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Wednesday, July 8, 2009
MEDIUM POWER FM TRANSMITTER
The range of this fm transmitter is around 100 meters at 9v dc supply. the circuit comprises 3stages.the first stage is microphone preamplifier built around BC548 transister.the next stage is a VHF oscillator wired around another BC548transistor.BC series transistors are generally used in low frequency stages. but these all are works fine in RFstagesas oscillator.
We all are familiar with the electrical wiring arrangement that connects an electrical bulb with two switches: one at the bottom of the stair case and other at the top. wiring is done such that either of the two swithes can be used to switch the bulb on or off. in such a wiring arrangement, while climbing up the staircase which is in dark, the switch H located at the bottom of stair case used to switch on the light.
After you have climbed the staircase, you use the switch located there to switch of the light.
This circuit measures the distance covered during a walk. Hardware is located in a small box slipped in pants' pocket and the display is conceived in the following manner: the leftmost display D2 (the most significant digit) shows 0 to 9 Km. and its dot is always on to separate Km. from hm. The rightmost display D1 (the least significant digit) shows hundreds meters and its dot illuminates after every 50 meters of walking. A beeper (excludable), signals each count unit, occurring every two steps.
Light emitting diodes are advantageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED arrangement light up progressively. Once all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2).
The circuit described here is that of a digital dice with numeric display. Timer IC 555 wired as an astable multivibrator produces pulses at about 48 kHz rate. These pulses are fed to pin 14 of the decade counter IC 7490. The oscillator is activated by depression of switch S1.
This circuit was developed since a number of visitors of this website requested a timer capable of emitting a beep after one, two, three minutes and so on, for jogging purposes.
As shown in the Circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thing happens after a 2 minutes delay, and so on, reaching a maximum interval of 9 minutes in position 9.
The device turns on automatically when power is supplied to the unit, through a power toggle switch. Once voltages are allowed to stabilize the unit will prompt you with a test, configuration and calibration, and active mode option menu. It is trivial to adapt this to send a string to a client such as a palmpilot for offboard processing and logging (the embedded design I have here is limited; A single board computer is a much better choice).
There is a driver for using DAC connected to parallel port as Windows 3.1 sound output device for playing back sample and sound effects. The driver was originally written for Covox Speech Thing, but works nicely with this compatible circuit.
This circuit is intended to signal when a plant needs water. A LED flashes at a low rate when the ground in the flower-pot is too dry, turning off when the moisture level is increasing. Adjusting R2 will allow the user to adapt the sensitivity of the circuit for different grounds, pots and probe types.
Automatic railway gate control and track switching.
Present project is designed using 8051 microcontroller to avoid railway accidents happening at unattended railway gates, if implemented in spirit. This project utilizes two powerful IR transmitters and two receivers; one pair of transmitter and receiver is fixed at up side (from where the train comes) at a level higher than a human being in exact alignment and similarly the other pair is fixed at down side of the train direction. Sensor activation time is so adjusted by calculating the time taken at a certain speed to cross at least one compartment of standard minimum size of the Indian railway. We have considered 5 seconds for this project. Sensors are fixed at 1km on both sides of the gate. We call the sensor along the train direction as ‘foreside sensor’ and the other as ‘aft side sensor’.
We know that the railway network of India is the biggest in south Asia and perhaps the most complicated in all over the world. There are so many different types of trains local, fast, super fast, passenger, goods…. etc. and their so many multiple routs. Although the time table is perfect it is not at all possible to maintain it. And that’s why the train accidents are becoming more and more usual. So why not we add a kind of intelligence to the train engines itself so that it tries to avoid accidents.
About 13 years ago, I made a salt water battery to operate a single AA battery quartz clock. It ran for several months until I got tired of adding water to compensate for evaporation. The batttery consisted of 5 cells each producing about 300 millivolts. As I remember, I used 5 small olive jars filled with about a cup of water and a tablespoon of salt to create 5 cells in series each producing about 300 millivolts for a total of around 1.5 volts. The positive electrode was made from a strip of double sided copper circuit board (about 1 inch by 4 inch) and the negative electrode was a similar sized strip of aluminum. I recently tried some galvanized iron instead of aluminum and found it produces a little higher voltage so the battery may be made with only 3 cells. But any two different metals used with salt water or citrus juice will create a low voltage battery.
