Archive for category Computer
A few weeks ago we had a serious storm here in the SF Bay area and the power went out for about 5 hours. It took a few days for me to realize that the internet connection was running pretty slow, so I started trying to trace it.
I’m using Comcast IP service and right out of the cable modem I was getting 21Mbps (using the Speakeasy speed test). After the first Netgear gigabit switch the bandwidth dropped to about 3.g Mbps and after the second, it dropped less than 1.0 Mbps. Killin’ me!
So after some Google searching I found that the Netgear GS605 v2 was susceptible to power surges which often happen during or after power outages. The problem is apparently in the poor quality capacitors used. Once replaced, they are back to full force with less than $10 worth of parts and about 20 minutes. Here’s how I replaced the capacitors.
- Soldering Iron
- Solder Sucker
- Torx Screwdriver (T8)
- 2 x 1000 uF 10V, 1 x 470 uF 25V capacitors
Open it up:
On the bottom there are some rubber feet that can be peeled back to reveal tiny torx head screws (from my set I used a T8). Unscrew the 4 screws. The PC board is not secured further, so when you remove the back, you can jiggle the PCB and it will come out as a single unit.
Removing the capacitors:
On the PCB you can see 4 capacitors:
- 2 x 1000 uF, 10V
- 1 x 470 uF, 25V
- 1 x 100uF, 16V (looks like part of the power regulator, I did not replace)
To remove the capacitors, I first tried using one of those solder sucker tools but I think my soldering iron it not getting hot enough. I basically put some side pressure on the exposed post oposite the capacitor side of the PCB and when the solder melted, the capacitor slipped out at an angle. Doing the same on the other post released the capacitor. I removed the 2 1000 uF caps and the 470 uF cap.
I went to Radio Shack and purchased:
- 2 x 1000 uF, 35V – $1.79 ea.
- 1 x 470 uF, 35V – $1.49 ea
The replacements from Radio Shack were their generic versions, bigger in size and higher in rated voltage but I wanted to get it done and not wait a few days for an online order.
Because the new capacitors were so large, I had to mount them sideways. on the PCB. This is generally straight forward if you pre-bend the leads. Put the cap in place and with needle nose pliers, pre-bend at the appropriate lengths. The 1000 uF cap closest to the edge needed to be bent with the leads in a slightly overlapping form, but once you get in there it should be obvious. Here’s what it looked like.
This is going to be a base post (I’ll make it sticky) to hold the outline of tutorials related to various aspect of wireless sensor networks. From the sensors and radios, to a gateway, to web services, data logging and eventually, charting and analysis. Look at this overview of Wireless Sensor Networks on Wikipedia.
Our interest is in developing a wireless sensor network platform that is inexpensive and simple to use. There is a sweet spot between super high tech and older outdated technology where we believe there exists a meaningful set of technologies that will fit our goals.
What we’ve discovered is that we can use radios, like the xBee radios from Digi, with up to 4 sensors hooked up to each one, as our remote sensor boards. We have also discovered that we can transform a wifi router into a tiny, low powered computer running an embedded, open source, operating system called OpenWRT. Many wifi routers have a serial port available on the main pcb inside the device to which we can hook up a coordinating xBee radio; the counterpart to the ones on each sensor board. Then we install a scripting language, Python, into the Linux operating system. Finally, we install python scripts which can be used to collect the data being transmitted from the sensor boards and send that data to web services like Cosm (formerly Pachube), ThingSpeak, Open.sen.se, Paraimpu, etc.
So we have wireless sensor boards sending sensor data to a radio wired into the serial port of a wifi router. The wifi router has been re-flashed with an open source embedded Linux operating system, OpenWRT, and to that we’ve added Python as an easy to use scripting language. We have then added various scripts to bundle the incoming data and send it to the internet for further processing, charting, and so forth.
It is an inexpensive, flexible, easy to use, wireless sensor network platform.
In this ongoing quest to learn more about sensor networks I’ll add links to the Resources Page.
Here’s a list of notes we’ll be updating with information about how to build you’re own wireless sensor network.
- WSN: Sensors: this is where is all begins. The sensor responds to some environmental events and generates a voltage or a digital signal. I’ll be going over a few sensor types that I’ve built; Tweet-a-watt, Temperature, Gas (example of indoor air quality), and a Force Sensitive Resistor (FSR) as an example of Elder Care.
- Radio: XBee – Radios allow us to create the wireless part of sensor networks. The XBee radio is very accessible to beginners even if configuration is a bit challenging. I’ll describe the various aspects of XBee radios that I’ve used.
- Gateway: Wifi Router – in the original design for the Tweet-a-watt the output from the sensor’s transmitter sent data to an XBee receiver hooked into a PC (via FTDI-USB). The approach I describe uses a low powered (about 4 watts) Asus wi-fi router in place of a PC. I’ll describe using OpenWRT as a replacement OS and adding a USB memory stick to extend the storage memory of the device. I’ll also show how I added python with web service calls in order to send data to the internet.
- Client facing site: a site for users to register their gateway devices and manage the sensors associated with each. Also the place to look at the charts and subsequent analysis for the sensor data. This is an MVC web application written in C# and ASP.NET using Visual Studio 2010 Express and SQL Server 2008 Express.
Next: WSN: Sensors
Computerized Electricity Systems has a software/hardware home energy solution that tracks energy usage in a residential setting. They offer a replacement electrical panel that allows for monitoring of energy usage within the various breakout lines of the house wiring. They also provide a software tool, a portal, for displaying the energy being used.
System prices range from $600-$3000 depending on the options.