MODEL RAILWAY LEVEL CROSSING LIGHTS

CIRCUIT OPERATION

        The weight of the train operates push button switch positioned on the track. The trigger push button switch starts the sequence by switching on the amber light, a few seconds later the two red lights lit ON. When the train has passed the level crossing it operates the cancel push button switch which switches OFF the red lights and switches the green lights ON to allow cars to cross the railway until the next train arrives.

The circuit contain two 555 timer

1.  Monostable

2.  Bistable

        This project uses a 555 monostable circuit to switch on the amber LED for a few seconds. When this switches off it triggers a 555 bistable circuit.

1.  Monostable

        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.              

                        

                    

Monostable operation

        Monostable mode: in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers, missing pulse detection, bounce free switches, and touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) and so on.

2. Bistable (flip-flop) - a memory circuit

        Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce-free latched switches

        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'.

Model railway level crossing lights is the circuit which designed to prevent cars from accident when the train crossing the road.

        This circuit allows car to cross the railway when green LED lights ON. When the train is coming it trigger the circuit through push button that placed a certain distance before the crossing level, amber LED lights ON for a few seconds and red LED lights ON that predicts the train is crossing.

        After crossing railway, the train cancel through push button, red LED lights OFF and green LED lights ON that allow cars to cross the railway until the next train arrives.

                                                      

Interesting news!!

Memristor circuits lead to ultrasmall PCs. Intel and AMD unleash massively multicore CPUs. Samsung TVs respond to your every gesture. These and other developing technologies will fundamentally change the way you think about--and use--technology.

The memristor, a microscopic component that can "remember" electrical states even when turned off. It's expected to be far cheaper and faster than flash storage. A theoretical concept since 1971, it has now been built in labs and is already starting to revolutionize everything we know about computing, possibly making flash memory, RAM, and even hard drives obsolete within a decade.

The memristor is just one of the incredible technological advances sending shock waves through the world of computing. Other innovations in the works are more down-to-earth, but they also carry watershed significance. From the technologies that finally make paperless offices a reality to those that deliver wireless power, these advances should make your humble PC a far different beast come the turn of the decade.

In the following sections, we outline the basics of 15 upcoming technologies, with predictions on what may come of them. Some are breathing down our necks; some advances are still just out of reach. And all have to be reckoned with.

iPhone 5 Features and specifications

Many Apple fans and present Apple iPhone consumers are wondering what would be the groundbreaking iPhone 5 features that can be expected when the iPhone 5 is released. Let us now a comprehensive roundup of all the widely speculated iPhone 5 features. This being a comprehensive list, there is all probability that many of these iPhone 5 features could actually appear in the iPhone 5 when it is expected to be release in June 2012.

iPhone 5 could be having a greater resolution
One of the hotly discussed topics with regard to the iPhone 5 features is its resolution. This is the most impressive of all iPhone 5 features doing rounds as it is rumored that the iPhone 5 could be sporting a Retina Display. And this is the state-of-the-art resolution that can possibly expect. Possibly, with an increased UI size, the resolution can get much stronger and consumers could hope to have a more brilliant video-viewing experience.
iPhone 5 could have a bigger form factor than the iPhone 4S?  The iPhone 5 testing hasn't been leaked “accidentally” so far like the case with iPhone 4. What this means is all the iPhone 5 features are built on speculation. Still, certain clues like the 4-inch iPhone 5 screen throw some light into the iPhone 5 form factor. The iPhone 5 can be a bit larger than the palm-friendly iPhone 4 or iPhone 4S. But then the iPhone 5 could merely have a larger display screen and not the whole body. iPhone 5 could come with the 4G / LTE capability
The iPhone 5 could have the 4G capability because Samsung has got its Infuse 4G released already. Hence it would be only logical that Apple get iPhone 5 to support 4G capability. The LTE capability, if it comes, would be a boon.
iPhone 5 could incorporate a quad-core processor
A dual-core processor has become a pretty common thing in the smartphones of these days. There is a stiff competition between the processors of Apple smartphones running iOS and Samsung smartphones running Android. The A6 quad-processor expected to features in the iPhone 5 could leave any competition far behind.
Wireless charging feature in iPhone 5
It is expected that the iPhone 5 could sport the wireless charging feature and this could give the customers yet another break. However, whether the wireless charging feature is actually churning out a mass appeal is a moot question. This could be a distinct possibility with the inductive wireless charging technology.

Apple Hopes to Improve the Picture for the iPad

  With its new iPad, Apple focuses on a better screen and high-speed connectivity to stay ahead of competitors.

Apple's newest iPad sports a higher-resolution display.

The iPad is getting a facelift as Apple tries to stay way ahead of the competition.
The third version of the tablet, which Apple CEO Tim Cook introduced Wednesday in San Francisco, will include a high-resolution "retina display" like the iPhone, as well as the ability to access high-speed LTE wireless networks. Other features include a more powerful processing chip called the A5X, an improved rear camera, and dictation capabilities.
The event marked the company's first gadget unveiling since cofounder Steve Jobs died in October after a lengthy battle with pancreatic cancer. Cook and Apple's marketing head, Phil Schiller, shared the duties of introducing the device.
Schiller said the new iPad will be available March 16, though orders can be placed now. Apple is keeping the price of the new version between $499 and $829, depending on its storage capacity and wireless capabilities, and it will lower the price of the most inexpensive iPad 2 to $399.

