Android Wifi Mesh - Serval

(Serval Project) ... It is a free and open-source app for Android 2.2 “Froyo” and later, under continuous development. The latest official release of the Serval Mesh app is freely available from Google Play.

Serval Mesh allows people to make voice calls, send text messages and share files with other Serval Mesh users, without requiring infrastructure like satellites, cell phone towers, Wi-Fi hot spots, or radio repeaters. The primary motivation is to provide resilient communications during crisis and disaster situations, when vulnerable infrastructure like phone cell towers and mains electricity are cut off. Serval Mesh is also useful for remote communities who lack conventional telephone services, small organisations who need an internal telephone system, and dissidents in oppressive countries that deny or monitor their citizens' telecommunications.

Serval Mesh uses an Android device's Wi-Fi in Ad Hoc mode to communicate directly with other devices within range. To do so requires root permission on the Android device. On devices where root permission is not available, Serval Mesh can communicate using Wi-Fi in the normal Client mode, which requires an Access Point within range. Serval Mesh can use standard Internet connections such as 3G mobile data, home/office Wi-Fi router-modems, and wired networks (USB or Ethernet) to communicate with other devices.

Read more: http://developer.servalproject.org/dokuwiki/doku.php?id=content:servalmesh:main_page

How AM and FM Works

Hello World! Processing

processing.org

Arduino - Oscilloscope

(instructables) ... First, download processing. It's free Click here to download. You don't need to install anything, It runs like the Arduino IDE.
Now upload this code into your Arduino 
After Run this code in Processing IDE

And then you just need to connect the Arduino analog pin 0 to the signal you want to read.
And It's done!

Read more: http://www.instructables.com/id/Arduino-Oscilloscope...

Another one via Open-electronics.org

Project Summary:

We have designed an Oscilloscope using PC and Arduino Board. The signal is first of all fed to the Arduino Board where the analog signal is converted to a digital signal by the ADC which is then serially outputted to the PC and is read by the MATLAB software via the COM ports. Here the signal is read in the form of digital data but then is converted to analog one by using the resolution of the ADC used by the Arduino Board. The MATLAB software was then used to plot the signals...

Full project in PDF: DESIGNING A PC OSCILLOSCOPE
Read more: http://www.open-electronics.org/guest_projects/a-pc-and-an-arduino-heres-your-diy-oscilloscope

Converting Computer ATX Power Supply to Lab Bench Power Supply

Fully Regulated ATX Power Supply: http://boginjr.com/electronics/lv/atx-mod/
AT and ATX PC computersupplies schematics: http://danyk.cz/s_atx_en.html

Free Online Circuit Simulators

http://www.indiabix.com/electronics-circuits/
http://www.falstad.com/circuit/
Download it, so you can save your circuits: http://www.falstad.com/circuit/circuit.zip

http://www.partsim.com/

Free at a limited level: http://www.docircuits.com/

Free circuit simulators @ wikipedia:
http://en.wikipedia.org/wiki/List_of_free_electronics_circuit_simulators

Shift registers - how to multiply the i/o lines of your microcontroller

	PINS 1-7, 15	Q0 " Q7	Output Pins
	PIN 8	GND	Ground, Vss
	PIN 9	Q7"	Serial Out
	PIN 10	MR	Master Reclear, active low
	PIN 11	SH_CP	Shift register clock pin
	PIN 12	ST_CP	Storage register clock pin (latch pin)
	PIN 13	OE	Output enable, active low
	PIN 14	DS	Serial data input
	PIN 16	Vcc	Positive supply voltage

Shifting Out & the 595 chip

At sometime or another you may run out of pins on your Arduino board and need to extend it with shift registers. This example is based on the 74HC595. The datasheet refers to the 74HC595 as an "8-bit serial-in, serial or parallel-out shift register with output latches; 3-state." In other words, you can use it to control 8 outputs at a time while only taking up a few pins on your microcontroller. You can link multiple registers together to extend your output even more. (Users may also wish to search for other driver chips with "595" or "596" in their part numbers, there are many. The STP16C596 for example will drive 16 LED's and eliminates the series resistors with built-in constant current sources.)

Read more: http://arduino.cc/en/Tutorial/ShiftOu

Shift register @ Wikipedia

In digital circuits, a shift register is a cascade of flip flops, sharing the same clock, in which the output of each flip-flop is connected to the "data" input of the next flip-flop in the chain, resulting in a circuit that shifts by one position the "bit array" stored in it, shifting in the data present at its input and shifting out the last bit in the array, at each transition of the clock input. More generally, a shift register may be multidimensional, such that its "data in" and stage outputs are themselves bit arrays: this is implemented simply by running several shift registers of the same bit-length in parallel.
Shift registers can have both parallel and serial inputs and outputs. These are often configured as serial-in, parallel-out (SIPO) or as parallel-in, serial-out (PISO). There are also types that have both serial and parallel input and types with serial and parallel output. There are also bi-directional shift registers which allow shifting in both directions: L→R or R→L. The serial input and last output of a shift register can also be connected to create a circular shift register.

Read more: http://en.wikipedia.org/wiki/Shift_register