Here is my YouTube video Hindi version about this circuit:
This BH1417 pll fm transmitter includes features like: pre-emphasis, sound limiter, stereo transmission, low pass filter, pll circuit, fm oscillator and rf output buffer. The sound limiter maintains the same audio level so no distorsions occur, the stereo encoder separates the left and right channel enabling stereo transmission, the low pass filter blocks any audio signal above 15 Khz to prevent rf interference and the pll circuit provides a rock solid frequency stability.
There are 14 possible transmission frequencies with 200KHz increments selected with a 4-DIP switch. Starts from 88.7 up to 89.9 MHz and 107.7 up to 108.9 MHz.
S4
S3
S2
S1
Frequency
1
1
1
1
88.7 MHz
1
1
1
0
88.9 MHz
1
1
0
1
89.1 MHz
1
1
0
0
89.3 MHz
1
0
1
1
89.5 MHz
1
0
1
0
89.7 MHz
1
0
0
1
89.9 MHz
1 = ON, 0 = OFF
Simply select transmission frequency at which you would like to transmit, set the combination for 4-DIP switch and BH1417 will tune to that frequency. If you can’t hear the transmitted audio signal on your FM receiver then re-adjust 2.5 turn variable coil until you can hear the signal.
Description of Home security system: There are several home security systems out there. Different manufacturers use different techniques and topology in their design. Cameras are also very popular for the purpose of security. Main problem with security cameras is to monitor them. They have capability to record the view in DVR hard drive but they could not stop intruder from intrusion. They are just providing the proof after the incident happens. Whereas in most cases we want to stop an intruder from intrusion. for this purpose different types of alarming systems are developed which warns the intruders not to enter in a specific area. also these system are kind of passive systems which needs only power up and they stays in sort of sleeping mode when everything is normal. They activate an alarm at the time of intrusion. They don't normally need to observe. So such systems are better in the way that all the time monitoring is not needed. Monitoring all the time is not easy. It needs a team of three people minimum all the time to observe the cameras in 24 hours a day. In some very sensitive areas it is mandatory to keep system system in observation all the time but in normal situations an alarming system with no observation is the best choice. Such alarming systems use sort of activating sensing system which is activated by some parameter. mostly they use pyroelectric sensor which are activated by human body temperature. When a person is passing through the pir or piroelectric sensor, its body infrared radiation which is in the form of body temperature activates the pyroelectic sensor and it sends its output signal to an amplifier. The amplifier is amplifying the signal as well there is a timer operation also in the circuit. The amplifier activates a alarm which informs the intruder not to enter in the specific area as you are under observation.
Principle of operation:
When power is applied to the circuit, The pir sensor or piroelectric sensor senses human passed in front of it and it produces an electrical signal, the pir sensor output signal from sensor pin 2 is applied to one transistor VT1 and here it is amplified. Without amplification the signal is small enough so that it could not be fed to the next stage, then this signal is applied to the operational amplifier IC2A pin 3 which performed as high gain low noise amplifier stage, and latter the signal is supplied to IC1A for further amplification.
The IC2B works like a voltage comparator and it compares the two inputs. One is the signal coming from the prvious stage and the other is the reference provided by R10 and VD1. Transistor VT is used to drive the output buzzer.
Halogen bulbs are standard light bulbs used in most automotive applications. Halogen light bulbs have very nice nature light. They provides light quality which is very close to natural light. Halogen light buts uses iodine from halogen group to prolong the lamp life and prevent is from blackening. The halogen iodine provides the cyclic process in which the light bulb can provide good efficiency at higher temperature with prolonged life. Due to this halogen in light bulb the bulb is not blackening with time and use. Halogen bulbs are available in two basic types which are most commonly used in automotive. One type of light bulbs have single filament in them. They can only be used as low or high beam at a time. These bulbs have type number like H1,H3, H7, H9, H11, HB4 and HB3. There light bulbs had smaller glass tube and they are consuming less power. There are other type with high efficiency they are H7 and H1 bulbs. Where are the other type or the second type that is H4 light bulb which has two elements. One element is used at a time. These both elements could be used both for low and high beam in one single tube. There glass tube is a little bit thicker in diameter. There bulbs were very common a few decades ago in cars, trucks and buses.
Halogen bulb cyclic process
Supply of electronic energy makes the
filament glow and metal evaporates off
the filament. A halogen filling (iodine or
bromine) inside the bulb lets the filament
temperature rise to near the melting
point of the tungsten (around 3 400°C)
and this causes the high light output. In
the immediate vicinity of the hot bulb
wall, the evaporated tungsten combines
with the filling gas (tungsten halogenide)
to form a gas which is transparent.
