sensor

249 Articles

Microwave Motion Detector Notifies Your Smart Phone

February 20, 2025 by 16 Comments

Your garden variety motion detector uses IR, but these days, there are fancier technologies for achieving similar goals. If so desired, you can source yourself a microwave-based presence sensor instead. Indeed, like [N-08 Labs], you might like to whip one up into a basic intrusion detection system.

The idea is simple enough—take a RCWL-0516 microwave presence sensor, and set it up to detect motion and warn you when it happens. It’s a simple part to use—it simply drives a 3.3 volt logic output high if it detects someone or something. It basically just emits a microwave signal and detects a change in phase when someone or something—usually something fleshy—is in front of it. [N-08 Labs] simply hooked one up to an IO pin on an ESP8266, with the microcontroller board set up to communicate wirelessly with a Blynk IoT app, which then in turn fires off a smartphone notification that the sensor picked something up. The whole thing is built inside the shell of an AC adapter that provides power and let it easily hide in plain sight.

A project like this doesn’t just have to be for security purposes. You might even just use it to determine when your pet (or a racoon) is using the cat door, or similar. Indeed, we’ve seen great solutions to that particular problem, too. Video after the break.

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Fully Submerge This Modernized PH Sensor

November 29, 2024 by 18 Comments

There’s a school of thought that says you shouldn’t mess around with a solution that’s already working, but that’s never seemed to stop anyone in this community. When [Skye] was looking at the current state of connected pH meters they realized there was incredible room for improvement.

Called the Nectar Monitor, this pH meter is a more modern take on what is currently offered in this space. Open source and based on the ESP32, it’s accessible to most people with a soldering iron, fits into a standard project box, and includes other modern features like USB and WiFi connectivity. It can even measure conductivity and temperature. But the main improvement here is that unlike other monitors that can only be submerged temporarily, this one is designed to be under water for long time periods thanks to a specially designed probe and electrical isolation.

This design makes it an appealing choice for people with aquariums, hydroponic farms, or any other situation where constant monitoring of pH is extremely important to maintaining a balanced system. We’ve seen some unique takes on hydroponics before especially, including this build that moves the plants instead of the nutrient solution and this fully automated indoor garden.

Fundamentals Of FMCW Radar Help You Understand Your Car’s Point Of View

October 19, 2024 by 3 Comments

Pretty much every modern car has some driver assistance feature, such as lane departure and blind-spot warnings, or adaptive cruise control. They’re all pretty cool, and they all depend on the car knowing where it is in space relative to other vehicles, obstacles, and even pedestrians. And they all have another thing in common: tiny radar sensors sprinkled around the car. But how in the world do they work?

If you’ve pondered that question, perhaps after nearly avoiding rear-ending another car, you’ll want to check out [Marshall Bruner]’s excellent series on the fundamentals of FMCW radar. The linked videos below are the first two installments. The first covers the basic concepts of frequency-modulated continuous wave systems, including the advantages they offer over pulsed radar systems. These advantages make them a great choice for compact sensors for the often chaotic automotive environment, as well as tasks like presence sensing and factory automation. The take-home for us was the steep penalty in terms of average output power on traditional pulsed radar systems thanks to the brief time the radar is transmitting. FMCW radars, which transmit and receive simultaneously, don’t suffer from this problem and can therefore be much more compact.

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Why Use A Sensor When A Pseudo-Sensor Will Do?

August 28, 2024 by 30 Comments

Usually, when you need to sense something in a project, the answers are straightforward. Want to sense air temperature? There’s a sensor for that. Particulate content in the air? There’s a sensor for that, too. Someone sneaking up on you? Get yourself some passive infrared sensors (PIRs) and maybe a smart camera just to be sure.

But sometimes you can be sneaky instead, saving the cost of a sensor by using alternative techniques. Perhaps there’s a way to use the hardware you already have to determine what you need. Maybe you can use statistical methods to calculate the quantity you’re looking for from other measurements.

Today, we’ll examine a great example of a “pseudo-sensor” build in an existing commercial device, and examine how these techniques are often put to good use in industry.

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Programming Tiny Blinkenlight Projects With Light

August 1, 2024 by 18 Comments

[mitxela] has a tiny problem, literally: some of his projects are so small as to defy easy programming. While most of us would probably solve the problem of having no physical space on a board to mount a connector with WiFi or Bluetooth, he took a different path and gave this clever light-based programming interface a go.

Part of the impetus for this approach comes from some of the LED-centric projects [mitxela] has tackled lately, particularly wearables such as his LED matrix earrings or these blinky industrial piercings. Since LEDs can serve as light sensors, albeit imperfect ones, he explored exactly how to make the scheme work.

For initial experiments he wisely chose his larger but still diminutive LED matrix badge, which sports a CH32V003 microcontroller, an 8×8 array of SMD LEDs, and not much else. The video below is a brief summary of the effort, while the link above provides a much more detailed account of the proceedings, which involved a couple of false starts and a lot of prototyping that eventually led to dividing the matrix in two and ganging all the LEDs in each half into separate sensors. This allows [mitxela] to connect each side of the array to the two inputs of an op-amp built into the CH32V003, making a differential sensor that’s less prone to interference from room light. A smartphone app alternately flashes two rectangles on and off with the matrix lying directly on the screen to send data to the badge — at a low bitrate, to be sure, but it’s more than enough to program the badge in a reasonable amount of time.

We find this to be an extremely clever way to leverage what’s already available and make a project even better than it was. Here’s hoping it spurs new and even smaller LED projects in the future.

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You Can Use LEDs As Sensors, Too

July 23, 2024 by 63 Comments

LEDs are a wonderful technology. You put in a little bit of power, and you get out a wonderful amount of light. They’re efficient, cheap, and plentiful. We use them for so much!

What you might not have known is that these humble components have a secret feature, one largely undocumented in the datasheets. You can use an LED as a light source, sure, but did you know you can use one as a sensor?

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RepTrap Keeps Watch Over Our Cold-Blooded Friends

May 7, 2024 by 1 Comment

Wait a second, read that title again. This isn’t a throwback 3D printing project at all. That’s “RepTrap” as in reptile trap, and it’s a pretty clever way to study our cold-blooded friends in their natural habitat.

Now, game cameras — or trail cameras, if you’re less interested in eating what you see — are pretty much reduced to practice. For not that much money you can pick up one of these battery-powered devices, strap it to a tree, and have it automatically snap high-quality pictures of whatever wildlife happens to wander past. But nearly all of the commercially available game cameras have pyroelectric infrared sensors, which trigger on the temperature difference between a warm-blooded animal and the ambient temperature of the background. But what to do when you’re more interested in cold-blooded critters?

Enter [Mirko], who stumbled upon this problem while working with a conservation group in Peru. The group wanted to study snakes, insects, and other ectothermic animals, which are traditionally studied by trapping with pitfalls and other invasive techniques. Unable to rely on PIR, [Mirko] rigged up what amounts to a battery-powered light curtain using a VL53L4CD laser time-of-flight sensor. Mounted above the likely path of an animal, the sensor monitors the height of everything in its field of view. When an animal comes along, cold-blooded or otherwise, RepTrap triggers a remote camera and snaps a picture. Based on the brief video below, it’s pretty sensitive, too.

[Mirko] started out this project using an RP2040 but switched to an ESP32 to take advantage of Bluetooth camera triggering. The need for weatherproofing was also a big driver for the build; [Mirko] is shooting for an IP68 rating, which led to his interesting use of a Hall sensor and external magnet as a power switch.

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