Hack-a-Day

In the world of electronics we have impedance; the combination of all forces which oppose the flow of electric current. Often times we have circuits with different impedances, 50 ohms for RF, or 75 for cable TV. It’s pretty important to use the right coax in these circuits, else you’ll be wondering why your RG-58 antenna feed line doesn’t give you anything good to watch.

It’s pretty important to match impedances when connecting different circuits. Apart from the obvious flaws such as a 50 ohm load blowing up a 300 ohm amplifier, there are subtler things such as signal reflection and destructive interference which might just be enough to break whatever it is your playing with. RF mosfets are not cheap! But how could we match impedances? Well we could always use a transformer, but those are rather expensive and bulky. What if we only have a box of resistors to play with? Well, we could build an attenuator! Most of you probably know what an attenuator is; if not, it’s a de-amplifier. Simply put, it’s a circuit which reduces the strength of a signal. Often these are called ‘pads’ in the RF world, and the pad most often used is the pi pad. By looking at the network’s schematic it becomes rather obvious *why* we call it that.

It looks like a π.

Now our guests want a 50 ohm signal attenuation of 3dBm, or 50%. Let’s pick some toppings for our pi then, shall we?

When Z=50, R1 and R3 equal…

[292.4 ohms].

Now R2 equals…

[17.61 ohms]

Well that was a pain. Luckily, there’s a cheat sheet for this.

So now we have our values, and assuming a 50 ohm load everything should work just fine. But wait! Somebody F*cked up and put a 300 ohm feed line on the end of the pad! Crap. Let’s look at the resistance values of the network now, from A to ground. I’m assuming you should know how to calculate resistances…

…105.7 ohms. That’s near double the 50 ohm input impedance and is going to wreak all hell upon the other circuitry. Sure, it does its job of reducing the signal 3dBm but still.

Now here’s the neat thing. Let’s pick some new resistor values so that we attenuate by 10dBm, or about 90%. According to our cheat sheet we’d need 71.75 ohms of attenuating resistance and 96.25 ohms to ground on either end. What’s the impedance mismatch now?

57.78 ohms, or 7.78 away from 50. That’s a lot better than before, and should actually be usable as an impedance matching network. Sure, you lose 10dBm or about 90% of your signal strength, but that’s nothing that can’t be compensated for by putting a Class-C amplifier in series with the attenuator. Even with an active component it’s still cheaper and smaller than a transformer. What I’m trying to prove here is that pi pads can be used as the poor man’s impedance matcher; as attenuation goes up the impedance mismatch goes down.

What’s nice about resistive pi pads is that they are ultra-wideband; since there are no reactive components this network will always attenuate by 10dBm and always match the impedance by 7.2 ohms. An inductive network such as a transformer might not work at both 200kHz and 200MHz. Actually, it certainly won’t work! Capacitive networks would have the same limitations.

</ LESSON>

Filed under: Ask Hackaday

There’s no question that Apple has their industrial design down pat; comparing a cell phone charger made by Blackberry or Motorola to the tiny 1-inch-cube Apple charger just underscores this fact. [Ken Shirriff] posted a great teardown of the Apple iPhone charger that goes through the hardware that makes this charger so impressive.

Like most cell phone chargers and power supplies these days, Apple’s charger is a switching power supply giving it a much better efficiency than a simple ‘transformer, rectifier, regulator’ linear power supply. Inside the charger, mains power is converted to DC, chopped up by a control IC, fed into a flyback transformer and converted into AC, and finally changed back into DC, and finally filtered and sent out through a USB port.

The quality of the charger is apparent; there’s really no way this small 1-inch cube could be made any smaller. In fact, if it weren’t for the microscopic 0402 SMD components, it’s doubtful this charger could be made at all.

Comparing the $30 iPhone charger of a cheap (and fake) iPhone charger, the budget charger still uses a flyback transformer but there are serious compromises of the safety and quality. The fake charger doesn’t use a power supply controller IC and replaces the four bridge diodes for a single diode to rectify the AC; a very efficient cost-cutting measure, but it does lead to a noisier power supply.

There’s also the issue of safety; on the Apple charger, there is a (relatively) huge physical separation of  ~340 VDC and your phone. With the off-brand charger, these circuits are separated by less than a millimeter – not very safe, and certainly wouldn’t be UL approved.

