Monday, March 17, 2014

Mitsubishi Electric Research Laboratories

MERL is the North American arm of the Corporate R&D of Mitsubishi. MERL conducts application-motivated basic research and advanced development in optimization, control and signal processing.

Mitsubishi Electric Research Laboratories

Mechatronics - Advanced control algorithms, system dynamics, modeling & performance analysis....

Digital Communications - High speed mobile communications, ubiquitous networking, reliable wireless...

Data Analytics - Predictive analytics (statistical machine learning, data analysis); decision analytics...

TR2003-35 Very Low-Cost Sensing and Communication Using Bidirectional LEDs

A novel microprocessor interface circuit is described which can alternately emit and detect light using only an LED, two digital I/O pins and a single current limiting resistor. This technique is first applied to create a smart illumination system that uses a single LED as both light source and sensor.

MERL - TR2003-35 Communication Using Bidirectional LED

Bidirectional communication with LEDs

These test boards use a simple protocol for data transfer which allows two unsynchronized devices to phase-lock to each other and exchange pulse-width- modulated data bidirectionally. A basic explanation of the protocol is that the two devices take turns flashing their LEDs at each other. A short flash indicates a 0 or SPACE state, and a long flash indicates a 1 or MARK state.

Saturday, March 15, 2014

Basics of Electronics

Basics of Electronics -

Electronics is the study of the antics of electrons, for that first a bit of static electricity which is the way non moving electrons behave.

Static Electricity -

Basics of Electronics
If you Rub a plastic comb or ruler on a dry cloth and hold it over very small bits of paper you will see the paper jump to the comb, this is electric charge an accumulation of electrons on the plastic comb which produced a field to attract the bits of paper.

Opposite charges attract each other, the comb now has negative charge pulls the bits of paper which is uncharged, and the comb loses its excess electrons to the bits of paper, the movement of electrons is current.

All Charged matter try to reach ground potential an uncharged state, which is the state of earth, earth is taken as zero potential.

Energy transforms from one form to another, when the comb was rubbed mechanical energy was changed to electric energy and the electric energy of the comb moved the paper, here electric energy changed back to mechanical energy.

When the comb was rubbed on the cloth friction caused vibration in the molecules of cloth, vibration causes heat which dislodges the electrons and these collect on the comb.

Same static electricity is the cause of lightning bolts and the crackling of your hair when you comb it on a dry day.
Insulators do not have free electrons but conductors have free electrons it is this reason the comb being an insulator could not stabilize its surface which had become charged, conductors like copper cannot get charged like this as electrons quickly distribute all over instead of accumulating on the surface. Conductors play an important role as they form the means to route the current formed by electrons to do work for us like lighting a bulb or running the Fan.
Electrons -
Like charges repel and unlike charges attract, This is because matter is assumed to be made of protons '+' , electrons '--' and neutrons '0' without charge. Protons could be absence of electrons or vice versa. What is important to remember is when stable matter is disturbed by friction, heat, light, other chemicals, even sound there is electrical activity which is interpreted in various ways even heat is an electrical activity a simple candle flame is also electrical activity, but we come out of that to study basic electronics which is the play of electrons in conductors, insulators and the most magical of them all the semiconductors.

The Ground that we walk on is made of mostly silicon dioxide or sand or quartz this silicon along with germanium and others are semiconductors, silicon forms most of the ICs in electronics. Selenium is another material but this is photoconductive, this is used in photocopying and printing. Gallium Arsenide is one other which is useful in high frequency components.

Most matters exhibit electrical properties piezoelectricity is one more, the long lasting gas lighter uses piezoelectricity (titanium derivative), these materials when hit generate electricity, this effect is used in record players (sapphire) to convert bumps on the record to electric voltages, batteries convert chemical energy to electric energy, and you know magnets produce electricity when moved over a conductor.

Conductors : Copper Cu , Aluminum Al, silver, gold, iron, tin, carbon, etc. .

