Some Definitions of Electronics

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AC 
Alternating current. Consists of a periodic oscillation between two different voltages. Usually said to look like a sine wave, but is not always.
AM 
Amplitude modulation. In radio communications, a signal controls the amplitude of a carrier wave that is at a much higher, constant frequency. The carrier wave is filtered out and a loudspeaker plays based on the amplitude of the signal.
Ampere (A) 
The SI unit for current I. (Commonly spoken as "amps", "milliamps", etc.) The ampere is officially defined as that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in vacuum, would produce between these conductors a force equal to 2×10-7 newton per meter of length. There is another definition which is based on the deposition rate of silver (in electrolysis?), which is much easier to measure. The other electronics units are derived units based on the ampere definition.
Amplify 
To increase the strength of the signal. Often an "amplifier" is used to pass a signal with both an increase or a decrease in gain.
 
Anode 
An electron collector. Means up the path from a negative to a positive voltage. An anode has a more positive voltage relative to a cathode.
Attenuate 
Decrease the strength of a signal.
Band-Pass Filter 
An analog filter that absorbs low and high frequencies (f) but allows a band of frequencies in the middle to pass through.
BJT 
Bi-polar junction transistor. A transistor in which the resistance of the channel is controlled by a current at the gate. Can be thought of as a current-controlled resistor. FET is the other major type of transistor.
Capacitor 
An electronics component that stores energy in the form of electric charge (static electricity). It resists a sudden change in voltage.
Cathode 
An electron emitter. A cathode has a more negative voltage relative to some other place.
Choke 
Another name for an inductor, specifically referring to those used in power regulation.
CMOS 
Complementary metal oxide semiconductor. Complementary means that it has N-channel and P-channel transistors. Metal oxide is the type of gate. CMOS is a type of Integrated Circuit (IC) that is voltage based, since it is made of FETs. Digital circuits tend to use very little current, because the paths for current flow are effectively open or closed circuits except during the transition between states.
Coil 
A helix of wire (the same shape as a spring or Slinky). Its height, width, thickness, and material can all vary. Used as an inductor. The loops of wire can overlap.
Condenser 
Another name for capacitor.
Conductance 
The inverse of resistance. Measured in siemens (obsolete name mhos), which are the inverse of ohms. 1 S = 1/Ω = 1 A/V = 1 A2/W
Coulomb (C) 
The SI unit for electric charge Q. Defined in terms of the ampere. 1 coulomb is the amount of electric charge carried by a current of 1 ampere flowing for 1 second. It is also about 6.24×1018 times the charge on an electron. 1 C = 1 A·s
Current 
The drift of electrons in an electric field. This is perceived as a flow. It is measured in amperes.
Cycles per second (cps) 
An obsolete name for hertz, the standard SI unit. As the name implies, a measurement of frequency in full cycles of a wave per second. The unit cps (or kilocycles, megacycles, etc.) is more often seen in older documents.
dB 
Decibel. Used to measure logarithmic ratios like signal to noise ratio (SNR), total harmonic distortion (THD), volume relative to a nominal level. Similar to percent (%) in that it has no units. dB SPL is used to measure sound levels relative to 20 micro-pascals (µPa). dBu is used to measure voltage relative to 0.775 V.
