// In addition to voltage and current, there is another measure of free electron activity in a circuit: power. First, we need to understand just what power is before we analyze it in any circuits.

Power is a measure of how much work can be performed in a given amount of time. Work is generally defined in terms of the lifting of a weight against the pull of gravity. The heavier the weight and/or the higher it is lifted, the more work has been done. Power is a measure of how rapidly a standard amount of work is done.

For American automobiles, engine power is rated in a unit called “horsepower,” invented initially as a way for steam engine manufacturers to quantify the working ability of their machines in terms of the most common power source of their day: horses. One horsepower is defined in British units as 550 ft-lbs of work per second of time. The power of a car’s engine won’t indicate how tall of a hill it can climb or how much weight it can tow, but it will indicate how fast it can climb a specific hill or tow a specific weight.

The power of a mechanical engine is a function of both the engine’s speed and its torque provided at the output shaft. Speed of an engine’s output shaft is measured in revolutions per minute, or RPM. Torque is the amount of twisting force produced by the engine, and it is usually measured in pound-feet, or lb-ft (not to be confused with foot-pounds or ft-lbs, which is the unit for work). Neither speed nor torque alone is a measure of an engine’s power.

A 100 horsepower diesel tractor engine will turn relatively slowly, but provide great amounts of torque. A 100 horsepower motorcycle engine will turn very fast, but provide relatively little torque. Both will produce 100 horsepower, but at different speeds and different torques. The equation for shaft horsepower is simple:

Notice how there are only two variable terms on the right-hand side of the equation, S and T. All the other terms on that side are constant: 2, pi, and 33,000 are all constants (they do not change in value). The horsepower varies only with changes in speed and torque, nothing else. We can re-write the equation to show this relationship:

• REVIEW:

Power is the measure of how much work can be done in a given amount of time.

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.

Electrical power is distributed via cables and electricity pylons like these in Brisbane Australia

When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Devices convert electrical energy into many useful forms, such heat (electric heaters), light (light bulbs), motion (electric motors), sound (loudspeaker) or chemical changes. Electricity can be produced mechanically by generation, or chemically, or by direct conversion from light in photovoltaic cells, also it can be stored chemically in battery

Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of power is the watt.

[edit] Direct current

In direct current resistive circuits, instantaneous electrical power is calculated using Joule’s Law, which is named after the British physicist James Joule, who first showed that heat and mechanical energy were interchangeable.

where

P is the power (watt or W)

V is the potential difference (volt or V)

I is the current (ampere or A).

2.45GHz RF Signal Detector
This passive RF indicator is made from a few simple parts.  A 100uA moving coil meter is used to display the relative intensity of the RF signal.  This circuit can be used with some cellphones and many cordless telephones.

Scientists Invent 30 Year Continuous Power Laptop Battery

Your next laptop could have a continuous power battery that lasts for 30 years without a single recharge thanks to work being funded by the U.S. Air Force Research Laboratory. The breakthrough betavoltaic power cells are constructed from semiconductors and use radioisotopes as the energy source. As the radioactive material decays it emits beta particles that transform into electric power capable of fueling an electrical device like a laptop for years.

Although betavoltaic batteries sound Nuclear they’re not, they’re neither use fission/fusion or chemical processes to produce energy and so (do not produce any radioactive or hazardous waste). Betavoltaics generate power when an electron strikes a particular interface between two layers of material. The Process uses beta electron emissions that occur when a neutron decays into a proton which causes a forward bias in the semiconductor. This makes the betavoltaic cell a forward bias diode of sorts, similar in some respects to a photovoltaic (solar) cell. Electrons scatter out of their normal orbits in the semiconductor and into the circuit creating a usable electric current.

The profile of the batteries can be quite small and thin, a porous silicon material is used to collect the hydrogen isotope tritium which is generated in the process. The reaction is non-thermal which means laptops and other small devices like mobile phones will run much cooler than with traditional lithium-ion power batteries. The reason the battery lasts so long is that neutron beta-decay into protons is the world’s most concentrated source of electricity, truly demonstrating Einstein’s theory E=MC2.

The best part about these cells are when they eventually run out of power they are totally inert and non-toxic, so environmentalists need not fear these high tech scientific wonder batteries. If all goes well plans are for these cells to reach store shelves in about 2 to 3 years.

An electric circuit is an interconnection of electrical elements.

A simple electric circuit consists of three basic elements: a battery, a lamp, and connecting wires.

for an independent current source , where the arrow indicates the direction of the current i.