It’s worth pointing out that [Ken] compares a similar $7 Samsung charger favorably to the $30 Apple charger. Both are functionally identical, but Apple also has their  marketing down pat, to say the least.

Tip ‘o the hat to [George] for sending this in.

EDIT: In case a 1-inch cube wasn’t impressive enough, check out the euro version of the iPhone/iPad charger. It supplies 1A @ 5V, and isn’t much thicker than the USB port itself. Thanks [Andreas] for bringing this to our attention. If anyone wants to do a teardown of the euro version, send it in on the tip line.

Filed under: hardware, teardown

We’ll admit that we haven’t been following Minecraft like we used to; its been a while since we’ve seen something amazing in Minecraft, but [eloraam]‘s 6502 emulator (part of her RedPower Minecraft mod) takes the cake.

The RedPower mod adds a lot of industrial technology to Minecraft. Pumps, solar panels, and pneumatic tubes to move blocks around are the staple of this mod, but with the addition of a fully emulated 6502 computer, Minecraft moves from an anachronistic medieval-themed steampunk aesthetic to a full-on machine age, mainframes everywhere style.

The heart of the 6502 portion of the RedPower mod are three craftable blocks; a CPU, a monitor, and a disk drive. All these blocks are connected together with ribbon cables and can interact with other blocks in the Minecraft universe. The CPU is an emulated 6502, with a few instructions borrowed from the 65816 and the addition of MUL and DIV. It’s possible to program this computer in assembly, but [eloraam] a Forth interpreter with the OS to make programming a little easier.

It’s been almost two years since we first saw the beginnings of a CPU made in Minecraft, but this mod takes everything to the next level. In actuality, this isn’t very different from the game [notch] is currently working on; both feature an emulated 80′s era computer that can do all your in-game bidding. We can’t imagine anything better to get us hooked on Minecraft again, and we’ve got to commend [eloraam] for some seriously awesome work.

After the break is a 23-minute tutorial on the functions of the RedPower CPU, as demonstrated by Minecraft aficionado [direwolf20].

Filed under: classic hacks, toy hacks

In a decision we completely agree with, these industrious young women decided that playing in the rain would only be more fun if it included an interactive light show. They wanted the rain itself to cause LEDs in their umbrella to light up. To achieve this, they put piezo sensors on each of the 8 panels of the umbrella. When that panel gets hit, its LEDs light up. You can see in the video after the break that it was quite effective.

Their next step should be to somehow increase the resolution to be similar to this one, while maintaining interactivity with the rain. How would you sense rain drops with more definition though?

[via Adafruit]

Filed under: led hacks

[Matthew Riese] got frustrated waiting for the future to arrive so he could have his flying car. He decided to take things into his own hands and construct the closest thing he could. This turned out to be a hovercraft. Not only that, but he thought that the most fitting shape for this thing would be a DeLorean.  We can’t say that we disagree with him. Unfortunately, there isn’t a whole lot of information on his build. There is this cool video on his kickstarter page (don’t worry, he got funded back in 2010). To make up for the fact that the build information is sparse, we’ve found you some plans to make your own hovercraft. Just add whatever shape body you want, though we have some suggestions.

[via Makezine]

Filed under: transportation hacks

[radicade] wanted to know what real life portals would look like; not something out of a game, but actual blue and orange portals on his living room wall. Short of building a portal gun, the only option available to [radicade] was simulating a pair of portals with a Kinect and a projector.

One of the more interesting properties of portals is the ability to see through to the other side – you can look through the blue portal and see the world from the orange portal’s vantage point. [radicade] simulated the perspective of a portal using the head-tracking capabilities of a Kinect.

The Kinect grabs the depth map of a room, and calculates what peering through a portal would look like. This virtual scene is projected onto a wall behind the Kinect, creating the illusion of real-life orange and blue portals.

We’ve seen this kind of pseudo-3D, head tracking display before (1, 2), so it’s no surprise the 3D illusion of portals would carry over to a projected 3D display. You can check out [radicade]‘s portal demo video after the break.

Filed under: Kinect hacks

If you’re running your own recording studio, you’re going to need a lot of gear that seems excessively esoteric to the non-musically inclined. A rack full of synth gear looks just like any other cabinet of technology you would find in a server room. Electronic music is, for the most part, very utilitarian looking, but there are a few pieces that add a very nice aesthetic touch to any studio. [Peter] made two great looking pieces of hardware – both reverbs – that significantly add to the decor of his studio. As a bonus, they also sound really good.