DC 
Direct current. A constant voltage and a constant current flow in one direction.
Diode 
A one way valve for current. Semiconductor diodes typically have a voltage drop of 0.6 V (silicon) or 0.2V (germanium) when conducting in the forward direction.
EMF (E
Electro-Motive Force. A force for moving electrons. See Voltage.
Ethernet
is a family of frame-based computer networking technologies for local area networks (LAN). It defines a number of wiring and signaling standards for the Physical Layer of the standard networking model as well as a common addressing format and a variety of Medium Access Control procedures at the lower part of the Data Link Layer.
Farad (F) 
The SI unit for capacitance (C). A capacitor is one farad if it has a coulomb (1 C) of charge on it with a voltage separation of a volt (1 V). 1 F = 1 C/V
FET 
Field Effect Transistor. Can be thought of as an Electric Field Transistor. A transistor in which the voltage at the gate controls the resistance of the channel. (i.e. a FET has voltage-controlled resistance.) BJT is the other major type of transistor.
FM 
Frequency modulation. Changing the frequency of a carrier signal to represent the amplitude of the original signal.
Forward Biased 
The voltage polarity through a part which causes it to conduct current.
Frequency (f
The number of revolutions (cycles) per unit time. Usually expressed in either radians per second or cycles per second (Hz).
Gain 
A multiplier of voltage or current.
Ground 
Ground is defined as the point in the circuit which is at zero voltage. Voltage is relative, and is the same throughout a conductor, so any point in the circuit can be defined as ground, and all other voltages are referenced to it. Usually it is defined as the most negative point in the circuit, for convenience. Sometimes it is defined in the middle of two bi-polar rails, for "balanced" circuits. In many cases this circuit point is connected to the Earth (Ground) by some buried conductor.
Henry (H) 
The SI unit for inductance. 1 H = 1 Wb/A
Hertz (Hz) 
The SI unit for frequency. One Hz is one cycle per second. 1 Hz = 1/s
High-Pass Filter 
An analog filter that absorbs low frequencies (f) but allows high frequencies to pass.
Horsepower (hp) 
The amount of force F a horse can exert. I don't think it is related to horses anymore. 1 hp = 746 W
IC 
Integrated circuit. A circuit constructed on one chip of semiconductor, rather than as discrete components.
Impedance 
A more generalized form of resistance. The impedance of a device varies with the frequency of the electricity applied. A perfect resistor will have a constant impedance for all frequencies. Capacitors and inductors have varying impedances at different frequencies. Measured in ohms.
Inductor 
An inductor is a device that stores energy in a magnetic field. It opposes a sudden change in the flow of current. A solenoid is usually shaped like a spring or a Slinky.
Joule (J) 
The work required to exert a force of a newton (1 N) for a meter (1 m). 1 J = 1 N·m
LASCR 
Light activated silicon controlled rectifier. A light activated SCR.
LDR 
Light dependent resistor. As light intensity increases, its resistance decreases.
Length (l
Distance is measured in meters (m).
Low-Pass Filter 
An analog filter that absorbs high frequencies (f) but allows low frequencies to pass.
Magnetron 
A special form of vacuum tube, typically used as the microwave emitter in a microwave oven, or in Radar systems.
Meter (m) 
The SI unit for distance. The distance light travels in 1/299,792,458 second.
MOSFET 
Metal-oxide-semiconductor field effect transistor. An FET that uses a thin layer of oxide (usually silicon) to insulate the gate terminal from the underlying channel