I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is high, low or OK.  When connected to other converters, such as a frequency to voltage converter, a current to voltage converter or a power to voltage meter, it could provide a quick indication of a proper level.

A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad

‘Major Discovery’ Primed To Unleash Solar Revolution: Scientists Mimic Essence Of Plants’ Energy Storage System

Until now, solar power has been a daytime-only energy source, because storing extra solar energy for later use is prohibitively expensive and grossly inefficient. With today’s announcement, MIT researchers have hit upon a simple, inexpensive, highly efficient process for storing solar energy.

Requiring nothing but abundant, non-toxic natural materials, this discovery could unlock the most potent, carbon-free energy source of all: the sun. “This is the nirvana of what we’ve been talking about for years,” said MIT’s Daniel Nocera, the Henry Dreyfus Professor of Energy at MIT and senior author of a paper describing the work in the July 31 issue of Science. “Solar power has always been a limited, far-off solution. Now we can seriously think about solar power as unlimited and soon.”

Inspired by the photosynthesis performed by plants, Nocera and Matthew Kanan, a postdoctoral fellow in Nocera’s lab, have developed an unprecedented process that will allow the sun’s energy to be used to split water into hydrogen and oxygen gases. Later, the oxygen and hydrogen may be recombined inside a fuel cell, creating carbon-free electricity to power your house or your electric car, day or night.

A snapshot showing the new, efficient oxygen catalyst in action in Dan Nocera’s laboratory at MIT. (Credit: MIT/NSF)

About Thomson Reuters

Circuitry discovery could lead to beefier memory

By JORDAN ROBERTSON

The Associated Press

Wednesday, April 30, 2008; 4:35 PM

SAN JOSE, Calif. — For nearly 40 years, scientists have speculated that basic electrical circuits have a natural ability to remember things even when the power is switched off. They just couldn’t find it.

Now researchers at Hewlett-Packard Co. have proven them right, with a discovery they hope will lead to memory chips that store more data but consume far less power than those found in today’s personal computers and other digital devices.

The newly discovered circuit element _ called a memristor _ could enable cell phones that can go weeks or longer without a charge, PCs that start up instantly, and laptops that retain your session information long after the battery dies.

It also could challenge flash memory, which is now widely used in portable electronics because of its ability to retain information even when power is off. Chips incorporating the HP discovery would be faster, suck up less power and take up far less space than today’s flash.

“It certainly looks promising,” said Wolfgang Porod, professor of electrical engineering at the University of Notre Dame and director of the university’s Center for Nano Science and Technology. “However, if it’s going to be 100 times better or 1,000 times better (than today’s flash), it’s very hard to say at this point.”

Scientists Create First Memristor: Missing Fourth Electronic Circuit Element

By Bryan Gardiner April 30, 2008 | 12:03:41 PM Categories: Research

Researchers at HP Labs have built the first working prototypes of an important new electronic component that may lead to instant-on PCs as well as analog computers that process information the way the human brain does.

The new component is called a memristor, or memory resistor. Up until today, the circuit element had only been described in a series of mathematical equations written by Leon Chua, who in 1971 was an engineering student studying non-linear circuits. Chua knew the circuit element should exist — he even accurately outlined its properties and how it would work. Unfortunately, neither he nor the rest of the engineering community could come up with a physical manifestation that matched his mathematical expression.

Thirty-seven years later, a group of scientists from HP Labs has finally built real working memristors, thus adding a fourth basic circuit element to electrical circuit theory, one that will join the three better-known ones: the capacitor, resistor and the inductor.

Researchers believe the discovery will pave the way for instant-on PCs, more energy-efficient computers, and new analog computers that can process and associate information in a manner similar to that of the human brain.

According to R. Stanley Williams, one of four researchers at HP Labs’ Information and Quantum Systems Lab who made the discovery, the most interesting characteristic of a memristor device is that it remembers the amount of charge that flows through it.

Indeed, Chua’s original idea was that the resistance of a memristor would depend upon how much charge has gone through the device. In other words, you can flow the charge in one direction and the resistance will increase. If you push the charge in the opposite direction it will decrease. Put simply, the resistance of the devices at any point in time is a function of history of the device –- or how much charge went through it either forwards or backwards. That simple idea, now that it has been proven, will have profound effect on computing and computer science.

“Part of what’s going to come out of this is something none of us can imagine yet,” says Williams. “But what we can imagine in and of itself is actually pretty cool.”

For one thing, Williams says these memristors can be used as either digital switches or to build a new breed of analog devices.

