Hackaday Prize Entry: MappyDot, a Micro Smart LiDAR Sensor

[Blecky]’s entry to the Hackaday Prize is MappyDot, a tiny board less than a square inch in size that holds a VL53L0X time-of-flight distance sensor and can measure distances of up to 2 meters.

MappyDot is more than just a breakout board; the ATMega328PB microcontroller on each PCB provides filtering, an easy to use  I2C interface, and automatically handles up to 112 boards connected in a bus. The idea is that one or a few MappyDots can be used by themselves, but managing a large number is just as easy. By dotting a device with multiple MappyDots pointing in different directions, a device could combine the readings to gain a LiDAR-like understanding of its physical environment. Its big numbers of MappyDots [Blecky] is going for, too: he just received a few panels of bare PCBs that he’ll soon be laboriously populating. The good news is, there aren’t that many components on each board.

It’s great to see open sourced projects and tools in which it is clear some thought has gone into making them flexible and easy to use. This means they are easier to incorporate into other work and helps make them a great contestant for the Hackaday Prize.

Garage Distance Sensor Kicks Tennis Ball To Curb

Those with small garages might be familiar with the method of hanging a tennis ball from a ceiling to make sure they don’t hit the back wall with their car. If the car isn’t in the garage, though, the tennis ball dangling from a string tends to get in the way. To alleviate this problem, [asaucet] created a distance sensor that can tell him when his car is the perfect distance from the garage wall.

At the heart of the distance sensor is an HC-SR04 ultrasonic rangefinder and a PIC16F88 microcontroller. [asaucet] uses a set of four LEDs to alert the driver how close they are to the garage wall. [asaucet] also goes into great detail about how to use an LCD with this microcontroller for setting up the project, and the amount of detail should be enough to get anyone started on a similar project.

While this isn’t a new idea, the details that [asaucet] goes into in setting up the microcontroller, using the distance sensor, and using an LCD are definitely worth looking into. Even without this exact application in mind, you’re sure to find some helpful information on the project page.

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Going Digital: Upgrading A Boat’s Analog Gauge

The odds are that many of you do not own a boat that you get to tinker around with. [Mavromatic] recently acquired one that had — much to his consternation — analog gauges. So in order to get his ship ship-shape, he built himself a custom digital gauge to monitor his vessel’s data.

Restricted to the two-inch hole in his boat’s helm, trawling the web for displays turned up a 1.38-inch LCD display from 4D Systems. Given the confined space, a Teensy 3.2 proved to be trim enough to fit inside the confined space alongside a custom circuit board — the latter of which includes some backup circuits if [mavromatic] ever wanted to revert to an analog gauge.

Two days of acclimatization to the display’s IDE and he had enough code to produce a functional display right when the parts arrived.

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Autonomous Boat Sails the High Seas

As the human population continues to rise and the amount of industry increases, almost no part of the globe feels the burdens of this activity more than the oceans. Whether it’s temperature change, oxygen or carbon dioxide content, or other characteristics, the study of the oceans will continue to be an ongoing scientific endeavor. The one main issue, though, is just how big the oceans really are. To study them in-depth will require robots, and for that reason [Mike] has created an autonomous boat.

This boat is designed to be 3D printed in sections, making it easily achievable for anyone with access to a normal-sized printer. The boat uses the uses the APM autopilot system and Rover firmware making it completely autonomous. Waypoints can be programmed in, and the boat will putter along to its next destination and perform whatever tasks it has been instructed. The computer is based on an ESP module, and the vessel has a generously sized payload bay.

While the size of the boat probably limits its ability to cross the Pacific anytime soon, it’s a good platform for other bodies of water and potentially a building block for larger ocean-worthy ships that might have an amateur community behind them in the future. In fact, non-powered vessels that sail the high seas are already a reality.

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A Flexible Sensor That Moves With You

If you have a project in mind that requires some sort of gesture input or precise movements, it might become a nettlesome problem to tackle. Fear this obstacle no longer: a team from the Wyss Institute for Biologically Inspired Engineering at Harvard have designed a novel way to make wearable sensors that can stretch and contort with the body’s natural movements.

The way they work is ingenious. Layers of silicone are sandwiched between two lengths of silver-plated conductive fabric forming — by some approximation — a capacitance sensor. While the total surface area doesn’t change when the sensor is stretched — how capacitance sensors normally work — it does bring the two layers of fabric closer together, changing the capacitance of the band in a proportional and measurable way, with the silicone pulling the sensor back into its original shape as tension relaxes. Wires can be attached to each end of the band with adhesive and a square of thermal film, making an ideal sensor to detect the subtlest of muscle movements.

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Measuring Air Flow with Ultrasonic Sensors

Measuring air flow in an HVAC duct can be a tricky business. Paddle wheel and turbine flow meters introduce not only resistance but maintenance issue due to accumulated dust and debris. Being able to measure ducted airflow cheaply and non-intrusively, like with this ultrasonic flow meter, could be a big deal for DIY projects and the trades in general.

The principle behind the sensor [ItMightBeWorse] is working on is nothing new. He discovered a paper from 2015 that describes the method that measures the change in time-of-flight of an ultrasonic pulse across a moving stream of air in a duct. It’s another one of those “Why didn’t I think of that?” things that makes perfect sense in theory, but takes some engineering to turn into a functional sensor. [ItMightBeWorse] is using readily available HC-SR04 sensor boards and has already done a proof-of-concept build. He’s getting real numbers back and getting close to a sensor that will go into an HVAC automation project. The video below shows his progress to date and hints at a follow-up video with more results soon.

Here’s wishing [ItMightBeWorse] the best of luck with his build. But if things go sideways, he might look to our post-mortem of a failed magnetic flow meter for inspiration.

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The 4-20 mA Current Loop

The I/O capabilities built into most microcontrollers make it easy to measure the analog world. Say you want to build a data logger for temperature. All you need to do is get some kind of sensor that has a linear voltage output that represents the temperature range you need to monitor — zero to five volts representing 0° to 100°C, perhaps. Hook the sensor up to and analog input, whip up a little code, and you’re done. Easy stuff.

Now put a twist on it: you need to mount the sensor far from the microcontroller. The longer your wires, the bigger the voltage drop will be, until eventually your five-volt swing representing a 100° range is more like a one-volt swing. Plus your long sensor leads will act like a nice antenna to pick up all kinds of noise that’ll make digging a usable voltage signal off the line all the harder.

Luckily, industrial process engineers figured out how to deal with these problems a long time ago by using current loops for sensing and control. The most common standard is the 4-mA-to-20-mA current loop, and here we’ll take a look at how it came to be, how it works, and how you can leverage this basic process control technique for your microcontroller projects.

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