Ohm (Ω) 
A measure of resistance or impedance. 1 Ω = 1 V/A = 1 W/A2
Op-amp 
Short for operational amplifier. An op-amp amplifies the voltage between its two inputs.
Oxidation 
A reaction where something loses electrons. Given that oxygen will strip electrons from most elements, this has historically meant a reaction involving oxygen. A cathode (electron emitter) is constantly oxidized as it looses electrons.
PCB 
Printed circuit board. This is a piece of plastic or fiberglass with copper attached. The copper is typically chemically etched away to leave "traces" for the electricity to be conducted through. Other electrical components are soldered to the traces.
Period 
The time between cycles of a periodic wave.
PM1 
Phase modulation. Sending information by modifying relative phases.
PM2 
Pulse modulation. Sending information in binary pulses.
Power 
Voltage times current. The amount of work being done by a circuit.
Rectify 
Convert AC current to DC current.
Redox 
A reaction where oxidation and reduction take place. A cathode (electron emitter) is oxidized (loses electron). The electron travels and is absorbed by an anode (electron acceptor) that is reduced (gains electron).
Reduction 
A reaction where something gains electrons. In gaining electrons its charge value is reduced. An anode (electron acceptor) is constantly reduced as it gains electrons.
Resistance 
Properties of a circuit that impede the flow of electrons. Resistance converts electrical energy into photons that are given off as waste heat. Resistance is measured in ohms.
Reversed Biased 
The inverted voltage polarity on a part.
Root-Mean Squared (RMS) 
The effective DC value for an AC value.
SCR 
Silicon-controlled rectifier.
Second (s) 
The SI unit for time.
SI 
The standard system of units.
SMT 
Surface mount technology. This is a circuit built on a PCB with the components soldered directly to pads on the surface, without going through the board. The components and boards are usually much more compact than through-hole boards.
Speed of light 
Varies depending on the medium it is traveling through. Maximum speed c of 299,792,458 m/s is only in a perfect vacuum. Light has been slowed down to less than 17 m/s (~40 mph) in special mediums.
Speed of wave propagation (v) 
Speed that an electromagnetic wave travels through air, cables, or wires. A typical speed for a typical coax cable is (2/3)·c.
Thermistor 
Temperature based resistor. As temperature increases resistance decreases.
Thyristor 
A type of electronic switch. It has two states which are triggered by another voltage or current. SCRs and switching transistors are examples of thyristors.
Tesla (T) 
Unit of magnetic flux density. 1 T = 1 Wb/m2
Through-hole 
This means the circuit is built on a PCB with holes drilled in it for the component leads to go through. The leads are soldered on the other side of the board.
Time (t) 
The symbol for time in seconds (s).
Transformer 
Used to raise or lower the AC voltage between two circuits. This is based on the ratio of turns between the two coupled inductors. Transformers operate by way of induction between two inductors.
Triode 
A three-element vacuum tube.
TTL 
Transistor-Transistor Logic
Volt-amperes (VA) 
Voltage AC (VAC) 
AC Voltage
Voltage-amperes reactive (VAR) 
Reactive voltage.
Variac 
A type of transformer with a movable tap to provide a variable output voltage. Also "Powerstat".
Volt (V) 
A potential due to an electric field. One volt is defined as the potential difference across a resistor that is passing one ampere and dissipating one watt. 1 V = 1 W/A