24V DC Powered Beeper with 4 Separate Inputs
designed by David A. Johnson, P.E.

May 17, 2007

24v DC is a very popular voltage used in iettings.  The circuit below was designed to accept four different 24v DC alarm input signals, which are then used to drive a single low power beeper.  The beeper is a magnetic type with its own oscillator/driver.  The four diodes form an “OR” gate so any one of the four inputs will cause the beeper to make noise.  A CMOS version of the popular 555 timer is used to strobe the beeper on and off at about 1Hz.

Click on the Drawing to view PDF

working and theory

Electric Circuits

A Simple Electric Circuit.

We want to use binary numbers in computers because it is easy to build electronic circuits that can reliably distinguish between two states. In order to understand how electronic components can compute Boolean functions and ultimately form a complete computer, we need to understand the concept of an electric circuit.

Figure 1 shows a simple electric circuit. The stylized symbols represent a battery, a switch, and a lamp. The lines represent wires. A diagram that uses stylized symbols such as these is called a schematic diagram. The symbols used in schematic diagrams and the digital logic diagrams we will work with later have been standardized to make it easier for us to communicate.

In order for electricity to perform work, such as lighting a lamp, there must be a complete path from the power source through the parts of an electrical appliance and back to the power source.

In the schematic diagram of Figure 1, the switch is initially shown in the open or off position. There is a path from the battery (the power source) to the switch, and from the switch to the lamp and back to the battery. However, there is no path through the switch. Because the switch is off, the path is interrupted and no current flows. Click on the switch to close it.

When the switch is closed, the path is completed, current flows, and the lamp lights. The necessity for a complete path is why we call this a circuit. In case you are wondering about real-world applications, the diagram in Figure 1 is a good representation of how a flashlight works.

Electric Circuits Can Represent Boolean Functions.

It is possible to arrange switches in an electric circuit to represent Boolean functions. We will consider two possible arrangements before we leave mechanical switches and turn to transistors for our circuits.

In Figure 2 there are two switches arranged one after the other. For current to flow and make the lamp light, both switches must be closed. If either is open, the path through the circuit is not complete. Two switches arranged in this way are said to be in series.

You can experiment with this circuit by clicking on the switches. The lamp lights only when both switches are closed.

Notice that this circuit is like the Boolean AND function. Both the left switch and the right one must be closed before the circuit is completed and the lamp lights.

Basic Electric Circuits

The Open Circuit

The open circuit is a very basic circuit that we should all be very familiar with. It is the circuit in which no current flows because there is an open in the circuit that does not allow current to flow. A good example is a light switch. When the light is turned off, the switch creates an opening in the circuit, and current can no longer flow.

You probably figured that since there are “open circuits” that there are probably also “closed circuits”. Well, a closed circuit is when the switch is closed and current is allowed to flow through the circuit.

A fuse is a device that is used to create an open circuit when too much current is flowing. We will see how that can be caused in the following section…

The Short Circuit

A short circuit can be caused by incoming power wires (wires that are normally insulated and kept separate) coming in contact with each other. Since a circuit usually has resistance, and the power wires that “short out” have very little resistance, the current will tend to flow through the path of least resistance… the short. Less resistance at the same amount of voltage will result in more current to flow.

Therefore a short circuit will have too much current flowing through it. What’s the best way to stop a short circuit from doing damage (because it is drawing too much power from the source)? By using a fuse. Fuses are designed to work up to a certain amount of current (e.g. 1 amp, 15 amps, …). When that maximum current is exceeded, then the wire within the fuse burns up from the heat of the current flow. With the fuse burnt up, there is now an “open circuit” and no more current flows.

Which of these light bulbs uses the most power? The 100 Watt bulb uses the most power.

Biblography

http://blog.wired.com/gadgets/2008/04/scientists-prov.htmlCroft, Terrell; Summers, Wilford I. (1987). American Electricans’ Handbook, Eleventh Edition, New York: McGraw Hill. ISBN 0-070-13932-6

Fink, Donald G.; Beaty, H. Wayne (1978). Standard Handbook for Electrical Engineers, Eleventh Edition, New York: McGraw Hill. ISBN 0-070-20974-X.

Circuits Designed by Dave Johnson, P.E. :

http://blog.wired.com/gadgets/2008/04/scientists-prov.html

http://www.discovercircuits.com/

School of Computing and Software Engineering

Southern Polytechnic State University

Copyright © 2000, 2002 by Bob Brown

aa0ni@yahoo.com

Daniel Reynolds – A