[Peter]‘s spring reverb (Dutch, Google translate) works just the same as any other spring reverb; a speaker puts some music into a slightly stretched spring, and this sound is picked up by another transducer at the opposite end. For this build, [Peter] used a Slinky and a piece of PVC pipe left over from a bathroom remodel. Adding a few jacks, pots, and a preamp, [Peter] had a very nice and extremely large spring reverb.

The plate reverb (translation) is also a staple of pro recording studios around the globe. This reverb is somewhat similar to a spring reverb, except the spring is replaced with a tuned metal plate. [Peter] used a cymbal from a drum set for this piece of kit. Two speakers are attached to the back of the cymbal, one feeds a sound into the cymbal, the other speaker picks up those sounds and sends it to the mixing board.

There’s a lot of really cool musical DIY projects over on [Peter]‘s site, along with a few audio demos for each of his DIY projects. We’ve included his reverb demos after the break, feel free to give those a listen.

Thanks go to [geekabit] for sending this one in.

Plate reverb:

Spring reverb:

Filed under: musical hacks

Many of you will remember [Mikey Sklar] from the multitude of times he’s been on hackaday. What you may not have noticed is that he is an ubergeek, living off the grid.

He has Solar PV battery bank, three electric vehicles, a shipping container loaded with battery powered tools and a small army of iRobot Roomba’s for cleaning. Getting the maximum lifetime out of a battery by removing sulfation is essential to keep expenses down.

Keeping expenses down is nearly a full time job when trying to live the homestead lifestyle. Our current culture makes it extremely difficult to survive completely on self made/grown things and bartering. They seem to be doing pretty well though. One way he can reduce his costs while still getting to enjoy some modern gadgets is to get longer life out of his batteries.  He does this by using a capacitive battery charger and desolfator that he designed and affectionately calls “Da Pimp”. He also brings in a little bit of income by selling kits!

 A capacitive charger behaves like a constant current power supply dynamically adjusting the voltage to get over the batteries internal resistance. Plus there is a pulse from the AC/DC conversion. This allows for old batteries to last longer and for dumpster dived to be used as replacements. Capacitive chargers are small, silent and super efficent (up to 60% more so than cheap transformer based chargers).

Of course, [Mikey] is a supporter of sharing information so you can also go to his site and download the schematics,bill of materials, gerber files, and files for the housing,  to build one yourself.

Filed under: tool hacks

[Richard Osgood] is back again with an interesting project. This time he has constructed a color sensor. His initial design was to use three LEDs and a photoresistor. He would shine a red, then green, then blue LED on a surface and record the reflected light with the photoresistor allowing him to determine how much reflected light there was of each color. Unfortunately, he found it to be completely unreliable. An attempt at using a light frequency sensor didn’t work either. What did finally work, was a luminosity sensor shown above.

Finally, his prototype worked. Unfortunately only the red LED gives readings that he considers to be adequate with the blue and green being “not all quite right”.  With this type of circuit, he could build a clone of the magic chameleon lamp.

Filed under: led hacks

There isn’t a hacker out there that isn’t interested at least a little bit in the prospect of building a mission specific rocket to explode someone off the face of the planet… without killing them. We got a tiny taste of what is coming when they let us watch their engine test a few weeks ago. Tomorrow, May 19th, they are going to broadcast a launch live! You can watch it on their site beginning at 1:15 AM pacific. For some additional insight, you can also read the tweets of [Elon Musk], the founder of spaceX during the event.

Take a few minutes and enjoy the video below that discusses the program and some of the engineering obstacles they’ve had to overcome.

[via BoingBoing]

Filed under: news

This glowing LED is proof that the experiments [Nvermeer] is doing with conductive ink are working. We’re filing this one as a chemistry hack because  you need to hit the lab ahead of time in order to get the conductivity necessary for success. He reports that this technique uses a copper powder suspended in an epoxy intended for spray painting. Before mixing the two he etched the powder in ammonium persulfate, then washed it in deionized water which made it a much better conductor.

We gather that the ink was applied with the brush seen in the photo. But since this uses that spray paint friendly solution to host the copper powder we wonder about stenciling with something like masking tape in order to spray the circuit paths onto the substrate.