Volt

(changed to demonstrate subsection headings)
A potential due to an electric field. One volt is defined as the potential difference across a resistor that is passing one ampere and dissipating one watt. 1 V = 1 W/A
Voltage (V) 
An electric field between two charges. Similar to gravity this acts as an electric potential. Measured in volts.
VCC 
Common-collector voltage source (+). This is an alternate label for the power supply in electronic diagrams for BJT-based circuits such as common-collector amplifiers. (There is also VEE, VDD, VSS do we want one for each?) That might work if they were grouped together.
  • http://encyclobeamia.solarbotics.net/articles/vxx.html
  • http://www.control.com/1026184337/index_html
Watt (W) 
A measure of power (P). A watt is a joule (1 J) of work done in a second (1 s). 1 W = 1 J/s
Wavelength (λ) 
The distance between two peaks of a wave.
Weber (Wb) 
Unit of magnetic flux. 1 Wb = 1 V·s

to be merged

superfluous stuff from "overview of electronics", which should be merged in with these definitions:
Charge: Particles can have three possible types of charge: positive, negative, or neutral (no charge). Electrons are negatively charged, protons are positively charged, and neutrons are (surprise!) neutral. Opposite charges tend to attract, while particles with the same charge (both positive or negative) tend to repel.
Electricity: the flow of electrons.
Electronics: is the study of gadgets that use electricity, typically creating or handling signals, not just switching power.
??? are devices which take in input, perform some function, and return some output, through the use of electricity.
Circuit: The path electrons take as they are pushed by some power source, flow through various electrical components in a gadget, and return to the power source.
Electric Field: field created by the presence of charge. The field represents the force that would be felt by a positive charge.
Voltage: Accelerates charge.
Voltage is a gravity-like potential due to the separation of a negative and a positive charge. Voltage accelerates negatively charged electrons from the negative to the positive charge, and accelerates positive charged protons and ions the other way. Pushing accelerates the charges in what is known as current.
Resistance: When moving electrons (current) collide with atoms, energy is given off as heat. Resistance is the measure of a material's tendency to cause this type of energy loss. Resistance acts to limit the flow of current due to a given voltage. As the resistance becomes infinite the current stops flowing and becomes an open circuit. When there is no resistance the circuit shorts and the current becomes infinite. (Current 'prefers' the path with the lowest possible resistance.)
  • Air has higher resistance than wire.
Resistor: A device whose primary use is to provide resistance.
Short Circuit: there is no resistance between two points. Current flows without a change in voltage.
Open Circuit: there is infinite resistance between two points. Current is unable to flow, but there is still a voltage between the two points.
Voltage Source creates a voltage, which creates a current.
Current Source, which creates a current and a voltage for the current.
Voltage Drop When the current goes through resistance it loses some of the push of the voltage.
When the current comes to an intersection it has multiple paths it can take and flows according to its resistance.
Permittivity: (ε) A measure of how much energy a material absorbs in response to an electric field. Materials (εr) absorb more energy than the vacuum (ε0). The permittivity of a material is known as its dielectric constant.
Cell: Two materials with a voltage difference between them.
Capacitor: Two metal plates with a gap between them. Voltage causes charge to drain from one plate and accumulate on the other plate. This charge separation creates a voltage in the capacitor that opposes the other voltage and stops the flow of current. When a dielectric is placed between the plates it weakens the electric field between the plates and allows more charge to accumulate.
Capacitance: Any two pieces of conducting material separated by some distance have capacitance. Simply, a measure of the tendency of some configuration of metal to act as a capacitor.
Inductor: A coil of wire. Current starts to flow through the wire and creates a magnetic field. This magnetic field creates an opposing magnetic field which stops the current through the wire. Over time the inductor stops opposing current and turns into a wire.
Transformer Two connected inductors, which operate through mutual inductance. Current flows through the first inductor and creates a magnetic field that is fed to the second inductor. In response the second inductor creates an opposing magnetic field and current. Having a permanent magnet between the two inductors intensifies their magnetic fields.
Vacuum tube: An arrangement of two or more electrodes in a vacuum. Typically placed in a glass bulb to keep air from leaking in.
Triode: The first electrical amplification device. A triode is a type of vacuum tube with three connections:
  • The cathode emits electrons.
  • The anode accepts electrons.
  • The 'grid, placed in the middle, which controls the flow of electrons from the cathode to the anode.
Diode: A 2 wire device that allows current to flow easily in only one direction.
Transistor: A 3 wire device, with one wire (the "base" or "gate") that controls the flow of electrons between the other 2 wires. Replaced vacuum tubes.

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Next-Generation Space Ambitions Keep Rolling

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As space shuttle Atlantis rolled to its new home at the Kennedy Space Center Visitor Complex earlier this month, NASA and its commercial crew partners reflected on the Space Shuttle Program's tremendous accomplishments and vowed to continue America's leadership in space.

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Mercury's Water Ice Bodes Well for Alien Life Search

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Water Ice Deposits in Mercury’s North Polar Region
The radar image of Mercury’s north polar region from Image 2.1 is shown superposed on a mosaic of MESSENGER images of the same area. All of the larger polar deposits are located on the floors or walls of impact craters. Deposits farther from the pole are seen to be concentrated on the north-facing sides of craters. Image released Nov. 28, 2012.
CREDIT: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory
The discovery of huge amounts of water ice and possible organic compounds on the heat-blasted planet Mercury suggests that the raw materials necessary for life as we know it may be common throughout the solar system, researchers say.
Mercury likely harbors between 100 billion and 1 trillion metric tons of water ice in permanently shadowed areas near its poles, scientists analyzing data from NASA's Messenger spacecraft announced Thursday (Nov. 29).
Life on sun-scorched Mercury remains an extreme longshot, the researchers stressed, but the new results should still put a spring in the step of astrobiologists around the world.

