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        

When [GG] was 12 years old, he was introduced to BugBooks, the wonderful ‘introduction to digital design’ books from the early 1970s. It has always been a dream of [GG] to build the TTL computer featured in the BugBooks, and now that he has the necessary time and money available to him, the Apollo181 has become a reality.

[GG]‘s computer is built around a 74181 ALU, an exceptionally old-school chip that provides the core of a computer in a neat 24-pin chip. With a 256-byte RAM and a few additional logic chips, [GG]‘s computer is anexceptional piece of engineering able to perform 625,000 instructions per second when clocked at 2.5 MHz.

This isn’t [GG]‘s first homebrew computer build; last year we saw his incredible Z80 minicomputer. Now we can’t wait to see what’s on tap for next year. After the break, you can check out [GG] loading in operands and operators into his computer and letting the Apollo181 churn away on its program.

Popout
Filed under: classic hacks         

When its time to select a new phone we start looking for different brands with different features. And it is truly hard to find what you need or what you want. We don’t argue with the fact that for everyday use it is best to select a manufactured phone which is small sized, tested and reliable. But for sake of curiosity why not to build another one to play with.

The following project is a cell phone prototype developed by check guy Adam. It is based on Atmega128 microcontroller featuring 128kB of flash and 4kB of SRAM. Barebones cellphone is is equipped with nice big LCD touch screen driven with 16-bit bus. GSM SIM100S module made it possible to make calls and send SMS. Phone is powered with 1000mAh LiPo battery. Probably more fun in it is a software. It seems that Adam spent some time on it to make it convenient and easy to use. It has nice user interface controlled with touch screen. Settings are accessible using icon based menu. You can store contacts so as you would do in a regular phone.

The 6502 is an 8-bit microprocessor introduced in 1975 for $25.  At the time, the 6502′s competition, the Intel 8080 and the Motorola 6800 were each selling for $179.  The processor was an immediate success.  It found its way into many iconic consumer electronics, such as the Apple I, Apple II, Atari 2600, Commodore 64, and a version of the chip is the brains in the original Nintendo Entertainment System (NES).

Thankfully, the 6502 is still being produced today, and there is a large group of home computer makers who are ready to share their knowledge with you.  Over at 6502.org, user Garth Wilson put together a primer for making your own 6502 computer.  Garth will walk you through sourcing components, construction, programing, and debugging your own 6502 computer.

Garth’s goal with this primer is to “give a good grasp of computer design basics, so that with good construction, you can make a computer that works on first try, with no hardware troubleshooting.”

Check out the guide here, and then head over to 6502.org and check out the many other projects made with the 6502.

How to use Geiger Bot with the MightyOhm Geiger Counter. Jeff writes -

Geiger Bot is an iOS application that allows you use your iPhone or iPad as a sophisticated display for an ordinary Geiger counter. It works with most Geiger counters that make an audible “click” for each event or count that is detected.

Here’s how to get your MightyOhm Geiger Counter working with Geiger Bot. These instructions were tested with an iPhone 4, but should work with other iOS devices (iPads and other versions of the iPhone).

Geiger Counter Kit – Radiation Sensor. Detect particles and/or make a cool random number generator with this handsome Geiger counter kit. This easy-to-make pack of parts turns a simple Geiger-Muller tube (included) into a portable blink, beeping radiation detector. You can also connect an FTDI friend to the header, to get serial output for datalogging on your computer.

We put this kit together in a couple of hours and hand lots of fun bringing it around and listening for ticking sounds near our smoke detectors, bananas, countertops, Brazil nuts, chunks of Uranium, etc. It includes all components (PCB, tube, & parts) but you will need basic soldering tools and two AAA batteries to complete it.

Get one!

NASA recently showed flashes of its old bravado by announcing plans for a lunar waypoint near the far side of the moon. Cold, hard reality brought the agency back to Earth this week, however, as it just announced a scaling back of its Mars exploration program. Thanks to funding cuts, NASA is scuttling its “ambitious” (i.e. expensive) flagship missions to the Red Planet for the near term. That means withdrawing from the ExoMarsmissions led by Europe and putting on hold plans to collect samples — though the Mars Science Laboratory is still a go. NASA is slated to receive $1.2 billion for its planetary science program, down 20 percent from what it gets now, with more cuts likely on the way. In the meantime, the agency is still hopeful about sending humans — or perhaps a wascally wabbit — to Mars by the 2030s.

