This is an Arduino porting of the excellent work by Markus Frejek.
The final aim is to create an economic component tester using Arduino and a few passive components;

You can see more about ArduTester in our Arduino Forum.

NEW PRODUCT – SD/MicroSD Memory Card (8 GB SDHC) – Add mega-storage in a jiffy using this 8 GB class 4 micro-SD card. It comes with a SD adapter so you can use it with any of our shields or adapters, and a USB mini reader that will let you get data on/off. Preformatted to FAT so it works out of the box with our projects. Tested and works great with our Wave shield, Data logger shield and GPS shield, and micro-SD adapter as well as any other device in the Adafruit shop that uses (micro)-SD cards!

Please note! This is an SDHC card, and may not work with very old projects or products that only support SD cards. All of the Adafruit projects and products use SD/HC-compatible code. Make sure you can use this card before purchasing for non-Adafruit products. The brand itself may vary but we use only quality name-brand from reputable suppliers.

In stock and shipping now!

“ADA 9000″ faceplate created using Adafruit 100mm Massive Arcade Button with LED and an afternoon with a laser cutter, spray paint and a few bits and bobs. Not as detailed or authentic as the HAL replica that ThinkGeek used to sell…but about $480 cheaper!

Fist bump to Amadeus Prokopiak of the Replica Prop Forum for his amazing HAL 9000 blueprint.

adafruit.com/products/1185
www.therpf.com/f9/hal-9000-panel-2001-space-odyssey-pg-11…

NEW PRODUCT – Speaker – 3″ Diameter – 4 Ohm 3 Watt – Listen up! This 3″ diameter speaker cone is the perfect addition to any audio project where you need an 4 ohm impedance and 3W or less of power. We particularly like this cone as it has 4 handy mounting tabs 60mm apart.

Works great with our class D amplifier board.

NEW PRODUCT – Speaker – 3″ Diameter – 8 Ohm 1 Watt – This 3″ diameter speaker cone is the perfect addition to any audio project where you need an 8 ohm impedance and 1W or less of power. This has four mounting tabs 60mm apart as well.

Works great with our Wave shield or class D amplifier board.

Technical Details for 4 Ohm 3 Watt and 8 Ohm 1 Watt:

• Weight: 50.48g
• Dimensions: 77.8mm x 77.8mm x 25.49 / 3.06″ x 3.06″ x 1″

In stock and shipping now!

Innovative parts sourcing via 3D model search! From 3D Part Source:

We are harnessing the power of next generation 3D search to revolutionize the way you source parts. We provide a tool that makes this critical process rapid, accurate and cheap. (It’s faster, better, cheaper!)

Our philosophy is, if “a picture paints a thousand words”, then “a 3D model contains a thousand specs”!

As a supplier, 3Dpartsource.com makes your catalog fully accessible, giving you the greatest chance possible of making sales worldwide. It gives you unparalleled global access and exposure. Your database can be interrogated comprehensively. No opportunity to match a buyer’s demands or a call for parts need be missed ever again. 

As a buyer, 3Dpartsource.com puts the world of parts at your fingertips. It connects your designing with your part sourcing in a smooth end-to-end process. Barriers to sourcing drop. You find the part you are looking for with a simple click. Put an end to the tedious and endless task of wading through specs and printed catalogs to find approximations for the part you are seeking. Save time, money, and frustration. 

Once you try the power of 3Dpartsource.com, you will never look at sourcing the same way again!

Read more.

Now here’s a project that gets us excited!

For the month of February, talented educator Liz Arum created daily curriculum assignments aiming to help educators and instructors introduce new students to the extremely handy OpenSCAD parametric design tool — the tool used to make many of Thingiverse’s most popular items, from Emmett’s Blossoming Lamp and Screwless Heart Gears to Tony Buser’s wildly helpful pin connectors and Mars Exploration Rover.

The MakerBot Customizer app is at heart a hosted version of the open source OpenSCAD app, with GUI tools to allow users to adjust parametric factors within OpenSCAD designs to produce their own custom objects.

