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Radio circuit diagrams electronics projects

Radio circuit diagrams electronics projects for radio transmitter, radio receiver circuit, rf amplifiers, rf boosters and some other related RF circuits like: fm antenna booster, microwave transmitter and wireless modules.

Radio motor controller schematic

A very nice radio controlled circuit that can be used to control a small motor is described in the circuit shown below . This circuit is very similar with a car radio controlled toy with seven control functions: forward, forward-left, forward-right, backward, backward-left, backward-right, and stop. Also you can use this radio frequency circuit for some other electronic circuits that require a simple wire less motor controller. The remote control work’s at a frequency of 27.9 MHz and require a 9 volts power supply .
This RF motor controller circuit consist from two parts a Radio Transmitter and a Radio Receiver .
For remote control contacts you can use some push buttons or a mini-joystick .
Commands are controlled by different sets of electrical contacts that are used to encode a sequence of electrical pulses; the number of pulses depends on which command is being sent.
An electrical circuit that is tuned to a frequency of 27.9 MHz creates a signal that is sent to the antenna when the pulses are active. The antenna converts the electrical energy into radio energy, creating a stream of radio energy bursts, which travel through the air and are picked up by and understood by the radio receiver in the car.

The car antenna collects radio energy and transform it back into electrical energy.
If the car is turned on then the radio receiver in the car is continuously monitoring the electrical energy from its antenna. The receiver is a filter which is tuned to amplify any energy around 27.9 MHz and block energy the antenna picks up outside this region. If the Remote Control Transmitter is sending commands then its radio signal will be picked up by the receiver and converted back into the original pulse sequence. Decoding circuitry then determines which commands were sent by measuring the number of received pulses in the sequence. Signals are then sent to the motors to execute the commands.
When operated with strong batteries and in an open area the range will be at least 40 ft. Obstacles will degrade the radio signal’s ability to travel through air and reduce operating range, but will never block it completely. In the car, weak batteries will reduce power to the Motor and degrade the receiver’s ability to filter, amplify, and decode commands from the Transmitter.

When a command is received to turn left or right, a voltage is applied to the Steering Motor Since the Front Wheels are connected to the Steering Bar, the car will turn. To the turn the other direction, the voltage to the motor is reversed.
The Driving Motor works the same as the Steering Motor. When a command is received to go forwards a voltage is applied to the Driving Motor; this voltage is reversed to go backwards.
Both circuits receiver and transmitter are based on the AF2310 integrated circuit .

car radio receiver circuit

TV audio video transmitter

A very simple TV audio video transmitter circuit can be constructed using this schematic diagram . This TV audio video transmitter circuit can be used to transmit video signals from VCR ( or some other device ) to a TV without using any cable .
Video signals input at jack J1 are first terminated by resistor R6 and coupled through capacitor C1 to clamping-diode D1. Potentiometer R3 is used to set the gain of the video signal; its effect is similar to that of the contrast control on a TV set.
Bias-control R7 can be used to adjust the black level of the picture so that some level of signal is transmitted, even for a totally dark picture.
RF-transformer T1 and its internal capacitor form the tank circuit of a Hartley oscillator that's tuned to 4.5 megahertz. Audio signals input at J2 are coupled to the base of Q3 via C2 and R4: the audio signal modulates the base signal of Q3 to form an audio subcarrier that‚s 4.5-megahertz higher than the video-carrier frequency.

The FM modulated subcarrier is applied to the modulator section through C5 and R9.
Resistor R9 adjusts the level of the subcarrier with respect to the video signal.
Transistors Q1 and Q2 amplitude modulate the video and audio signals onto an RF-carrier signal. The operating frequency is set by coil L4, which is 3.5 turns of 24- gauge enameled wire on a form containing a standard ferrite slug.

The RF output from the oscillator (L4, C7 and C9 ) section is amplified by Q5 and Q6, whose supply voltage comes from the modulator . Antenna matching and low-pass filtering is performed by C12, C13, and L1.
Resistor R12 is optional; it is added to help match the output signal to any kind of antenna.
To align this audio video transmitter you need to tune a TV receiver to an unused channel between 2 and 6. The TV must have an indoor antenna connected directly to it; an outdoor antenna or cable won't work. Make sure both potentiometers (R3, R7) are in middle position and apply power to the transmitter. Adjust L4 with a nonmetallic tool until the TV screen goes blank ,then fine-adjust L4 for the "most-blank" picture.
Connect the video and audio outputs from a VCR(AV source) to jacks J1 and J2 (respectively) of the transmitter .

After that you should see a picture on the TV screen: if you do, readjust L4 for the best picture; if you don't, check the board for any bad connections. Next, adjust R3 for the best picture brightness and R7 for the best overall picture.
Finally, adjust T1 with a nonmetallic tool for the best sound .
The TV transmitter combines line level audio and video signals, and transmits the resulting signal up to 300 feet. The circuit can be powered from a 9-12V power supply circuit .
simple TV audio video transmitter circuit schematic

9V FM transmitter circuit diagram

This circuit diagram transmitter is a very simple and useful circuit that require few external components and operates in FM band ( above 100 MHz ) .
This circuit diagram transmitter needs to be powered from a 9 volts battery or from another 9 volts regulated power supply .
The tuned coil L1, has two output tappings for the antenna connection, marked "A" and "B". These are both low-level outputs and you choose which tapping you want to use ( stable low range, or more unstable but higher range).
Tap B (2.5%) takes just a very small portion of signal from the oscillator circuit and therefore gives a very frequency stable transmitter. The output level (around 2.5mW) and range are therefore somewhat reduced.

Tap A (10%) delivers very much more power (around 10mW) to the antenna load. This gives you a greater range, but at the expense of frequency stability.
All component leads should be kept as short as possible. The LINK wire on the PCB should
lay flat on the PCB. Use the cutoff from a resistor leg.
Antenna length for circuit diagram transmitter varies with frequency for optimum distance: 90MHz 80 cm, 95MHz 75cm, 100MHz 70 cm, 105 MHz 68 cm.

The frequency determining elements (L1, C5 and C6) form a simple LC tuned oscillator. The inherent problem with this type of circuit diagram transmitter is that any external load (antenna) will change the operating frequency.
 9 volts circuit diagram transmitter
The inductor L1 must have around 5.5 turns of enameled 0.5 mm Cu wire , and must have a diameter ( coil diameter) around 5 mm .


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