Encasement!

One of the things I want to do with this tiny computer system is build a PWCS (Personal Wearable Computer System) [I just made that up - like it?]. In order to do this I needed "something" to mount the actual computer system in and keep it's size down to a minimum. Currently there is no case for the Overo Earth computer as it's original design is for embedded applications, and I don't think they had "embedding within clothing" in mind when it was designed (grin).

I could have used most anything to make a case for the micro-beast (that is the Nickname I have for the machine). At first I thought about building up a case using either brass or thin copper and putting my "Leet" soldering skills to work but then realized that would not only be a little expensive (given the price of brass and copper sheet now days) but would have looked rather "tacky" as well - solder beads along seams just are not the same as welded ones (grin).

Next stop - the local Radio Shack store to see what they might have. That was a rather good choice as they have a 4-inch by 2-inch by 1-inch (10.16 x 5.08 x 2.54-cm for you metric geeks) Plastic Project Enclosure with a choice of aluminum or plastic lid (comes with both) for about $3.00 (USD).

Radio Shack Model: 270-1802 Catalog #: 270-1802

Since the enclosure is made of plastic it was rather easy to 'carve' the connector holes in the case with an X-Acto Knife (just be careful not to slice and dice yourself). Now - while I can solder with the best of them my X-Acto Knife skills leave a "little" to be desired! Who cares! Not me!!! It got the job done!

Here is my Overo Earth/Summit board (micro-beast) mounted in the enclosure. As you can see access to all of the "standard" interfaces is available from outside the case. Even the console USB connection is possible through the cutout in the back of the enclosure. I have not configured anything to access the 40-pin connections (yet) but that is a future project. There was a fair amount of modification to the stock case to mount the board in the enclosure - there are stand-offs in the case in totally the wrong locations that had to be removed and there are "slide-slots" running from the top to the bottom of the enclosure that have to be carved away but I think the effort was worth it - especially since there is not a commercial case for the board.

Now that I have the "computer" mounted within a case to protect it the next order of business will be to build the "world" interfaces for it. That will be the subject of a future blog entry!

Does Size Matter - You Bet It Does!

OK - I guess the title could be read as "something" from a certain type of "Television Commercial" but I could not resist!

The Overo Earth, mounted on the Summit Expansion board is still a very small computer system. If you don't believe this statement then take a look at the picture to the right!

Yes - that is an American Quarter and that is a Double-A (AA) Ni-Cad battery below the board.

If you look real close you can make out the outline of the actual Overo Earth board - it is just below the 40-pin holes under the Quarter and above the audio, HDMI, USB Host connectors on the Summit Expansion board.

The configuration shown in the picture is the most likely one most hobbiests or experimenters will use. You don't have to have "Leet" soldering skills or Microscopic Vision to build and solder the 70-pin connectors to access most of the capabilities of the Overo Earth computer - and - as a bonus you have video, audio, USB and console access directly off the Summit Expansion board - not to mention you don't have to build power conversion circuits for the 3.3-VDC/1.8-VDC power supplies needed to run the Overo Earth computer. For the price the Summit Expansion board is well worth it - just in the reduction of the "frustration factor" alone.

If you decide to access some of the more interesting interfaces, such as the SPI, I2C, 1-wire, PWM, ADC and the rest of the input/output connections brought off the Overo Earth computer you will need to keep the following points in mind:

1. All of the voltages to the different interfaces are 1.8-VDC. If you exceed this by very much you probably will let the "magic smoke" out of the Overo Earth OMAP-3503 integrated circuit as most of the interface connections go directly to the integrated cirtcuit.
   ( I will be describing a method to "translate" the 1.8-VDC logic levels to something more in line with current inexpensive sensor technologies - read: 3.3 - 5.0 VDC in a later blog entry)
   
   
2. You will need to supply the power externally to any interface devices you want to connect to the Overo Earth computer interfaces - the Overo Earth computer does not have the additional power capacity to run very many sensors, if any at all. The on-board power regulator does not have much additional reserve power capacity so it would be wise to power external sensors with an external power source.
   
   
3. If you decide to put a socket in the 40-pin holes on the Summit Expansion board instead of soldering wires directly to the hole locations put the socket on the BOTTOM side of the expansion board. The reason for the bottom placement location is to allow you access to the micro-SD location without requiring the removal of the Overo Earth computer from the Summit Expansion board. The 70-pin connector connections are pretty fragile and each time you remove and insert the Overo Earth on the Summit Expansion board you run a risk of damaging one or both 70-pin connectors. Better safe than sorry!

Overo Connections - reaching the outside world....

While the Overo Earth computer, in it's present form, has a great potential for all sorts of applications it has a "minor" drawback... Very little in the way of outside communications! While the computer has two 70-pin connectors with all sorts of input and output capabilities most, with the exception of companies with the skilled workforce, will have problems connecting to the computer!