Well, for her March 1st entry, Liz put up a Call to Action challenging those who have been exploring OpenSCAD to pool together to collectively build an Adafruit electronic parts library on Thingiverse to help the huge influx of DIY electronics hobbyists joining the 3D community to have the tools they need to make awesome mounts, bezels, cases, and interactive parts using a 3D printer.

Check out her March Ideas challenge below:

Adafruit Library: OpenSCAD and Customizer

You know about the MCAD library and about the Write library, but what about a library for all your favorite electronic components? The Adafruit library doesn’t exist. At least not yet, but it should. Wouldn’t it be great if you could just go to Thingiverse and open the Customizer App and get an stl for an electronic component? You could then download the stl and use it for a boolean difference or just to help you design your object that incorporates the component or components.

What might the interface look like? (see image above)

You don’t have to design all the parts. You don’t have to design two parts. Just design one part using OpenSCAD and upload it to . Tag it with Adafruit.

Don’t forget to use a digital caliper to get precise dimensions.

Read more.

UCLA researchers develop new technique to scale up production of graphene micro-supercapacitors:

While the demand for ever-smaller electronic devices has spurred the miniaturization of a variety of technologies, one area has lagged behind in this downsizing revolution: energy-storage units, such as batteries and capacitors.

Now, Richard Kaner, a member of the California NanoSystems Institute at UCLA and a professor of chemistry and biochemistry, and Maher El-Kady, a graduate student in Kaner’s laboratory, may have changed the game.

The UCLA researchers have developed a groundbreaking technique that uses a DVD burner to fabricate micro-scale graphene-based supercapacitors —  devices that can charge and discharge a hundred to a thousand times faster than standard batteries. These micro-supercapacitors, made from a one-atom–thick layer of graphitic carbon, can be easily manufactured and readily integrated into small devices such as next-generation pacemakers.

The new cost-effective fabrication method, described in a study published this week in the journal Nature Communications, holds promise for the mass production of these supercapacitors, which have the potential to transform electronics and other fields.

“The integration of energy-storage units with electronic circuits is challenging and often limits the miniaturization of the entire system,” said Kaner, who is also a professor of materials science and engineering at UCLA’s Henry Samueli School of Engineering and Applied Science. “This is because the necessary energy-storage components scale down poorly in size and are not well suited to the planar geometries of most integrated fabrication processes.”

“Traditional methods for the fabrication of micro-supercapacitors involve labor-intensive lithographic techniques that have proven difficult for building cost-effective devices, thus limiting their commercial application,” El-Kady said. “Instead, we used a consumer-grade LightScribe DVD burner to produce graphene micro-supercapacitors over large areas at a fraction of the cost of traditional devices. Using this technique, we have been able to produce more than 100 micro-supercapacitors on a single disc in less than 30 minutes, using inexpensive materials.”

The process of miniaturization often relies on flattening technology, making devices thinner and more like a geometric plane that has only two dimensions. In developing their new micro-supercapacitor, Kaner and El-Kady used a two-dimensional sheet of carbon, known as graphene, which only has the thickness of a single atom in the third dimension.

Read more.

Makers of addressable LED projects have an unhealthy obsession with speed. Which code is fastest? Which hardware? If I tweak this just so, I can shave 2 milliseconds per frame! You can stop obsessing, because Paul Stoffergen’s latest simply buries all others.

Check out this great “doomsday” clock project shared on the Adafruit Forums – with as many sources for accurate time and place as you could hope for! As the sources to keep this clock accurate go down, the person reading the clock knows that it is time to hit the bunkers and prepare for the end of the world. Check out the list further down for all of the awesome Adafruit gear used for this project, and read just below for notes from the Doomsday Atomic Alpha Clock Five project page:

I wanted a clock that would display precision time and date in “all” worst case scenarios.
If this clock does not show the precise time then its time to gather up food, water, ammunition,
and the family and head for the underground bunker!

This could happen – imagine this scenario ….

