High quality scanning vs. small file size

This post will not talk about scanning only, but about the whole process of turning a sheet of paper, a magazine or a book into a high quality digital document of the smallest possible size. Nothing will be lost during the conversion as lossless compression will be used and OCR will be run on documents. A low quality scan is hard to read (impossible to run OCR). A high quality scan must preserve as much detail as possible, must have the correct page size (when printed at 100%, the resulting copy should be exactly the same size as the original), must load as quick as possible on low-end devices and shouldn't eat the whole drive space. Software processing of the raw image from scanner plays a very important role. Yet, if the image from scanner has a low resolution, further processing is useless and may have negative results. All software used in this tutorial is free (some apps are open-source). But let's start with the basics.

Draw electronic schematics using LibreOffice

Draw is a powerful vector graphics drawing software. It is part of the free office suites LibreOffice and Apache OpenOffice.

There are a lot of free EDA software solutions but none of them allows users to 'customize' the schematics as they want (for example part colors - outline, background, including high resolution images in the schematic etc.). This tutorial will cover some aspects of drawing schematics in Draw. Similarly, schematics can be drawn in any other graphics software (for example Inkscape, even GIMP and Scribus).

Make a bootable Windows USB from Linux

Ubuntu has already an application called Startup Disk Creator, but this can only be used to make Linux bootable USB drives. To make a Windows bootable USB there was an application called WinUSB but it is no longer under active development. The following guide has been updated and works on any Linux distribution as long as it has GRUB and GParted installed and can make bootable USB for any Windows version newer than Vista: Windows Vista, Windows 7, Windows 8, Windows 8.1 and Windows 10. UEFI boot is only supported for Windows 7 x64 and newer.

Before starting, let's mention that there are two types of boot methods. There is the MBR code type where the bootable executable is stored in a reserved section at the beginning of the storage device. And there is the EFI type, where the boot loader executable file is stored at a standard path in an FAT32 filesystem. You must decide in advance what you will use. There are some variables for each boot type. If you have no idea what to use, the most common setup that works with unmodified Windows sources, is msdos partition table with fat32 filesystem and flag the partition with boot. In this way you will get both an MBR and UEFI bootable drive.

The latest Windows release can be downloaded from Microsoft as an ISO image. The ISO download page is available to non-Windows users. Otherwise, you are directed to download Media Creation Tool, which is Windows only software.

Change DPI in Ubuntu

By default Ubuntu assumes you use a 96 DPI monitor. But nowadays pixel density keeps increasing as monitors with high resolution became accessible. There is no straightforward option in Ubuntu with Unity to change the default DPI which is considered to be 96 DPI (run in  a terminal xrdb -query). But there are two parameters which control the user interface DPI (this affects font rendering too) and font rendering only.

The parameter that controls user interface and fonts DPI is scaling-factor and the font rendering parameter is text-scaling factor. These parameters can be modified by the Displays application, by GNOME Tweak Tool and by Unity Tweak Tool, but none of these allows you to set a value with 3-4 decimals.

Computer PSU start circuit with bicolor LED

There are a lot of tutorials on the internet on how to turn a computer PSU into a bench top power supply. Most of them involve adding a load on the 5V line and turning the PSU on by grounding the PS_ON wire via a switch. Here is a nice indicator and turn on/off switch for computer PSUs.

ATX PSUs work well under rather constant loads. So if you power up the PSU with a small load of a few tens miliamps and then connect a greater load, for example a car light bulb which may require 3-4 A, the PSU may shut down. The same happens in case of an accidental shortcircuit. You may believe that the PSU got broken or its fuse got blown. That's not true. The PSU automatically shut itself off.

Regular backups using Grive2 on Ubuntu

Grive is a Google Drive client for Linux that can do two-side synchronization between Google Drive and a local folder. The synchronization is done whenever the user launches the application, either from a launcher or from command line (it is a CLI application).

By adding grive to crontab, periodic backups of important folders can be made. And no user interaction is required because the process is automated. Here is how to do it in Ubuntu. There is no system load when the process is not running, but this comes with a disadvantage: no filesystem monitoring. Any updates are made during the automatic execution of Grive.