Ian Lesnet, Bus Pirate creator, has a new project for working with IR signals – the USB IR Control. We’ve talked about how to handle IR a bit in our meetings, but this looks to let you get a bit more in depth if you like. The cool piece is being able to view the IR information as signals in the SUMP logic analyzer. Looks like Seeed is building some for about $20 each (likely delivered in March.)

Just a quick site modification – the Next Meeting will now be posted in a section to the upper right portion of the page giving the date / time. We will try to post an update accordingly for all you RSS readers out there, but in case it gets missed it should always be to the right.

And just in case – the next meeting will be Dec 11, 2009 at 6:00pm at Company|Dallas.

The workshop is held at the facilities of CompanyDallas. The doors to Suite 2000 will be open. That door is just to your right as you exit the elevator on the second floor. The building is located at 1701 North Collins Boulevard Suite 2000 in Richardson, Texas. There are 3 entrances to the building. Go to the largest one, which has a small circle in front of it.

The front door of the building locks at 6 PM. There are three ways to get in. First, someone can let you in. If you come around the starting time, we will be watching the door and letting people in. Second, there will be a sign on the door with a phone number you can call. Third, in decent weather, there will be a buzzer to the right of the door. The buzzer is attached to a post with magnets.
You can get a map of the location at Google Maps by visiting this link. CompanyDallas is owned by Language Computer Corporation and the map will refer to that company.

We use resistors a lot on these projects. You need to understand a few things about them. Most resistors you find are barrel shaped pieces with wires coming out of each end. There are 4 bands of color painted on those. Those colors identify what the resistance is for the resistor. There is a nice online guide I use to lookup the values.
http://www.dannyg.com/examples/res2/resistor.htm

There is another style of resistor I use. I don’t know much about them. They are available at a couple of local stores I frequent and they work well for taking pictures of projects. They are large white box shaped pieces with the resistance value printed on the side in easy to read numbers. There is no guessing as to whether that band is violet or blue or if it is orange or yellow. These resistors handle a lot more power than is needed for a single LED. Most LEDs only need 1/8 watt resistors and these big white one range from 3 to 10 watts. So, if you wondered why I used them, it was not because I thought my LEDs were drawing that much power.

10k ohm barrel and 100 ohm box resistors

For LEDs, a common question is how big a resistor to use. If you buy your LEDs new, you should be able to get some specifications. There are 2 things you need to find out. What is the voltage drop on the LED and how much current does it draw? Then, visit the LED resistor calculator from ledz.com. There are certainly ways to figure it out yourself, but I just visit that website for a quick answer.

I am not a big fan of javascript, but both of the websites listed in this article use it to do their calculations.

There are several decisions you need to make when you purchase an Arduino. Arduino is a trademarked name that strictly speaking applies to only those parts made by the Arduino team. But, the design is open and they encourage people to adapt it and make varieties. Most of the products from third parties are completely compatible with the software that a branded Arduino would use. Strictly speaking, and as a class, those clones are known as Freeduinos.

First, what is an Arduino? Note that I am going to use the term Arduino to refer to the branded products and their clones. An Arduino is an Atmel AVR microcontroller loaded with a small amount of firmware(the bootloader) which gives it several characteristics. The bootloader makes the chip listen on certain pins for a remote computer to download programs. This saves on the amount of hardware needed to program the Arduino. It also make the chip execute the downloaded program in a certain way. The communications to the outside world occur on what is essentially a simplified serial port. The communications take place using only 2 voltages, unlike standard RS-232(see http://en.wikipedia.org/wiki/RS-232). The word microcontroller is also used in two ways on this web site. The Atmel AVR chip is strictly speaking the microcontroller. The Arduino is mostly a way of making the Atmel chip easier to use and interface to, and so I sometimes mean the microcontroller board.

The main decisions you need to make are:

1. how to communicate with the board
2. how to power the board
3. how to connect to the board
4. how much memory do you need

1. There are two main options you see on Arduino boards. Some have 9 pin serial port connections. Those have circuitry on the board to convert from standard Serial to the version the Arduino uses. If your computer has a serial port, I recommend a serial port connected Arduino as the simplest to use. Some Arduinos have USB connections. That must also be converted to the signaling the microcontroller uses and that is normally accomplished using a FTDI FT232 chip. Since that FTDI chip is a little expensive, some Arduino boards don’t put it on the board, but require you to buy a special USB cable that includes it. That saves you money, since you can use that cable on all of your Arduinos that need one.

2. One option here is to power the Arduino from the USB cable. The Arduino needs very little power and the USB cable has enough, as long as you don’t make the Arduino drive too much stuff connected to it(like 30 LEDs). But, you probably don’t want to leave a computer powered on and connected to the Arduino all the time. That kind of defeats the purpose of having a stand alone microcontroller. So, there is usually a way to plug in an external battery or power adapter. The simplest Arduino clones have no voltage regulation built in and need a 5 volt regulated supply. The type of regulator built in will govern what range of input voltages the board will run with. A common range is 7.5V to 18V. Anything in that range will work for a plug in power adapter. You are better off using a voltage near the bottom of the range, so the voltage regulator on the Arduino does not work as hard and get as hot. Don’t go lower than they specify, or the voltage regulator on the Arduino won’t be able to keep pumping out 5V to the circuits on the Arduino board. One thing to be careful about is that on some boards, you can cause a problem if the external board is connected at the same time as a USB cable. Sometimes there is a jumper that allows it. Be careful and check.

3. Some boards have rows of female pins along two sides of the board. You can then plug jumper wires from these to your breadboard. Some have pins on the bottom with the right spacing to plug right into breadboards. I personally like that style a lot. I would use them all the time, except I have not found any that also use a real serial port to talk to the computer. The ones with two rows of female connectors on top have a bonus feature. There are little daughter boards you can plug in there. They are called shields. More on shields later. I’d love to have a Danger Shield

4. The two main microcontrollers you will find on Arduino boards at the moment are the 168(Atmega168) chip and the 328(Atmega328). The 168 has 16k of program memory, 1K of ram, and 512 bytes of eeprom. The 328 has twice as much of all three. They both run at the same speed. There are bigger and smaller microcontrollers available, but start with one of those. I have not filled up a 168 yet, so don’t worry if that is all you can get.

A few recommended boards:

We have several ways to communicate with members of the group.

• We have an irc channel.  It is #embeddedworkshop on the irc.freenode.net network.
• We have this web site at embeddedworkshop.org where members are encouraged to add articles.  This is a family friendly website, so content that might embarrass someone’s little brother will be redacted or deleted.
• We are looking into adding a SIP conference room for use during the meeting, so check back for information on that.
• We have a micro-blogging on the system the cool guys use, identi.ca  See us at:http://identi.ca/embeddedworkshop
• Most recently, we have added a mailing list. Send an email to discuss-subscribe@embeddedworkshop.org to subscribe. The mailing list is moderated, but lightly. The intent is to foster discussion, and just to decline messages that are spam, or are not family friendly. All submissions must be plain text.