The World Wide Web (Internet) goes down.
All the US Military global positioning satellites (GPS) stops working.
The 60Khz WWVB pulse radio towers (Atomic clock) at Fort Collins, Colorado cease operation.
The electrical power grid cease to function.
All cellphone towers are in-operational.
All POS telephone land lines stop functioning.
All TV and cable systems are in-operational.

It’s the end of civilization … Doomsday! Do you have the precision time and date?
I may be dead and long gone but my Doomsday Atomic Alpha Clock Five would be still functional, working and indicating the precision time!

In this project, we used a GPS, a WiFi Electric IMP (network time), a custom built WWVB Atomic radio receiver, two precision TXCO real time clocks (+- 2 PPM SPI DS3234 and I2C DS3232) and two micro controllers – (Teensy 3 ARM stamp & Arduino 328P clone). We then use the three precision clock sources (UNIX seconds) to drive or sync to the Evil Mad Scientist huge, very bright, “Alpha Clock Five” 2.5″ clock display.

Read more.

And here is the list of Adafruit gear involved and further details about this project:

• Alpha Clock Five kit
• LCD I2C shield with 5 tact switches replaced by tact joystick (hacked or modified)
• RGB backlight negative LCD 20×4 (modified to fit 2×16 LCD shield)
• Ultimate GPS (modified-remote mounted fix LED)
• +5 VDC to 3 VDC level converter (for I2C LCD)
• INA219 High Side DC Current Sensor Breakout
• Electric IMP SD WiFi card (modified for network time and status)
• Tact joystick (modified for LCD display)
• CR2032 battery holder(s) (Standardize battery holder for all lithium backups)
• Spring loaded terminal blocks for 5 V bus bar
• Protoboard for 5 V bus bar
• Panel mount power connector 2.1 mm
• Teensy 3 ARM Stamp

In our “DoomsDay Atomic Alpha Clock Five Project” we used a Ultimate GPS, a WiFi Electric IMP (network time), a WWVB Atomic radio receiver, two precision TXCO real time clocks (+- 2 PPM SPI DS3234 and I2C DS3232) and two microcontrollers – (Teensy 3 ARM stamp & Arduino 328P clone). We then use the three precision clock sources (UNIX seconds) to drive or sync to the Evil Mad Scientist huge, very bright, “Alpha Clock Five” 2.5″ clock display.

This week on Community Corner, we used the “search” function within the G+ Community to see all of the recent tutorials our community members have been creating and sharing about the ULN2803.

Take a look at some videos and posts from Matt Heilman, Sylvain Leroux, and William Foster — and dive into the conversation yourself!

Check out the video on YouTube.

Featured Adafruit Products

ULN2803: 8 Channel Darlington Driver (Solenoid/Unipolar Stepper) – ULN2803A: Bring in some muscle to your output pins with 8 mighty Darlingtons! This DIP chip contains 8 drivers that can sink 500mA from a 50V supply and has kickback diodes included inside for driving coils. This will let your little microcontroller or microcomputer power solenoids, DC motors (in one direction) and unipolar stepper motors. Please note, this is an ‘open collector’ driver – it can only be used to connect the load to ground and there will be a 1 Volt (or more) ‘drop’ across the internal transistors. The inputs can be driven by 3.3V or 5V logic. Fits nicely in any breadboard or perfboard. (read more)

Each Wednesday on Community Corner, we share something we have enjoyed the previous week on the Adafruit Google+ Community site “Makers, hackers, artists & engineers: Learning and sharing with Adafruit!” (Note: Google+ login required.)

If you haven’t joined us at this public community yet, stop on by for a visit. And bring something to share!

]]> http://www.adafruit.com/adablog/?feed=rss2&p=52057 0 http://www.adafruit.com/blog/2012/12/26/custom-rectified-acdc-power-supply-using-adafruit-current-and-volt-meters/ http://www.adafruit.com/blog/2012/12/26/custom-rectified-acdc-power-supply-using-adafruit-current-and-volt-meters/#comments Wed, 26 Dec 2012 06:00:00 +0000 Matt http://www.adafruit.com/blog/?p=50365

It is not everyday that you run into people designing their own power supplies — check out this great project from the Adafruit Forums by community member “Physics_Dude”:

Alright, I recently had the need to build a rectified AC/DC power supply. Yes, I mean rectified, not regulated. It won’t be used to power sensitive projects.

