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[TC] Physicists just built the world's smallest optical switch - based on a single atom

As our need for more data and faster transmissions grows, existing network infrastructure is being put under more strain than ever before. As a result, scientists are working hard to miniaturise these systems and switch from current electron-based computers to super-fast optics-based communications, where data is quite literally sent at the speed of light.
Now scientists working at ETH Zurich in Switzerland have made crucial progress in the design of a modulator - the device that converts electronic signals into optical ones. These devices are currently around 3 cm wide, which means when you have a data centre full of them, they take up a substantial amount of room. But this new modulator is based on an optical switch that uses just one atom.
As Gizmag's Colin Jeffrey reports, that's a level of miniaturisation that's surprised even the scientists themselves - it essentially allows light to pass through a gap that's smaller than the wavelength of light itself. A modulator built around this switch could be some 100,000 times smaller than the devices in use today.
Here's how it works: silver and platinum pads are placed on top of an optical waveguide made of silicon with just an atom's gap between them. Once voltage is applied to the silver pad, a single atom is drawn towards its furthermost point, closing up the gap and creating a circuit between the two pads. When voltage is removed, the atom retracts, and thus the modulator can transmit millions of switch signals every second.
But what about the physics-bending light compression? As the light is beamed across the waveguide, it gets converted into surface plasmon, made up of electrons that oscillate at the frequency of the laser light. These electrons can pass through the single atom gap before being reconverted on the other side. By reconfiguring the design of the modulator, the light is effectively squashed to squeeze through the gap.
"Until recently, even I thought it was impossible for us to undercut this limit,"said lead researcher, Jürg Leuthold. "This allows us to create a digital switch, as with a transistor. We have been looking for a solution like this for a long time."
Now the team wants to improve the modulator production process so it's suitable for large-scale use and reliable in operation - at the moment, only one out of every six attempts at fabrication is successful. Eventually, though, this single atom modulator could be helping to shift data around the planet faster than ever before.
Source: Science Alert

[TC] Frequency counter using arduino

Many guys here were asking for a frequency counter and at last I got enough time to make one.  This frequency counter using arduino is based on the UNO version and can count up to 40KHz. A 16×2 LCD display is used for displaying the frequency count. The circuit has minimum external components and directly counts the frequency. Any way the amplitude of the input frequency must not be greater than 5V. If you want to measure signals over than 5V, additional limiting circuits have to be added and i will show it some other time. Now just do it with 5V signals.
The frequency to be counted is connected to digital pin 12 of the arduino. pulseIn() function is used here for counting the frequency connected to pin 12. pulseIn() function counts the number of pulses (HIGH or LOW) coming to a particular pin of the arduino. The general syntax of this function is pulseIn(pin, value, time) where pin is the name of the pin, value is either HIGH or LOW and time is time for which the function to wait for a pulse. The function returns zero if there is no valid pulse with in the specified time. The pulseIn() function can count pulses with time period ranging from 10 μS to 3 minutes. Circuit diagram of the frequency counter using arduino is given below.

Potentimeter R1 is used to adjust the contrast of the LCD screen. Resistor R2 limits the current through the back light LED.
In the program, high time and low time of the input signal is measured using separate pulseIn() functions. Then the high and low times are added together to get the total time period of the signal. Frequency is just 1/time period in seconds. The pulseIn() function returns the time period in microseconds. Total timeperiod in microseconds first divided by 1000. Then 1000 is divided by the result to get the frequency in hertz. The program of the frequency counter using arduino is shown below.


#include <LiquidCrystal.h>
int input=12;

int high_time;
int low_time;
float time_period;
float frequency;
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);
void setup()
lcd.begin(16, 2);
void loop()
lcd.print("Frequency Meter");


lcd.print(" Hz");
The circuit can be powered through the 9V external power jack of the arduino. 5V DC required at some parts of the circuit can be tapped from the built in 5V regulator of the arduino itself. This is actually a simple counter circuit using arduino. We can modify this circuit for other applications like tachometer, intrusion counter etc.


