Does Your Home Assistant Know When You Are Sleeping?

It always gives us a sense of wonder when we realize that what would be a simple task for a human child is a big deal for a computer. For example, if you asked someone if you or someone else was in bed, that’s a pretty simple thing to check. For you, that is. For a computer, it requires some sort of sensor. [Lewis] used load cells to tell if someone is in a particular bed or not. He uses Home Assistant and has a great post about how he created and interfaced the sensors. Of course, the sensors really only tell you if something heavy is in the bed. It doesn’t know who it is or even that it isn’t an overstuffed suitcase.

Load cells aren’t exactly high tech. There are several different types that use hydraulic pressure or pneumatics to measure force. However, the most common that we encounter use strain gauges. A strain gauge is a resistor that changes value when it deformed and a load cell usually has several strain gauges wired in a bridge configuration so that small forces create larger output changes.

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Let Your Pi Make A Pie Chart For Your Pie

March 14th is “Pi Day”, for reasons which should be obvious to our more mathematically inclined readers. As you are not reading this post on March 14th, that must mean we’re either fashionably late to Pi Day 2019, or exceptionally early for Pi Day 2020. But in either event, we’ve got a hack for you that celebrates the day using two things we have it on good authority most hackers overindulge in: food and needless complexity.

This project comes from [Mike MacHenry], and it’s just as straightforward as it looks. Put simply, he’s using a load cell connected to the Raspberry Pi to weigh an actual pie and monitor its change over time. As the pie is consumed by hungry hackers, a pie graph (what else?) is rendered on the attached screen to show you how much of the dessert is left.

One might say that this project takes a three dimensional pie and converts it to a two dimensional facsimile, but perhaps that’s over-analyzing it. In reality, it was a fun little hack [Mike] put together just because he thought it would be fun. Which is certainly enough of a motive for us. More practically though, if you’re looking for a good example for how to get a load cell talking to your non-edible Raspberry Pi, you could do worse than checking this out.

We’ve also got to give [Mike] extra credit for including the recipe and procedure for actually baking the apple pie used in the project. While we’re not 100% sure the MIT license [Mike] used is actually valid for foodstuffs, but believe it or not this isn’t the first time we’ve seen Git used in the production of baked goods.

Quartet Of SMD Resistors Used To Sense Z-Axis Height

Here’s a neat trick for your next 3D-printer build or retrofit: a Z-axis sensor using a DIY strain gauge made from SMD resistors. We’re betting it could have plenty of other applications, too.

Conventional load cells, at least the ones you can pick up cheaply from the usual sources or harvest from old kitchen or bathroom scales, are usually way too big to be used on the extruder of a 3D-printer. [IvDm] wanted to build a touch sensor for his Hybercube printer, so he built his own load cell to do it. It consists of four 1000 ohm SMD resistors in the big 2512 device size. He mounted them to an X-shaped PCB and wired them in the classic Wheatstone bridge configuration, with two resistors on one side of the board and two on the other.

The extruder mounts into a hole in the center of the board and floats on it. Through an HX711 load cell driver chip, the bridge senses the slight flex of the board when the extruder bottoms out on the bed, and an ATtiny85 pulls a limit switch input to ground. [IvDm] even did some repeatability testing with this sensor and it turned out to be surprisingly consistent. The first minute or so of the video below shows it in action on the Hypercube.

We found the use of SMD resistors as strain gauges pretty clever here, but there’s plenty to do with off-the-shelf load cells: measuring how much filament is left on a roll, checking the thrust of a model rocket engine, or even figuring out if you’re peeing correctly.

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Arduino-Powered Rocket Test Stand

If you’re into amateur rocketry, you pretty quickly outgrow the dinky little Estes motors that they sell in the toy stores. Many hobbyists move on to building their own homebrew solid rocket motors and experimenting with propellant mixtures, but it’s difficult to know if you’re on the right track unless you have a way to quantify the thrust you’re getting. [ElementalMaker] decided he’d finally hit the point where he needed to put together a low-cost test stand for his motors, and luckily for us decided to document the process and the results.

The heart of the stand is a common load cell (the sort of thing you’d find in a digital scale) coupled with a HX711 amplifier board mounted between two plates, with a small section of vertical PVC pipe attached to the topmost plate to serve as a motor mount. This configuration is capable of measuring up to 10 kilograms with an 80Hz sample rate, which is critically important as these type of rocket motors only burn for a few seconds to begin with. The sensor produces hundreds of data points during the short duration of the burn, which is perfect for graphing the motor’s thrust curve over time.

