Weird Wireless

-
I'm visiting a friend who has a new house and a new wireless setup from Telefónica. He needed some help from his company IT department to get the thing working. On arrival he tells me that he can use the wifi connection and it works, but at the same time the computer says it is not connected.

I suspected that odd behaviuor could be due to the common WinXP/manufacturer driver schizophrenia where both the system and the wifi card manufacturer's software are trying to manage the card settings. I tried to disable the WinXP handling of the card but then I was getting disconnected. So I tried the wifi card's software: Hmmm, cool! Network scanning shows a beautiful sonar-like display where you can the different networks on your neighbourhood, names, MAC addresses, channels and ... surprise: There are two different AP using the same ESSID nearby on different channels. This is probably because a neighbour has a similar setup as my friend's.

Ok, time to change the ESSID to something different, like my friends first name. However, I cannot log on the wireless router web interface. I do not know the admin password and it is not provided together with the user documentation. What it is provided is a windows software that does the configuration of the wifi router. A couple of attempts gets the ESSID changed to unique name (unless in this neighbourhood).

Now I should be able to get my laptop and my wife's working at my friend's but it is a no go. My laptop just cannot see that network name even if am ten inches away from the router. It does not seem like a signal problem as my friend's laptop is working ok. I started my trusty Ubuntu and I can see the network and I can received the beacons using ethereal with the card on monitor mode but I cannot log on the network. The problem becomes apparent when I try to select the channel: iwconfig eth1 channel 12 gives me an error. So the problem is that channel 12 is not allowed in this country and both Ubuntu and WinXP are avoinding it. Time to change to a new channel.

Once the channel has been set to a valid channel everything goes ok with any of our systems. Please note that setting your ESSID to a unique name in your neighbourhood is a key point to get a trouble-free wireless experience. If you use the default ESSID of your router you are calling for trouble. You can or cannot be lucky, but if you are unlucky the problem is that you'll have intermitent connectivity.

Comments

Post a Comment

Popular posts from this blog

VFD control with Arduino using RS485 link

-
Image
Variable Frequency Drives ( VFD ) allow the control of spindles so speed can accurately be controlled and a detailed acceleration profile for the spindle and reverse rotation can all be handled. In essence a VFD is an three phase inverter for three-phase AC motor. I am using a popular (I mean cheap) Chinese VFD and though the reference manual is not great, I could see there is a built-in RS-485 port. I usually control the start, stop and speed selection using the keyboard on the unit but I thought it will be more useful if I could control everything from the same Arduino is doing our CNC table control. Some cheap RS-485 off eBay and some lines of code later, I can start, stop and change the speed from an Arduino. What a cool thing to have! Some configuration of your VFD are needed before you can use it like that.  You need to set PD163=1 (I am using address 1 in the code). PD=164=1 (for setting serial to 9600bps) and PD165=0 (for using ASCII and 8N1 character format)
Read more

How to get sinusoidal s-curve for a stepper motor

-
Image
After some experimentation, and delving a bit into the math of motion, I realized there can be a significant difference on the motion of a machine by just making small changes. A common and popular approach to smooth one axis of motion is to use a trapezoidal speed pattern, where acceleration and deceleration are uniformly accelerated movements (aka constant acceleration motion) separated by a portion happening at cruising speed. The problem comes with the fact that, while that approach is simple to understand and to code, it does contain sudden changes in the acceleration, that show as spikes on the acceleration derivative, called jerk. These sudden changes in the acceleration translate into undesired vibration in our machines. Most of that can be eliminated by selecting a motion pattern that does not contain sudden changes of acceleration. If we chose a mathematical function for our speed whose second derivative is continuous, then we reduce system vibration quite a lot. One ma
Read more

Importing OpenSCAD designs into Onshape

-
Image
After using Onshape CAD software for a while I am really fond of it. So one natural thing to do, specially once they have released the Instructor's kit is to start using it in the classroom too. But one thing I was not so sure how to do was to use old designs I made using OpenSCAD. It does not mean I am completely quitting using OpenSCAD but suddenly I can see I can do assemblies in Onshape that will look quite nice for showing and documentation purposes if only I could easily import from OpenSCAD. I am glad to report that the route OpenSCAD --> FreeCAD --> Onshape worked brilliantly. Even more when a few tricks were applied. While some people suggest to import CSG files from OpenSCAD to FreeCAD, I have had more success by directly importing SCAD files into FreeCAD. One trick that worked well for me was to get rid of $fn references, so now circles become real circles (or cylinders) in FreeCAD. If a part keeps some $fn references then your cylinders or circles wi
Read more