Sending Music Long Distance Using A Laser

This isn’t the first time we’ve seen DIYers sending music over a laser beam but the brothers [Armand] and [Victor] are certainly in contention for sending the music the longest distance, 452 meter/1480 feet from their building, over the tops of a few houses, through a treetop and into a friend’s apartment. The received sound quality is pretty amazing too.

In case you’ve never encountered this before, the light of the laser is modulated with a signal directly from the audio source, making it an analog transmission. The laser is a 250mW diode laser bought from eBay. It’s powered through a 5 volt 7805 voltage regulator fed by a 12V battery. The signal from the sound source enters the circuit through a step-up transformer, isolating it so that no DC from the source enters. The laser’s side of the transformer feeds the base of a transistor. They included a switch so that the current from the regulator can either go through the collector and emitter of the transistor that’s controlled by the sound source, giving a strong modulation, or the current can go directly to the laser while modulation is provided through just the transistor’s base and emitter. The schematic for the circuit is given at the end of their video, which you can see after the break.

They receive the beam in their friend’s apartment using solar cells, which then feed a fairly big amplifier and speakers. From the video you can hear the surprisingly high quality sounds that results. So check it out. It also includes a little Benny Hill humor.

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RC Drag Racing Christmas Tree and Speed Trap

In the drag racing world, a Christmas tree is the post at the start line that sequentially lights up a set of yellow lights followed shortly after by a green light to tell the drivers to go, the lights obviously giving it its seasonal name. Included at the base of the tree are lasers to detect the presence of the cars.

[Mike] not only made his own Christmas tree for his RC cars, but he even made an end-of-track circuit with LED displays telling the cars how long they took. Both start and finish hardware are controlled by Pololu Wixel boards which has TI CC2511F32 microcontrollers with built-in 2.4 GHz radios for wireless communications.

In addition to the LEDs, the Christmas tree has a laser beam using a 650nm red laser diode for each car at the start line that’s aimed at a TEPT5600 phototransistor. If a car crosses its beam before the green light then a red light signals the car’s disqualification.

The end-of-track circuit has 7-segment displays for each car’s time. [Mike] designed the system so that the Christmas tree’s microcontroller tells the end-of-track circuit’s microcontroller when to reset the times, start the times, and clear the times should there be a disqualification. The finish line controller has lasers and phototransistors just like the starting line to stop the timers.

Oh, and did we mention that he also included 1980’s car racing game sounds? To see and hear it all in action check out the video after the break. If the cars seem a little drunk it’s because pushing left or right on the controller turns the wheel’s fully left or right.

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Etching PCBs With A 3D Printer

With the coming of very cheap blue laser diodes, PCB fabrication has become increasingly interesting. Instead of making a photoresist, placing it over a piece of pre-sensitized copper clad board, and putting the whole assemblage under a blacklight, it’s possible to put a photomask on a board with a tiny bit of very blue light. All you need is a CNC machine. A 3D printer can be a very precise CNC machine, and when you combine these two ideas together, you can make printed circuit boards with an Ultimaker.

[Geggo] had the idea of attaching a blue laser diode to his Ultimaker to burn a few traces into presensitized copper board. With a 3D printed adapter, he was able to mount the diode and associated electronics right on the extruder body. With a small ring to tighten up the aperture, [geggo] was able to put a 50 micrometer wide dot of light on a piece of copper. The laser is powered directly from the PWM fan output on the printer controller board, allowing this entire mish-mash of cheap electronics to be controlled via G-code.

A few experiments were necessary to determine the correct speeds and power settings, with the best results being 1000 mm per minute at 40 mA. The finished board looks fantastic, and a few minutes after [geggo] was done etching a board, he started using his 3D printer as a printer. It’s a result that is so good, so easy to accomplish, and requires so little effort it makes us wonder why we don’t see more of this.

A DIY Fourier Transform Spectrometer

Typical spectrometers use prisms or diffraction gratings to spread light over a viewing window or digital sensor as a function of frequency. While both prisms and gratings work very well, there are a couple of downsides to each. Diffraction gratings produce good results for a wide range of wavelengths, but a very small diffraction grating is needed to get high-resolution data. Smaller gratings let much less light through, which limits the size of the grating. Prisms have their own set of issues, such as a limited wavelength range. To get around these issues, [iliasam] built a Fourier transform spectrometer (translated), which operates on the principle of interference to capture high-resolution spectral data.

[iliasam]’s design is built with an assortment of parts including a camera lens, several mirrors, a micrometer, laser diode, and a bunch of mechanical odds and ends. The core of the design is a Michelson interferometer which splits and recombines the beam, forming an interference pattern. One mirror of the interferometer is movable, while the other is fixed. [iliasam]’s design uses a reference laser and photodiode as a baseline for his measurement, which also allows him to measure the position of the moving mirror. He has a second photodiode which measures the interference pattern of the actual sample that’s being tested.

