Friday, December 27, 2013
Preamplifier for Microphones and Tape Heads
This circuit consists of a single transistor as amplifier and it gives a nice amplification to weakest and unipolar signals for feeding to a real amplifier. The center of this circuit is a BC547 OR BC548 transistor and the rest of the circuit is few resistors, and capacitors. The diagram and also the PCB layout is below. [Link]
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Tuesday, December 24, 2013
Telephone Ring Repeater
Even though cordless phones have invaded our homes and offices, you don’t always have them at hand, and as their ringtones are usually very much quieter than the old rotary-dial- type analogue phones, it can happen that you miss a call you’ve been waiting for while you’ve been going about your daily business.
Until quite recently, you could still find remote ringers that could be plugged into any standard phone socket in order to have an additional ringer, but it seems as if these accessories are currently being phased out as everyone is ‘going cordless’. So we decided to suggest something better, with this phone ring repeater that makes it possible to control any device connected to the AC power outlet using the ringtone available on any subscriber line, and naturally, with all the guarantees of safety and isolation that are of course rightly expected. So it’s capable of driving a ringer, or indeed even a high-powered sounder to alert you when you are in the garden, for example; but it is equally able to light a lamp for a ‘silent ring’ so as to avoid waking a sleeping baby or elderly person.
This circuit has been designed to be compatible with all phone systems the author is aware of and also to be totally stand-alone. What’s more, the circuit can be connected to the phone system without any danger though in some countries, it is forbidden to connect non-approved devices to the public switched telephone network (PSTN). Check local regulations in this respect.
In order to understand the principle of it, we just need to remember that the ringtone present on a phone installation is an alternating voltage, whose amplitude and frequency vary somewhat between countries, but always with comparable orders of magnitude except in the case of exchange systems used in large companies. However, when the line is quiescent or a call is in progress, it carries only a direct voltage. Capacitor C1 makes it possible to pick off just the AC ringing volt-age, which is then rectified by D2 and amplitude-limited by D1. The resulting DC voltage charges capacitor C2, which makes it possible to light LED D3 as well as the LED in the optocoupler IC1. This is no ordinary optocoupler, but is in fact an AC power zero-crossing detecting optotriac, which allows us to con-trol the chosen load while generating no, or less, interference, which would not be the case using a standard optotriac.
The output triac it contains is not powerful enough to drive a load directly connected to the mains, so it is used to drive the trigger of triac TRI1, which is a totally standard 400 V device, rated at x amps, where x is chosen to suit the maximum power of the load you want to control using this circuit. Resistors and capacitors R5 and C3 on the one hand, and R6 and C4 on the other help, serve to suppress the switching transients, which are already inherently low because of the AC zero-crossing switching provided by IC1.
Construction is not at all difficult, but does require a few precautions in choosing some of the components. First of all, capacitor C1 must be an MKT type, mylar or equivalent, with a 250 V operating voltage because of the relatively high amplitude of the ringing voltage. For safety reasons, it is essential that capacitors C3 and C4 are self-healing types intended for AC power use at 250 VAC. These capacitors are generally known as Class X or X2 capacitors.
As for the triac, it should have a 400 V operating voltage (but see below for users on 120 VAC power) and maximum current slightly greater than the maximum current drawn by the load being driven. As this will usually be a sounder or a common lamp, a 2 A type will usually be more than adequate in most situations. As the circuit can be expected to operate for short periods only, there is no need to mount the triac on a heatsink. One final important point: as the right hand part of the circuit is connected directly to AC power, it is vital to fit this inside a fully-insulated housing, for obvious safety reasons. Make sure you cannot touch any part when the circuit is in use.
The circuit should work at once and without any problems, but if you notice that D3 doesn’t light up fully, and hence incorrect or erratic triggering of the triac, because of too low a ringing voltage, all you need to put things to rights is reduce the value of resistor R1. The circuit as shown was dimensioned for operation from 230 VAC power. Readers on 120 VAC power should modify the following component values: R4 = 180 Ω; R5 = 220 Ω; TRI = 200 V model; IC1 = MOC3031. Option-ally, C3 and C4 may be rated at 120 VAC.
Source: http://www.ecircuitslab.com/2012/05/telephone-ring-repeater.html
Sunday, December 22, 2013
It is the function and feature of cell phone jammer
It is the function and feature of cell phone jammer .
