Description.
With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.
Notes.
Assemble the circuit on a good quality PCB.
The circuit can be powered from anything between 9 to 24V DC.
Inductor L3 can be a VK220J type RFC.
For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L1 and that will be L2.
Frequency can be adjusted by varying C9.
R9 can be used to adjust the gain.
For optimum performance, value of C8 must be also adjusted.
Using a battery for powering the circuit will reduce noise
Read more: http://www.circuitstoday.com/2-km-fm-transmitter#ixzz1YbDCl2Xt
Under Creative Commons License: Attribution
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MEDIUM-POWER FM TRANSMITTER
Description.
This is the circuit diagram of a moderate power FM transmitter circuit employing two transistors.The voice signals picked by the microphone will be amplified by the transistor Q1.The second transistor is wired as an oscillator operating in the FM band.The output of T1 is given to the base of T2.T2 performs the modulation also.The tank circuit comprising of components L1 and C6 determines the frequency of the signal, and can be varied by adjusting C6.The capacitor C7 couples the FM signal to the antenna.
Notes.
You can assemble the circuit on a general purpose PCB.
The circuit can be powered from a9V PP3 battery.
The Antenna A1 can be a 1M long wire.
The inductor L1 can be made by making 6 turns of 0.8mm enameled copper wire on a 5.5mm diameter/4.5mm length plastic former.
With a matching antenna and proper tuning this transmitter can have range upto 100meters.
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REMOTE OPERATED SPYBOT
Here is a remote operated spy robot circuit which can be controlled by using a wireless remote controller. It can capture audio and video information’s from the surroundings and can be sent to a remote station through RF signals. The maximum range is 125 meters. It overcomes the limited range of infrared remote controllers. This robot consists of mainly two sections. They are explained in detail below.
1. Remote Control Section
The circuit uses HT 12E, HT 12D encoder and decoder. 433MHz ASK transmitter and receiver is used for the remote control. H-bridge circuits are used for driving motors. Two 12V DC/100RPM gear motors are used as drivers. The working of the circuit is as follows.
When we are pressing any key in remote controller the HT 12E generate 8 bit address and 4 bit data .The DIP switches are used for setting the address. Then the ASK transmitter sends the 8 bit address and 4 bit data to the receiver Then the ASK receiver receives the 8 bit address and 4 bit data and HT 12D decoder decodes the data, thus enabling the appropriate output. Thus the output signals that are generated controls the H-bridge which then rotates the motors.
The 433 MHZ ASK transmitter and receivers are extremely small, and are excellent for applications requiring short-range RF remote controls. The transmitter module is only 1/3rd the size of a standard postage stamp, and can easily be placed inside a small plastic enclosure. The transmitter output is up to 8mW at 433.92MHz. The transmitter accepts both linear and digital inputs and can operate from 1.5 to 12 Volts-DC, and makes building a miniature hand-held RF transmitter very easy. The 433 MHZ ASK transmitters is approximately the size of a standard postage stamp
433 MHZ ASK receivers also operate at 433.92MHz, and have a sensitivity of 3uV. The receiver operates from 4.5 to 5.5 volts-DC.
2. Video Transmission Section
In this project we are using a wireless CCD camera. Now these types of cameras are commonly available in the market. It works on 12VDC supply.
To know more about CCD camera, click on the link below.
TAKE A LOOK : CHARGE COUPLED DEVICES (CCD)
The 12 Volt DC supply is taken from the battery placed in the robot. The camera has a receiver, which is placed in the remote station. Its output signals are in the form of audio and video. These signals are directly connected to a TV receiver or a computer through a tuner card.
Components Required
IC HT 12E 1
HT 12D 1
LM 7805 2
TRANSISTOR TIP 127 4
TIP 122 4
S 8050 4
DIODE 1N 4148 8
RESISTOR 1K 4
220E 4
39K 1
1M 1
ASK TRANSMITTER 433 MHz 1
ASK RECEIVER 433 MHz 1
DIP SWITCH 2
PUSH TO ON SWITCH 4
GEAR MOTOR 12V DC 100rpm 2
BATTERY 12V 1.3 Ah rechargeable 1
9V 1
WIRELESS CCD CAMERA 1
Construction
The steps for the construction are…
1. Take a hylam sheet with (20cm*15cm) size.
2. Fix two gear motors (12VDC 100rpm) in the hylam sheet by using aluminum pieces and nut bolts as shown in the figure below.
3. Fix the ball castor as shown in the figure below.
4. Then fix the battery (12VDC 1.2Ah) on the top of the spy robot as shown in the figure below.
5. Connect two motors to the PCB. The PCB is then connected to the battery.
6. Connect the wireless CCD camera to the battery.
7. Connect the camera receiver to the TV or computer. Video information’s will thus appear in the screen.
8. Switch on the remote controller and control the spy robot.
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