However, once the gas gets back near the
filament, it disintegrates due to the high
filament temperature and forms an even
tungsten layer. For the cyclic process to
stop, the outer temperature of the bulb
must be 300°C. The bulb made of quartz
glass must closely enclose the filament.
Another advantage is that a higher filling
pressure can be used to counteract the
evaporation of the tungsten. The gas
composition in the bulb is also a major
factor controlling the light output.
Inclusion of a small amount of a noble
gas such as xenon reduces the heat transfer away from the filament. However,
despite the regeneration process inside
the bulb, the tungsten filament is slowly
consumed and thus service life is limited.
This is not just you who's internet is slow and is not browsing YouTube and other services like facebook etc. This is a common problem for many countries as a submarine cable had been disconnected and we are facing slow internet connection. Hope this problem will be cured and the disconnected cable will be restored back soon. There is no need to give complaint to the local service provider for speed issue as they can't solve it. Also stay with your other relation and enjoy the time with them which you people are normally wasting on system! Take this disconnection in positive manner and even enjoy this time with your other activities as long as it restores. Unfortunately to day is the time when we can't survive without internet. This thing is compulsory in our day to day life. Stay creative and do some other work which you can do offline at PC or anything out of PC world. At the moment it can only browse google or blogger or similar but not YouTube or facebook.
Photo resistors are light sensitive resistors whose resistance decreases as the intensity of light they are exposed to increases.
Characteristics
Types of photo resistors and working mechanisms
Based on the materials used, photo resistors can be divided into two types; intrinsic and extrinsic. Intrinsic photo resistors use undoped materials such as silicon or germanium. Photons that fall on the device excite electrons from the valence band to the conduction band, and the result of this process are more free electrons in the material, which can carry current, and therefore less resistance. Extrinsic photo resistors are made of materials doped with impurities, also called dopants. The dopants create a new energy band above the existing valence band, populated by electrons. These electrons need less energy to make the transition to the conduction band thanks to the smaller energy gap. The result is a device sensitive to different wavelengths of light. Regardless, both types will exhibit a decrease in resistance when illuminated. The higher the light intensity, the larger the resistance drop is. Therefore, the resistance of LDRs is an inverse, nonlinear function of light intensity.
Wavelength dependency
The sensitivity of a photo resistor varies with the light wavelength. If the wavelength is outside a certain range, it will not affect the resistance of the device at all. It can be said that the LDR is not sensitive in that light wavelength range. Different materials have different unique spectral response curves of wavelength versus sensitivity. Extrinsic light dependent resistors are generally designed for longer wavelengths of light, with a tendency towards the infrared (IR). When working in the IR range, care must be taken to avoid heat buildup, which could affect measurements by changing the resistance of the device due to thermal effects. The figure shown here represents the spectral response of photoconductive detectors made of different materials, with the operating temperature expressed in K and written in the parentheses.
Sensitivity
Light dependent resistors have a lower sensitivity than photo diodes and photo transistors. Photo diodes and photo transistors are true semiconductor devices which use light to control the flow of electrons and holes across PN-junctions, while light dependent resistors are passive components, lacking a PN-junction. If the light intensity is kept constant, the resistance may still vary significantly due to temperature changes, so they are sensitive to temperature changes as well. This property makes LDRs unsuitable for precise light intensity measurements.
Latency
Another interesting property of photo resistors is that there is time latency between changes in illumination and changes in resistance. This phenomenon is called the resistance recovery rate. It takes usually about 10 ms for the resistance to drop completely when light is applied after total darkness, while it can take up to 1 second for the resistance to rise back to the starting value after the complete removal of light. For this reason the LDR cannot be used where rapid fluctuations of light are to be recorded or used to actuate control equipment, but this same property is exploited in some other devices, such as audio compressors, where the function of the light dependent resistor is to smooth the response.
Construction and properties of Photo resistors
Since the discovery of selenium photoconductivity, many materials have been found with similar characteristics. In the 1930s and 1940s PbS, PbSe and PbTe were studied following the development of photoconductors made of silicon and germanium. Modern light dependent resistors are made of lead sulfide, lead selenide, indium antimonide, and most commonly cadmium sulfide and cadmium selenide. The popular cadmium sulfide types are often indicated as CdS photoresistors. To manufacture a cadmium sulfide LDR, highly purified cadmium sulfide powder and inert binding materials are mixed. This mixture is then pressed and sintered. Electrodes are vacuum evaporated onto the surface of one side to form interleaving combs and connection leads are connected. The disc is then mounted in a glass envelope or encapsulated in transparent plastic to prevent surface contamination. The spectral response curve of cadmium sulfide matches that of the human eye. The peak sensitivity wavelength is about 560-600 nm which is in the visible part of the spectrum. It should be noted that devices containing lead or cadmium are not RoHS compliant and are banned for use in countries that adhere to RoHS laws.