Then the order of execution of its boot program data read from external memory (font, chip). If not read the information at this time, the CPU internal reset (via the CPU internal "watchdog" or
hardware reset command) bootloader If successful completion of implementation, the CPU was taken from the external font program execution, if acquisition procedures are abnormal, it can lead to a
"watchdog" to reset both the program and from address start. The CPU reads the character through the parallel data and address lines and address lines, together with the read and write control
clock line W / R, some readers may ask, font is how to distinguish between the program read, or read the data? Microcontroller with external program memory chip select signal line or the CS, CE,
and the W / R role, you can allow the character to distinguish between read data or program. Install the main machine of cell phone jammer first.
Phone all the software work processes are carried out under the action of the CPU, the specific division of the five processes described below. These processes are software in the form of data
storage in the phone in EEPROM and FLASHROM of when the phones power supply module detects a power key is pressed, the cell phone battery voltage is converted to a voltage suitable for the use of
the phone circuit value supplied to the power module, the clock circuit supply voltage oscillation signal into the logic circuit, CPU voltage and clock signal, performs the boot process, the first
read from the ROM boot code execution logic The self-test of the system. And all of the reset signal is set high, if the self-test through. cell phone jammer will only act on cell phone
communication.
The CPU is given Watchdog (Watchdog) signal to the module, then the power supply module in the role of watchdog (Watchdog) signal to maintain the boot. Phone is switched on, not only search for the
broadcast control signal Road (BCCH) carrier frequency. Because the system at any time be sent to each user in the community users to broadcast control information. Phone to collect the search to
the strongest (BCCH) carrier frequency. The carrier frequency corresponding to the read frequency correction channel (FCCH), frequency and synchronization of the mobile phone (MS). Each users
mobile phone in different morning (both residential) carrier frequency is fixed, it is to determine when the network by the GSM network operator, rather than determined by the users GSM phone.
Mobile phones to read the sync channel. It is 1 set of main machine of cell phone jammer .
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Then the order of execution of its boot program data read from external memory (font, chip). If not read the information at this time, the CPU internal reset (via the CPU internal "watchdog" or
hardware reset command) bootloader If successful completion of implementation, the CPU was taken from the external font program execution, if acquisition procedures are abnormal, it can lead to a
"watchdog" to reset both the program and from address start. The CPU reads the character through the parallel data and address lines and address lines, together with the read and write control
clock line W / R, some readers may ask, font is how to distinguish between the program read, or read the data? Microcontroller with external program memory chip select signal line or the CS, CE,
and the W / R role, you can allow the character to distinguish between read data or program. Install the main machine of cell phone jammer first.
Phone all the software work processes are carried out under the action of the CPU, the specific division of the five processes described below. These processes are software in the form of data
storage in the phone in EEPROM and FLASHROM of when the phones power supply module detects a power key is pressed, the cell phone battery voltage is converted to a voltage suitable for the use of
the phone circuit value supplied to the power module, the clock circuit supply voltage oscillation signal into the logic circuit, CPU voltage and clock signal, performs the boot process, the first
read from the ROM boot code execution logic The self-test of the system. And all of the reset signal is set high, if the self-test through. cell phone jammer will only act on cell phone
communication.
The CPU is given Watchdog (Watchdog) signal to the module, then the power supply module in the role of watchdog (Watchdog) signal to maintain the boot. Phone is switched on, not only search for the
broadcast control signal Road (BCCH) carrier frequency. Because the system at any time be sent to each user in the community users to broadcast control information. Phone to collect the search to
the strongest (BCCH) carrier frequency. The carrier frequency corresponding to the read frequency correction channel (FCCH), frequency and synchronization of the mobile phone (MS). Each users
mobile phone in different morning (both residential) carrier frequency is fixed, it is to determine when the network by the GSM network operator, rather than determined by the users GSM phone.
Mobile phones to read the sync channel. It is 1 set of main machine of cell phone jammer .
Friday, December 20, 2013
Voltage Tester for Model Batteries
With a suitable load, the terminal voltage of a NiCd or lithium-ion battery is proportional to the amount of stored energy. This relationship, which is linear over a wide range, can be used to build a simple battery capacity meter.
