Interfacing a PC to the outside world Part 2

by Mike Linnen 24. November 2005 20:26
Interfacing a PC to the outside world Part 2

In Interfacing a PC to the outside world Part 1 I mentioned that I wanted to work on a set of articles to discuss interfacing your PC to the outside world.  In part 2 I am going to continue the series and talk about what my first connection to the outside world is going to be. 

 

There are a number of devices that are designed to communicate over I2C.  I2C is a serial interface developed in the 1980's at Phillips Semiconductor.  The architecture allows for multiple devices to co-exist on the same 2 wire bus.  You can get more information on the I2C bus at the following: http://www.esacademy.com/faq/i2c/. 

 

There are a considerable number of devices that support the I2C bus.  A compass can be used to determine direction.  A sonar module can be used to detect obstacles.  A motor controller can be used to drive motors on a robot.  A servo controller to drive hobby servo motors.  All of these I2C capable devices (and several more) can be found at www.acroname.com.  I have done some research on PC I2C devices but so far everything I have found is fairly expensive.  I believe I can make a device that will bridge the PC to I2C gap and open up the world of I2C devices to PCs.

 

So a .Net I2C library is going to be the first project that I will do.  The library will support communicating on the I2C bus to other devices.  The consumers of this library should not care how the I2C communication is actually implemented.  So the primary goal of this exercise is to architect a provider model for communicating to these devices.  The benefits of this model allows for different I2C providers to be used without affecting the consumers. 

 

The first provider I will be creating will be a micro controller RS232 I2C Provider.  This will be  a small device that sits between the PC and the I2C devices.  The micro-controller's job is to intercept the serial commands from the PC and convert them into I2C commands.  I will be using a BX24 from Netmedia as this micro controller.  Later I will create a parallel port I2C provider that can be used in place of the micro controller RS232 provider.

 

The PC to BX24 I2C solution is a little more expensive than I intended to start with.  However I have a few BX24s lying around from other projects so it won't take a dent out of my pocket.  Also I have a Deventech compass to try the library out on.  Besides I also intend to use the BX24 for other interfacing projects.

 

    

Tags: , , ,

Robotics

Interfacing a PC to the outside world Part 1

by Mike Linnen 23. November 2005 10:15
Interfacing a PC to the outside world Part 1
 

I have been reading some of the Coding4Fun articles that are on MSDN.  Several of the articles are focused on connecting your computer up to external devices and writing .Net code to interface with the devices.  This has always been a main interest of mine since I am interested in robotics and home automation.  The resent release of .Net 2.0 has made some nice features available for doing serial communications.  Also Microsoft has made the Visual Studio Express editions freely available for 1 year.  This makes up a great solution for the general hobbyist to play with software and hardware.  So I thought it was time that I start my own set of articles on building software and integrating it to hardware devices.

 

So I gave it some thought on where to begin.  What project will be a prime candidate?  How would I build the foundation so I could leverage different hardware solutions to a given interface problem.  So I decided on a few goals to keep in mind about the project:

  • Provide a solution to an interfacing problem that could be used in many projects.
  • Build the library using .Net 2.0.
  • The library should extract the consumer from any hardware implementation.
  • The library should be testable without hardware implementation. 
  • The library can use external pluggable components to fulfill the interface to the hardware itself.  So 3rd party components can be built and plugged into the library.

 

Stay tuned for a series of articles on this project

Tags: , ,

Robotics

.Net 2.0 Serial Port

by Mike Linnen 19. November 2005 17:53
.Net 2.0 Serial Port

Hey looks like the new .Net 2.0 supports a serial class that makes serial communications a snap.

http://msmvps.com/coad/archive/2005/03/23/39466.aspx

I need to get going on some project to try this out.  Maybe a PC to BX24 project that will be useful in my house.  I need to give it some thought. 

VS.Net 2005 and NUnit

by Mike Linnen 17. November 2005 21:50
VS.Net 2005 and NUnit

Well I have been looking at VS.Net 2005 some since it has released.  I wanted to try out some of the new features.  Well I am pretty attached to using NUnit so once I got a little bit of code going in VS.Net 2005 I decided it was time to try NUnit.  Fortunately there is a new iteration release of NUnit (2.2.3) that works with VS.Net 2005. 