Despite its name, the Fourier transform spectrometer doesn’t directly put out a FFT. Instead, the signal from both the reference and measurement photodiodes is passed into the sound card of a computer. [iliasam] wrote some software that processes the sampled data and, after quite a bit of math, spits out the spectrum. The software isn’t as simple as you might think – it has to measure the reference signal and calculate the velocity of the mirror’s oscillations, count the number of oscillations, frequency-correct the signal, and much more. After doing all this, his software calculates an interferogram, performs an inverse Fourier transform, and the spectrum is finally revealed. Check out [iliasam]’s writeup for all the theory and details behind his design.

Robot Arm Wields Laser, Cares Not For Your Safety

Here at Hackaday we’ve covered a bunch of DIY laser diode projects. And for good reason, they are just cool. We’ve seen people add lasers to their 3D printers, stick one in a milling machine, use a highly modified scanner and even build a simple XY gantry specifically for the task. To say the least there is definitely a wide range of methods for moving around a laser but we’ve never seen anything like what [Sp4rky] sent in to us. He and his friends outfitted an old educational robot arm with a laser.

The robot arm is a 5 axis Armdroid 5100 picked up from eBay for a couple hundred dollars. It didn’t come with a controller but all of the stepper drivers were housed in the base of the arm. After a little tinkering around with the inputs the team was able to get the arm to move by sending serial commands from a PC, through an Arduino Mega which then sends the appropriate signals to the uni-polar stepper drivers. That was the easy part of the build.

The hard part was getting the arm to hold the laser at a consistent angle and height above the table. Inverse Kinematics to the rescue! Since the desired position of the laser, as well as the length of the arm segments is known, mathematical formulas can be derived to determine the necessary arm segment and joint positions while moving the laser around. The process flow starts out with an image in Inkscape, g-code is then generated with this plugin, then sent to the Arduino running a modified version of GRBL that has the inverse kinematic formulas. The Arduino directly controls the stepper drivers and the robotic arm moves. The Arduino also controls 3 constant-current laser drivers made from LM317 regulators. Three laser drivers, why?

Triple Laser Robot[Sp4rky] got his laser diode modules out of surplus medical equipment and, unfortunately, the rated optical wattage was quite low. Since he had 3 diodes, he decided to try to combine the 3 low power beams into one high power beam. This can be done using a prism. A prism splits sunlight into a rainbow of colors because each wavelength(color) of light that passes through the prism is bent a different amount. Since the laser diodes only put out one wavelength of light, the beam bends but does not split or diffuse. A 3D printed bracket points each laser diode at a 3-sided pyramidal prism which sends the combined beam of light straight out the bottom towards the object to be cut or engraved.

This project is cool enough that we would have covered it even if [Sp4rky] wasn’t burning a Hackaday logo. Although it doesn’t hurt for anyone wanting their project to get covered!

Paper Cutter Becomes A Laser Engraver

Small and powerful laser diodes are getting cheaper and cheaper, and there are a few commercial products that give anyone the ability to cut paper and vinyl with a computer-controlled cutting machine. What happens when you combine the two? The beginnings of a hacked together laser engraver.

For this build, [Peter] is using a Silhouette Portrait, a desktop CNC cutting machine that’s usually used for vinyl decals and intricately cut paper crafts. This machine isn’t limited to mere decorative crafts – it’s been used for cutting PCB stencils and other pseudo-industrial tasks.

Because the Silhouette Portrait has an interface that allows just about any CAM software to control it, the only thing [Peter] needed to make for his experiments in laser engraving was a mount to hold the laser diode. Luckily, the laser had a similar form factor to the cutting blades for the machine, and a bit of tape held everything together.

Focusing the laser was done by unscrewing the lens, and with a bit of trial and error, [Peter] was able to make a few marks in the material of his choice. This isn’t a laser cutter, but with a little more work it will make a fantastic laser engraver.

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Using Lasers for Hair Growth

HowToLou is back with a rather interesting build: One hundred laser diodes for hair growth.

Before you guffaw at the idea of lasers regrowing hair lost to male pattern baldness, there’s a surprising amount of FDA documents covering the use of laser diodes and red LEDs for hair growth and an interesting study covering teeth regrowth with lasers. Yes folks, it’s a real thing, but something that will never get a double-blind study for obvious reasons.

[Lou] is building his hat with 100 laser diodes, most of which were sourced from Amazon. These diodes were implanted in a piece of foam flooring, a rather interesting solution that puts dozens of diodes in a flexible module that’s pretty good for making a wearable device.

The lasers are powered by three AA batteries, stuffed into a four-slot battery holder that was modified to accommodate a power switch. [Lou] has been wearing a nine-diode hat for a month now, and if the pictures are to be believed, he is seeing a little bit of hair growth. At the very least, it’s an interesting pseudo-medical build that seems to be producing results.

Hats like these are commercially available for about $700. [Lou] built his for about $60. We’re calling that a win even if it doesn’t end up working to [Lou]’s satisfaction. Just don’t look at the lasers with your remaining eye.

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