Simplify using ur mouse change double click to single-click

When you browse the Web with Microsoft Internet Explorer, links open with a single click. Yet, when you browse My Computer or My Documents, a single click lets you select a file or folder, but you have to double-click to open it.

If you'd rather single-click to open files and folders, you can change the setting on your mouse (don't worry, this process doesn't require any double clicks).

To change the settings on your mouse

1.	Click Start, and then click My Computer.
2.	Click Tools, and then click Folder Options.
3.	Click Single-click to open an item. Then, click OK.

Now you can navigate folders and open files with a single rather than a double click. If you need to select a file, simply hold your mouse over the file for a few seconds without clicking.

Create a keyboard shortcut to open a folder

Do you have a folder that you'd like to be able to open quickly and easily whenever you want? If you create a keyboard shortcut for that folder, you can open it anytime by pressing a key combination, no matter which other programs you have open.

To create a keyboard shortcut to open a folder

1.	Click on Start, All Programs, Accessories, and then click Windows Explorer.
2.	In Windows Explorer (the program that appears when you open folders such as My Computer, My Documents, My Pictures, or My Music), right-click the folder to which you want instant access, click Send To, and then click Desktop.
3.	On your desktop, right-click the new shortcut, and then click Properties.
4.	On the Shortcut tab, click in the Shortcut key box. Now press the letter on your keyboard that you want to use to open the folder. Note: In the Shortcut key box, Microsoft Windows XP automatically adds CTRL+ALT before the key you press, because to use the shortcut to open a folder, you have to hold down both the CTRL and ALT keys simultaneously, while pressing the letter you chose. This way, your folder won't open every time you type that letter.
5.	Click OK.
6.	Now test your shortcut. Hold down the CTRL and ALT keys, and then press the letter you chose.

Tired of chasing your mouse? Use keyboard shortcuts

The mouse, one of the greatest advances in computing history, provides you with an intuitive point-and-click method for using your computer. Depending on the type of work you're doing, however, sometimes using a mouse actually slows you down. If you are a good typist, taking your hands away from the keyboard to move the mouse can use up a few seconds. Over the course of a full day, you could save several minutes by using keyboard shortcuts instead of the mouse.

You can use your keyboard instead of your mouse to do these three tasks:

•	Start a program
•	Navigate menus
•	Minimize, maximize, and close windows

Start a program using a keyboard shortcut

The Start menu is great for finding programs, but its multiple levels of folders can be time consuming to navigate. If there is a program you start frequently, you should set a keyboard shortcut for it so that you can start the program without taking your hands off the keyboard.

To set a keyboard shortcut to start a program

1.	Click the Start menu, and then click All Programs. Right-click the program that you want to start with a keyboard shortcut, and then click Properties.
2.	Click in the Shortcut key box. Now press the letter on your keyboard that you want to use to start the program. Make it easy to remember—for example, press I for Microsoft Internet Explorer. Note: You can use either uppercase or lowercase letters when creating your keyboard shortcuts—and when accessing them later. In the Shortcut key box, Microsoft Windows XP automatically adds Ctrl + Alt + before the key you pressed. When you want to start the program, hold down both the CTRL and ALT keys simultaneously, while also pressing the letter you chose. This way, your program won't start every time you type that letter.
3.	Click OK.
4.	Now test your shortcut. Hold down the CTRL and ALT keys, and then press the letter you chose. If you find it difficult to hold down two keys at once, read Turn on the Sticky Keys feature. Your program should start.

When your friends see you start up programs without touching your mouse, they just might think you have a psychic connection with your computer!

Top of page

Navigate menus using the keyboard

You can speed up tasks in almost any program by choosing menu items using your keyboard instead of your mouse. This operation is particularly handy when you're performing repetitive tasks.

To control menus using your keyboard

1.	With your program open, press the ALT key. Notice that one letter on each menu name is now underlined. To open the menu, press the underlined key. For example, in Internet Explorer, the View menu name shows the V underlined after you press the ALT key. To open the View menu, press the ALT key, and then press V.
2.	Now, each menu item will show one letter underlined. To access or activate the menu item you want, simply press the underlined key. For example, in Internet Explorer, after you open the View menu, the Privacy Report menu item shows the V underlined. Instead of clicking Privacy Report with your mouse, you can just press the V key.
3.	You can also choose menu commands by pressing key sequences quickly, without waiting for the menus to open. For example, to quickly view a Web page's privacy report in Internet Explorer, press ALT, V, V. Similarly, to save a Web page in Internet Explorer, you would normally click the File menu, and then click Save As. To choose the same commands using your keyboard, press ALT, F, A.