NASA scales back Mars exploration, Marvin the Martian thinks it’s just lovely originally appeared on Engadgeton Wed, 15 Feb 2012 13:32:00 EDT. Please see our terms for use of feeds.

Permalink   |  SPACE.com

The machines that made the Jet Age

By Tim Heffernan- Share this article

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This is a companion piece to Iron Giant: One of America’s great machines comes back to life, a feature by Tim published in The Atlantic

Germany, June 1945. The Nazi regime has been toppled; the war in Europe is over. But the Allied victory is largely the result of sheer overwhelming force, not technological superiority — and the victors know it. Most glaringly, while the Allies still rely on propeller-driven aircraft, the Luftwaffe has put three jets successfully into service.

A Messerschmitt Me 262, the first military jet to enter service. Brought to you by Krupp’s magnesium forging division. Photo: USAF

A Boeing B-29, the first bomber with pressurized crew compartments. Brought to you by Rosie the Riveter. Source: USAF

The reasons for German air superiority were several, of course, but a key one was their mastery of light-metal forging. While the Allies were still bolting together their planes out of steel plate, a slow, labor-intensive process ripe for error and unsuited to design optimization, the Germans were stamping and squeezing out complex structural elements from magnesium and aluminum alloys.

Not surprisingly, after Germany surrendered, both the U.S. and the USSR sought to take control of its forging facilities.

The Soviets got the good stuff.

In so doing they got a head start on the Cold War race for supersonic air superiority. Unwittingly, they also set in motion a larger, and largely forgotten, industrial revolution that shaped the second half of the 20th century and will shape the 21st. This is the story of the birth of the Jet Age — but it’s anchored firmly to the ground.

Photo: Library of Congress

The magnificent machine pictured above is a closed-die forging press, one of the biggest in the world. (For reference, check out the men standing at its foot, down there on the left.) It and nine other huge forges were built in 1950s by the U.S. government, in a long-forgotten endeavor called the Heavy Press Program. I wrote about the press and the program in the March Atlantic, and Maggie kindly invited me to write a bit more here, because — well, first of all, because just look at that thing. It stands nine stories tall (four of them are hidden under the floor), weighs 16 million pounds, exerts 50,000 tons of compressive force, and, like Vulcan’s own waffle iron, squeezes ingots of solid metal between its jaws until they flow like batter.

Here’s another picture for scale:

Each casting was loaded individually onto a specially built train car and carried from Pittsburgh to Cleveland. Photo: USAF Air Force Material Command

Those are just four of the 14 steel castings that make up the Fifty, as the press is known, and they aren’t even the biggest ones. Those would be the twin 250-ton upper stationary crossheads, shown in Figures 5 and 6 of this document— also a good source for more technical details about the press.

And here’s a before-and-after of the Fifty’s handiwork:

Press-forging minimizes waste metal compared to machining, and by realigning the metal’s internal crystalline structure along natural lines of stress, results in much stronger parts than casting would produce. Photos: Library of Congress

That’s a piece of titanium about 15 feet wide and a foot thick, in its raw state and after being forged in a single stroke between the Fifty’s hardened steel dies under 100 million pounds of pressure.

Though they were built nearly 60 years ago, the ten machines of the Heavy Press Program — four forging presses, the waffle irons, and six extrusion presses, basically giant caulking guns except the “caulk” is solid metal — are still among the most powerful ever made. Even more impressively, at least eight of the ten are still in use.

Extruded aluminum parts (not parts from Heavy Press Program machines). Photo courtesy Dalcio Metal

So, what do they do? Well, in strict terms, they make heavy components for aircraft, spacecraft, and power-generation facilities. That chunk of titanium, for example, became one of the bulkheads that anchor the engines, fuselage, and wings of an F-15. More familiarly, every time you fly on a Boeing or Airbus, you’re relying on parts made by the Heavy Press Program machines to keep you aloft—things like the wing spars, which connect the wings to the plane’s chassis.