There’s not too much info up yet, but [Nvermeer] does link to one of our other favorite conductive ink projects.

Filed under: chemistry hacks

[Gigafide] just finished building this flame-powered phone charger. The concept is not new. He grabbed a Peltier cooler and used the temperature differential between a flame and a heat sink to produce electricity used by the charger. If you search around here enough you’ll find plenty of candle-powered devices, and a few hacks that use a Peltier device in a bit more interesting way. But we really like his high-production value video, straightforward explanation of the concepts, and ability to source the components in consumer devices. We don’t think you’ll be disappointed by his video found after the break.

The Peltier device comes out of a USB drink chiller. It is supported by a metal stand made from electrical box covers and threaded rod. Underneath he’s using a gel fuel can used by the food industry, and above he’s got  CPU heat sink and fan. This setup puts out around 1.5V but he’ll need a boost converter to charge a phone with that. A single AA battery charger meant to power your phone in a pinch is perfect for this application.

Filed under: cellphones hacks, misc hacks

The NRF 24L01+ radio transceiver can be found in a lot of wireless project builds. But it’s only meant to work at a range of a few meters. [Achu Wilson] found that he could greatly extend the range by as much as 2 kilometers. All he needed to do was build this high-gain antenna.

He already had an idea of what he wanted to use the RF link for, so a directional antenna is no a problem. He chose a biquad setup with a back reflector, then used NEC2 to model the design and tweak it for the best performance possible. It only took him about two hours to complete the build, and manages a 10 dB gain. Not bad for some wire and a scrap of sheet meta.

This is the same transceiver chip used in the SNES wireless mod. If only we had a really powerful set of binoculars we could play the extremely long-distance game of Mario Kart we’ve always dreamed about.

Filed under: wireless hacks

Over on the RepRap blog, [Rhys] has been experimenting with molten metal to build circuits with the RepRap.

Last June, [Rhys] found a neat alloy made of Tin, Bismuth, and a little bit of Indium that melts at around 130° C, and has just the right properties to be extruded with a standard RepRap setup. The results were encouraging, but the molten metal quickly dissolved the brass and aluminum nozzles [Rhys] was pushing liquid metal through.

The solution to this problem was solved by anodizing the heck out of a RepRap nozzle to make a hard, protective oxide layer. Already [Rhys] has logged hundreds of hours squirting molten metal out of his RepRap with no signs of any damage to the nozzle.

Since [Rhys] figured out how to print in metal, he whipped up an extremely minimal Sanguino board. You can see this RepRapped PCB running a LED blink program after the break. Now to work on the RepRap pick and place…

Filed under: cnc hacks, hardware

[Chris] hasn’t managed to get his hands on a Raspberry Pi yet, so he ordered a BeagleBone and got down to business. He was surprised to find that there isn’t much info out there about using LIDD type displays with the hardware. This protocol is used in many of the 320×240 smart LCD modules on the market, so he hammered out his own drivers and is sharing the details.

The system is designed to run a Linux kernel and [Chris] has chosen to go with Angstrom. His journey started by working out how to compile and patch the kernel himself. From there it was just a matter of getting the pin mapping right, and compiling a driver (it sounds way too simple when put like that).

Apparently he’s pretty close to getting the X desktop environment up and running. No idea what he plans for the hardware, but we’re all for people sharing their work to make it easier for others. Thanks!

Filed under: linux hacks

Ever wonder what’s under the hood with a competitive battle robot like this one? It’s usually a big secret as teams don’t care to give their competition any help. But [AlexHrn] decided not only to give us a peek, but also shows us his step-by-step build process for Phoenix, the 30 pound flipping battle robot.

[Alex] has already seen quite a bit of success with a different robot, but he couldn’t quite beat another competitor whose bot included a flipping arm which threw its competition across the ring. So [Alex] decided to join in on the technique with this build. The arm itself uses air pressure to exert a large force very quickly. Inside, a paintball gun tank powers the pneumatic ram. It looks like this tank is charged up before the competition and only gets about 12 shots before it’s depleted. You can see the power in the quick clip after the break.

For locomotion the unit uses a couple of cordless drill motors. These have a fairly high RPM and work well when powered by batteries.