"The more we examine the solar system, the more we realize it's a soggy place," Jim Green, the director of NASA's Planetary Science Division, said during a press conference today.
"And that's really quite exciting, because that means the amount of water that we have here on Earth — that was not only inherent when it was originally formed but probably brought here — that water and other volatiles were brought to many other places in the solar system," Green added. "So it really bodes well for us to continue on the exploration, following the water and its signs throughout the solar system."



Organics, too?
The observations by Messenger, which has been orbiting Mercury since March 2011, provide compelling evidence that reflective patches first spotted near the planet's poles by the Arecibo radio telescope in Puerto Rico two decades ago are indeed water ice, researchers said.
In the coldest parts of Mercury — permanently shadowed regions where temperatures drop to perhaps minus 370 degrees Fahrenheit (minus 223 degress Celsius) — this ice can lie bare and exposed. But Messenger's data also show that much more frozen water is found in slightly warmer areas, buried beneath a strange dark material that acts as an insulator.
This dark stuff is likely a mixture of complex organic compounds, the carbon-containing building blocks of life as we know it, researchers said during Thursday's news conference.
"This organic material may be the same type of organic material that ultimately gave rise to life on Earth," said Messenger participating scientist David Paige of UCLA.

Planet Mercury: Simple Facts, Tough Quiz
The closest planet to the sun is also an elusive world, revealing itself in our night sky only fleetingly. But that doesn’t excuse you from knowing some basic facts. Don’t think this’ll be easy, though.


Helping scientists read the book of life
Mercury probably acquired much of its water and organic material the same way Earth did, researchers said — via comet impacts and asteroid strikes. Ice and organics are common on the frigid bodies in the solar system's outer reaches.
"There's a lot of water out there, as there is a lot of water around other stars, but at substantial distance," said Messenger principal investigator Sean Solomon, of Columbia University's Lamont-Doherty Earth Observatory.
With its ultra-thin atmosphere and proximity to the sun, Mercury is probably not a good bet to host life as we know it. But finding ice and organics there should still inform the hunt for organisms beyond Earth and aid scientists' quest to learn more about how life took root on our planet.
"The history of life begins with the delivery to some home object of water and of the building blocks, the organic building blocks, that must undergo some kind of chemistry, which we still don't understand on our own planet," Solomon said.
"And so Mercury is becoming an object of astrobiological interest, where it wasn't much of one before," Solomon added. "That's not say to say that we expect to find any lifeforms — I don't think anybody on this table does — but in terms of the book of life, there are some early chapters, and Mercury may indeed inform us about what's in those chapters."
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NASA | Tour of the Moon

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Although the moon has remained largely unchanged during human history, our understanding of it and how it has evolved over time has evolved dramatically. Thanks to new measurements, we have new and unprecedented views of its surface, along with new insight into how it and other rocky planets in our solar system came to look the way they do. See some of the sights and learn more about the moon here!
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What is a Higgs Boson (Quick overview in plain english)

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A quick description of what a Higgs Boson is and why it's important.
Want a more in depth look into CERN and the research? check out my 1hr BBC documentary http://youtu.be/HVHxSOm1oEo
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Contactless Mains Voltage Indicator