Given such a small window in which to make measurements, [ElementalMaker] didn’t want to leave anything to chance. So rather than manually igniting the motor and triggering the data collection, the stand’s onboard Arduino does both automatically. Pressing the red button on the stand starts a countdown procedure complete with flashing LED, after which a relay is used to energize a nichrome wire “electronic match” stuck inside the motor.

In the video after the break you can see that [ElementalMaker] initially had some trouble getting the Arduino to fire off the igniter, and eventually tracked the issue down to an overabundance of current that was blowing the nichrome wire too fast. Swapping out the big lead acid battery he was originally using with a simple 9V battery solved the problem, and afterwards his first test burns on the stand were complete successes.

If model rockets are your kind of thing, we’ve got plenty of content here to keep you busy. In the past we’ve covered building your own solid rocket motors as well as the electronic igniters to fire them off, and even a wireless test stand that lets you get a bit farther from the action at T-0.

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Kinetic Sculpture Achieves Balance Through Machine Learning

We all know how important it is to achieve balance in life, or at least so the self-help industry tells us. How exactly to achieve balance is generally left as an exercise to the individual, however, with varying results. But what about our machines? Will there come a day when artificial intelligences and their robotic bodies become so stressed that they too will search for an elusive and ill-defined sense of balance?

We kid, but only a little; who knows what the future field of machine psychology will discover? Until then, this kinetic sculpture that achieves literal balance might hold lessons for human and machine alike. Dubbed In Medio Stat Virtus, or “In the middle stands virtue,” [Astrid Kraniger]’s kinetic sculpture explores how a simple system can find a stable equilibrium with machine learning. The task seems easy: keep a ball centered on a track suspended by two cables. The length of the cables is varied by stepper motors, while the position of the ball is detected by the difference in weight between the two cables using load cells scavenged from luggage scales. The motors raise and lower each side to even out the forces on each, eventually achieving balance.

The twist here is that rather than a simple PID loop or another control algorithm, [Astrid] chose to apply machine learning to the problem using the Q-Behave library. The system detects when the difference between the two weights is decreasing and “rewards” the algorithm so that it learns what is required of it. The result is a system that gently settles into equilibrium. Check out the video below; it’s strangely soothing.

We’ve seen self-balancing systems before, from ball-balancing Stewart platforms to Segway-like two-wheel balancers. One wonders if machine learning could be applied to these systems as well.

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Never Go To The Office Breakroom Again

If you’re tired of having to make small talk with random people in the office break room every time you need a cup of coffee, or simply don’t have the time to get up to pour yourself some more, it would be nice if there was a way you could have your cup filled for you, right at your desk. With this new drink dispenser, you won’t have to get up or even pour your drinks yourself!

We’ve certainly seen plenty of automatic drink makers, but those are more suited to parties and complicated drink mixing. This beverage dispenser is more for the person who knows their tastes and simply wants to save some time. It’s also much simpler, using a peristaltic pump for serving a single liquid from a large bottle into a glass, and using a load cell to know when to stop filling. The peristaltic pump is a little slow though, so it’s best to set the glass back in the dispenser and let it top you off each time.

We’re a big fan of time savers around here, especially when it comes to improving workflow. Of course, the best time saver is a clean, well-organized shop which will help you out whether you’re building a drink dispenser or anything else.

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Assess Your Output With A Cheap DIY Urine Flowmeter

Some things about the human body are trivial to measure. Height, weight, blood pressure, pulse, temperature — these are all easily quantifiable with the simplest of instruments and can provide valuable insights into our state of health. Electrical activity in the heart and the brain can be captured with more complex instruments, too, and all manner of scopes can be inserted into various orifices to obtain actionable information about what’s going on.

But what about, err, going? Urine flow can be an important leading indicator for a host of diseases and conditions, but it generally relies on subjective reports from the patient. Is there a way to objectively measure how well urine is flowing? Of course there is.

The goal for [GreenEyedExplorer]’s simple uroflowmeter is simple: provide a cheap, easy to use instrument that any patient can use to quantify the rate of urine flow while voiding. Now, we know what you’re thinking — isn’t liquid flow usually measured in a closed system with a paddlewheel or something extending into the stream? Wouldn’t such a device for urine flow either be invasive or messy, or both? Rest assured, this technique is simple and tidy. A small load cell is attached to an ESP8266 through an HX711 load cell amp. A small pan on the load cell receives urine while voiding, and the force of the urine striking the pan is assessed by the software. Reports can be printed to share with your doctor, and records are kept to see how flow changes over time.

All kidding aside, this could be an important diagnostic tool, and at 10€ to build, it empowers anyone to take charge of their health. And since [GreenEyedExplorer] is actually a urologist, we’re taking this one seriously.

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