Top of page

Control windows using your keyboard

If you like to keep four or five windows open while you work (or play) on your computer, you'll appreciate knowing these keyboard shortcuts. You can quickly switch between your Web browser, e-mail, instant message windows, and other programs without taking your hands off the keyboard.

Action	Shortcut
Minimize a window to your taskbar	ALT, SPACEBAR, N
Maximize a window so it takes up your whole desktop	ALT, SPACEBAR, X
Restore a window so it's visible but doesn't take up your whole desktop	ALT, SPACEBAR, R
Close a window	ALT+F4
Switch to the last window you had open	ALT+TAB
Switch to any window	Hold down the ALT key, and press TAB until the window you want is active

Programs often start up in a "restored" state, where the window takes up only part of the screen. To maximize the window so that it takes up the entire screen, press the ALT key, press the SPACEBAR, and then press X. This will feel natural after you do it a few times, and you will feel much more efficient while using your computer.

How to draw the circuit diagrams

Drawing circuit diagrams

Drawing circuit diagrams is not difficult but it takes a little practice to draw neat, clear diagrams. This is a useful skill for science as well as for electronics. You will certainly need to draw circuit diagrams if you design your own circuits.
Follow these tips for best results:

• Make sure you use the correct symbol for each component.
• Draw connecting wires as straight lines (use a ruler).
• Put a 'blob' () at each junction between wires.
• Label components such as resistors and capacitors with their values.
• The positive (+) supply should be at the top and the negative (-) supply at the bottom. The negative supply is usually labelled 0V, zero volts.
  If you are drawing the circuit diagram for science please see the section about drawing diagrams the "electronics way".

If the circuit is complex:

• Try to arrange the diagram so that signals flow from left to right: inputs and controls should be on the left, outputs on the right.
• You may omit the battery or power supply symbols, but you must include (and label) the supply lines at the top and bottom.

Drawing circuit diagrams the 'electronics way'

Circuit diagrams for electronics are drawn with the positive (+) supply at the top and the negative (-) supply at the bottom. This can be helpful in understanding the operation of the circuit because the voltage decreases as you move down the circuit diagram.

Circuit diagrams for science are traditionally drawn with the battery or power supply at the top. This is not wrong, but there is usually no advantage in drawing them this way and I think it is less helpful for understanding the circuit.

I suggest that you always draw your circuit diagrams the 'electronics way', even for science!

Quantities and units

Quantities

The table shows electrical quantities which are used in electronics.
The relationship between quantities can be written using words or symbols (letters), but symbols are normally used because they are much shorter; for example V is used for voltage, I for current and R for resistance:
As a word equation:
voltage = current × resistance

The same equation using symbols: V = I × R
To prevent confusion we normally use the same symbol (letter) for each quantity and these symbols are shown in the second column of the table

Quantity	Usual Symbol	Unit	Unit Symbol
Voltage	V	volt	V
Current	I	amp*	A
Charge	Q	coulomb	C
Resistance	R	ohm
Capacitance	C	farad	F
Inductance	L	henry	H
Reactance	X	ohm
Impedance	Z	ohm
Power	P	watt	W
Energy	E	joule	J
Time	t	second	s
Frequency	f	hertz	Hz
* strictly the unit is ampere, but this is almost always shortened to amp.

Units

The first table shows the unit (and unit symbol) which is used to measure each quantity. For example: Charge is measured in coulombs and the symbol for a coulomb is C.
Some of the units have a convenient size for electronics, but most are either too large or too small to be used directly so they are used with the prefixes shown in the second table. The prefixes make the unit larger or smaller by the value shown.

Some examples:
25 mA = 25 × 10^-3 A = 25 × 0.001 A = 0.025 A
47µF = 47 × 10^-6 F = 47 × 0.000 001 F = 0.000 047 F
270k = 270 × 10³ = 270 × 1000 = 270 000

Why not change the units to be better sizes?