I used Adafruit’s current and volt meters to read out said values.

Read more.

Featured Adafruit Products

Panel Current Meter – 0 to 9.99A: Put a current meter anywhere with this very handy display. This panel meter requires a DC voltage to run, and then has two thick gauge wires to measure current draw. A shunt is already on board so its very easy to hook up! (read more)

Panel Volt Meter – 4.5V to 30VDC: Put a voltage meter anywhere with this very handy display. This panel meter simply connects to whatever DC supply you are trying to track, easy to wire up! (read me)

NEW PRODUCT! Tactile Switch Buttons (12mm square, 6mm tall) x 10 pack – Medium-sized clicky momentary switches are standard input “buttons” on electronic projects. These work best in a PCB but can be used on a solderless breadboard as shown in this tutorial. The pins are normally open (disconnected) and when the button is pressed they are momentarily closed.

They come in a pack of 10, they’re pretty handy so you’ll want to keep them around.

You can find an EAGLE cad package for these in switch-omron:B3F-40XX

In stock and shipping now!

A couple of weeks ago we blogged about Joe Walnes’s http://resisto.rs/ website — a lightweight web app tool to look up resistor color codes. Well, he has integrated this tool into the DuckDuckGo search engine here. Check it out:

Remember a few weeks back I announced resisto.rs, a no-frills resistor color code calculator?

Welllll, if you happen to be a user of DuckDuckGo, it’s now even easier. See the resistor colors directly in your search results!

Try it out at DuckDuckGo: https://duckduckgo.com/?q=4.7k+ohms

And thanks to DuckDuckGo for making it so easy to extend your search engine.
Here’s the code.

Read more.

NEW PRODUCT! Breadboard-friendly MIDI Jack (5-pin DIN) – To celebrate the 30th Anniversary of the invention of MIDI we’re carrying these handy 5-pin MIDI jacks. They’re what you see on the back of nearly every synthesizer and drum machine. These are nice sturdy jacks, and breadboard-friendly, with all the pins on 0.1″ spacing for easy wiring.

This handy tutorial and wiring diagram will show you how to easily turn your Arduino into a MIDI controller!

Also compatible with DINSYNC cables, if you have a really old drum machine!

In stock and shipping now!

This is the perfect use put to Adafruit’s Chainable 16-Channel Servo Controller boards. 50 servos: one for each key! We first heard about this project on our “Raspberry Pi™ Accessories” forums — and can’t wait to learn more about it!

Featured Adafruit Product!

Adafruit 16-Channel 12-bit PWM/Servo Driver – I2C interface – PCA9685: You want to make a cool robot, maybe a hexapod walker, or maybe just a piece of art with a lot of moving parts. Or maybe you want to drive a lot of LEDs with precise PWM output. Then you realize that your microcontroller has a limited number of PWM outputs! What now? You could give up OR you could just get this handy PWM and Servo driver breakout. When we saw this chip, we quickly realized what an excellent add-on this would be. Using only two pins, control 16 free-running PWM outputs! You can even chain up 62 breakouts to control up to 992 PWM outputs (which we would really like to see since it would be glorious) (read more)

NEW PRODUCT! In-line power switch for 2.1mm barrel jack – Add a power switch to any project simply by plugging this between the power supply. This is the most useful thing you never knew you needed! You’ll want to pick up a bunch for your electronic projects.

Comes with a 5.5/2.1mm barrel jack on one end an a plug on the other. In between is an in-line switch that is rated for 125V and 2Amps (its normally used for lamps, we suppose). Since most people will be using it with no more than 12VDC, we think it can probably handle up to 5A at that voltage.

In stock and shipping now!

