e14 Project: A Silent Wireless Laser Tripwire Doorbell

I’ve had a problem since moving into my new place that I can’t hear people knock at my front door. Sure I could get a doorbell at the hardware store, but those things stink. Instead, I thought I’d create a quick and simple Arduino and XBee based system to do it for me:

Doorbells are the 20th century version of today’s perpetually-interrupting cell phone. There you are, cooking a delicious dinner or reading a nice book when the doorbell rudely goes off in your ear. Sure, you’re glad to see whoever is at the door, but interruptions that chime can be so obnoxious. Needless to say, I do not have a doorbell.

The problem with the knocking system is that I usually can’t hear when someone knocks from my lab. I depend on Penny the Dog to alert me when someone is at the door. Except Penny sleeps most of the day. And then there are the delivery people (UPS/FEDEX) who can’t be bothered to knock, even if it is a next-day-early-AM shipment of parts from element14 that I am eagerly waiting for.

I decided that I’d create a project that solves all of my problems: a silent LED that flashes whenever someone approaches my door. It is based on a laser tripwire and will be able to run day or night, even in the bright Denver sun. And if the blinking LED is annoying, a simple button press disables the alert and resets the trigger.

Read the Full Article Here!

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Using Paper Protos to Check EAGLE Footprints

Checking Paper FootprintChecking footprints in a PCB layout review with only the on-screen file can be a pain in the neck.  There are many different measurements that need to be made for each individual part, and the mouse-based measurement tool can be somewhat obnoxious to get exactly on the edge of a pad.

There is a much faster way assuming one has all of the parts on hand: print out a to-scale paper prototype and place all of the components on the board.  It is fast to setup, and visually inspecting each component takes about 30 seconds.  There are, however a few tricks to be sure the printout is to scale.  I wrote an article on Element14 with step-by-step instructions.

Read the Full Article Here!

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E14: Reviewing Fluke’s VT04 Visual IR Thermometer

This past week I got a Fluke VT04, a Visual IR Thermometer.  It is basically a $1,000 version of the very expensive IR cameras.  While it doesn’t have the resolution or nice image viewing computer software, boy was it easy to use!

Still, given the amazing performance of the Mikron TH7515 from my Keithley days I can say you get what you pay for.  The more precise uses for an IR camera can’t be used with the VT04, but the grunt measurements work just fine, making it a wonderful addition to an EE’s bench!

To read the review and learn how an IR camera can be used by someone who designs electronics,

Read the Full Article Here!

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Arduino Clones Can Be Better Than Shields


Evil Mad Science's 'Diavolino' Clone

Evil Mad Science’s ‘Diavolino’ Clone

Arduino is certainly the most popular method of getting info electronics, or at least embedded electronics.  My BlueStamp Engineering students seem to gravitate to them when selecting their projects.  But what about after the first few projects have been created with the Arduino?  What if the designer wants to add a relay, or another LED to the board?  Most people create a shield which allows them to plug in, but for simple projects I believe there is a better way: creating their own Arduino clone (AKA Derivative).  This is where the designer modifies the public Arduino EAGLE PCB files to add their extra parts, and then makes their own board! It can save cost, space, and connectors!  I go into more detail on my latest Element14 post:

Derivatives enjoy some significant design benefits over a shield.  First, a single board is less than half the size and more robust than stacking an additional PCB on top of the purchased Arduino via headers.  Second, it will be a cheaper solution than buying a stock Arduino and the custom shield PCB/parts.  Finally, there is a lot to learn from starting with an existing PCB design and tweaking it.  Not to mention the pride one would get from creating their own stand-alone design, even if it is attained by standing on the shoulders of giants.

Read The Full Article Here!

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Finally, an Arduino library for EAGLE!

Arduino Library

Have you put together an Arduino-based circuit and looking to nicely (but easily) document it?  Or perhaps you’re looking to create an Arduino Shield with EAGLE and want to start with the correct dimensions of the headers.  Element14 has come to the rescue with the Arduino library of EAGLE parts for exactly that.  There are two types of components in this library: the standard version with a PCB footprint showing the key connections and the ‘EXT version which has no PCB footprint.

The Standard version will be great for those looking to create a shield or want to somehow integrate the Arduino somewhere on another PCB.  While the EXT version allows people to create a schematic that doesn’t bother with a PCB.  In the EXT case, the user can create a PCB that is intended to connect to an Arduino via cables that are shown on the schematic, but isn’t included on the PCB.

Faster documentation, easier creations!

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Compiling Chris’ Context: An Interview with Chris Gammell


Chris Gammell is an accomplished Electrical Engineer who currently works in electronics design by day and talks his head off about electronics by night to anyone that’ll listen.  He co-hosts The Amp Hour podcast, writes on ChrisGammell.com, tweets more than most engineers, and is on the cusp of launching a new way to learn electronics: Contextual Electronics.  I’ve known him from our time at Case Western Reserve University and two different jobs, and was able to catch up with him for an hour to discuss the direction he is taking, his experience, and a few lessons he’s learned along the way.  Check it out on Element14!

Read The Full Interview And Download The Audio Here!

