Homebrew Phase Laser Rangefinder

laser

Just when you thought ARM micros couldn’t get any cooler, another project comes along to blow you away. [Ilia] created a phase laser rangefinder (.ru, Google translatitron) using nothing but a laser diode, a pair of magnifying glasses, a few components and an STM32F4 Discovery dev board.

The theory behind this build is using a laser’s phase to determine how far away an object is. By modulating the laser diode’s output at a few hundred Mhz, the reflection from the laser can be compared, giving a fairly reasonable estimate of how far away the target is. This method has a few drawbacks; once the reflection is more than 360 degrees out of phase, the distance ‘loops around’ to being right in front of the detector.

The laser diode used does not have any modulation, of course, but by using an STM32F4 ARM chip, [Ilia]was able to modulate the amplitude of the laser with the help of a driver board hacked out of a 74HC04 chip and a few resistors. Not ideal, but it works.

The receiver for the unit uses a photodiode feeding into the same microcontroller. With an impressive amount of DMA and PLL wizardry (the STM32F4 is really cool, you know), the phase of both the transmission and reflection can be compared, giving a distance measurement.

It’s all an impressive amount of work with a hacked together set of optics, a cheap dev board, and a few components just lying around. For any sort of application in a robot or sensor suite this project would fall apart. As a demonstration of the theory of phase laser rangefinding, though, its top notch.

You can check out a video of [Ilia]‘s rangefinder below. Be sure to full screen it and check out the distance measurement on the LCD. It’s pretty impressive.

Thanks [Володимир] for the link.

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Sump pump alarm sends text message as water rises

sump-pump-monitor

We’ve got some friends who have two sump pumps. One is a backup and sounds an alarm when it is switched on. But this only works as long as they’re home to hear it. [Felix Rusu] came up with a solution what will text him if the sump pump fails. This way he can head home, or call someone to check in on the problem if he’s away.

We saw a pretty complicated monitoring system back in January. This one uses a single ultrasonic rangefinder which we think is much simpler. It’s accurate to about 1cm and is simple to use — it’s very popular with the hobby electronics crowd which helps with price and availability of sample code. We hem and haw about the use of a Raspberry Pi board with the project. On the one hand it’s a cheap way to get the sensor on the network and provides the infrastructure you need to send any number of alerts. On the other hand, it’s a lot of power for this particular application. But we figure it can be extended to monitor other utilities in [Felix's] home, like a sensor to alert him of a leaking water heater. And we think everyone can argue that a monitor like this is well worth the time and effort he spent to develop it.

No-touch music player

no-touch-mp3-player

This little box not only plays tunes, but it lets you control several aspects of playback without touching a thing. [Thomas Clauser] calls it the LighTouch and we like it because it uses inaudible sound to control audible sound.

We think the pair of cylinders sticking up through the top of this project enclosure will be recognized by most readers as the business end of an ultrasonic rangefinder. This is the only control interface which [Thomas] chose to use. Although he didn’t write very extensively about the specific control scheme he implemented, the video embedded in his post shows some of the gestures that cause the Arduino inside to change its behavior. For instance, a swipe of the hand at higher level starts playback, swiping at a lower level pauses it. When adjusting the volume the box responds to how close his hand is to that sensor. With this control in place, the music side of these things is simply handled by a music shield he is using.

Garage parking monitor guides you in every time

THEPARKINGSPOTTER2

The live Adafruit Show and Tell stream from last weekend featured this project put together by [Silent Jeff]. He’s called “Silent” because when it came time to present his project on the show his microphone wasn’t working. As you can see in the video after the break, [PT] and [Ladyada] worked together to explain the project (of which they had no prior knowledge) using a game of charades. This is one of the follow-up images he sent them which details his parking spotter project.

[Ladyada] compliments [Jeff] on the finished look of the device and we agree. Not only does this do a great job of letting a driver know if they have pulled far enough into the garage, but it’s finished appearance ensures it won’t ever look out-of-place. The two silver discs near the lower end of the box are the sensors of an ultrasonic rangefinder. You mount this box so that the sensor is measuring distance between itself and the bumper of your vehicle. As the distance decreases the LEDs change to let you know when to stop. Inside the case you’ll find a voltage regulator and single-chip running the Arduino bootloader. [Jeff] says this is just his second Arduino project and we hope that at this rate we’ll be looking for big things from him in the not too distant future!

This is basically the same idea as cars that use parking assist sensors in the bumper. It’s just attached to the building instead of to the vehicle itself.

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Heat-seeking firebot drowns out the flames

This robot can find and extinguish fires automatically. It is the culmination of an Embedded Design class project from last school year. [Dan] and his classmates developed a turret that holds both a spray nozzle and heat sensor which would be a fantastic building block for a real-life tower defense game.

The jewel of the sensor array is a TPA81 thermopile array. Note the use of the term ‘array’ in the name. This is more like eight temperature sensors aligned with each other. By monitoring them all, the direction from which the most heat is coming can be determined. Once it’s zeroed in on the fire getting water to the right place can be a difficult task. That’s where the other sensors come into play. An accelerometer allows the bot to determine the angle of the spray nozzle (a weed sprayer was used in this case). An ultrasonic range finder and few algorithms let the Arduino which drives it all make sure that the arc of the water lands on the hot spot. This is all shown quite clearly in the clip below the jump.

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Joystick operated security cam will overlook the moat

What good is a moat if nobody is guarding it? We suppose that depends on what beasties lurk beneath the surface of the water, but that’s neither here nor there. The members of LVL1 continue their quest to outdo each other in augmenting the building’s automated features. The latest offering is this security camera which is operated with an analog thumb stick.

These are the people who are building a moat (which the city things is a reflecting pool) in front of their main entrance. Now they will be able to see and sense if anyone is trying to get across the watery hazard. The hack marries an ultrasonic rangefinder and camera module with a pair of servo motors. The brackets for the motors allow a full range of motion, and the signal is translated by an Arduino and Video Experimenter shield to put out a composite video signal. That’s not going to make streaming all that easy, but we’re sure that is just one more hack away.

Cat trainer will keep them off the counters

Our cats are not allowed on the kitchen counters, and [Iron Jungle] has the same rule. But he spotted some foot prints on the hood above his range and the addition of a security camera caught this picture of [Kelso] breaking the rules. Since he’s not always around to make the fur-ball behave he built an electronic cat trainer to do it for him.

The functionality needed isn’t very intricate. You need to monitor when the cat is where it shouldn’t be and then chase it away. For the latter he grabbed an infrared range finder. When the cat passes in front of the sensor it will trigger the second part of the system: a high-pitched buzzer that’s extremely loud. Any microcontroller will have no trouble driving the system. In this case it’s a PICAXE 28X1.

You can see the trainer in action after the break. It definitely works, because just playing the video chased our own sleeping kitty out of the room.

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