To aleviate this problem Gumstix has an expansion board the Overo Earth plugs into that brings all sorts of connectivity to the miniscule computer board - Enter the Summit Expansion Board.

As you can see from the image to the right there are several connecitons available on the expansion board that allow you to access different aspects of the Overo Earth computer:

Features:

1. USB OTG mini-AB


2. USB host mini-A (experimental)


3. DVI-D (HDMI) video out


4. Audio In / Audio Out (stereo)


5. USB Serial Console


6. 40-Pin connector location on board
   (Signals available on 0.100-inch through-holes at 1.8V logic levels)

• Two (2) two-wire serial ports


• One 1-wire port


• 6-ea. PWM output lines


• I2C port


• SPI Bus


• 6 ea. A/D lines (at 1.8-V logic)


• processor control signal lines.
  

Power: 4V to 5.5V input

Connectors: 2-ea. 70-pin AVX 5602-24 connectors
(interface to Overo Earth board)

Size: 80mm x 39mm

Mounting: Four (4) x #2 mounting holes

Points of Interest:

1. As delivered the Overo Earth/Summit USB-OTG port is configured as a host port - you will need either a mini-A USB to mini-B cable (available from Gumstix for a reasonable price) or you will need to perform a modification (add a jumper) to the USB-OTG port. If you have really good soldering skills (the connector pins are really small!) you can put a solder bridge between pin-4 and pin-5 on the circuit board side of the USB-OTG connector to fool the computer into detecting a mini-A connector when you have a mini-B connector plugged into the USB-OTG port (this is exactly what the mini-A connector does). Personally I think it is better to just spend the small amount of money and order the correct cable - and if you plan to use the USB Host connection you will need a mini-A to mini-B cable anyway as the USB Host connector is designed for mini-A USB connector ONLY.
   


2. While the video output port is labeled "HDMI" and the Overo Earth is capable of HD-720P the factory configuration is currently 1024 X 768. If you want a different resolution you will need to setup a development environment and recompile the kernel to make the change to a different display resolution. If you don't have a monitor which supports DVI-D (or HDTV) then you will need to get a DVI-D to RGB converter to see the display.
   


3. The USB Console port is just that - the console connection to access the Overo Earth operating system during bootup or as a local terminal. In the Linux/Unix world there is a "console" that can be seperate from the normal display, and usually is. This allows debugging and initial configuration or configuration changes without the need for the system to be booted completely up where the connected keyboard, mouse and or display may not be active yet. Normally you don't need to have a "console" connected but it sure can come in handy if there is no other way to communicate with the system (provided the operating system is running and recognizes the console). During the bootup process messages are printed to the console so this port is very handy during bootup troubleshooting.

So Little Info - So Much Capability!

The Overo Earth by Gumstix is a very powerful, and VERY small computer capable of performing a great many tasks - if you know how to use it!

My reasons for building this blog about the device are two-fold.

1. I needed a "place" to put information as I found it that would be rather safe and easy to access (beats doing backups all the time and I tend to reformat things a lot).

2. I wanted to "share" the information with anyone interested in it. From the discussions I have seen on some of the mailing lists dealing with the Gumstix machines I thought this would be a pretty good way of sharing the information.

As I find information I will be posting it here. Hopefully you will find it helpful or at least entertaining.

Now, one thing that should be pretty apparent is the Overo Earth computer does not have any obvious interfaces available to allow you to see the display (neither a console or video display), any form of recognizable connectors to allow you to connect a keyboard or mouse to the unit, nor any form of additional connectors for such things as USB or audio (microphone or headphone/speaker). Hmmm - all of that is actually available, but not in the "form" you are used to seeing! If you look real close at the picture you will notice two connectors on the bottom of the circuit board. Each connector is a 70-pin connector with all sorts of input/output connections to the computer system.

I know - you are probably thinking you have to fire up the ole soldering iron (micro-tip please), get out the microscope (these pins are REALLY REALLY SMALL!) and make an interface board just so you can use the computer. Well, you can do all of that if you want to but I am basically lazy and the ole eyes are not what they used to be! You can purchase an expansion board from Gumstix which already has the different interfaces built on-board and is also configured with a 5-VDC power supply that converts the 5-VDC to the 3.3-VDC needed to power the Overo Earth board. The Overo board has it's own 3.3-VDC to 1.8-VDC triple-converter built directly on the Overo Earth board but requires only 3.3-VDC to operate. More on this in a following posting as this is the key to allowing low-power operation that extends battery life.


The expansion board is called the Summit Expansion board and is directly available from Gumstix, the same folks who build the Overo Earth computer.