Insulators : Wood, Glass, Ceramic, Mica, Sand, Paper, Cloth, Plastic. etc. .

Certain organic compounds are also conductors, and water with some electrolyte like salt is also a conductor but this is ionic or electrolytic conduction.

Wet wood or cloth with impurities can become very conductive and to some extent air itself becomes a bit conductive if humidity is very high. (RH relative humidity is high means the moisture content of air is high, very wet air).
DC and AC Current -
Current is the movement of electrons in a material, direct current is DC and alternating current is AC. If electrons move in a single direction it is DC.

Conventional Current flows from Positive point / terminal to a negative point / terminal.

{ the movement of electrons is opposite of this but don't bother about this was a bug fix done in those days :-) we all make mistakes }

A battery is the best example for a DC generator, The conventional current flows from higher potential + ve to lower -- ve, the water analogy of this is the + ve terminal is an overhead tank and the negative terminal is the ground tank the pipe carrying water is the conductor/wire and flow of water itself the current.

Positive + (red) and Negative -- (black) are called Polarities.
DC flows in a battery circuit as the battery by chemical reaction maintains one terminal with more electrons and the other with a shortage of electrons.

In AC the voltage or current alternates its direction periodically, in other words the polarities of the terminals change from + to -- and vice versa with respect to time.

Why AC ? this is a fundamental law of nature, from the macro movement of planets in the solar system to the micro movement of electrons in an atom there is a pattern called the sinusoidal waveform or sine graph or sine wave.

The movement of a pendulum is the best representation of a sine wave, when a magnet is rotated in a loop (coil) of wires or a coil is rotated in a magnetic field (near a magnet), the voltage that is generated is AC.

As rotation is the fundamental mechanical motion, it is also used to generate electricity which you use at home, AC power which is produced by moving magnets and coils of wire (generator) with the help of water power (hydroelectric waterfalls), steam, fossil fuel (petroleum,coal) driven machines, to nuclear plants.

"Sine graph is true even in the way civilizations have changed in history and to this day the life cycles of corporations, many believe when plotting a graph of profits or growth it is "up up and away" but the truth is that it is " up and down then round and round" !!"

- Solderman 1702

This is an old article i wrote, which may have errors or misconceptions, if you have any doubts verify with a Local Ham. If you want to study and learn the science yourself, then start here HyperPhysics.

Friday, March 07, 2014

Design of a Constant Current Source

This article will explain the way a simple transistor based current source is designed, this will give an idea on how some components can be used in a practical way to make the circuit do some function, the objective is not design but to become familiar with the basic ideas.

Tutorials on Basics and Instrumentation Electronics

Requirement.

We need a fixed current around 20mA for a voltage variation of 10V to 20V to drive a LED flasher circuit.
Component Selection. The transistor should handle 20V * 2 = 40V and a current of 20mA * 5 = 100mA. We have to overrate the components for long term reliability and make the design rugged. Chosen MPSA92 PNP-300V-500mA which is good for this job.

 Look at the pin details of MPSA92 in the bottom view given in the right of this page in its TO-92 package, it has a beta of 25 . The Power dissipation of MPSA92 can be upto 650mW , our requirement may be a max of 20V*20mA = 400mW which is just within limits.

Now we need a voltage reference a low cost voltage reference is a LED which has a 1.6V forward drop. As the circuit is a not an accurate one CFR 5% resistors are fine.

Circuit design.

The LED at 40mW will last long, some energy emits as heat and some as light. 40mW / 1.6V = 25mA. so let us choose 20mA max LED current as a thumb rule.

In this circuit the LED is used as a reference so to keep it cool a 2.2K is chosen. (20V - 1.6V) / 2.2K = 8.3mA on the high side and when voltage is 10V the current will be 3.8mA min. .