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This is a CMOS IC (CD4033) based circuit which can be used to detect presence of mains AC voltage without any electrical contact with the conductor carrying AC current/voltage. Thus it can be used to detect mains AC voltage without removing the insulation from the conductor. Just take it in the vicinity of the conductor and it would detect presence of AC voltage. If AC voltage is not present, the display would randomly show any digit (0 through 9) permanently. If mains supply is available in
the conductor, the electric field would be induced into the sensing probe. Since IC used is CMOS type, its input impedance is extremely high and thus the induced voltage is sufficient to clock the counter IC. Thus display count advances rapidly from 0 to 9 and then repeats itself. This is the indication for presence of mains supply. Display stops advancing when the unit is taken away from the mains carrying conductor. For compactness, a 9-volt PP3 battery may be used for supply to the gadget

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A simple Remote control Tester

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Here is a handy gadget for test- ing of infrared (IR) based re- mote control transmitters used for TVs and VCRs etc. The IR signals from a remote control transmitter are sensed by the IR sensor module in the tester and its output at pin 2 goes low. This in turn switches on transistor T1 and causes LED1 to blink. At the same time, the buzzer beeps at the same rate as the incoming signals from the remote control transmitter. The pressing of different buttons on the remote control will result in different pulse rates which would change the rate at which the LED blinks or the buzzer beeps. When no signal is sensed by the sensor module, output pin 2 of the sensor goes high and, as a result, transistor T1
switches off and hence LED1 and buzzer BZ1 go off. This circuit requires 5V regulated power supply which can be obtained from 9V eliminator and connected to the circuit through a jack. Capacitor C1 smoothes DC input while capacitor C2 suppresses any sudden spikes appearing in the input supply. Here, a plastic moulded sensor has been used so that it can easily stick out from a cut in the metal box in which it is housed. It requires less space. Proper grounding of the metal case will ensure that the electromagnetic emissions which are produced by tube-lights and electronic ballasts etc (which lie within the bandwidth of receiver circuit) are effectively grounded and do not interfere with the functioning of the circuit. The proposed layout of the box containing the circuit is shown in the figure. The 9-volt DC supply from the eliminator can be fed into the jack using a banana-type plug.
Tech. Editor’s note: In fact, the complete gadget can be assembled in the eliminator’s housing itself and a cut can be made in its body for exposing the IR module’s sensor part.
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Light Barrier Detector

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This simple circuit using a single transistor turns ON the relay when light falls on the LDR.
The potentiometer is adjusted for the required sensitivity.
The power supply is 6V.
Be careful about the impedance of the relay. Its impedance should not be less that 60ohm.
Its working can be explained as follows:
With the light falling on the LDR,its resistance is low and the transistor is saturated and turns the relay ON.
When light is obstructed, the LDRs resistance becomes very high. The potentiometer shorts the transistors

base to ground and it is cut off. Hence the relay is OFF.
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Telephone operated remote control using PIC16F84A microcontroller

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This design controls up to 8 devices using a PIC microcontroller (PIC16F84A) connected to the phone line. The unique feature here is that unlike other telephone line based remote control, this device does not need the call to be answered at the remote end so the call will not be charged. This device depends on number of rings given on the telephone line to activate/deactivate device
 Instructions for the telephone operated remote switch:
A) While constructing the main circuit, make sure you use 18pin sockets (base) for the PIC16F84A. Do not solder the IC directly to the board since you may have to remove it for programming. Before you use the PIC on the main circuit, you have to first program it.

B) To program the PIC16F84A microcontroller:
There are lots of programmers on the Internet available to program PIC microncontrollers. Given below are links to some free PIC programmer hardware/software:


