Sensitive LPG Leakage Alarm

Here is an ultra-sensitive LPG sensor that generates loud beeps when it senses any gas leakage. It detects vapours of liquefied petroleum gas anywhere between 200 and 10,000 ppm and drives a piezobuzzer to catch attention for immediate action. The buzzer beeps until the concentration of gas in the air decreases to a safe level. The circuit uses an MQ6 gas sensor, which is designed to sense LPG, propane and isobutane gases.

Circuit and working
Fig. 1 shows the circuit of the LPG sensor. The circuit is built around 5V voltage regulator 7805 (IC1), gas sensor MQ6 (GS1), counter IC 4060 (IC2) and a few discrete components.GS1 is a six-pin gas sensor that can detect very small traces of LPG in the air and has a swift response time. However, it has very less sensitivity to alcohol and smoke. The sensor’s output is in the form of resistance.

As indicated in Fig. 1, the pins of GSI are H, A and B, two each on either side. H pins are for the heater with no polarity. Input pins A or B and output pins A or B can be connected either way round.The coil heater inside the sensor can be easily heated with 5V DC. If pin A is connected to 5V DC through variable resistor VR1, use pin B as the output or vice versa. Both A and B pins can be shorted. In short, H pins are connected to positive and negative rails, A or B pin to 5V DC, and B or A for output.The resistance value of GSI is different for various kinds and concentration of gases. So when using this sensor, sensitivity arrangement is very important. For accurate detection, it is necessary to calibrate the sensor for 1000 ppm of LPG concentration in the air with load resistance of about 20 kilo-ohms. (In the datasheet, the load resistance range of MQ6 is mentioned as 10 kilo-ohms to 47 kilo-ohms.)

Preset VR1 is used to adjust the sensitivity of the sensor to a particular gas concentration. Output from the sensor is connected to the base of transistor T1, which acts as a switch to trigger the alarm generator built around IC2.IC2 is a binary counter IC that oscillates using capacitor C2 and resistor R5. Transistor T1 controls the reset pin (pin 12) of IC2. When the reset pin is high IC2 does not oscillate, and when this pin goes low IC2 starts oscillating.Working of the circuit is simple. When the sensor detects LPG in the air, its output becomes high and transistor T1 conducts to make reset pin of IC2 low. This triggers IC2 to oscillate, which is indicated by LED1. After a few seconds, the buzzer starts beeping to indicate gas leakage.The circuit works off 12V DC from a battery (BATT.1) or you can use an adaptor. IC1 provides regulated 5V DC supply for the sensor and IC2.

Construction and testing
An actual-size, single-side PCB for sensitive LPG sensor is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on a PCB, enclose it in a suitable case with an opening to allow the gas to enter. Place the unit near the LPG cylinder or gas stove within a distance of one metre. Vary preset VR1 to adjust the sensitivity of the sensor.To test the circuit, check 12V at test point TP1 with respect to TP0 to verify the correct power supply. Place the unit near the gas stove burner and turn on the burner for a few seconds without igniting. Then, turn ’the burner ‘off’ and adjust VR1 until you see LED1 glowing. TP3 should be low at this moment.

Circuits

A circuit is a complete and closed path through which electric current can flow. In other words, a closed circuit would allow the flow of electricity between power and ground. An open circuit would break the flow of electricity between power and ground.

Anything that is part of this closed system and that allows electricity to flow between power and ground is considered to be part of the circuit.

4K TV goes mainstream, but there’s more to come

UltraHD TVs were in every major booth, and they were the most talked-about productat the show. These TVs have a resolution of 3840 x 2160 pixels, or four times as detailed as the 1920 x 1080 pixels of high-definition TV. They’re sharper and don’t pixelate as much when you focus in on one section of the screen. On top of that, many of the TVs can accommodate faster-moving imagery, and they’re all inherently connected. And many of the screens are curved. No doubt the costs are coming down as well. All of that means that the variety of UltraHD TVs we will see this year will grow.

Samsung talked about its SUHD TVs that will have resolution just shy of 8K TV, or 16 times the number of pixels in a high-definition TV. And Sharp also described a screen with 167 percent the resolution of 4K TV. One difference this year: Companies such as Samsung and Sony were making a big effort to make more UltraHD content available, and that’s the ultimate driver of sales.

Electricity

There are two types of electrical  signals , those being alternating current (AC), and direct current (DC).

With alternating current, the direction electricity flows throughout the circuit is constantly reversing. You may even say that it is alternating direction. The rate of reversal is measured in Hertz, which is the number of reversals per second. So, when they say that the US power supply is 60 Hz, what they mean is that it is reversing 120 times per second (twice per cycle).

With Direct Current, electricity flows in one direction between power and ground. In this arrangement there is always a positive source of voltage and ground (0V) source of voltage. You can test this by reading a battery with a multimeter.

Speaking of voltage, electricity is typically defined as having a voltage and a current rating. Voltage is obviously rated in Volts and current is rated in Amps. For instance, a brand new 9V battery would have a voltage of 9V and a current of around 500mA (500 milliamps).