Here’s a charming, minimalist resistor color value lookup tool, Resisto.rs, from Joe Walnes:

I never have a resistor color chart handy when I need one. So I built a little web-app. Fast loading, simple, mobile friendly, and to the point.

Also check out Circuit Playground!

Here’s the first of a series of posts where Andrew Gibiansky will address the physical principles underlying the abstractions that allow complex modern computers to function using detailed discussions and infographics such as the above to help connect the physical components/EE principles to where they reach over to assembly language and the basis for computer programming:

For many years, I studied computers without ever understanding how they work. On the inside, a computer is a monstrously complex beast, with layers upon layers of abstraction which ultimately boil down to electrons running through silicon, obeying the fundamental laws of physics. We’ve built up so many layers of abstraction that the vast majority of people using computers – even the vast majority of highly technical programmers – don’t know (and don’t need to know!) how it all works on the inside. But while understanding every single layer of abstraction to its fullest extent is practically impossible, it’s incredibly fascinating how modern computers are built and what physical principles allow them to function.

In this series of blog posts, I’d like to introduce you to many of the layers of abstraction bridging the gap between the laws of physics and assembly language.  Given the rather large scope, I’m going to end up leaving out a lot of information about every topic I discuss. Just note that every topic I mention has, essentially, a field and a half solely devoted to it. With that said, let’s begin with circuits.

Read More.

NYC Resistor will be offering a class this weekend focused on USB Human Input Device: 14 October 2012! And check out the Adafruit arcade console buttons on this project!

The class covers writing firmware for the AVR to implement various USB HID classes, such as keyboards, mice and joysticks, using both raw USB calls and Arduino libraries. Included in the class is a Teensy 2.0, a breadboard and switches for building a simple human input device that you can take home to prototype your next gadget project. Anything with buttons, pedals, sliders or knobs can be used to make an input device once you know how!

Read more.

Need a specific value current sense resistor, perhaps to customize your INA219 DC current sensor?  This handy 1% 2W 2512 resistor kit from Stackpole may come in handy. It’s not particularly cheap ($84 USD), but it’s still a very good value since it includes 25 each of 27 different resistor values between 0.0005 and 0.75 ohms (675 total), and many of those resistors are around $1 a piece in single quantities.

Getting the big question right out of the way: no, we won’t be selling these. Legally, we can’t, for trademark reasons. But it’s generally okay for anyone to create replica props for their own personal use, so we hope this writeup will inspire some cool projects among our readers…

From the moment these LED displays made an appearance on our weekly Ask an Engineer show, comparisons were being made to the DeLorean time circuit from the Back to the Future films. It was a moral imperative then to make a demo! If you’re handy with Arduino and some shop tools, you should be able to pull off something similar (better, even), or adapt the ideas to other projects. This was quickly built in fun, so please don’t expect the same level of polish as a finished product tutorial.

Taking Some Liberties

When accepting this assignment, I might’ve failed to mention a small detail: I don’t own a car, let alone a DeLorean, for displaying the finished prop. Instead, mostly inspired by Jeri Ellsworth’s NES purse, I had this goofball idea of a slim, battery-powered device that could be placed in ironic settings: on a bicycle, on public transit, hung from a Flavor Flav necklace, and so forth.

While the general idea could have been accomplished quickly and easily with an iPad running the Flux Capacitor™ app, I wanted to preserve somewhat the staggered design of the original, and it had to have real 7-segment LED displays…there’s no substitute for seeing the genuine thing. In much the way that nixie tubes have a certain vintage coolness about them, LED displays too are reaching a nostalgic threshold, iconic of 1980s technology.

Using stock parts required some design compromises. The date and time formats would be changed to fit these 4-digit displays (the film prop used back-painted glass fakes for the month display, with some segment changes being physically impossible, making a 100% match unattainable anyway…iPad wins there). Also took liberties with some LED colors and various spacings, but overall the piece is still highly recognizable.