Note: Programm the chip with the hex file attached above and remember to set the fuse bits to use "EXTERNAL HS OSCILLATOR" mode!
C) Remove the PIC from the programmer socket and put it into the main circuit socket.
 Set the DIP SWITCH as follows:
Switch3   Switch4      No. of initial rings to Switch ON(activate half of the board)
OFF        OFF             5
ON         OFF             4
OFF        ON              3
ON         ON              2
The number of initial rings to Switch OFF is one more than the number of rings to switch ON. For example, if you have set switch3 OFF & Switch4 ON then number of initial rings to activate half of the board to switch ON the relays is 3 and number of initial rings to activate half of the board to switch OFF the relays is 3+1 = 4
Switch1  Swtich2        Delay before making the second set of rings
OFF        OFF             20sec
ON         OFF             15sec
OFF        ON              10sec
ON         ON              5sec
This is the maximum delay the board can take after it is half activated. It will reset after this delay.
D) Now connect the circuit to the phone line and switch on its power supply.
E) You can test the board now. For example set the DIP switch to Switch1 ON, Switch2 OFF (15 sec delay) & switch3 ON, switch4 OFF (4 rings to activate half for switching ON). If you want to switch ON relay 1 (connected to RB0 of main circuit) then you have to do the following:
  1. Give 4 rings and put down the receiver
  2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
  3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
  4. then within 5 sec the relay1 will switch ON
To switch off relay1:
  1. Give 5 rings and put down the receiver
  2. Wait 5 seconds (this 5 seconds wait is required to prevent the board from detecting continous rings)
  3. then within 15 seconds give 1 ring (1 ring for relay1, 2 rings for relay2 and so on) and put down the receiver
  4. then within 5 sec the relay1 will switch OFF
IMPORTANT: This circuit has been tested by me and found to work correctly. I cannot guarantee that the circuit will work at your end since it depends on error free construction and usage. Please do not contact for any support and requests, any such requests will not be entertained.
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PC based Frequency Meter

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Here is a simple technique for measuring frequencies over quite a wide frequency range and with acceptable accuracy limits using a PC. It follows the basic technique of measuring low frequencies, i.e. at low frequency, period is measured for a complete wave and frequency is calculated from the measured time-period. Cascaded binary counters are used for converting the high-frequency signals into low-frequency signals. The parallel port of a computer is used for data input from binary counters. This data is used for measuring time and calculating the frequency of the signal. The block diagram shows the basic connections of the counters and parallel port pin numbers on 25-pin ‘D’ connector of a PC (control register 379 Hex is used for input). External hardware is used only for converting the higher frequency signals into low frequency signals. Thus, the major role in frequency-measurement is played by the software. The PC generates a time-interrupt at a frequency of 18.21 Hz, i.e. after every 54.92 millisecond. Software uses this time-interrupt as a time-reference. The control register of the PC’s parallel port is read and the data is stored continuously in an array for approximately 54.9 ms using a loop. This stored data is then analysed bit-wise. Initially, the

higher-order bit (MSB or the seventh-bit) of every array element is scanned for the presence of a complete square wave. If it is found, its time period is measured and if not then the second-highest order bit (sixth bit) is scanned. This operation is performed till the third bit and if no full square wave is still found, an error message is generated which indicates that either there is an error in reading or the frequency signal is lower than 19 Hz. Lower three bits of the control register are not used. When a wave is found, along with its time-period and frequency components, its measurement precision in percentage is also calculated and displayed. Number of data taken in 54.9 ms is also displayed. As stated above, the lower starting range is about 19 Hz. Data is read for approximately 54.9 ms. Thus, the lowest possible frequency that can be measured is 1/.0549 Hz. Lower range depends only on the sampling time and is practically fixed at 19 Hz (18.2 Hz, to be precise). Upper range depends on factors such as value of the MOD counter used and the operating frequency range of the counter IC. If MOD-N counter is used (where N is an integer), upper limit (UL) of frequency is given by UL=19xN5 Hz. Thus for MOD 16 counters UL@20 MHz, and for MOD 10 counters UL@1.9 MHz. Care should be taken to ensure that this upper limit is within the operating frequency range of counter IC used. Precision of measurement is a machine-dependent parameter. High-speed machines will have better precision compared to others. Basically, precision depends directly upon the number of data read in a standard time. Precision of measurement varies inversely as the value of MOD counter used. Precision is high when MOD 10 counters are used in place of MOD 16 counters, but this will restrict the upper limit of frequency measurement and vice-versa.
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