Single chip metal detector circuit

This is a simple single chip metal detector circuit based on IC CS209A from the Cherry Semiconductors. A 100uH coil is used to sense the presence of metal. The IC CS209A has a built in oscillator circuit and the coil L1 forms a part of its external LC circuit which determines the frequency of oscillation. The inductance of the coil change in the presence of metals and the resultant change in oscillation is demodulated to create an alarm. The LED gives a visual indication too. This circuit can sense metals up to a distance of few inches.

Note:

• Assemble the circuit on a general purpose PCB.
• The switch S1 can be a slide type ON/OFF switch.
• The IC must be mounted on a holder.
• The POT R1 can be used to adjust the sensitivity of the circuit.

Add-On Stereo channel selector

The add-on circuit presented here is useful for stereo systems. This circuit has provision for connecting stereo outputs from four different sources/channels as inputs and only one of them is selected/ connected to the output at any one time. When power supply is turned ‘on’, channel A (A2 and A1) is selected. If no audio is present in channel A, the circuit waits for some time and then selects the next channel (channel B), This search operation continues until it detects audio signal in one of the channels. The inter-channel wait or delay time can be adjusted with the help of preset VR1. If still longer time is needed, one may replace capacitor C1 with a capacitor of higher value. Suppose channel A is connected to a tape recorder and channel B is connected to a radio receiver. If initially channel A is selected, the audio from the tape recorder will be present at the output. After the tape is played completely, or if there is sufficient pause between consecutive recordings, the circuit automatically switches over to the output from the radio receiver. To manually skip over from one (selected) active channel, simply push the skip switch (S1) momentarily once or more, until the desired channel inputs gets selected. The selected channel (A, B, C, or D) is indicated by the glowing of corresponding LED (LED11, LED12, LED13, or LED14 respectively). IC CD4066 contains four analogue switches. These switches are connected to four separate channels. For stereo operation, two similar CD4066 ICs are used as shown in the circuit. These analogue switches are controlled by IC CD4017 outputs. CD4017 is a 10-bit ring counter IC. Since only one of its outputs is high at any instant, only one switch will be closed at a time. IC CD4017 is configured as a 4-bit ring counter by connecting the fifth output Q4 (pin 10) to the reset pin. Capacitor C5 in conjunction with resistor R6 forms a power-on-reset circuit for IC2, so that on initial switching ‘on’ of the power supply, output Q0 (pin 3) is always ‘high’. The clock signal to CD4017 is provided by IC1 (NE555) which acts as an astable multivibrator when transistor T1 is in cut-off state. IC5 (KA2281) is used here for not only indicating the audio levels of the selected stereo channel, but also for forward biasing transistor T1. As soon as a specific threshold audio level is detected in a selected channel, pin 7 and/ or pin 10 of IC5 goes ‘low’. This low level is coupled to the base of transistor T1, through diode-resistor combination of D2-R1/D3-R22. As a result, transistor T1 conducts and causes output of IC1 to remain ‘low’ (disabled) as long as the selected channel output exceeds the preset audio threshold level. Presets VR2 and VR3 have been included for adjustment of individual audio threshold levels of left stereo channels, as desired. Once the multivibrator action of IC1 is disabled, output of IC2 does not change further. Hence, searching through the channels continues until it receives an audio signal exceeding the preset threshold value. The skip switch S1 is used to skip a channel even if audio is present in the selected channel. The number of channels can be easily extended up to ten, by using additional 4066 ICs.

Digital Set-Top Boxes and Integrated Digital Television Systems

Digital set-top boxes (DSTBs) receive and decode television broadcasts from satellite, cable, and/or terrestrial sources. Integrated digital televisions (DTVs) have built-in digital tuners, demodulators, and source decoders, so they do not require digital set-top boxes that receive digital broadcasts. Traditional DSTBs are designed to receive standard definition (SD) Moving Pictures Experts Group-2 (MPEG-2) video format broadcasts. However, many of today’s DSTBs are high-definition (HD)-ready. In fact, selected cable television service providers, networks, and local terrestrial TV stations are concurrently transmitting both SD and HD content. Over time, MPEG-4 will displace the MPEG-2 format for both SD and HD. When MPEG-4 becomes the standard compression standard, systems implementing reprogrammable logic devices (such as FPGAs) will be able to seamlessly upgrade without having to scrap inventory items or make new hardware. Using FPGAs, manufacturers can design a STB that can decode MPEG-2 video format, and then later upgrade that same STB for MPEG-4 by simply reprogramming the FPGA in-system. High-end DSTBs usually offer personal video recorder (PVR) and/or an HD DVD recorder for Blu-ray functions. Microcontrollers in DSTBs or integrated DTVs can perform a number of functions for these systems, including control panel management and on-screen display (OSD). Many current DSTBs can be classified either as free to air (FTA) or pay TV versions. A pay TV example would be DSTBs designed for DirecTV or Dish Network (in the USA), which require conditional access to decode the audio and video. DSTB manufacturers typically design the PCBs for both low-end and high-end DSTB systems and require a flexible solution for implementing their various designs.