For the sake of a quick demo, I had to cut this short. Though all the displays are addressable, the destination and last-departed dates are simply fixed values from the first film; there’s no interaction. I may revisit this to add a keypad later, but for now it’s all just a fancy clock (it does show the current time accurately, using a ChronoDot RTC). Also, the vector files are not available, because they’re utter garbage! Creating something of finished kit quality requires many iterations and refinements…but with a rushed, one-shot piece like this, course corrections would come in the form of a Dremel tool and epoxy putty. If you plan to build one, give it some time and prepare your blueprint carefully.

Number Problems

These 4-digit displays can be assigned one of eight fixed I2C addresses via solder jumpers on the back. But the time circuit needs nine displays. A few possibilities were considered, including driving the one extra display “manually” with shift registers, or use a software I2C library and split the displays among multiple I2C buses. Either would require lots of library code changes and some intense concentration, but I was hit with a massive sinus headache at the time and really didn’t want to think about it.

Instead, exploiting the fact that we need just one way, write-only access to use the displays, I used a simple hardware hack to split the I2C bus to communicate with one row of three displays at a time (saving some code by repeating the same addresses in each row). The I2C data line fans out to all the displays as normal, but the clock feeds the enable lines of a 74HC138 3-to-8 line decoder, and the microcontroller can then select which output line forwards the clock signal. The data on the other I2C buses is ignored without the corresponding clock.

To keep this ultra slim, a Teensy microcontroller board was used — a standard Arduino wouldn’t fit, not even the headerless Leonardo. After prototyping the full circuit on a breadboard, all the parts were soldered point-to-point and “dead bug” style inside the case. Power is provided by three AA cells in series — a bit under the ideal 5 Volts, but still sufficient to run everything. The cells fit in the “chin” below the three dates. I’d mail-ordered a special battery holder for this, and then in my rush to complete the project I went ahead and made all the case parts based on the holder dimensions on a web site. Naturally then, with the case already cut and glued, the part that arrived was slightly larger than the dimensions posted. The fix was to break off the battery contacts from the ends of the holder and epoxy putty them directly into the case. This eliminated just enough girth for everything to fit. The remaining electronics were delicately folded into the case with copious amounts of hot-melt glue, tape and swearing.

The case was fabricated from laser-cut acrylic and sprayed with faux hammered metal paint. A metal enclosure would have been more authentic (and more work), but a corollary to “Maslow’s hammer” dictates that when you have a laser cutter, every project appears ideally suited to acrylic. The labels were inkjet printed and made into stickers with a Xyron applicator, trimmed with an X-Acto knife, then painstakingly touched up with a Sharpie marker to hide the white edges. After the labels were applied, the bezels received a thick spray of acrylic sealer, then attached to the front of the case with epoxy.

Go for it! If you don’t own a DeLorean, this will still impress your co-workers and look great on your desk. Or maybe you can devise a scheme around Halloween or a geek-fest like Dragon*Con. Bolt it just below the arc reactor on your Iron Man suit (you do have an Iron Man suit, right?). Or if you have a young son in a stroller, attach the time circuit to the tray, dress junior in mirrored shades and a life preserver down vest, while dad dons a Doc Brown getup. Instant father-son cloying adorableness!

Even if you don’t build this exact item, if it inspires any nifty electronics projects (*cough*Proton Pack*cough*), please share them in the forums, bring them to the Saturday night show-and-tell or document your build on a site like Instructables. Customer projects are frequently showcased on the Adafruit blog!

Resources

Here’s the Arduino sketch that runs the show.

Parts from the Adafruit store include:

• Teensy (ATmega32u4 USB dev board)
• ChronoDot Ultra-precise Real Time Clock
• 0.56″ 4-Digit 7-Segment Display w/I2C Backpack – Red
• 0.56″ 4-Digit 7-Segment Display w/I2C Backpack – Green
• 0.56″ 4-Digit 7-Segment Display w/I2C Backpack – Yellow
• Diffused Red 3mm LED (note: film prop used yellow LEDs on destination time)
• Diffused Green 3mm LED

Additional parts acquired from Digi-Key include:

NEW PRODUCT! – SMA to uFL/u.FL/IPX/IPEX RF Adapter Cable

This RF adapter cable is super handy for anyone doing RF work. Often times, small electronics save space by having a pick-and-placeable u.FL connector (also called uFL, IPEX, IPAX, IPX, MHF, and AM). But most antennas have SMA or RP-SMA connectors on them. This little cable will bridge the two!