Filed under: robots hacks

[Chris Suprock] is interested in using technology to improve your accuracy with a firearm. To that end, he’s using an Accelerometer mounted to a gun to gather feedback about each shot.

The hardware setup is pretty simple. We don’t have specific details, but it looks like he’s using a QFN accelerometer chip like you would find in a cellphone. The milled aluminum mounting bracket that holds the board has ‘USB’ printed on it, although the connector is something we don’t really recognize.

In the video after the break [Chris] demonstrates the feedback he can get when the device is mounted on the stock of a Ruger Mini-14. The graph of the data makes it obvious when the trigger was pulled. The most useful part may be the period leading up to that event, as it shows any unnecessary movement prior to the shot. If you’re into sport shooting, this may be one more tool that will help give you the edge on your competitors.

Filed under: weapons hacks

The Sansa Clip+ is a nice little MP3 player and recorder. But it doesn’t offer an input connector, instead relying on the built-in microphone. [Simon Frank] wanted to extend its functionality so he figured out how to add a standard audio jack for analog input.

This is not the first time this has been done, but [Simon] has found a different method of accomplishing the task at hand. The other external input hack we saw cannibalized the internal microphone, rerouting its connections as an external input. But the method seen here keeps that microphone intact. The device includes an FM radio chip which is attached to an ADC on one of the devices other integrated circuits. [Simon] just patched into those signals. Now all he has to do is set up the device to record from the radio and connect his source to the jack which he epoxied to the base of the enclosure.

Filed under: digital audio hacks

It’s no secret that we’re fans of open source, and open hardware. And we have to applaud companies like SparkFun who also keep their customers in the loop about what’s going on with the business end of the company. For instance, they were recently contacted by a Sheriff’s office and asked for customer information and are sharing the story. One of their products had been used in a series of credit card skimmers and the officers wanted to get purchase information to track down the bad guys. SparkFun doesn’t just give out customer data and so was subsequently served with a subpoena.

The thing is, the document asks for all customer orders shipped to Georgia during a six month period. This seemed like it covered way too many orders, since the majority of them didn’t include the part in question. But the officials were willing to work with the company and narrowed the request to just the 20 or so orders that had the item in them.

It’s an interesting read, and we agree with SparkFun’s point about white hats and black hats. Often when posting about projects here we wonder about the potential to use the knowledge for no-good. But restricting the availability of knowledge (or hardware in this case) because of a few bad-actors is a concept we oppose. It’s like being a hacking super hero, with great skill comes great responsibility.

Filed under: news

There’s something special about improvised weapons built for the upcoming zombie apocalypse. Whether it’s a Lousiville Decapitron or a shotgun revolver, we’re always fascinated by homemade weapons. Here’s a few that rolled into the tip line over the last few weeks:

You call that a knife?

[Joerg Sprave], a.k.a. that German guy on YouTube that has fun with slingshots, built a spinning steak knife saw thing. Basically, it’s eight steak knives attached to a wheel and driven with an electric drill. It’s not a terribly complex build, but it does give off a zombie apocalypse/first person shooter melee weapon vibe.

Battery cannon, because why not

Why use potatoes when you can use D-cell batteries? [CasterTown] on YouTube put together a small propane-powered spud gun that can put a battery through a car door. This isn’t the first time we’ve seen batteries used as ammo, but it’s still an extremely powerful build.

Oh man the 60s were cool.

Back in the 60s, safety wasn’t a huge concern. Any 10-year-old could walk into a dime store and buy Jarts – a game consisting of kids throwing sharp spikes at each other. Also, magazines had descriptions of how to build a freaking mortar in a backyard. Able to make a 20-foot grouping at 1900 feet, this would probably merit a visit from a SWAT team today. Needless to say, don’t try this at home.

Don’t do this. Please.

Last but not least is [Rocketlab] and [SadisticTheory]‘s $15 flamethrower. It’s just a gas tank from a 2-stroke engine, a 12 volt battery and a pump. Common sense requires us to mention this build is very, very illegal (apparently it is legal)and extremely unsafe. Don’t replicate this build.

Actually, we take that back. You shouldn’t build any of these weapons because they’re very dangerous. Just think of these as a neat thing to look at. Let other people hurt themselves. You may complain about how unsafe these weapons are in the comments.

Filed under: roundup, weapons hacks