So I downloaded it and wrote my first test like I always do.  Create a test project, add a reference to NUnit, add a new class, put a TestFixture attribute on the class, and add a public method that returns void that also has the Test attribute. I then proceeded to fire up NUnit GUI and run the test. However the test I wrote does not show up in the GUI. I fiddled around with the test code for a while and I even downloade the NUnit source code to try and figure out why my test was not seen by NUnit. Well after about 30 minutes of messing around I realized that when you add a new class to VS.Net 2005 project it looks like the following

using System;
using System.Collections.Generic;
using System.Text;
namespace ProtoSystem.Scrum.Business.Tests
{   
   class Class1
   {
   }
}
I never noticed the fact that public does not appear before the keyword class. So the test class could not be seen by NUnit.

Building water rockets

by Mike Linnen 14. November 2005 11:54
Building water rockets

I have wanted to do this with my kids for some time.  I have seen several kits that are expensive that I just don't care to purchase.  Well now I have no excuse http://homepage.ntlworld.com/telescope/Rocketweb/index.htm

 

Tags:

Misc

Another Test example for the BX24

by Mike Linnen 20. October 2005 01:25
Another Test example for the BX24

A previous post I explained how simple it is to test your code even though you might not have a fancy test framework like NUnit.  In this post I am going to give another example of what I did to tackle a robot navigation problem and fully testing it without actually running the code in a real robot.  My point here is that it is a good practice to write test code to test sub modules to simulate all possible scenarios that would be tough to do in the real robot.

So here is the problem:

I have a compass module that outputs a heading value that equates to 0-359 degrees. I needed a module that when given a target heading and a current heading it could return the differance between the two in degrees. The return heading difference would range from -180 to 180 degrees. This return value could be processed further to determine which direction the robot needed to turn to reach the target heading. A negative heading ment to turn left and a positive number would mean turn right.

So my approach was to first identify a list of target and current headings and what I would expect the return value would be for these input parameters. I did this for 17 different scenarios. I placed the values in a spread sheet and analyzed the pattern that emerged. I took this pattern and coded a simple class (module) that would impliment the pattern.

Here is the method of the class:

Public Function GetHeadingDifference(currentHeading as Integer) As Integer
  ' Returns the following
  ' -180 to + 180
  ' Negative number means the robot would have to turn to the left to get closer 
  ' to the targetHeading
  ' Uses module variable targetHeading
  
  Dim targetMinusCurrent as Integer
  targetMinusCurrent = targetHeading - currentHeading
  
  If (targetMinusCurrent<181) And (targetMinusCurrent>-181) Then
    GetHeadingDifference=targetMinusCurrent
    Exit Function
  End If
  
  If (targetMinusCurrent<-180) Then
    GetHeadingDifference=360 - ABS(targetMinusCurrent)
    Exit Function
  End If
    GetHeadingDifference=(360-ABS(targetMinusCurrent)) * (-1)
End Function

I then created another test class (module) that would call the navigation module and pass in the 17 scenarios and validate the return heading.

Public Sub Main()
  '.......... Test code ..........
  'This needs to be done only once per program, or when you want to change the baud
  Call UARTsetup(3, 19200)  
  InitializeNavigation
  Dim testResult as Integer
  Dim newHeading as Integer
  Dim targetHeading as Integer
  Dim currentHeading as Integer
  
  '****************************************
  'Test TestHeading
  '****************************************
  DebugPrintLine "TestHeading Tests"
  newHeading=180
  currentHeading=180
  SetTargetHeading newHeading
  testResult=TestHeading(currentHeading)
  If (testResult<>0) Then
    DebugPrintLine "Test 1 Failed"
  Else
    DebugPrintLine "Test 1 Passed"
  End If
  newHeading=180
  currentHeading=183
  SetTargetHeading newHeading
  testResult=TestHeading(currentHeading)
  If (testResult<>-1) Then
    DebugPrintLine "Test 2 Failed"
  Else
    DebugPrintLine "Test 2 Passed"
  End If
........... more test code omitted for clarity 
End Sub 

I used the 17 scenaros that I layed out on the spread sheet to prove out my logic. Since the module is fully tested based on these scenarios I have complete confidence that the module will work when it is included in the main robot code project.