Circuit Image :
Voltage Tester for Model Batteries Circuit Image
This model battery tester has two functions: it provides a load for the battery, and at the same time it measures the terminal voltage. In addition, both functions can be switched on or off via a model remote-control receiver, to avoid draining the battery when it is not necessary to make a measurement. The load network, which consists of a BC517 Darlington transistor (T2) and load resistor R11 (15 Ω /5 W), is readily evident. When the load is active, the base of T1 lies practically at ground level. Consequently, T1 conducts and allows one of the LEDs to be illuminated.
Circuit Diagram :
Voltage Tester for Model Batteries Circuit Diagram
The thoroughly familiar voltmeter circuit, which is based on the LM3914 LED driver, determines which LED is lit. The values of R6 and R7 depend on the type and number of cells in the battery. The objective here is not to measure the entire voltage range from 0 V, but rather to display the portion of the range between the fully charged voltage and the fully discharged voltage. Since a total of ten LEDs are used, the display is very precise. For a NiCd battery with four cells, the scale runs from 4.8 V to 5.5 V when R6 = R7 = 2 kΩ. The measurement scale for a lithium-ion battery with two cells ranges from 7.2 V to 8.0 V if R6 = 2 kΩ and R7 = 1 kΩ.
For remote-control operation, both jumpers should be placed in the upper position (between pin 1 and the middle pin). In this configuration, either a positive or negative signal edge will start the measurement process. A positive edge triggers IC1a, whose output goes High and triggers IC1b. A negative edge has no effect on IC1a, but it triggers IC1b directly. In any case, the load will be activated for the duration of the pulse from monostable IC1b. Use P12 to set the pulse width of IC1a to an adequate value, taking care that it is shorter than the pulse width of IC1b.
If the voltage tester is fitted into a remote-controlled model, you can replace the jumpers with simple wire bridges. However, if you want to use it for other purposes, such as measuring the amount of charge left in a video camera battery, it is recommended to connect double-throw push-button switches in place of JP1 and JP2. The normally closed contact corresponds to the upper jumper position,while the normally open contact corresponds to the lower position.
Parts :
Resistors: R1,R2 = 47kΩ
R3 = 100kΩ
R4 = 500kΩ
R5 = 1kΩ
R6,R7 = see text (1% resistors!)
R8 = 1kΩ5
R9 = 1kΩ2
R10 = 330Ω
R11 = 15Ω 5W
R12 = 15kΩ
P1 = 100kΩ preset
Capacitors:
C1 = 10nF
C2 = 100nF
Semiconductors:
D1-D10 = LED, red, high effi-ciency
T1 = BC557
T2 = BC517
IC1 = 74HC123
IC2 = LM3914AN
Miscellaneous:
PC1,PC2,PC3 = solder pin
JP1,JP2 = jumper or pushbutton
PCB Layout :
Voltage Tester for Model Batteries PCB Layout
Wednesday, December 18, 2013
MAINS OPERATED CHRISTMAS STAR
Here is a low-cost circuit of Christmas star that can be easily constructed even by a novice.
The main advantage of this circuit is that it doesn’t require any step-down transformer or ICs. Components like resistors R1 and R2, capacitors C1, C2, and C3, diodes D1 and D2, and zener ZD1 are used to develop a fairly steady 5V DC supply voltage that provides the required current to operate the multivibrator circuit and trigger triac BT136 via LED1.
The multivibrator circuit is constructed using two BC548 transistors (T1 and T2) and some passive components. The frequency of the multivibrator circuit is controlled by capacitors C4 and C5 and resistors R3 through R7. The output of the multivibrator circuit is connected to transistor T3, which, in turn, drives the triac via LED1. During positive half cycles of the multivibrator’s output, transistor T3 energises triac BT136 and the lamp glows.
Monday, December 16, 2013
High Voltage Pulse Supply Circuit Diagram
This high-voltage pulse supply will generate pulses up to 30 kV. Ql and Q2 form a multivibrator in conjunction with peripheral components Rl through R6 and CI, C2, C3, C5, C6, and D2. R9 adjusts the pulse repetition rate. R2 should be selected to limit the maximum repetition rate to 20 Hz. II is a type 1156 lamp used as a current limiter.
R9 can be left out and R2 selected to produce a fixed rate, if desired. Try about 1 as a start. Q3 serves as a power amplifier and switch to drive Tl (an automotive ignition coil). NE1 is used as a pulse indicator and indicates circuit operation. Because this circuit can develop up to 30 kV, suitable construction techniques and safety precautions should be observed.
High-Voltage Pulse Supply Circuit Diagram
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