increase.

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Dog Weight Scale part 6: Calculating the Dog’s Weight and Position

In my previous post I found the center of gravity of the top plywood circle of the Dog Bed Weight Scale. This post goes through the math of calculating the weight W on the scale and the position {X, Y} of that weight’s center of gravity.  That is, how much does our dog PIppa weigh when resting on the bed, and what is her position on the bed?

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Dog Weight Scale Part 5: Center of Gravity and a mounting Fail

In my previous post I described how to calibrate a load sensor. This post shows how to measure center of gravity, and shows a failed attempt to mount the load sensors to the scale.

Now that I’m using 4 load cell amplifiers rather than 1, I can calibrate each load sensor separately.  This in turn will let the Arduino calculate Pippa’s real weight accurately regardless of what part of her bed/scale she’s lying on.

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Dog Weight Scale Part 4: Calibration and its difficulties

Calibrating the scale using exercise weights
Calibrating the scale using exercise weights

In my previous post I finished assembling the Dog Bed Weight Scale, at least enough to allow testing it. In this post, I relate how I calibrated and tested it.

Using the Bogde HX711 Load Cell Amplifier library and examples, and the Sparkfun HX711 Example Arduino Sketches, I quickly wrote a little Sketch to output the raw value from the scale (SCALE = 1.0 and OFFSET = 0L).  The library made talking to the HX711 trivial.

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Dog Weight Scale part 3: the woodworking and assembly

In my previous post I described the electronics of the Dog Bed Weight Scale. In this post, I’m doing the final woodworking and assembly – at least enough assembly to test the thing.

First I needed to design some sort of support for the load sensors.  Because of the design of the sensor – a “T” bar surrounded by a “C” shaped bar – I needed to make blocks that were 1) tall enough to keep the top piece of plywood from resting on or crushing the electronics and 2) cut out to allow the “T bar to bend below the “C” shaped part as weight was added.  You can find plenty of videos of people trying to use load sensors by mounting them on a flat surface; that won’t work.

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5 things Project Runway taught me about creative work

Red and white warning sign at Beaumaris Castle

I started watching Project Runway years ago as a guilty pleasure.  My wife had watched it for a while and slowly drew me in because, unlike other reality/survivor shows, it minimized the People Behaving Badly aspect of competition.

As I watched more and more – the show has run more than 17 seasons – I realized that Project Runway is really a show about how to do creative work and live the creative life.  It even won a Peabody Award for using the Reality genre to inform and enlighten.

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Dog Weight Scale, part 2: the electronics

As I said in the previous post, I’m using 4 Sparkfun load sensors, a Load Sensor Combinator board, a Load Cell Amplifier board, and an Arduino 101 to build a scale I can put under our dog’s bed, to passively weigh her whenever she’s in bed.

In the previous post, I cut the base for the scale from a sheet of plywood.  In this post, I’m assembling the circuit.

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Dog Weight Scale, part 1: cutting the circular base

I want to learn how to use Load Sensors to continuously weigh stuff with an Arduino, so I thought it would be fun to continuously weigh our dog, Pippa, while she sleeps in her bed each night.  The project is a little like Nate Seidle’s Beehive scale, but simpler.

The idea is to turn Pippa’s bed into a scale. Pippa’s in fine shape right now, but it’s always good to keep an eye on your dog’s weight, and a custom-made scale is a great way to do it.

Continue reading Dog Weight Scale, part 1: cutting the circular base