But in broader terms, what the machines do is make the Jet Age possible. On a plane, a pound of weight saved is a pound of thrust gained—or a pound of lift, or a pound of cargo. A lighter plane also puts less stress on its chassis when it goes through maneuvers. Supersonic military jets are optimized for speed and strength. Subsonic passenger and cargo jets are optimized for fuel efficiency and load capacity. Without the ultra-strong, ultra-light components that only forging can produce, they’d all be pushing much smaller envelopes.

Dawn of the Military-Industrial Complex

Back to 1945 for moment. The Soviet acquisition of Germany’s biggest forges made it all but inevitable that the U.S. would build its own heavy presses—but it’s important to note that it did not make the Heavy Press Program inevitable. Private industry could have built its own machines. The government could have built them, too, and indeed early plans called for the military to construct a “pilot plant” and dole out chunks of time to the air industry to experiment on government-run machines. The idea that it was in the public’s interest to pay for the machines but cede their control to industry was a controversial one, and many leaders in Congress strongly resisted it as a dangerous blurring of private and civic concerns.

On the other hand, with millions of WWII servicemen and women being demobilized, mass unemployment was a threat, and shoring up the aerospace industry was an attractive way to stave it off and harness wartime technology to the peacetime economy. Cold War policy also encouraged massive defense spending, but (as ever) a secondary war was being waged by the military branches for funding, and heavy forging wasn’t of much use to the Army or Navy. It was a complex situation, and one that could have been resolved in several ways. But by 1949 it had been decided that the government would build a number of heavy forging machines and the factories to support them, and that these facilities would be leased to the great metals companies of the day on very generous terms. The Heavy Press Program had begun.

Nifty Fifty

The Fifty was installed at Alcoa’s Cleveland Works facility and began operations on May 5, 1955. A complementary 35,000-ton press was installed shortly after. I have their initial production list, and it reads like catalog of American military air power of the age: wing roots for the Republic F-105, wing spars for the Convair B-58, landing gear trunions for the Boeing B-52, bulkheads for the Lockheed C-130—in all, hundreds of items. From the start, the forges were busy machines.

The Heavy Press Program also supplied Wyman-Gordon of Grafton, Massachusetts, with a 50,000- and 35,000-ton pair of forging presses. Here’s their 50K, nicknamed Major (yep, the 35K is Minor), and again, note the man standing at its foot for scale:

The two 50,000-ton presses were of very different design — those interested can compare them here and here — but their dies were made to be interchangeable, so that production would not be disrupted if one of the machines broke down or was attacked during war. Photo: Library of Congress

To these four were added the six huge extrusion presses: a 12,000-tonner for Curtiss-Wright in Buffalo; twin 8,000-tonners for Kaiser in Halethorpe, Maryland; a 14,000-tonner for Alcoa in Davenport, Iowa; and an 8,000- and a 12,000-tonner for Harvey Aluminum in Torrance, California, just south of L.A. With stroke lengths of up to 92 feet, the extruders were used to produce long, hollow structures like aluminum missile bodies and wing struts in a single, seamless piece, saving time, weight, and material. Here’s the Harvey 12K, which went into service in August 1957:

Though it was nearly 300 feet long and weighed 8 million pounds, the maximum variance along the Harvey 12K’s chassis was just 0.004 inches. Source: USAF Materiel Command

This iron giant—which reminds me somehow of a steam train—is the one Heavy Press Program machine that definitely no longer exists: it was cut up for scrap in the 1990s. And I haven’t been able to confirm the fate of the 8,000-tonner at Harvey—though it may have been shipped to Korea or China.

As for the other eight machines, they’re still working. Curtiss-Wright’s extruder ultimately was bought by Precision Castparts and moved to Houston, and Kaiser’s pair was taken over by Alcoa, but their jobs haven’t changed. They make the things that make us fly, and they’ll be doing so for decades yet.

A Stamp on History

I see three main legacies of the Heavy Press Program.