It might seem a good idea to make the farad (F) much smaller to avoid having to use µF, nF and pF, but if we did this most of the equations in electronics would have to have factors of 1000000 or more included as well as the quantities. Overall it is much better to have the units with their present sizes which are defined logically from the equations.
In fact if you use an equation frequently you can use special sets of prefixed units which are more convenient... For example: Ohm's Law, V = I × R
the standard units are volt (V), amp (A) and ohm (),
but you could use volt (V), milliamp (mA) and kilo-ohm (k) if you prefer.
Take care though, you must never mix sets of units: using V, A and k in Ohm's Law would give you wrong

Prefix	Prefix Symbol	Value
milli	m	10-3	= 0.001
micro	µ	10-6	= 0.000 001
nano	n	10-9	= 0.000 000 001
pico	p	10-12	= 0.000 000 000 001
kilo	k	103	= 1000
mega	M	106	= 1000 000
giga	G	109	= 1000 000 000
tera	T	1012	= 1000 000 000 000

555 & 556 Timer circuits

Introduction

Example circuit symbol (above) Actual pin arrangements (below)

The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. With just a few external components it can be used to build many circuits, not all of them involve timing!
A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.
Low power versions of the 555 are made, such as the ICM7555, but these should only be used when specified (to increase battery life) because their maximum output current of about 20mA (with a 9V supply) is too low for many standard 555 circuits. The ICM7555 has the same pin arrangement as a standard 555.
The circuit symbol for a 555 (and 556) is a box with the pins arranged to suit the circuit diagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 output on the right. Usually just the pin numbers are used and they are not labelled with their function.
The 555 and 556 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18V absolute maximum).Standard 555 and 556 ICs create a significant 'glitch' on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor (eg 100µF) should be connected across the +Vs and 0V supply near the 555 or 556.
The input and output pin functions are described briefly below and there are fuller explanations covering the various circuits:

• Astable - producing a square wave
• Monostable - producing a single pulse when triggered
• Bistable - a simple memory which can be set and reset
• Buffer - an inverting buffer (Schmitt trigger)

Inputs of 555/556

Trigger input: when < ¹/₃ Vs ('active low') this makes the output high (+Vs). It monitors the discharging of the timing capacitor in an astable circuit. It has a high input impedance > 2M.
Threshold input: when > ²/₃ Vs ('active high') this makes the output low (0V)*. It monitors the charging of the timing capacitor in astable and monostable circuits. It has a high input impedance > 10M.
* providing the trigger input is > ¹/₃ Vs, otherwise the trigger input will override the threshold input and hold the output high (+Vs).

Reset input: when less than about 0.7V ('active low') this makes the output low (0V), overriding other inputs. When not required it should be connected to +Vs. It has an input impedance of about 10k.
Control input: this can be used to adjust the threshold voltage which is set internally to be ²/₃ Vs. Usually this function is not required and the control input is connected to 0V with a 0.01µF capacitor to eliminate electrical noise. It can be left unconnected if noise is not a problem.

The discharge pin is not an input, but it is listed here for convenience. It is connected to 0V when the timer output is low and is used to discharge the timing capacitor in astable and monostable circuits.

Output of 555/556

The output of a standard 555 or 556 can sink and source up to 200mA. This is more than most ICs and it is sufficient to supply many output transducers directly, including LEDs (with a resistor in series), low current lamps, piezo transducers, loudspeakers (with a capacitor in series), relay coils (with diode protection) and some motors (with diode protection). The output voltage does not quite reach 0V and +Vs, especially if a large current is flowing.
To switch larger currents you can connect a transistor.The ability to both sink and source current means that two devices can be connected to the output so that one is on when the output is low and the other is on when the output is high. The top diagram shows two LEDs connected in this way. This arrangement is used in the Level Crossing project to make the red LEDs flash alternately.

Loudspeakers

A loudspeaker (minimum resistance 64) may be connected to the output of a 555 or 556 astable circuit but a capacitor (about 100µF) must be connected in series. The output is equivalent to a steady DC of about ½Vs combined with a square wave AC (audio) signal. The capacitor blocks the DC, but allows the AC to pass as explained in capacitor coupling.

Piezo transducers may be connected directly to the output and do not require a capacitor in series.

Relay coils and other inductive loads

Like all ICs, the 555 and 556 must be protected from the brief high voltage 'spike' produced when an inductive load such as a relay coil is switched off. The standard protection diode must be connected 'backwards' across the the relay coil as shown in the diagram. However, the 555 and 556 require an extra diode connected in series with the coil to ensure that a small 'glitch' cannot be fed back into the IC. Without this extra diode monostable circuits may re-trigger themselves as the coil is switched off! The coil current passes through the extra diode so it must be a 1N4001 or similar rectifier diode capable of passing the current, a signal diode such as a 1N4148 is usually not suitable

555/556 Astable

555 astable output, a square wave (Tm and Ts may be different)

555 astable circuit

An astable circuit produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). Note that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state: the output is continually changing between 'low' and 'high'.
The time period (T) of the square wave is the time for one complete cycle, but it is usually better to consider frequency (f) which is the number of cycles per second.