Typical applications for photoresistors
Photo resistors are most often used as light sensors. They are often utilized when it is required to detect the presence and absence of light or measure the light intensity. Examples are night lights and photography light meters. An interesting hobbyist application for light dependent resistors is the line following robot, which uses a light source and two or more LDRs to determine the needed change of course. Sometimes, they are used outside sensing applications, for example in audio compressors, because their reaction to light is not instantaneous, and so the function of LDR is to introduce a delayed response.
Light sensor
If a basic light sensor is needed, an LDR circuit such as the one in the figure can be used. The LED lights up when the intensity of the light reaching the LDR resistor is sufficient. The 10K variable resistor is used to set the threshold at which the LED will turn on. If the LDR light is below the threshold intensity, the LED will remain in the off state. In real-world applications, the LED would be replaced with a relay or the output could be wired to a microcontroller or some other device. If a darkness sensor was needed, where the LED would light in the absence of light, the LDR and the two 10K resistors should be swapped.
Audio compressors
Audio compressors are devices which reduce the gain of the audio amplifier when the amplitude of the signal is above a set value. This is done to amplify soft sounds while preventing the loud sounds from clipping. Some compressors use an LDR and a small lamp (LED or electroluminescent panel) connected to the signal source to create changes in signal gain. This technique is believed by some to add smoother characteristics to the signal because the response times of the light and the resistor soften the attack and release. The delay in the response time in these applications is on the order of 0.1s.
Light dependent resistor symbol
The following symbol is used to depict light dependent or photo resistors according to the IEC standard. Sometime the resistor symbol is circled, with the arrows outside the circle.
Here is my YouTube video supporting this document:
Here is my YouTube video supporting this document Hindi/ Urdu version :
Use of ccfl or cfl light bulbs
CCFL or CFL light bulbs are very commonly used everywhere. In the last three decades they were very popular and still are considered excellent as electrical lighting source. They are reliable and energy saving light sources. Their light quality is excellent as they have light close to daylight.
Having all good features, they have problems also. First they have definite tube light. Second they have electronic ballast circuit with is going sometimes defective. The good news is they are totally repairable now a days. Their parts like glass tube or glass element and other electronic parts are easily available. All they need are replacement parts which restores the lamp to new life. The parts price is also very low. Their repair is a cost effective solution as for the 1/5th of the price of the lamp one can restore the defective lamp to a new one.
CCFL light ballast circuit details
Here is the typical circuit for a CFL lamp electronic ballast:
Typical CFL lamp circuit showing all components
First of all you should verify that the lamp is not glowing by inserting it in 220V lamp holder.
Open the cover of the lamp ballast circuit using a small screw driver.
Carefully look at the circuit and look for any burning mark or any burnt or broken component.
Turn your multimeter selector switch or dial to ohm or continuity range.
Check the continuity of the two power prong of the lamp to the lamp circuit. There should be continuity from both prongs to circuit. otherwise check for blown line fuse i one of the wires.
If continuity is there, you should check for lamp heater filament continuity. There should be some 5 to 10 Ohm resistance in each filament. If there is no continuity of specified resistance or open circuit, the grass element filaments are fused and the glass needs replacement.
Put the lamp in a plastic bag and break the glass tube using some metal like a file or something. Break the glass inside the bag to protect you from glass chunks and from gas inside the tube.
Now look at the lamp and you will see the fused filament easily.
Now remove all four wires of the broken lamps from the pcb pins to remove the circuit pcb from the lamp.
Now break the remaining of the glass tube chunks and clean the lamp cover for new tube.
Now put four small piece of 1 mm glass fiber slew on wires to prevent them from shorting.
Now insert the new glass to the cover by passing the wires throw the plastic cover.
Now secure the glass tube temporarily by fixing it to the plastic cover using sticking tape pieces.
Now use some glue to fix the lamp glass with cover. I am using wood glow Vinamol Dura. You can use any glue of your choice.
Put some quantity of glue on glass and cover and spread it using a screw driver. Keep the lamp for some 24 hours to settle and dry the glue.
After the glue is settled, fix all the four wires on the ballast circuit board to make the connections complete.
Now fix the lamp covers and secure its locks.
Now verify your repair by powering up the lamp. The lamp should glow perfect with the new glass tube.
When a transformer installation is completed, it is required to do some tests on transformer to determine the transformer electrical, mechanical and thermal stability for the utility and facility are are supposed to used. Such tests for a transformer are defined as standard test in national standards created by IEEE, NEMA and ANSI. A few tests which are normally performed on a transformer after supplied are as following.