You should know that the LED forward drop can change with ambient light as it is photo sensitive and will vary with temperature.
Look at the circuit in the right, the LED has a forward drop of 1.6V which is applied across the resistor R4 and the base-emitter diode. That means 1V across R4 as a diode drop is around 0.6V. The base-emmiter now gets forward biased and a small base current Ib flows . The Ic or collector current is 1V / 50E = 20mA. The Ib = Ic / beta, That means 20mA / 25 = 0.8mA which flows thru R4 and R5.

The Load Resistor R6 represents the LED flasher circuit that consumes 20mA, even on short circuit of R6 the current is limited to 20mA.

When more current flows in R6 the voltage at emitter falls, the voltage at base is 20V - 1.6V =18.4V, and the voltage at emitter should be 18.4 + 0.6V = 19V for bias and Ibto flow. When Ic increases the Ib reduces to that extent as only to maintain emitter voltage at 19V, this way Ic is kept constant, if Ic reduces the voltage at emitter builds up to rise Ibwhich in turn builds up Ic. so we made a current regulator.

Circuit Improvement.

The circuit can be improved by using a zener in place of the LED or better still a temperature compensated reference like LM336.


The circuit on the right will be more stable, but still the forward drop on base-emmiter junction is temperature sensitive. The base current will also introduce an error, so you can get a 8 bit stability, that means around 255 counts on an A-D converter. If you need a more stable current source you should design with FET and opamps.
LM336-2.5 pdf details, It has a 2.5V drop. A LM336-5.0 pdf version is also available for 5V. these are from National Semiconductor.

Operating Current of LM336 is 400uA to 10mA, 20V The max. voltage 20V / 3.3K = 6mA. so within limits. Then you can compute the rest, wire it up to see if your design works.
"If all parts are working, connected in proper polarities and there are no dry solders and loose connections then any circuit well designed ought to work. "

- Solderman 1702



docc00009.html 21:46 01-Aug-04  delabs

Contents

Basic Electronics
Basics of Electronics
Product Production
Work Discipline
Testing Points
Learning Electronics
Electronics Theory

Production Notes
Prototype Fabrication
Electrical Circuits
Electromechanical


Library
Scots Guide Electronics
Engineering - Wikibooks
Design Lab - Jim Svoboda
DC Circuits UOG
Socratic Electronics
Blobz Guide Electric Circuits


Product Design
Product Development
Constant Current Source
Good Voltage Regulators
Insulation Resistance
Digital Insulation Tester
DN Schematic PCB 04
DN Product Design 07


Hobby Circuits
VU Meter Circuits
LED brightness control
555 Incredible Chip
Process Control
liquid level measurement
Thermocouples and RTD
Design ADC Interface uC
Thermocouple Amplifier
IA Instrumentation 02
Temperature on DMM
Optical Proximity Switch
Analog Mux - Data Acquisition


Test Measurement
Instrumentation Automation
NI Test and Measurement
DMM Digital Multi Meter
Oscilloscope in T&M
IA Automation 01
Build Instruments
Tektronix T&M Equipment
Educators Corner – Agilent


Power Electronics
UPS Background
Transformer Connections
DN Power Electronics 03
DN Power Electronics 02
Half Bridge Convertor SG3525


Embedded
Interfacing Microcontrollers
Embedded Process Control
80C31 8052 Microcontroller
Microprocessors and uC
Embedded Systems Design

Components
Good Voltage Regulators
Relays and Contactors
Potentiometers Trimpots
Prototype Boards Types
Types of Capacitors
Types of Switches
Resistors How they Work
Coils Transformers SMPS
Mains Transformers Types
DN Components Selection 05

Tutor Gadgets
Count-Up Timer
Digital Logic Gates
Electronics Tutors

History
Teaching Instruments
Charles Proteus Steinmetz
Muntzing a Circuit Design
Teralab Electronics projects
Historical Instruments


Tables, Charts, Videos
Binary and Hex
Resistor Color Code
Ohms Law
Giga, Tera, Pico, Nano
High Resistance Materials

Analog
School - Analog Design
DN Analog Basics 06
DN Op-Amps 01
TI Semiconductors

Search This Blog