T = 0.7 × (R1 + 2R2) × C1 and f =	1.4
	(R1 + 2R2) × C1

T = time period in seconds (s)
f = frequency in hertz (Hz)
R1 = resistance in ohms ()
R2 = resistance in ohms ()
C1 = capacitance in farads (F)

The time period can be split into two parts: T = Tm + Ts
Mark time (output high): Tm = 0.7 × (R1 + R2) × C1
Space time (output low): Ts = 0.7 × R2 × C1
Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is much larger than R1.

For a standard astable circuit Tm cannot be less than Ts, but this is not too restricting because the output can both sink and source current. For example an LED can be made to flash briefly with long gaps by connecting it (with its resistor) between +Vs and the output. This way the LED is on during Ts, so brief flashes are achieved with R1 larger than R2, making Ts short and Tm long. If Tm must be less than Ts a diode can be added to the circuit as explained under duty cycle below.

Choosing R1, R2 and C1

555 astable frequencies
C1	R2 = 10k R1 = 1k	R2 = 100k R1 = 10k	R2 = 1M R1 = 100k
0.001µF	68kHz	6.8kHz	680Hz
0.01µF	6.8kHz	680Hz	68Hz
0.1µF	680Hz	68Hz	6.8Hz
1µF	68Hz	6.8Hz	0.68Hz
10µF	6.8Hz	0.68Hz (41 per min.)	0.068Hz (4 per min.)

R1 and R2 should be in the range 1k to 1M. It is best to choose C1 first because capacitors are available in just a few values.

• Choose C1 to suit the frequency range you require (use the table as a guide).
• Choose R2 to give the frequency (f) you require. Assume that R1 is much smaller than R2 (so that Tm and Ts are almost equal), then you can use:
  

  R2 =	0.7
  	f × C1

• Choose R1 to be about a tenth of R2 (1k min.) unless you want the mark time Tm to be significantly longer than the space time Ts.
• If you wish to use a variable resistor it is best to make it R2.
• If R1 is variable it must have a fixed resistor of at least 1k in series
  (this is not required for R2 if it is variable).
  

Astable operation

With the output high (+Vs) the capacitor C1 is charged by current flowing through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage and when it reaches ²/₃Vs (threshold voltage) the output becomes low and the discharge pin is connected to 0V.

The capacitor now discharges with current flowing through R2 into the discharge pin. When the voltage falls to ¹/₃Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start charging again.

This cycle repeats continuously unless the reset input is connected to 0V which forces the output low while reset is 0V.
An astable can be used to provide the clock signal for circuits such as counters.
A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are too fast to be seen clearly. Driving a loudspeaker or piezo transducer with a low frequency of less than 20Hz will produce a series of 'clicks' (one for each low/high transition) and this can be used to make a simple metronome.
An audio frequency astable (20Hz to 20kHz) can be used to produce a sound from a loudspeaker or piezo transducer. The sound is suitable for buzzes and beeps. The natural (resonant) frequency of most piezo transducers is about 3kHz and this will make them produce a particularly loud sound.

Duty cycle

The duty cycle of an astable circuit is the proportion of the complete cycle for which the output is high (the mark time). It is usually given as a percentage.

For a standard 555/556 astable circuit the mark time (Tm) must be greater than the space time (Ts), so the duty cycle must be at least 50%:

Duty cycle =	Tm	=	R1 + R2
	Tm + Ts		R1 + 2R2

555 astable circuit with diode across R2

To achieve a duty cycle of less than 50% a diode can be added in parallel with R2 as shown in the diagram. This bypasses R2 during the charging (mark) part of the cycle so that Tm depends only on R1 and C1:

Tm = 0.7 × R1 × C1 (ignoring 0.7V across diode)
Ts = 0.7 × R2 × C1 (unchanged)

Duty cycle with diode =	Tm	=	R1
	Tm + Ts		R1 + R2

Use a signal diode such as 1N4148.