Transformer Turns Ratio TTR testing
The Transformer Turns Ratio test is used to make sure that the Turns Ratio between the winding of the transformer is correct.
With this information, one can decide what the output voltage of the transformer will be. The ratio is calculated and tested under no-load conditions.
Simultaneous readings of voltage are taken to low voltage and high voltage windings area taken after the voltage is applied to one winding. The ratio is the division between the high reading and low reading. If it is a three-phase transformer, each phase is tested individually.
Insulation Resistance testing
The insulation resistance testing is commonly known as the Megger test. It measures the quality of insulation within the transformer. Some variations will be obtained depending on the moisture, cleanliness and the temperature of the insulation. It is recommended that tank and core should always be grounded when this test is performed. Each winding should be short-circuited at the bushing terminals. Resistances are then measured between each winding and all other winding and ground.
Transformer Power Factor test
This test will detect the dryness of transformer insulation.
It is the ratio of the power dissipated divided by the input volt-ampere multiplied by 100. The test is made with a capacitance bridge, and the connections are the same as for the Megger test. This test can be repeated during the service life of the transformer and verified against the result obtained during manufacturing to check if the insulation is malfunctioning or decaying.
Transformer Resistance Test
For this test the transformer must be cold. The transformer must be kept no load or switched off for several hours before performing this test. Winding resistance is calculated by measuring the voltage and current simultaneously, with the current as close to the rated current as possible. Performing this test will allow you calculate and compensate for major component of load losses as a whole.
Transformer Polarity test
This test on a transformer is either additive or subtraction. When voltage is applied between the primary bushings and the resultant voltage between the secondary bushings is greater, then it means that the transformer has additive polarity. Polarity is a vital concern if transformers are to be paralleled or bank connected. Three-phase transformers are also checked for polarity by the same means.
Transformer Phase Relation
This test will detect if transformers have been connected in a correct phase relationship. It calculates the angular displacement and relative phase sequence of the transformer, and can be tested at the same time as ratio and polarity tests. The voltages of the phase of primary and secondary can be recorded and comparisons made to get the phase relation.
Transformer Oil Tests
An oil sample will detect several things on a transformer. The following tests can be performed with the oil sample.
Acid number
Dielectric breakdown
Power factor
Moisture content
Interfacial tension
Oil test are really useful to determine the condition of the insulation and the oil so based on these results a maintenance program can be established.
Transformer Visual Inspection
The simplest of all. It can reveal potential problems that may not be detected by diagnostic testing. A standard procedure must be established to perform the visual routine test.
Here is the YouTube video showing all these details in motion:
Here is the YouTube video showing all these details in Hindi and Urdu:
A mouse when use with a PC or Laptop for years, it develop different problems. A very common defect is a double click problem. The double click defect is one in which you are encountering to multiple clicks of mouse buttons when you click once. This is due to switches defect. Switches are working hard all the time during their service life. They are exposed to dust also.
Switches have springs and contacts. With use the springs loose their elasticity and the contacts accumulates dust and debris. Then one experiences double or multiple clicks due to those defective switches. This becomes sometimes horrible when you need precise one click job. Especially if you are working on some drawing software or video editing software.
The solution to such defect is to replace the bad switches with good and new switches or to swap switches from one position to another within the defective mouse. I would explore the way how to do it in the following images and lines.
Locate which button in creating double click. Normally left click because it is frequently and most used in the entire service life of a mouse.
Unscrew a small screw using a small Philips screw driver.
Create space between the two covers of the mouse using your nails.
Carefully pry the top half cover backward and take care of the locks in front and don't break them during the opening process.
Take off the cable from its position.
Take off the wheel assembly from its position.
Give attention to the wheel springs. Make sure install the wheel assembly in the same way latter as it had come off.
Take off the circuit board from the mouse.
Here S1 and S3 are the switches to be swapped. Mark the defective switch so that you may know it latter on.
Give attention to the three legs soldered to the board.
Solder the legs using a soldering iron and soldering wire. This will help providing heat to the existing soldering and will make it easy to melt.
Hold the switch and melt the soldering on its legs using soldering iron.
Remove the switches after the soldering is melt. Keep the switches side.
Swap the positions for both switches which is in the left click and under the wheel. Fix them in those swapped positions.
Solder the legs of the switches. Solder them properly to avoid any loose of dry solder.
Clean the mouse covers and glass part to make sure there should be no dust inside.
Put the cover back after fixing the board, wheel and cable inside. Carefully lock the front tabs in their corresponding positions.
Fix the small screw and tight it using the small Phillips screw driver.
The mouse is ready to use. Test it with your PC or laptop. Hope it will work like a new mouse.