External Drive what a life saver

by Mike Linnen 8. July 2005 23:15
External Drive what a life saver

Well I have wanted to get an external drive to solve one primary problem I have. Desktop and Laptop synchronization.

First Some Background

I am a permanent virtual employee for a company in Scottsdale Arizona. I use the company desktop PC in my home office. I routinely travel to Scottsdale which forces me to take along a laptop. The main problem I have is getting my files off the desktop and onto the laptop for the trip. Then when I return from the trip I like to move the files from the laptop onto the desktop. Well to transfer a large amount of files over ethernet from desktop to laptop and back can be a very slow process while VPNed in. The transfer goes through Scottsdale. I can't even use local IP addresses to route the traffic. Currently I only had one option. Disconnect from VPN and transfer the files. This basically keeps me from working at all while the copy is happening. So I needed another solution.

Enter the solution

Since I had a Comp USA gift card of a sizeable amount I decided to start at my local store looking for an external drive solution. I had an old 5 1/4 30 gig hard drive that I intended to just get an external USB case for. The drive came out of an old computer and I wasn't even sure if it was fully functional. Looking at external cases they where around $40. Seemed like a large amount of changed to drop on just a case. So I started to look for another solution. I stumbled across the Hammer Storage 80 gig USB 2.0 device that was on sale (with rebate) for $69. Most other external drive solutions started at $99 so this seemed in my price range. So I grabbed one of these drives and took it home.

Conclusion

I am very happy with the device. You don't even have to load any drivers for it! It just works! I made some simple batch files to copy the data from my desktop to the external drive. And it worked relatively fast. The best thing is that I can continue to work as it is copying files. Now getting my laptop ready for a trip is no longer a painful process.

Tags:

Misc

Copy podcast program update

by Mike Linnen 30. June 2005 20:26
Copy podcast program update
Noticed another little problem with my copy podcast program. I need to do some clean up on the directories of the destination (SD card). After I delete podcasts on my pocket PC many empty folders start to accumulate. So I need to add a process to clean up empty folders on the destination folder.
So far I have been using this program for almost 2 weeks. I like this setup a lot better than just relying on Doppler and Microsoft Media Player to manage the synchronization process. All I need to do is make the copy program a little more friendly and add a few abilities to the Media Player to support bookmarks and auto delete.

Adjustments to my podcast copy program

by Mike Linnen 22. June 2005 14:45
Adjustments to my podcast copy program
In my program that copies podcasts over to my SD card I noticed a few things that need to be changed.
The way I am using this the copy process is really a move. I am moving the file to the SD card from it's original place on the local PC hard drive. This means the file should retain it's original date. I do not think it is doing that in my program.
Files should be moved in chronological order. This helps to ensure the oldest files get copied first in the event there is not enough room on the destination.

Tags:

Software

Getting podcasts onto a Pocket PC

by Mike Linnen 21. June 2005 00:35
Getting podcasts onto a Pocket PC
This is a follow up on my post about Listening to Podcasts. I went ahead and developed a small application that grabs the podcast files and moves them to the removable media card. Here is a little idea on what it does.
  • Tests to be sure the destination folder (removable media card) is available
  • Looks for files of type MP3 in the source folder walking all the directories
  • If a file is found verifies that enough room is on the destination folder
  • Copies the file to the destination
  • Removes the file from the source
  • When all files are processed it looks for empty directories in the source directory and deletes them

All I have to do when I am done with listening to the podcast on my Dell is delete it. The only problem I have left is that the Windows Media Player does not support bookmarks.

Room for improvement:

 Currently the application must be launched manually and pass into it the source and destination directories. It would be nice to have a service that just watches the source folder for new files and process them as they come in. The program looks for mp3 files only. It would be nice to add support for other media files.

Tags:

Software

About the author

Mike Linnen

Software Engineer specializing in Microsoft Technologies

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