The circuit below illuminates an LED to indicate unequal charges between two 12 volt lead batteries. It can be used to verify that two batteries are connected in parallel or isolated since the LED will be off when the voltages are equal within a tollerance, or on if the voltage difference is greater than 100 millivolts. Three comparators and three voltage dividers are used to determine battery conditions.
Requested by some correspondents, this simple design allows an accurate speed control of 12V dc fan motors, proportional to temperature.
A n.t.c. Thermistor (R1) is used as temperature sensor, driving two directly coupled complementary transistors wired in a dc feedback circuit.
An optional circuitry was added to remotely monitor fan operation and to allow some sort of rough speed indication by means of the increasing brightness of a LED.
This circuit is intended to control a heating system or central heating plan, keeping constant indoor temperature in spite of wide range changes in the outdoor one. Two sensors are needed: one placed outdoors, in order to sense the external temperature; the other placed on the water-pipe returning from heating system circuit, short before its input to the boiler. The Relay contact wiring must be connected to the boiler's start-stop control input.
This circuit, though simple, has proven very reliable: in fact it was installed over 20 years ago at my parents' home. I know, it is a bit old: but it is still doing its job very well and without problems of any kind.
There are three possible base addresses for the parallel port You may need to try all three base addresses to determine the correct address for the port you are using but LPT1 is usually at Hex 0378. The QBasic "OUT" command can be used to send data to the port. OUT, &H0378,0 sets D0-D7 low and OUT, &H378,255 sets D0-D7 high. The parallel port also provides four control lines (C0,C1,C2,C3) that can be set high or low by writing data to the base address+2 so if the base address is Hex 0378 then the address of the control latch would be Hex 037A. Note that three of the control bits are inverted so writing a "0" to the control latch will set C0,C1,C3 high and C2 low.
In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable (VFO) with a capacitor/resistor combination. A 100pF capacitor is used in place of the crystal for VFO operation. Amplitude modulation is accomplished with a second transistor that controls the DC voltage to the output stage. The modulator stage is biased so that half the supply voltage or 6 volts is applied to the output stage with no modulation. The output stage is tuned and matched to the antenna with a standard variable 30-365 pF capacitor.
This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5k preset. The oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor.
This is a basic 555 square wave oscillator used to produce a 1 Khz tone from an 8 ohm speaker. In the circuit on the left, the speaker is isolated from the oscillator by the NPN medium power transistor which also provides more current than can be obtained directly from the 555 (limit = 200 mA). A small capacitor is used at the transistor base to slow the switching times which reduces the inductive voltage produced by the speaker. Frequency is about 1.44/(R1 + 2*R2)C where R1 (1K) is much smaller than R2 (6.2K) to produce a near square wave.
The LED traffic Light circuit controls 6 LEDs (red, yellow and green) for both north/south directions and east/west directions. The timing sequence is generated using a CMOS 4017 decade counter and a 555 timer. Counter outputs 1 through 4 are wire ORed using 4 diodes so that the (Red - North/South) and (Green - East/West) LEDs will be on during the first four counts. The fifth count (pin 10) illuminates (Yellow - East/West) and (Red - North/South). Counts 6 through 9 are also wire ORed using diodes to control (Red - East/West) and (Green - North/South). Count 10 (pin 11) controls (Red - East/West) and (Yellow - North/South). The time period for the red and green lamps will be 4 times longer than for the yellow and the complete cycle time can be adjusted with the 47K resistor. The eight 1N914 diodes could be subsituted with a dual 4 input OR gate (CD4072).
SOLID STATE RELAY REQUIRES ONLY 50uA DRIVE CURRENT
This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR, the circuit can control about 600 watts of power to load while providing full isolation and transient protection.
The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.
Name: technical projects Home: sirpur kaghaznagar, andhra pradesh, India About Me: Hi this is udaya bhasker.i just completed my engineering in hyderabad.
i completed my technical education in raja mahendra engineering college.ibrahimpatnam See my complete profile
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