This cable is RG178 and is 15cm (5.9″) long not including the RP-SMA connector. It has a panel-mount SMA connector on the end, often used for GPS and cellular connections. Most WiFi devices/routers that have a connector use RP-SMA. Check the antenna you want to connect, and the close up image above to verify if you need RP-SMA or SMA as they are not compatible!

In stock and shipping now!

NEW PRODUCT! – RP-SMA to uFL/u.FL/IPX/IPEX RF Adapter Cable

This RF adapter cable is super handy for anyone doing RF work. Often times, small electronics save space by having a pick-and-placeable u.FL connector (also called uFL, IPEX, IPAX, IPX, MHF, and AM). But most antennas have SMA or RP-SMA connectors on them. This little cable will bridge the two!

This cable is RG178 and is 15cm (5.9″) long not including the RP-SMA connector. It has a panel-mount RP-SMA connector on the end, often used for wifi routers and antennas. GPS and cellular connections often use SMA. Check the antenna you want to connect, and the close up image above to verify if you need RP-SMA or SMA as they are not compatible!

In stock and shipping now!

One of our favorite chip searching tools, findchips.com, has just posted a pretty great update.  The update includes a nice new user interface, and a very useful ‘In Stock Only’ search.

Here’s two tiny engineers-in-training (nice Ada Lovelace onesie!) playing with a color ball containing an Arduino, our RGB LED tape, and some other fun stuff. Full specs in the YouTube description… via Facebook

NEW PRODUCT – MCP23017 – i2c 16 input/output port expander! Add another 16 pins to your microcontroller using a MCP23017 port expander. The MCP23017 uses two i2c pins (these can be shared with other i2c devices), and in exchange gives you 16 general purpose pins. You can set each of 16 pins to be input, output, input with a pullup or open drain. There’s even the ability to get an interrupt via an external pin when any of the inputs change so you don’t have to keep polling the chip.

Use this chip from 2.7-5.5V (good for any 3.3V or 5V setup), and you can sink/source up to 20mA from any of the I/O pins so this will work for LEDs and such. Team it up with a high-power MOSFET if you need more juice. DIP package means it will plug into any breadboard or perfboard.

You can set the i2c address by tying the ADDR0-2 pins to power or ground, for up to 8 unique addresses. That means 8 chips can share a single i2c bus – that’s 128 I/O pins!

We used this chip in our RGB LCD + Keypad shield to both control an LCD and read a 5-way keypad and found it to be very reliable and easy to get up and running. We even have an Arduino library with example code written which will set pin state, read and write from individual pins, and set the pullups.

We even have an Arduino library with example code written which will set pin state, read and write from individual pins, and set the pullups.

Datasheet for MCP23017

In stock and shipping now.

Learning to design your own PCBs and being able to put together a schematic to solve a specific problem is both a valuable and rewarding skill.  There are a number of resources out there to help you avoid common mistakes, but it isn’t always obvious to know where the values of certain common components come from, particularly common parts like resistors and capacitors.  Figuring this out is part of the learning process, but it isn’t always easy to know where to look since you first need to know exactly the right terms to search for.

One good example that I haven’t seen a lot of attention paid to is deciding which crystal to use for your board and which caps go with it. Most people just copy and paste what they found on some other schematic (“12MHz + 22pF? … sounds good!”).   Unfortunately, if you want to get accurate and stable results out of the crystal, you need to match the capacitors to the specific crystal you chose, and it varies from model to model even with the same manufacturer.   Fortunately, it’s trivial to calculate the right capacitors for your crystal.

