ABOUT:

This is a circuit I designed to generate a PWM signal for an RC servo given an analog voltage or high frequency PWM.  It has no microcontroller and can be built with one quad op-amp and passive components.

The op-amp I used in my implementation is a NJU7034D-ND, available from digikey, but any rail-to-rail quad op-amp will do.

Since the input stage has a low pass filter built in this circuit will accept a high frequency (>~5kHz) PWM as an input in addition to analog voltages.

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March 2nd, 2010  |  James  |  Link  |  No Comments

We recently had a computer in the shop that had a Hard Disk password and a BIOS password set on it.

The Hard Disk password is stored not only on the logic controller, but also on the disk itself, and make the drive unusable without entering the password.

Under normal circumstances, people will password protect their windows logon, but their data is easily obtainable just by removing the hard drive and accessing it from another computer.  If you set the Hard Disk Password, this is not the case.

This customer happened to know their Hard Disk password, though they had inadvertently set it while going through tech support with someone else (I don’t know how it came to this, but we don’t ask questions, we just fix what people want us to fix.

The hard disk password was just an extra step to go through at startup… it wasn’t really a problem, just a nuisance.  She asked if we could remove it, which is usually an easy process by entering the BIOS.  To our delight, when we attempted to enter the BIOS, there was a password on that as well.

Again, the system started up just fine, so being locked out of the bios only becomes a problem when you need to get into the BIOS.  Most people never do, but it’s a fairly common thing around a computer shop.  The customer didn’t know her BIOS password, or that it had even been set.

If you start your googlehunt for BIOS password recovery, you will find everything from default backdoor passwords for various BIOS vendors, methods for resetting EEPROM memory by shorting out pins, removing the CMOS battery, and a hundred other “proven methods”, but not one thread that ends with “thanks, that worked!”

The bottom line is that the BIOS password is a security measure that is meant to protect your computer in the event that it is stolen.  Most never enable theirs at all, but if you do, make sure you put it somewhere secure and remember it.

In the case of our customer, after a few hundred tries we were able to guess the password, which was derived from the other passwords of hers that we already knew.  (That’s lesson number 2, don’t make your passwords to similar or people like us can guess them!)

-Chris

March 2nd, 2010  |  Chris  |  Link  |  No Comments

A clean install is a reinstallation of your operating system “from scratch”.  Under most circumstances, this is a last resort when the operating system is so badly damaged, corrupted, or otherwise uncooperative, that other options won’t work.

Some other reasons to do a clean install are:

• When transferring a computer from one owner to another.  This is to delete any personal data and make the computer “new again”.  This is a great option for parents who want to “hand-me-down” their computers to kids.
• When buying a new computer.  It’s a stretch, but some new computers are so bogged down with crapware from the manufacturer that customers just want a clean copy of Windows without popups from HP and Dell appearing every 5 minutes.  (It’s usually simple enough to disable or remove these programs individually, but some people just feel better with a clean install)
• When moving a computer to another user in an office.  Many employees like to make the computer “their own” and add every toolbar known to man, icon and sound tweaks, weatherbug, ding!, and a hundred other background apps.  Sometimes it’s easier and faster to do a clean install then to manually remove lots of programs.

The biggest causes for concern when doing a clean install are personal data and programs.  After the installation is complete, you’ll have a pristine copy of Windows with NO PROGRAMS, and NO DATA in the user’s My Documents, Desktop, and other personal folders.

Moving data from one installation of Windows to another is pretty straightforward.  When we do a clean install, we will generally backup the Documents and Settings folder in its entirety, storing it on one of our temporary file shares, and then restoring everything to the clean install.

The original inspiration for this blog entry was to emphasize that a clean install means you will lose ALL of your programs.  If all you use is Firefox, AIM, and BitTorrent, then your reinstallations are just a download away.  However, that expensive Microsoft Office Suite, Quickbooks, Games, and anything else that is not a part of Windows will NOT be there waiting for you after a clean install.  You will need the installation media and license keys that came with these applications, and you will need to run each installer separately.

We like to remind people that however their computer is running, it’s just a period between clean installs (like a warm period between ice ages).  You should always have installation media and get yourself int he mindset that you might have to rebuild your system tomorrow.

-Chris

March 1st, 2010  |  Chris  |  Link  |  No Comments

We often find ourselves the new owners of our customer’s old computers. Some cheerfully donate them for parts, some just don’t want to ever look at their old laptop again (this stems from the same bitterness that caused them to get a new one in the first place).

This post will show you how to put a nearly dead laptop to good use: Make it a digital sign! You will need the following:

• A dying, old, or otherwise neglected laptop.
• A spare LCD display.
• Display cable, power cables, network cables.

First, we gut the laptop.  The screen was failing, the case was cracked, and it’s lugging around a dead battery, CD drive, and other parts we won’t need anymore.  We carefully remove the motherboard and discard the pile of screws, connectors, and plastic that’s leftover.

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February 25th, 2010  |  Chris  |  Link  |  No Comments

This program lets you download all the results of a Gmail search query.

Download the source here.

Download the windows executable here.

About:

One of the things I love about Gmail and Gchat is the logging. Every chat I make using Gchat is stored in my archives just like an email.

Unfortunately, though you can download and archive all your regular emails through Gmail’s POP interface using regular email backup tools, for some reason they don’t allow access to the chat logs this way.

Another thing I love about Gmail is the powerful search feature. Google writes search software well, ’nuff said. Unfortunately, you can’t really download emails through a standard POP-based program based on a Gmail search query (if there’s a tool that does this let me know!).

So I hacked together a small program that addresses all of these issues. GmailDownloader is a command line program through which you can:

• Log into your Gmail account
• Run a Gmail search
• Download the results (including chat logs!)

It runs on the Gmail web interface, so it bypasses the restrictions of POP access.  There are limitations to this program:

• If you download too many messages in too short a time, Gmail could detect this as unusual activity and lock you out of your account. I’ve successfully downloaded 1100 messages in one query without being locked out.  I’ve been locked out several times though when trying to download much more all at once.  The lock was released several hours after filling out the unlock captcha each time.
• Since the Gmail web interface is not a standard like POP, it could change at any time and make this program stop working.  Let me know if that happens and I’ll try to update it.

This program uses python, libgmail, a hack to libgmail from this awesome guy, mechanize, ClientForm and ClientCookie.  It is based on the libgmail example program ‘archive.py’.  The Windows executable was generated using py2exe.

Howto:

1. Download and unzip the executable (or the source code… it should run out of box if you satisfy its dependencies)
2. Run the executable.
   

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February 19th, 2010  |  James  |  Link  |  2 Comments