sensor

246 Articles

Going Digital: Upgrading A Boat’s Analog Gauge

August 1, 2017 by 16 Comments

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

July 30, 2017 by 13 Comments

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

July 29, 2017 by 6 Comments

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

July 26, 2017 by 23 Comments

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

July 19, 2017 by 114 Comments

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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Improving The Accuracy Of Gas Sensors

July 13, 2017 by 12 Comments

If you need a sensor to detect gasses of some sort, you’ll probably be looking at the MQ series of gas sensors. These small metal cylinders contain a heater and some electrochemical sensor. Wire the heater up to a voltage, and connect one end of the resistor to an ADC, and you have a sensor for alcohol vapors, hydrogen sulfide, carbon monoxide, or ozone, depending on which model of sensor you’ve picked up.

These are simple analog devices, and as you would expect they’re sensitive to both temperature and humidity. [Davide Gironi] wanted a more accurate gas sensor, so he’s diving into a bit of overengineering and correlating the output of these sensors against temperature and humidity.

There’s a difference between accuracy and precision, and if you want to calibrate gas sensors, you’ll need to calibrate them against something. Instead of digging out a gas sensor of known precision, [Davide] took the easy way out: he graphed the curves on the datasheets for these sensors. It’s brilliant in its simplicity.

These numbers were thrown into R, and with a bit of work, [Davide] had a look up table of various concentrations of gasses plotted against certain resistances. In testing these sensors, he found a higher correlation between humidity and temperature and gas concentrations, which one would expect.

The files for these sensors are available on [Davide]’s website, and he included a neat little video showing everyone what went into these calculations. You can check that out below.

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Hacking Touch Screens To Count Pulses

July 9, 2017 by 5 Comments

Heart rate sensors available for DIY use employ photoplethysmography which illuminates the skin and measures changes in light absorption. These sensors are cheap, however, the circuitry required to interface them to other devices is not. [Petteri Hyvärinen] is successfully investigating the use of capacitive touchscreens for heart rate sensing among other applications.

The capacitive sensor layer on modern-day devices has a grid of elements to detect touch. Typically there is an interfacing IC that translates the detected touches into filtered digital numbers that can be used by higher level applications. [optisimon] first figured out a way to obtain the raw data from a touch screen. [Petteri Hyvärinen] takes the next step by using a Python script to detect time variations in the data obtained. The refresh rate of the FT5x06 interface is adequate and the data is sent via an Arduino in 35-second chunks to the PC over a UART. The variations in the signal are very small, however, by averaging and then using the autocorrelation function, the signal was positively identified as a pulse.

A number of applications could benefit from this technique if the result can be replicated on other devices. Older devices could possibly be recycled to become low-cost medical equipment at a fraction of the cost. There is also the IoT side of things where the heart-rate response to media such as news, social media and videos could be used to classify content.

Check out our take on the original hack for capacitive touch imaging as well as using a piezoelectric sensor for the same application.