[TC] Heart rate monitor using 8051

This article is about a simple heart rate monitor using 8051 microcontroller. Like the previous 8051 projects, AT89S51 is the microcontroller used here. The device senses the heart rate from the finger tip using IR reflection method and displays it on a three digit seven segment display in beats per minute. The circuit has an accuracy of 4 beats per minute and it is very easy to use. In medical terms, the technique used here for sensing heart rate is called photoplethysmography.


Photoplethysmography is the process of optically estimating the volumetric measurement of an organ. Pulse oximetry, cardiovascular monitoring, respiration detection, heart rate monitoring etc are few common applications of photoplethysmography. Let us have a look at the application of photoplethysmography in heart rate monitoring from the figer tip. When the heart expands (diastole) the volume of blood inside the finger tip increases and when the heart contrcats (systole) the volume of blood inside the finger tip decreases. The resultant pulsing of blood volume inside the finger tip is directly proportional to the heart rate and if you could some how count the number of pulses in one minute, that’s the heart rate in beats per minute (bpm). For this an IR transmitter /receiver pair is placed in close contact to the finger tip. When the heart beats, the volume of blood cells under the sensor increases and this reflects more IR waves to sensor and when there is no beat the intensity of the reflected beam decreases. The pulsating reflection is converted to a suitable current or voltage pulse by the sensor. The sensor output is processed by suitable electronic circuits to obtain a visible indication (digital display or graph).

Heart rate monitor using 8051.

Circuit diagram.

Working of the heart rate monitor

LTH1550-01 photo interruptor forms the photoplethysmographic sensor here. LTH1550-01 is simply a IR diode – photo transistor pair in single package. The front side of the IR diode and photo transistor are exposed and the remaining parts are well isolated. When the finger tip is placed over the sensor the volumetric pulsing of  the blood volume inside the finger tip due to heart beat varies the intensity of the reflected beam and this variation in intensity is according to the heart beat.
When more light falls on the photo transistor it conducts more, its collector current increases and so its collector voltage decreases. When less light falls on the phototransistor it conducts less, its collector current decreases and so its collector voltage decreases. This variation in the collector voltage will be proportional to the heart rate. Any way this voltage variation is so feeble and additional signal conditioning stages are necessary to convert it into a microcontroller  recognizable form.
The next part of the circuit consists of a two active low pass filters using opampLM324.  The LM324 is a quad opamp that can be operated from a single rail supply. Resistor R23, R17 and capacitor C5 sets the gain and cut off frequency of the first filter. With the given component values, gain will be 101 and cut off frequency will be 2.5Hz. The gain and cut off frequency are determined using the following equations.
Voltage gain Av =1 + (R17 / R23)
Cut off frequency Fc= 1/(2π *R17*C5)
The second low pass filter also have the same parameters. The two low pass filters form a very critical part of the circuit as any noise or false signals passing to the microcontroller stage will produce disastrous results. The output of the filter stage will be a voltage level fluctuating between 0 and 0.35 volts and this fluctuation is converted into a 0 to 5V swing using the comparator  based on the third opamp (IC1c). The reference voltage of the comparator is set to 0.3V. When ever the output voltage of the filter stage goes above 0.3V, the output of the comparator goes to zero and whenever the output voltage of the filter stage goes below 0.3V, the output of the comparator goes to positive saturation. The result will be a neat pulse fluctuating between 0 and 5V at a rate equal to the heart rate. This pulse is fed to the microcontroller for counting.