Adobe releases public beta of Photoshop CS6

Let the celebrating—and inevitable complaining—begin: Adobe has announced the public beta of Photoshop CS6, the latest and greatest version of its flagship photo editing program. The first big update of the product in about two years, CS6 has been overhauled with a new interface that now sports a customizable background color and redesigned icons. There will of course be much gnashing of teeth from those who don’t like change, but the look does feel more current, in my opinion.

Available as a free download (Mac or Windows) from the Adobe Labs site, the beta requires online registration activation and at least 2GB of free disk space on the Mac, or 1GB in Windows XP or 7. It includes features from both the standard and extended versions of Photoshop that will ship this spring, such as two new tools that take advantage of the very cool content-aware technology Adobe debuted in CS4, Content-Aware Move and Content-Aware Patch. Other cool improvements include a revamped crop tool, the ability to migrate presets (as well as import and export them), improved raw image processing, and a new Blur Gallery that allows you to add Tilt-Shift, Iris, and Field blur effects easily.

For a complete list of new features, check out the installation and feature notes for the Photoshop CS6 beta, and for a great hands-on take, don’t miss Lori Grunin’s post at our sister site, CNET Crave.

SMD FM transmitter circuit

Let’s construct a low-power FM transmitter using surface-mount devices (SMD) that will be received with a standard FM radio. Soldering surface mounted devices is not so hard and actually is quite easy. There are many designs for small FM transmitters but they have some problems. First, you need an audio amplifier to get enough modulation. Second, the antenna is attached directly to the collector. Third, the coil L must be wound by hand and adjusted by stretching. It all ads with a weak signal that tends to drift in frequency. In contrastm the transmitter schematic we present here eliminates some of those problems, using varactor diode for tuning and modulation, givind great sensitivity without an audio amplifier.



FM Transmitter – How it works
The figure below shows the schematic of the transmitter which consists of two stages: an oscillator and an output amplifier. Modulation is from an electret microphone but you can use a low power audio source.
Oscillator stage
Transistor Q1 is a Colpitts oscillator where the frequency is determined by the parallel resonant circuit formed by inductor L, varactor V1 and capacitors C7 and C8. Q1 is a common-collector amplifier where the power gain counts. V1 is actually a dual varactor that eliminate the possibility of forward conduction at the sinewave peaks.
The frequency of oscillation is set by adjusting the DC voltage on V1 with potentiometer R2. R4 and C3 form a low-pass filter to prevent RF from feeding back onto the DC.
Capacitors C7 and C8 form an AC voltage divider to provide feedback at the emitter of Q1 to sustain oscillation. A necessary condition for oscillation to start is for the radio (C7+C8)/C7 to be sufficiently bigger than 1.

SMD transmitter circuit schematic

 

 

 Frequency Modulation
Modulation is done by superimposing an audio signal from the electret mic onto the DC bias applied to V1. R3 and C1 form a low-pass filter to prevent RF from feeding back to the mic. R3, R4 and R2 form a votage divider for the audio.
Transmitter output stage
The output of the oscillator is fed through C9 to the Q2 emitter-follower. The output of Q2 drives the antenna through C11. The Q2 emitter-follower it ensures that the oscillator is not loaded down by the impedance of the antenna and it provides power gain to drive the antenna.
SMD Transmitter layout
The figure below shows the layout of the PCB and it uses surface-mounted devices like resistors and capacitors (non-polar devices). All the caps are size 0805 and all resistors are size 1206. use through-hole components for Q1, Q2, IC1 and V1. You can use an SOT-89 device for IC1 and an SOT-23 device for V1. Use MPSH10 or a transistor equivalent.

 

 

 The inductor
A coil would consist of two or three turns of wire but for this schematic we will use an inductor with loops of copper on the PCB. Such flat spiral inductor are common at these frequencies.
One formula for flat spiral inductors is:

where
L = inductance in uH
r = radius of coil (outer radius + inner radius divided by 2 ) inches
N = number of turns
d = depth of coil (outer radius minus inner radius) inches

Tuning range
While commercial FM band goes from about 88 MHz to 108 MHz, the L and C values used in this design allow tuning up to 100 MHz.

Transmitter testing
You will need a portable FM radio and an assistant. First, find an empty spot on the FM dial and set your radio about 30 feet away (9 meters). The radio’s volume control should not be set too high to prevend feedback. Next, power-up your transmitter and talk to yourself as you adjust the frequency with the trim-pot. When your assintant hears you, your transmitter is tuned. You might have to adjust the radio’s tuner slightly for best reception.
Have fun with it but remember that using the transmitter as a bugging device may not be legal in your country. To use the circuit as a wireless microphone, increase the value of R3. The transmitter range is about 100 feet (30 meters) inside a building.