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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Hackaday Dictionary: Transformers

Funny stuff, electricity. It’s all about the volts and the amps, and controlling these two factors. Most of the time, the electricity coming into your device is at a higher voltage than you need, so you have to convert it down to something more usable. The easiest way to do this is with a transformer.

The transformer in your power supply takes a high voltage from the mains and converts it down into a lower voltage to power your gadgets. You’ll find one in all power supplies, from the miniature USB version that powers your cell phone to the big ones hanging on a telephone pole that drive your home’s mains electricity. Although these transformers are different sizes, they share the same fundamental design.

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Powering A Lot Of Nixie Tubes

[Limpkin] has an idea for a project that uses a lot of IN-9 Nixie tubes. Where a Nixie tube clock would only use four or six tubes, [Limpkin] is looking at fifty IN-9 bar graph Nixie tubes. These tubes only light up above 100 Volts and draw about half an amp. That’s 64 Watts, according to the math on the project page, so how does [Limpkin] plan on powering these tubes? With a big high voltage power supply.

The power supply [Limpkin] designed is more or less what you would expect to find in any power supply. There’s a transformer, a bunch of caps, and a rectifier. Going with a standard laminated core transformer would mean this power supply would be huge and heavy, but once again eBay comes to the rescue with a small, 150 Watt toroidal transformer. The largest output on the transformer was two 24 V outputs. Combining those outputs gets [Limpkin] to 48V AC, or 68V peak to peak. A full wave voltage doubler with two caps and two diodes gives [Limpkin] the 136V DC that will power the tubes.

Combine the high voltage circuit with a 9V AC tap, a small bridge rectifier, and a few more caps, and [Limpkin] had a supply that would power the tubes and the rest of the electronics in his multiple Nixie tube project. A few passes with a CNC mill gave the power supply a nice case topped off with a foreboding toroidal transformer ready to power a beautiful neon project.

A Field Guide to the North American Utility Pole

We live under the umbrella of an intricate and fascinating web of infrastructure that enables every aspect of modern technology. But how often do we really look at it? I’ve been intrigued by utility poles for years, and I’ve picked up a thing or two that I’d like to share. Bear in mind these are just my observations from the ground in my area; I’m sure utility professionals will have better information, and regional practices will no doubt lead to very different equipment arrangements. But here’s a little of what I’ve picked up over my years as a pole geek.

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Spherical Robot Rolls then Walks into Action

Droideka [Source: Wookieepedia]
If ever any sci-fi robot form-factor made more sense than the Droideka of the Star Wars franchise, we’re not sure what it could be. Able to transform from a spheroid that rolls quickly onto the battlefield into a blaster-bristling tripodal walker, the Hollywood battle droid showed a lot of imagination and resulted in a remarkably feasible design. And now that basic design is demonstrated in a spherical quadrupedal robot that can transform from rolling to walking.

Intended as a proof of concept of a hybrid rolling-walking locomotion system, the QRoSS robot from Japan’s Chiba Institute of Technology is capable of some pretty amazing things already. Surrounded by a wire roll cage that’s independent of the robot’s legs, QRoSS is able to roll into position, unfurl its legs, and walk where it needs to go. Four independent legs make it sure-footed over rough terrain, with obvious applications in such fields as urban search and rescue; a hardened version could be tossed into a collapsed building or other dangerous environment and walk around to provide intelligence or render aid. The robot’s self-righting feature would be especially handy for that use case, and as you can see in the video below, it has a powered rolling mode that’s six times faster than its walking speed.

For a similar spherical transforming robot, be sure to check out the MorpHex robot with its hexapod design.

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Self Built Power Meter Uses Dual Sense Transformers

[Renaud] built a AC power meter from scratch. While commercial power meters like the Kill A Watt are available [Renaud’s] build gives an interesting insight into the methods used.

currentAt the heart of [Renaud’s] design lie two sense transformers. The first is a typical voltage stepdown transformer. This brings the AC line voltage down to +/- 10V, which is more amenable to digital sampling. The second is a current sense transformer. In current transformers the primary is typically a single wire (the AC line in this case) passing through the middle of a ring (see the picture to the right from wikipedia). The secondary is wrapped round the ring. When the secondary coil is shorted a current in the primary wire/coil induces a current in the secondary coil.

In practice, the voltage drop across a low value resistor is used to detect the current in the secondary. Clamp meters use this principle to make non-contact current measurements. Other power meters often use hall effect sensors for current measurements. It will be interesting to see how these methods compare when [Renaud] benchmarks this build.

[Renaud] takes the voltage and current readings from these transformers and samples them with a PIC in order to calculate power. As the AC voltage is periodic [Renaud] uses a method similar to Equivalent Time Sampling (ETS) to combine waveforms from multiple cycles and increase the effective sample rate.

Great stuff [Renaud]!

Solar-Cell Laser Communication System

Forget the soup cans connected by a piece of string. There’s now a way to communicate wirelessly that doesn’t rely on a physical connection… or radio. It’s a communications platform that uses lasers to send data, and it’s done in a way that virtually anyone could build.

This method for sending information isn’t exactly new, but this project is one of the best we’ve seen that makes it doable for the average tinkerer. A standard microphone and audio amplifier are used to send the signals to the transmitter, which is just a typical garden-variety laser that anyone could find for a few dollars. A few LEDs prevent the laser from receiving too much power, and a solar cell at the receiving end decodes the message and outputs it through another amplifier and a speaker.

Of course you will need line-of-sight to get this communications system up and running, but as long as you have that taken care of the sky’s the limit. You can find incredibly powerful lasers lying around if you want to try to increase the communication distance, and there are surprisingly few restrictions on purchasing others that are 1W or higher. You could easily increase the range, but be careful not to set your receiving station (or any animals, plants, buildings, etc) on fire!

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