ORG 000H // originMOV DPTR,#LUT // moves starting address of LUT to DPTRMOV P1,#00000000B // sets P1 as output portMOV P0,#00000000B // sets P0 as output portMAIN: MOV R6,#230D // loads register R6 with 230D SETB P3.5 // sets P3.5 as input port MOV TMOD,#01100001B // Sets Timer1 as Mode2 counter & Timer0 as Mode1 timer MOV TL1,#00000000B // loads TL1 with initial value MOV TH1,#00000000B // loads TH1 with initial value SETB TR1 // starts timer(counter) 1BACK: MOV TH0,#00000000B // loads initial value to TH0 MOV TL0,#00000000B // loads initial value to TL0 SETB TR0 // starts timer 0HERE: JNB TF0,HERE // checks for Timer 0 roll over CLR TR0 // stops Timer0 CLR TF0 // clears Timer Flag 0 DJNZ R6,BACK CLR TR1 // stops Timer(counter)1 CLR TF0 // clears Timer Flag 0 CLR TF1 // clears Timer Flag 1 ACALL DLOOP // Calls subroutine DLOOP for displaying the count SJMP MAIN // jumps back to the main loopDLOOP: MOV R5,#252DBACK1: MOV A,TL1 // loads the current count to the accumulator MOV B,#4D // loads register B with 4D MUL AB // Multiplies the TL1 count with 4 MOV B,#100D // loads register B with 100D DIV AB // isolates first digit of the count SETB P1.0 // display driver transistor Q1 ON ACALL DISPLAY // converts 1st digit to 7seg pattern MOV P0,A // puts the pattern to port 0 ACALL DELAY ACALL DELAY MOV A,B MOV B,#10D DIV AB // isolates the second digit of the count CLR P1.0 // display driver transistor Q1 OFF SETB P1.1 // display driver transistor Q2 ON ACALL DISPLAY // converts the 2nd digit to 7seg pattern MOV P0,A ACALL DELAY ACALL DELAY MOV A,B // moves the last digit of the count to accumulator CLR P1.1 // display driver transistor Q2 OFF SETB P1.2 // display driver transistor Q3 ON ACALL DISPLAY // converts 3rd digit to 7seg pattern MOV P0,A // puts the pattern to port 0 ACALL DELAY // calls 1ms delay ACALL DELAY CLR P1.2 DJNZ R5,BACK1 // repeats the subroutine DLOOP 100 times MOV P0,#11111111B RET DELAY: MOV R7,#250D // 1ms delay DEL1: DJNZ R7,DEL1 RET DISPLAY: MOVC A,@A+DPTR // gets 7seg digit drive pattern for current value in A CPL A RETLUT: DB 3FH // LUT starts here DB 06H DB 5BH DB 4FH DB 66H DB 6DH DB 7DH DB 07H DB 7FH DB 6FHEND

About the program.

For the counting purpose both the timers of 8051 (Timer0 and Timer1) are used. Timer 1 is configured as an 8 bit auto reload counter for registering the number of incoming zero going pulses and Timer0 is configured as a 16 bit timer which generate the necessary 1 second time span for the Timer1 to count.For counting the number of beats Timer0 and Timer1 are used. Timer1 is set as an 8 bit auto reload counter for counting the the number of pulses (indicating the heart beat) and Timer0 is set as a 16 bit timer which generates a 65536uS delay. When looped 230 times it will produce a 15 second time span (230 x 65536uS =15S)  for the Timer 1 to count. The number of counts obtained in 15 seconds is multiplied by 4 to obtain the heart rate in beats per minute.
 The Timer 0 which generates the 1 second time span is configured in Mode 1 (16 bit timer). So the maximum it can count is 2^16 and it is 65536. In 8051 the crystal frequency is divided by 12 using an internal frequency divider network before applying it as a clock for the timer. That means the timer will increment by one for every 1/12th of the crystal frequency. For an 8051 based system clocked by a 12MHz crystal, the time taken for one timer increment will be 1µS (ie; 1/12MHz). So the maximum time delay that can be obtained using one session of the timer will be 65536µS. Go through this article Delay using 8051 timer for a better grasp.
Setting up the circuit.
When power is switched ON, the indicator LED D4 will glow an continues in that state. Now place your finger tip over the sensor and adjust preset R14 so that the LED D4 starts blinking. After you got the LED blinking, reset the power and wait for 15 seconds. The display will show your heart rate in beats per minute.