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Frame-It: A Tool For Wading Through Millions of Parts

Hardware engineers everywhere know how crrazy selecting parts can be. Especially when a part change needs to occur months after intiial part selection. Why was this part so special? What were the nuances of it again?  Frame-it is a chrome extension that allows you to save a document or web page while taking notes as you go. Then everything is easily visible on your workbench.  I wrote a quick article to describe the tool, it’s quirks, and how I’ve been able to use it…

…Given the importance of the part selection process, surely there are many different tools out there to help discover, keep track of part possibilities, and manage notes that one comes up with while searching.  But sadly, the only tools that exist are the search tools provided by the part distributors.  These are great for finding parts based on a wide array of specs, however each search is merely a way to find information.  While some CAD tools like Cadence and Synopsys have solutions, they are expensive and generally only accesible to engineers at large companies.  Beyond that, taking notes and remembering parts is a job usually ascribed to Excel or a paper notebook.  That’s a great solution… for the year 1998!  That’s where Frame-It steps in…

Read the full article here!

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E14 Op Ed: A uC course for Everyone

Have you ever heard Hardware people swearing up and down that a failure cannot be a problem with the board?  What about hearing that after listening to the software folk extolling the virtues of their code while explaining how that very same failure cannot be a software issue?  Human nature can be a funny thing that affects all of us.
Maybe if more CEs and EEs took a microcontroller course, there would be more understanding and maybe even some humility among engineers…

….How can we prevent this unproductive riff raff?  It might help to have anyone involved in electronics (either the hardware or software side) take at least one course in microcontroller design to show the connections (and problems) that occur between hardware and software.   Any piece of circuitry will eventually need to be controlled or communicate with software, and software usually involves the real world at some point.  The most remarkable A/D circuit is useless if the communication bus that the digital signal must pass over does not have the required bandwidth.  Similarly, a beautiful chunk of code written to control an RGB LED matrix won’t work if the hardware isn’t designed to supply the required amount of power.  A course that forces the engineer to face problems on both sides can be humbling; for example a hardware engineer might spend hours troubleshooting his or her code only to find that the motor was connected to the wrong power rail…..

Read The Full Article Here!

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Chevy Keyless Entry Remote Failure & Repair

I currently drive a 2005 Chevrolet Cobalt which is a remarkable automobile in the most fundamental sense: providing reasonable transportation for a reasonable cost.  She currently has ~102k miles and going strong.  Although this last year I’ve had both of my keyless entry systems fail.  Since I’m the only one who usually drives the car, the solution was to switch the broken one out for the working one.  However the second keyless entry remote FOB failed last week, leaving me with only the key to access my car.  It’s a particularly big hassle since the alarm goes off when the door is unlocked and opened with only the key.  Ugh.

As with any failure, the first step is to understand the problem.  This involved cracking both broken units open to determine what might be the issue.  I was hoping for a dead battery, but no dice.  Each unit had a different, more significant problem:

Unit 1: Broken Solder Joint on the Batter Holder

The first unit had a bad solder join on the battery holder.  I love these problems.  2 minutes of soldering and I’ve repaired something that would cost well over $100 to replace, not to mention a trip to the dealer.  Yet another reason that anyone who owns anything electronic should have access to at least a cheap soldering iron :).

Bad Solder Joint

Unit 2: Worn out Carbon Pill Switch Actuator

After the first unit was repaired, I was hoping that the second unit had the same problem.  But when exploring it, I found that the trunk button worked great; it was the lock and unlock buttons that would not operate :(.  To test the silicone rubber keypad, I opened the unit and used the end of a flat head screwdriver to short the two exposed PCB traces, activating the switch.

This worked beautifully, suggesting that the carbon pill on the silicone button had worn out and is no longer conductive.  I measured the resistance of the carbon pill for the failing buttons and compared it against those of the working trunk button.  Sure enough, the working function had a resistance near 1Mohm, while the broken switch couldn’t get a decent reading.

To solve the problem, I brought out my conductive epoxy that I picked up years ago from the online surplus supplier, Electronics Goldmine.  As with most surplus stock, they don’t sell it any more.  But I’m pretty sure it’s simply normal glue with carbon dust mixed in.  After dabbing a little bit of glue on the carbon pill and allowing it to dry, I tested the switch and it worked great!  After pressing the refurbished switch many times, there was no dust or residue left on the PCB traces suggesting that it could work for a long time.  Although with these budget hobby solutions, there’s no telling how long it’ll last.

Carbon Pill Repair

And there you have it!  Two different reasons a keyless entry system could fail, and how to fix it.  All for less time and way less money than replacing them.  The same steps should also work for any carbon pill switch.  Most TV remotes, garage keypads, calculators, and test equipment all use this type of switch.


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E14 Article: EAGLE Autorouter Exploration

AutoRoutedAnyone who is getting into PCB design will automatically be intrigued by the autorouter. It would make sense to the outside observer that an algorithm would be able to process millions of iterations of routings that finds the best balance of short traces, few vias, and well-organized traces. Similar to cracking a random password – it is only a question of time before the ‘correct’ layout is found….

Head to Element14’s ‘knode’ to read the rest of my article that describes how to get started with EAGLE’s autorouter!

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