First, of course, is the aeronautics industry as it now exists. We are accustomed to talking about the ways abstractions like “technology” or “Washington” have affected life the world over. But the machines of the Heavy Press Program are a concrete—well, an iron-and-steel—example of how industry and politics can collide with enormous yet unpredictable effect. The civilian air industry was an afterthought when the program was conceived, yet it is arguably the program’s signal achievement. Again, every Boeing and Airbus jet you’ve ever flown, every one that has carried mail or freight across the oceans, on was built around vital structural components made by these huge machines. Their impact on global society and commerce has been incalculably great. But every American military jet that has fired a gun or dropped a bomb in war was also built around Heavy Press parts—and thus the greatness of the program’s impact is morally blurred.

You can’t have this…

…without this.

Second is the military-industrial complex. I don’t believe it’s possible to place its origin in any single spot. But I am also not aware of any defense program since the HPP that was meaningfully opposed by Congress on the grounds that it threatened the functioning of American democracy. That a given project was “wasteful” or “bloated,” sure—but that’s just bookkeeping. The Heavy Press Program was in many ways the test case for the proper division between private and public interest, and it was decided in favor of what amounts to a mutual aid society between American industry, the American military, and Congress. The consequences are plain, and not often pretty.

Lastly is a legacy of absence. Today, America lacks the ability to make anything like the Heavy Press Program machines. The Fifty, to pick the one I’m most familiar with, was made by the Mesta Machine Company of West Homestead, PA, just outside of Pittsburgh. Mesta built the machines that built Steeltown — the furnaces, the blowers, the rolling mills and the forges. Mech-heads will want to check out this digitized Mesta brochure of 1919, a kind of Whole Earth Catalog for the iron industry. The less avid can just enjoy the picture below, from the same era. Then imagine what Mesta Machine could do by 1950, with three decades worth of further innovation under its belt.

Mesta could mold, cast, forge, machine and field-test huge components under one roof — literally — a full-service shop of the sort that no longer exists in the U.S. Photo: Carnegie Museum of Art.

The company went under in the mid-1980s. It is not unambiguously bad that it and the rest of American ultra-heavy manufacturing are gone. But it’s not unambiguously good, either. Conventional wisdom would say that the industry went to less-developed nations, freeing American resources for higher-tech pursuits. In fact, the only companies today capable of producing Heavy Press-size equipment are in the backwaters known as Germany and Japan, with companies in Russia, Korea, and China rapidly catching up and the UK actively rebuilding its top firm, Sheffield Forgemasters, through cheap government loans. Just last year four Japanese companies joined forces to build a new 50,000-ton press for the aerospace and power industries, and while I was working on this piece China Erzhong, a nationalized conglomerate, announced that it will build an 80,000-ton press — the biggest ever — to support its nascent aerospace industry.

Now is not the time for America to build new forges: eight really is enough. But the original heavy presses, which have lived far longer and spurred far more innovation than was ever imagined, set an example that I think might yet be followed. Big machines are the product of big visions, and they make big visions real. How about a Heavy Fusion Program?

If you’re one of the hordes whose Xbox 360 died the fiery death associated with the RRoD you may be wondering what to do with that multi-hundred dollar door stop you’re left with. Why not salvage the parts for other uses? If you’ve ever wanted to use your wireless controller with a computer here’s a way to pull out the RF module and reuse it.

The concept is simple enough, there’s a daughter-board in the Xbox 360 which hosts the RF module for wireless controller connectivity. Once you extract it from the carcass of the beast, you just need to find a way to read and push the data to your computer. Any USB enabled microcontroller will do, in this case an Arduino nano was chosen for the task. A bit of level converting was necessary to interface with the device, but nothing too involved.

It sounds like at first there was an issue with syncing a controller with the hacked module, but as you can see in the clip after the break that problem has been solved.

Popout[via Build Lounge]
Filed under: xbox hacks        

The Philippines’ National Power Corporation is offering tours and overnight beachside holidays at its Bataan Nuclear Power Plant, built in the 1980s but never fired up. It’s been “uranium-free” since 1997 and is now marketed as an ecotourism site. From National Geographic:

The trip back in time takes about three hours by car from the Philippine capital, Manila. The entry fee—150 Philippine pesos (about U.S. $3.50)—includes use of a nearby private beach.