555/556 Monostable

555 monostable output, a single pulse

555 monostable circuit with manual trigger

A monostable circuit produces a single output pulse when triggered. It is called a monostable because it is stable in just one state: 'output low'. The 'output high' state is temporary.
The duration of the pulse is called the time period (T) and this is determined by resistor R1 and capacitor C1:

time period, T = 1.1 × R1 × C1

T = time period in seconds (s)
R1 = resistance in ohms ()
C1 = capacitance in farads (F)
The maximum reliable time period is about 10 minutes.

Why 1.1? The capacitor charges to ²/₃ = 67% so it is a bit longer than the time constant (R1 × C1) which is the time taken to charge to 63%.

• Choose C1 first (there are relatively few values available).
• Choose R1 to give the time period you need. R1 should be in the range 1k to 1M, so use a fixed resistor of at least 1k in series if R1 is variable.
• Beware that electrolytic capacitor values are not accurate, errors of at least 20% are common.
• Beware that electrolytic capacitors leak charge which substantially increases the time period if you are using a high value resistor - use the formula as only a very rough guide!
  For example the Timer Project should have a maximum time period of 266s (about 4½ minutes), but many electrolytic capacitors extend this to about 10 minutes!

Monostable operation

The timing period is triggered (started) when the trigger input (555 pin 2) is less than ¹/₃ Vs, this makes the output high (+Vs) and the capacitor C1 starts to charge through resistor R1. Once the time period has started further trigger pulses are ignored.

The threshold input (555 pin 6) monitors the voltage across C1 and when this reaches ²/₃ Vs the time period is over and the output becomes low. At the same time discharge (555 pin 7) is connected to 0V, discharging the capacitor ready for the next trigger.
The reset input (555 pin 4) overrides all other inputs and the timing may be cancelled at any time by connecting reset to 0V, this instantly makes the output low and discharges the capacitor. If the reset function is not required the reset pin should be connected to +Vs.

Power-on reset or trigger circuit

Power-on reset or trigger

It may be useful to ensure that a monostable circuit is reset or triggered automatically when the power supply is connected or switched on. This is achieved by using a capacitor instead of (or in addition to) a push switch as shown in the diagram.
The capacitor takes a short time to charge, briefly holding the input close to 0V when the circuit is switched on. A switch may be connected in parallel with the capacitor if manual operation is also required.
This arrangement is used for the trigger in the Timer Project.

Edge-triggering

edge-triggering circuit

If the trigger input is still less than ¹/₃ Vs at the end of the time period the output will remain high until the trigger is greater than ¹/₃ Vs. This situation can occur if the input signal is from an on-off switch or sensor.
The monostable can be made edge triggered, responding only to changes of an input signal, by connecting the trigger signal through a capacitor to the trigger input. The capacitor passes sudden changes (AC) but blocks a constant (DC) signal. For further information please see the page on capacitance. The circuit is 'negative edge triggered' because it responds to a sudden fall in the input signal. The resistor between the trigger (555 pin 2) and +Vs ensures that the trigger is normally high (+Vs).

555/556 Bistable (flip-flop) - a memory circuit

555 bistable circuit

The circuit is called a bistable because it is stable in two states: output high and output low. It is also known as a 'flip-flop'.
It has two inputs:

• Trigger (555 pin 2) makes the output high.
  Trigger is 'active low', it functions when < ¹/₃ Vs.
• Reset (555 pin 4) makes the output low.
  Reset is 'active low', it resets when <>

The power-on reset, power-on trigger and edge-triggering circuits can all be used as described above for the monostable.

555/556 Inverting Buffer (Schmitt trigger) or NOT gate

555 inverting buffer circuit (a NOT gate)

NOT gate symbol

The buffer circuit's input has a very high impedance (about 1M) so it requires only a few µA, but the output can sink or source up to 200mA. This enables a high impedance signal source (such as an LDR) to switch a low impedance output transducer (such as a lamp).
It is an inverting buffer or NOT gate because the output logic state (low/high) is the inverse of the input state:

• Input low (< ¹/₃ Vs) makes output high, +Vs
• Input high (> ²/₃ Vs) makes output low, 0V

When the input voltage is between ¹/₃ and ²/₃ Vs the output remains in its present state. This intermediate input region is a deadspace where there is no response, a property called hysteresis, it is like backlash in a mechanical linkage. This type of circuit is called a Schmitt trigger. If high sensitivity is required the hysteresis is a problem, but in many circuits it is a helpful property. It gives the input a high immunity to noise because once the circuit output has switched high or low the input must change back by at least ¹/₃ Vs to make the output switch back.