LED's and OPTICS

LED stands for Light Emitting Diode.  LED's convert an electrical current directly into light.  The light emitted by an LED is directly proportional to current through the LED.  This means LED's are ideal for transmission of information.   However, LED's need direct line of sight and they usually have a short range of light emission.  Because LED's are current dependent they need to be protected from excessive current with a resistor.  For most robotic applications with power sources of around 9 volts I find that a 1K resistor will always to the trick.  You'll notice one lead is longer than the other, in most cases a longer lead indicates that it is the positive lead.  It might be easy to dismiss the LED and assume all it does is light up, but LED's are very interesting electronics components and have some surprising functions.  For instance if you take a Jumbo LED (of any color) and connect your Multimeter up to it for voltage reading and point the LED towards a very bright light source you'll get a voltage reading.  In direct sunlight you can get a reading of 1.5 volts from a normal LED!  Some people even think it is possible to make a color sensor using a LED like this, however after much experimenting with this It is found that LED's to not be suitable for use as a sensor.

Capacitors

Capacitors have 3 primary functions:

1. To store a charge, much like a battery. These capacitors are normally
electrolytic and are used in situations like power supplies where a
fluctuating DC voltage needs to be smoothed, or, have the ripple taken out.

2. A capacitor is used to block DC while allowing AC to pass through such
as in an audio amplifier where we are passing the audio signal through from
one stage to the next.

3. To counteract inductive reactance in order to create a "tuned circuit".

4. A cap can also be used as a spike filtering, which is slightly different than smoothing an AC signal. The term for this purpose is "bypass cap" in case anyone out there was wondering about that one.

When power gets to them they hold a charge right away, but will eventually discharge if left alone or you can discharge a capacitor by hitting both of it's leads together or connect a resistor between both leads.  Capacitors have different levels, which are specified in farads.  Below are common schematics symbols for capacitors and common farad ratings.

1-Farad = 1F 1-Microfarad = 1mF or uF = .000001F 1-Picofarad = 1pF - .000000000001F

C1 shows a normal fixed capacitor, these you can connect in like resistors.  C2 shows one that is polarized, this means you must connect it's positive lead the most positive connection point in it's placement. With polarized capacitors you'll mind that they are marked with either a plus to show the positive side or with a negative to show the negative side.  C3 shows a variable capacitor, I have yet to see one of these in a circuit.

Capacitors are not color-coded but they do have a numbering system that tells you what their value is.  This can be tricky to find the value of an odd capacitor but most of the time you'll see number like this: 151K  The first and second digits are the capacitors value.  For the third number find it's multiplier value on the chart to the left and simple multiply.  So 151K is a 150pF capacitor.  You might also see a notation like this, EG 104 or 104K both of which are .1uf caps.  Caps, of course here is short for capacitor.

The letter tells you the tolerance of the cap, you can look up the tolerance on this chart.  A note I want to add to this capacitor section is that sometimes you may see the letter R on a cap, which would signify a decimal point.  So if you see 2R2 that would equal 2.2 (pF or uF).  My best advice is to keep your capacitors well organized and with their packaging if you are not confident you can distinguish one capacitor from another.

An important thing to take notice of is that capacitors DO NOT add in series like resistors, just the opposite, two 1mfd capacitors in series equal 0.5 mfd.

At ‘four sales a second’, Samsung’s Galaxy S4 passes 10 million mark in first month

“Launched globally on April 27, the phone is estimated to be selling at a rate of four units per second,” Samsung said in a statement announcing the news.

The Android-powered Galaxy S4, with its 5-inch 441-PPI display, 13-megapixel camera and slew of snazzy features, is evidently proving a big hit with consumers in the 110 countries where its currently sold. Ten million sales in less than a month makes sales of the previous iterations of the handset appear positively sluggish, though they were, of course, considered impressive at the time.

The Galaxy S3 crossed the 10-million mark 50 days after its launch in May last year, while the S2 took five months to reach the same milestone. As for the Galaxy S, the first handset in the range, that took all of seven months to sell 10 million units after launching in 2010.

“On behalf of Samsung, I would like to thank the millions of customers around the world who have chosen the Samsung Galaxy S4,” Samsung co-CEO JK Shin said in the statement. “At Samsung we’ll continue to pursue innovation inspired by and for people.”

The Galaxy’s S4’s impressive sales figures also indicate a narrowing of the gap previously comfortably enjoyed by Apple with its iPhone – for the first three months of this year, Apple sold an average of 12.5 million handsets per month. Could we see the S4 outselling the iPhone before the end of 2013, or will sales  tail off once the initial enthusiasm for the handset fades?

Late last year it was reported that Samsung is aiming to sell more than 500 million smartphones and feature phones in 2013, improving on sales in 2012 by around 20 percent. Based on Wednesday’s news, phones in the company’s Galaxy S range are likely to make up a sizable proportion of those sales.

In other S4 news, Samsung says in the summer it’ll be launching the S4 in a variety of new colors – Blue Arctic and Red Aurora, followed by Purple Mirage and Brown Autumn – to go with the currently available White Mist and Black Forest offerings.