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.
Most people wish they were more productive. Some buckle down and leverage some rare facet of their personality to force the work out. Some of them talk with friends. Some go on vision quests. There are lots of methods for lots of types of people. Most hackers, I’ve noticed, look for a datasheet. An engineer’s reference. We want to solve the problem like we solve technical problems.
There were three books that gave me the first hints at how to look objectively at my brain and start to hack on it a little. These were The Power of Habit by Charles Duhigg, Flow By Mihaly Csikszentmihalyi, and Getting Things Done By David Allen.
I sort of wandered into these books in a haphazard path. The first I encountered was The Power of Habit which I found to be a bit of a revelation. It presented the idea of habits as functions in the great computer program that makes up a person. The brain sees that you’re doing a task over and over again and just learns to do it. It keeps optimizing and optimizing this program over time. All a person needs to do is trigger the habit loop and then it will run.
For example: Typing. At first you either take a course or, if your parents left you alone with a computer for hours on end, hunt-and-peck your way to a decent typing speed. It involves a lot of looking down at the keyboard. Eventually you notice that you don’t actually need to look at the keyboard at all. Depending on your stage you may still be “t-h-i-n-k-i-n-g”, mentally placing each letter as you type. However, eventually your brain begins to abstract this away until it has stored, somewhere, a combination of hand movements for every single word or key combination you typically use. It’s only when you have to spell a new word that you fall back on older programs.
Physics gives us the basic tools needed to understand the universe, but turning theory into something useful is how engineers make their living. Pushing on that boundary is the subject of this week’s Fail of the Week, wherein we follow the travails of making a working magnetic flowmeter (YouTube, embedded below).
Theory suggests that measuring fluid flow should be simple. After all, sticking a magnetic paddle wheel into a fluid stream and counting pulses with a reed switch or Hall sensor is pretty straightforward, right? In this case, though, [Grady] of Practical Engineering starts out with a much more complicated flow measurement modality – electromagnetic detection. He does a great job of explaining Faraday’s Law of Induction and how a fluid can be the conductor that moves through a magnetic field and has a measurable current induced in it. The current should be proportional to the velocity of the fluid, so it should be a snap to whip up a homebrew magnetic flowmeter, right? Nope – despite valiant effort, [Grady] was never able to get a usable signal out of the noise in his system.
The theory is sound, his test rig looks workable, and he’s got some pretty decent instrumentation. So where did [Grady] go wrong? Could he clean up the signal with a better instrumentation amp? What would happen if he changed the process fluid to something more conductive, like salt water? By his own admission, electrical engineering is not his strong suit – he’s a civil engineer by trade. Think you can clean up that signal? Let us know in the comments section.
[Malebuffy] bought himself a used boat last year. Fuel isn’t exactly cheap where he lives, so he wanted a way to monitor his fuel consumption. He originally looked into purchasing a Flowscan off the shelf, but they were just too expensive. In the interest of saving money, [Malebuffy] decided to build his own version of the product instead.
To begin, [Malebuffy] knew he would need a way to display the fuel data once it was collected. His boat’s console didn’t have much room though, and cutting holes into his recently purchased boat didn’t sound like the best idea. He decided he could just use his smart phone to display the data instead. With that in mind, [Malebuffy] decided to use Bluetooth to transmit the data from the fuel sensors to his smart phone.
The system uses an older Arduino for the brain. The Arduino gets the fuel consumption readings from a Microstream OF05ZAT fuel flow sensor. The Arduino processes the data and then transmits it to a smart phone via a Bluetooth module. The whole circuit is powered from the boat battery using a DC adapter. The electronics are protected inside of a waterproof case.
[Malebuffy’s] custom Android apps are available for download from his website. He’s also made the Arduino code available in case any one wants to copy his design.
Flow sensors are useful tools for collecting data on the rate of liquid usage, but they need a device to display the data they collect. This three digit frequency meter was designed by [Turbokeu] to do just that, converting a Swissflow SF800 flow sensor’s square wave signal (similar to fan RPM signals) into an numerical expression of liters per minute on a 3 digit LCD. Fan RPM is
[Turbokeu] provides detailed schematics of different configurations for the frequency meter as well as schematics of the layouts of the two PCBs that are used. Even if you don’t have an immediate use for a frequency meter, his clean and readable schematics are worth a look in their own right. The display is installed on front of a tower case along side a CPU speed display.