5 Microcontroller Based Projects You Must Not Miss!

Looking for a microcontroller based project? From our collection of microcontroller based projects, we bring to you 5 super cool projects. Have fun!

A tachometer is nothing but a simple electronic digital transducer. Normally, it is used for measuring the speed of a rotating shaft. The number of revolutions per minute (rpm) is valuable information for understanding any rotational system. For example, there is an optimum speed for drilling a particular-size hole in a particular metal piece; there is an ideal sanding disk speed that depends on the material being finished. You may also want to measure the speed of fans you use.

Here is an easy-to-construct temperature indicator-cum-controller that can be interfaced with a heater coil to maintain the ambient room temperature. The controller is based on Atmega8535 microcontroller, which makes it dynamic and faster, and uses an LCD module to display and two keys to increase or decrease the set values.

Digital wall clocks, table clocks and desk clocks with pointer or LCD display are readily available in the market. Here we present a clock that can be built in a small budget using AT89C2051 microcontroller. Additional feature of the clock is that the time display is visible even in the dark.

Microcontroller-based embedded systems play major role in industrial automation. One such widely used system is the programmable timer.

The circuit that uses microcontroller AT89C51 can control four devices from a distance of upto 30 metres wirelessly. An LCD module is used to show the device number and preset control time at the transmitter module.


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$20 Robot From MIT Wins AFRON Design Challenge Made From Arduino Board

Robots, as anyone who has ever attempted to build or buy or fix a robot knows, tend to be expensive. This presents a problem for people who want to start learning about robotics, because getting a foot in the door with an actual robot to work on generally involves a substantial up-front investment in hardware. And for places where teachers and students don't have huge piles of money to throw at technology, this can mean that robots just don't happen.
The African Robotics Network (AFRON) and IEEE Robotics and Automation Society (RAS) collectively sponsor a biennial design challenge to "collaboratively create an educational robot that is an order of magnitude less expensive than existing products, to inspire young people around the world." For 2013/2014, MIT took home a win with their MIT SEG robot, a 3D-printed, Arduino-based wheeled robot that can be built for $20 in five steps with no training or tools.
The completed MIT SEG is shown in the picture above; below is an image of the unassembled robot in its entirety:
All you have to do to go from this to robot is fold up the chassis (the squareish bits at the lower left), fold the wheels together, fit the electronics in, stick the wheels onto the servos, and that's it, you're done. Here's the bill of materials:
MIT points out that if you don't go with a breakout board for the Arduino and instead wire-wrap the headers directly, you can drop the cost by about $2.50 per bot. You also need a programmer and a charger, which together will run you another $18.20, but these can be shared among multiple robots.
So great, you've got a robot that's easy to make and is dirt cheap. What can it do? Out of the box, MIT SEG includes an Arduino compatible drag-and-drop graphical programming interface. The LED and photosensor can be used to determine whether the robot is looking at something black, white, or gray, meaning that you can do line-following and some obstacle avoidance right away, and MIT has put together a bunch of examples and an entire curriculum that classrooms can follow. Plus, since the robot has an Arduino for a brain, you can leverage all of the hardware (and the community) that's been plugging into Arduinos for the last few years.
Second place in the hardware portion of the Design Challenge went toHarvard's $10.70 AERobot:
The Ultra Affordable Educational Robot Project Design Challenge also includes categories for Software, Curriculum, and Community Challenges.
"The AFRON organizers and RAS sponsors admire the ingenuity of the submissions in all categories," said Ken Goldberg, a roboticist at UC Berkeley who co-founded AFRON with Ayorkor Korsah, a professor of computer science at Ashesi University, in Ghana. Goldberg noted that two winning projects from Africa, PanyaBot (Kenya) and ARX LollyBot (Ghana), continue to make major advances in the Software and Community Challenge categories. "We look forward to connecting all the participants to share ideas and designs for next steps via the AFRON network, which anyone worldwide can join at no cost," he said.

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