The first part of the tour involves a presentation on the plant’s safety features, including its apparent ability to withstand an earthquake as strong as the one that shook Japan’s Fukushima plant on March 11, 2011.

The rest of the tour includes a guided walk through the guts of the unused plant. “Tourists can see the reactor, steam generators, control rooms, turbine-generators, etc.,” National Power’s Marcelo said.

 

 

“Nuclear-Resort Pictures: Come for the Reactor, Stay for the Beach”

Coming soon glow-in-the-dark “Radiation” badge. You learned about radiation and radioactivity! Adafruit offers a fun and exciting “badges” of achievement for electronics, science and engineering. We believe everyone should be able to be rewarded for learning a useful skill, a badge is just one of the many ways to show and share. This is the “Radioactivity and Radiation” badge for use at classrooms, workshops, Maker Faires, Hackerspaces, TechShops and around the world to reward beginners on their skill building journey! This special badge is white in the day time and glows green in the dark.

Should be in stock in a week or so! You can check out all the badges here and here.

I thought this would be a fun project to replicate with my 2 and 4 year old daughters, but I wanted to make a small tweak and display a picture of Frosty the Snowman. My two year old discovered the old Frosty the Snowman cartoons this year and is constantly asking to “watch a frosty”.

I downloaded John’s Arduino sketch and took a look at it to see what I’d have to do to change the picture displayed on the scope. His code is very well laid out and the picture is defined by the number of points and the X Y coordinates stored as two arrays.

Now how do I draw a picture of a snowman and get X Y coordinates out of it? I tried GIMP and Paint, but ended up using Scilab…… yes a fancy math program to draw a snowman! The nice thing about Scilab is you can plot pictures using the same X & Y arrays needed for the Arduino sketch.

I could have gotten all fancy and used sin & cos equations to get a nice smooth circle, but a line segment circle gets the job done too, and is equally impressive to a two year old

Once I got the X Y coordinates figured out I cut and paste them in to John’s sketch and loaded it into my ProtoStack Arduino Clone from a previous post.

Here is John’s sketch with my added X1 & Y1 coordinates for the snowman pic. link

We grabbed a bread board and I let my 4 year old insert the 10K Ohm and 0.1uF caps and hook up the scope probes.

With a few tweaks to the scope’s settings we got a nice picture of Frosty the Snowman.

My daughters had fun making him taller and shorter and skinny and fat all with a few button presses. Thanks John for the great idea; my girls and I had a lot of fun!

Hack a Day alum [Will O’Brien] recently upgraded his phone, and was trying to find a use for his old one. He always wanted a remote starter for his Subaru Outback, but wasn’t interested in paying for an off the shelf kit. Since he had this old smartphone kicking around, he thought that it would be the perfect starting point for an SMS-triggered remote start system.

He started off by jailbreaking his phone, which allows him to run some Perl scripts that are used to listen for incoming texts. Using a PodBreakout mini from Sparkfun he connected the phone to an Arduino, which is responsible for triggering the car’s ignition. Now, a simple text message containing the start command and a password can start his car from a anywhere in the world.

While [Will] is quite happy with his setup he already has improvements in mind, including a way for the Arduino to send a message back to him via SMS confirming that the car has been successfully started. He’s thinking about putting together a kit for others looking to add the same functionality to their own car, so be sure to check his site periodically for project updates.
Filed under: arduino hacks, cellphones hacks, iphone hacks, transportation hacks        

We’re giving away amazing kits from our new Make: Ultimate Kit Guide EVERY DAY — thousands of dollars worth of merchandise, including MakerBots!

To celebrate the release of our latest publication, the Make: Ultimate Kit Guide 2012 (and its companion website), we’re giving away at least one of the cool kits reviewed in the issue each day during the holiday season.

Today’s kit giveaway is the DIY Hologram Kit (a $100 value!) Here is MAKE Toolbox editor Arwen O’Reilly Griffith’s review from the issue:

Making holograms became faster and easier a few years ago when Litiholo introduced its Instant Hologram film. Like old Polaroids, these film plates require no developing after exposure, which means, in about an hour, you can make your own transmission hologram of anything that will sit still next to the plate. The kit also includes an LED darkroom light and the SafetyLight Laser Diode that you use to both make the exposure and view (or “reconstruct”) the hologram.

