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Applying micro controllers to the real world often involves sensing motion, position or the proximity of objects.  A very simple sensor is the optical switch consisting of an IR LED emitter and an IR-sensitive phototransistor.  These can be arranged to detect directly transmitted light (photo interrupter) or the reflection of light (proximity detector) and they can be packaged into a self-contained sensor or used as separate emitter / receivers.  The photo below shows an interrupter type and a proximity detector type that may be purchased for less than a buck a piece.

From KuzyaTech

KuzyaTech has a gerat article on producing printed circuit boards at OSH Park using files generated by DipTrace.  Following these recommendations will help ensure you get the boards you expect.

Well, my test design is complete and now I need a few prototypes to play with. The usual ways of ordering PCBs are rather expensive, with just tooling fees in hundreds of dollars. The remaining options are a few China based places, and an OSH Park ran by Laen from Dorkbot. He runs a community PCB service that groups orders and orders them periodically on a common panel, sharing costs between all people. The cost is very reasonable ($5 a square inch) and you get three boards. So a 2″ board in three copies will cost you $10 delivered. That definitely opens the door for quick prototyping of pretty much anything! After having used other company’s prototyping services, I must say OSH is also by far the most user friendly. Lets walk through the steps of ordering these boards.

First you need to check that the design complies with the design rules listed.  Ideally those are setup at the beginning so that you do not have to deal with things being too close or two narrow after the fact. Here is what they look like in DipTrace (Under Verificaton, Design Rules)

Read the entire story

As MrDEB contemplates using another LCD, Dave Jones has created another great video on using Dangerous Protptype's Bus Private for testing an LCD display.  I've mentioned the Bus Pirate here before - it'sa serial analyzer/interface that understands a number of protocols.  If you're trying to figure out an I2C, SPI, UART or One-Wire interface (among others) the Bus Pirate can be a huge asset.

Dangerous Prototypes makes an 74HC595- based converter to go from the serial protocol that the Bus Pirate understands to the parallel interface of a character LCD.  If this sounds at all familiar, it's a technique that been discussed by mrbasher and Mike here extensively in the past.

Dave makes quick work of checking out a 8x2 display with the Bus Pirate.  As with most of Dave's videos, there are lessons to be learned, including the dangers of using dual-row header cables.  Dave had a crossed cable between the Bus Pirate and the '595 adapter board which was quickly found and corrected.  If the cable had been reversed between the '595 adapter and the LCD, the outcome mat have been much worse.

Dave is very good at systematic troubleshooting - watch and learn.

Ignore the hype -this video shows a vine glass shattering using the system I built.  Note the incredible deflection before it shatters explosively. 

 Shatter Sessions TV from Creature on Vimeo.

In appreciation for my help on the glass buster and other projects, my producer friend gave me a new iPad .  Very generous and appreciated.  This of course opens up a new world of applications and projects and a sudden interest in magazine articles about interfacing to the device.

In the current issue of Nuts&Volts, there is an article about using an iPxxx as a moisture meter for watering plants.  It connects using only the audio port and uses no external power source.  At a quick glance, I guessed they were using the microphone input as a ADC to measure moisture content but a longer look showed there was more to the system than that.

The moisture meter is based on a Project HiJack interface.  This is a fascinating interface developed by Ye-Sheng Kuo, Thomas Schmid and Prabal Dutta at the University of Michigan and was presented at the ISLPED’10 Design Contest.  The paper presented for the contest is very informative and can be found here.   This incredibly cheap interface has two unique features that allow it to be used with many audio devices: 1) It derives power from an audio signal to power the required circuitry and 2) it used audio tones to create a bi-directional interface over the audio path.  One of the driving goals to to create a low-cost interface that could be used with a huge range of sensors in developing countries.  One of the awesome demonstration projects is a 2-lead EKG.

[Aurthor's Note: I wrote this article several years ago for another website.  The information is still accurate.  "Doug In The Woods" wrote to my Clever4Hire email address asking for some guidance, so this seemed like a useful reference to republish.]

Having your own web site used to be a daunting task, beyond the reach of casual users. Expensive hardware and software or costly hosting services were required to get a web site on line. Design of a web page required complicated software and an extensive knowledge of HTML to design nice looking pages.

I'm happy to report that recent technology has changed this situation so that nearly anyone can afford to have a nice looking web site! You might be surprised to learn that the total cost to have your own web page is only about $10/year! And no costly software is required to create the pages for the site.

Domain registration, hosting, page creation software? How can the web site cost only $10/year?

Dave's got another great video on how to use a simple push-button switch as an on/off power switch.  Using this circuit can save the cost of a high-current toggle switch and makes a very clean user interface.  As usual, Dave carefully explains the details of the circuit in a clear, concise manner.

Watch the video for complete details.

From EngBlaze comes a great article on turnings a rats nest of wires into a circuit board.  The article is filled with good tips!

I've quoted four sections of the article below.  Trust me, I know how easy it is to make these mistakes! 

The Full Article

Double check RX and TX pinout

In standard electronics nomenclature, serial TX stands for “transmit” and RX stands for “receive”.  Unfortunately, part manufacturers aren’t always so kind.  On some devices, TX is an input and RX is an output, defying all logic (or using some twisted reasoning where you need to tie both “RX”s  and “TX”s together).  Even if they do use the normal notation, it’s easy to get things crossed up, so make sure you double check your prototype connections before you implement them in your PCB schematic.

Check the overall footprint of your board

Notice a theme with the checking yet?  Welcome to the wonderful life of an engineer.  As a real engineer, you’re responsible for real things, often expensive ones.  As un-glamorous as it is, double checking just about everything ensures that you only have to make that expense once, not twice.

In this case, it’s important to check the footprint of your board to make sure that your components are placed and sized correctly, and won’t get in the way of each other.  The best way to do this is to print out your silkscreen layer 1:1 on paper.  If you have chips or components that you’ll be using on the board, place them on the paper to see if their footprints are correct.

Dave has posted another excellent video blog, this one a hack he did on a Hakko FX-880 soldering iron.  The hack is interesting because he solves a design problem  and explains in detail the circuit he uses.  It's a worthwhile watch to see his methodology in problem solving.  It's good to note that his solutions don't always work out, but he analyzes the results and adapts.