A 12MHz crystal that I use quite a bit is the NX3225SA-12.000000MHZ from NDK.  It’s a good size, stable (+/-15 ppm), and easy to find.  I use the more expensive +/-15 ppm model for better input to the PLL, but if you don’t use the right capacitors along with the crystal your signal will never be anything remotely close to +/-15ppm and you may as well buy a much cheaper crystal.

So how do you know which capacitors to use?  Easy.  Every crystal datasheet lists something called the Load Capacitance (CL).  In the case of the crystal above, it’s 8 pF.  C1 and C2 need to match this Load Capacitance, with the following formula being the key:

CL = (C1 * C2) / (C1 + C2) + Cstray

C1 and C2 are the two capacitors that you see attached to the crystal, but you might be wondering what Cstray is.  Unfortunately, every trace, every lead on your component, just about everything on your PCB has some stray capacitance.  The total of these values is represented by Cstray.  You can usually guestimate this in the neighbourhood of 2-5pF as long as you follow good layout practice and keep the trace from the crystal to the pins on the MCU as short as possible with no vias, etc.

We know CL since it’s stated in the crystal datasheet (8 pF), and we know Cstray (say ~5 pF), so all we need to do is test our value for C1 and C2 to make sure that it will match CL taking into account Cstray.  A commonly tossed around rule of thumb is to start with a pair of capacitors two times the CL of the crystal, which will get you to CL.  In this case, that would be 2*8 pF = 16pF for the capacitors.  Unfortunately, this ignores the stray capacitance (Cstray), and won’t give you the best results.  Even if you are guestimating Cstray you will get better results taking it into account, but it means just using a capacitor 2* CL won’t work:

CL = 8 pF
C1, C2 = 16 pF
Cstray = 5pF

(16 pF * 16 pF)/(16 pF + 16 pF) + 5 pF= 13 pF

13pF is much too high to get the best results from your crystal.  If instead of 16pF, we take a lower 6 pF value this will give much better results:

(6pF * 6pF)/(6 pF + 6 pF) + 5 pF =8 pF

If you think the stray capacitance is a bit lower, say 3pF, you might try a 10pF capacitor:

(10 pF * 10 pF)/(10 pF + 10 pF) + 3 pF = 8pF

There’s an obvious tradeoff between choosing a standard capacitor value, and having a good idea of what your Cstray is, but the above formula should at least explain HOW to determine what value those capacitors should be relative to your crystal.  Even using a ballpark Cstray plud good layout should give you far more accurate results than just copying and pasting a value you saw on another schematic unless you’re using the exact same crystal model (which is unlikely since they are rarely even listed in the schematic).

A better rule of thumb is: C1, C2 = 2*CL – 2*Cstray

Further Reading

AN2867 – Oscillator design guide (ST Microcontrollers)

Do you frequently find yourself looking for odd-ball resistor values or soldering resitors together to try to get as close as possible to some uncommon E96 (1% resistor) value?  If you make a lot of prototypes, you might be happy to learn that most major resistor manufacturers offer resistor ‘kits’ containing a certain number of every value.  While they aren’t cheap, they do represent a fair value for the amount of work involved packaging and producing them, and if you’re really serious about electronics it can be reassuring to know that you have every value you might need.

To find different kits, you can search Digikey for some variation of this phrase: “res kit 1% 0805″ (changing the package size to match what you want), or here are the Digikey part numbers for some kits manufactured by Yageo (who typically have very competitive prices on their reels of resistors):

0805 1% Resistors (50 of each value):
1.0-9.76: PHC1A-KIT-ND
10.0-97.6: PHC2A-KIT-ND
100-976: PHC3A-KIT-ND
1.00K-9.76K: PHC4A-KIT-ND
10.0K-97.6K: PHC5A-KIT-ND
100K-1.0M: PHC6A-KIT-ND

0603 1% Resistors (50 of each value)
1.0-7.5: PHH1-KIT-ND
10.0-97.6: PHH2-KIT-ND
100-976: PHH3-KIT-ND
1.00K-9.76K: PHH4-KIT-ND
10.0K-97.6K: PHH5-KIT-ND
100K-1M: PHH6-KIT-ND