To be eligible for today’s giveaway, all you have to do is leave a comment below in this post. The entry period for today’s prize will be until 11:59pm PST tonight. We’ll choose one person at random, you’ll be notified by email, and you’ll have 48 hours to respond. The Winners List is kept on the Giveaway landing page. That’s it! No purchase necessary or anything else to do. Please leave only one comment per post. You can enter as many giveaways as you like until you win. This giveaway is for US residents only. You also must be 18 years old to enter (Kids: Ask your parents to enter). See the Kit-A-Day Giveaway landing page for full sweepstakes details and Official Rules.

Important Note: If you enter this drawing, when it’s over, please check the place where you registered to comment (eg. Facebook, Yahoo, Twitter). Some people are winning these kits and then not responding when we send them a message using the available means of contacting them. We want to make sure you get your giveaway!

The guys over at Rusty Nail Workshop have put up an Internet controlled robotic arm for your amusement. While you’re waiting for the turkey to be done (or, you know, working), try your hand at moving some LEGO pieces around with a remote-controlled robotic arm.

The build log goes through the parts needed for the build. The arm itself is a Lynxmotion AL-5D, a heavy-duty device that’s far more capable and looks a lot better than our old Armatron.

The arm is controlled by an Arduino Uno. The Arduino is connected to the arm’s servo controller. Movement commands are received by an Ethernet shield and translated into servo commands. The entire build runs independently of a computer just like this project’s inspiration, the Orbduino.

Of course you can imagine the mayhem that would ensue if multiple people tried to take control of the robot simultaneously. A bit of code on the project’s website makes sure only one person has control of the robot at any given time. Check out what somebody else is building out of LEGO blocks with a Waldo. If you’re lucky, you’ll be able to knock that work down.

Lithium-polymer batteries are an excellent choice for portable projects. They are relatively cheap, hold a significant charge, and last for a long time. The drawback with these batteries is that they require rather complicated charging protocols. You have to watch out for overcharging, undercharging, overheating, etc…

We are looking for a standard part to use in our projects, so we decided to do a roundup of open source lithium polymer chargers from SparkFun, Seeed Studio, and Adafruit. With the exception of Seeed, all the chargers are based on Microchip’s MCP738xx family of battery management ICs that come in SSOP and DFN packages. They handle all the charging algorithms and usually only require a single external capacitor.

Lithium Polymer USB Charger and Battery from SparkFun is a basic charger designed around the MCP73831 IC. A solder jumper changes the charge current from 100mA to 500mA. LiPoly Fast Charger, also from SparkFun, supports currents up to 1A. This design uses the MCP73843 IC driving an external mosfet that handles higher current.

Seeed is up next with their Li-Po rider and Li-Po rider pro charger/power supplies. They are based on the CN3065 battery management IC. The charge current is 400mA when a powerful enough source is available. One thing to note is that Li-Po riders are not chargers but compact portable power supplies that deliver 5V at 350mA. Battery voltage is converted to 5V through a switching step up converter. The pro version delivers up to 1A of current.

Adafruit’s USB/DC Lithium Polymer battery charger uses the MCP73861 IC. A charging current of up to 1.2A can be selected through a resistor. This IC has thermal protection. A standard 10K thermistor can be added to the battery to shut down charging in case of overheating. Their USB LiIon/LiPoly charger uses the MCP73833 IC, and is similar to the previus product. This one doesn’t have the DC IN jack populated, and the maximum current is 1A.

After looking at what everyone is using we are going to add the MCP73833 to our part box. It is cheap, has programmable current, and thermal protection through a thermistor. We also liked Seeed’s use of a dc/dc converter for portable projects.

Arhi tipped us to a PID library for Arduino. If you require precision control of electro-mechanical devices like heaters, servos, water pumps, etc. PID is one  way to implement that control.

It is an algorithm that controls a device by constantly adjusting its control or power signals to keep the device at preset state. Using sensors to detect differences between the preset state and the actual state the device is in, the controller calculates which signals it should send to the device to eliminate the difference.

Via the forum.