THIS IS A PROJECT FOR ANALOG ELECTRONICS, WE BUILD A FREQUENCY MODULATED TRANSMITTER.
BY:
RAFAEL CHAVEZ ALEJANDRO TORRES
ESTRADA LUIS MANUEL GALLEGOS
3CM2
OBJECTIVE
The project's goal is to create an FM transmitter, which transmits, it redundancy, a signal or sound to an FM receiver, without the need for cables.
This signal is received through a microphone built into the circuit, which, in analyzing the vibration or sound is analyzed and passed through the circuit and such devices, which when finished, sends it to a coil installed for this through an antenna, sends the signal to the FM receiver that is capable of reproducing in the speakers of the same.
This signal can be heard on stations already occupied with a frequency, ie to listen to our sound emitted at the transmitter, we search the FM band station or frequency that is free or empty.
FM RECEIVER DIAGRAM
DESCRIPTION OF COMPONENTS, FUNCTIONALITY AND CONSTRUCTION STAGE
1. AMPLIFIER STAGE:
The sound modulation of the carrier we do with a preamplifier that is based on a 2N2222 transistor resistances R2, R3, R4 and R5 set the bias voltages of transistor Q1, C3 helps set the AC gain of Q1. C2 and R6 provide communication between the two stages, the capacitor C2 helps block the dc component of the signal and couples the AC signal to the next stage, R6 limits the current to the base of Q2.
2. PHASE MODULATION:
This stage is also responsible for a 2N2222 transistor, configured in a voltage-controlled oscillator, which is modulated by the audio voltage is amplified by Q1, the frequency of oscillation is determined by coil L1 (ANT) and the capacitor 5 -60 pF (variable), which can be adjusted between 88 and 108 MHz. The resistors R7 and R8 are responsible for polarizing the base of transistor Q2, capacitor C6 connected between the collector and emitter of the feedback is responsible for the oscillating transistor. The resistor R9 limits the current through the transistor and capacitor C8 acts as a filter capacitor.
3. CONSTRUCTION OF THE COIL:
To make the coil, the wire was taken for bridges and cut in half, the two resulting pieces are rolled up in a common pen giving six laps around it.
Once done, remove the pen and the coils are separated with special care not to deform them, then that is more uniform that is placed in the circuit.
The other may be used as an antenna.
4. TEST CIRCUIT AND CALIBRATION:
Once all components have been assembled can proceed with the testing and calibration of the circuit.
This is located near an FM radio circuit, is looking for a point on the dial in silence (without radio) and receiver volume up to a point where interference can be heard.
Slowly and with the help of a small screwdriver, preferably plastic, set the capacitor (trimmer C5) in the receiver until you hear a whistle or sound similar, which means that at this point has been tuned to the transmitter frequency dial.
At that point you can talk on the microphone and be heard on the radio what is spoken.
If the selected frequency is not achieved good reception, the process can be repeated elsewhere in the FM band.
If you prefer, instead of varying the capacitor, you tune the radio to find the point where it is best reception (silence).
If after doing this, do not get to tune the transmitter, you can adjust the bobbin that forms the oscillator circuit, joining their turns to raise the frequency, or spreading them if what you want is to reduce a little.
LIST OF MATERIALS AND COMPONENTS
• 2 Transistors 2N2222
• 1 Microphone Electret
• 2 10uF/25v Electrolytic Capacitors
• 2.2uF/25V an electrolytic capacitor
• 2 ceramic capacitors 0.1uF/50v
• 2 ceramic capacitors 2.7pF/50v
• an adjustable capacitor 5-60PF (trimmer)
• 2 1k resistors
• 1 Resistance 1M
• 1 Resistance 6.8K
• 2 10K resistors
• 2 4.7K resistors
• 1 Resistance 2.2K
• a 220 Ohm Resistance
• 50 cm. Wire bridges
• 1 Bakelite
• 1 9V Battery
• Soldering Iron
• Drill
• Tin
ISHIKAWA DIAGRAM
| PERCENTAGE /
| THE BIT BROKES | THE PLATE WAS BROKE | THE TRIMMER’S IMPEDANCE CHANGE | COIL NOT SEND THE SIGNAL | ADJUSTMENT OF THE SIGN OF THE COIL |
| UNDER | | | | | 1 |
| MIDDLE | | 2 | | 2 | |
| HIGH | 3 | | 3 | | |
One of the main issues presented was that the drill was broken repeatedly, phenolic plate had to get back to you in error and was removed bad pulse copper.
For the coil only had to squeeze more hoops to send the same signal but without much noise.
As for the trimmer, did not know that it changes the impedance of the metal, so it was necessary to align with a plastic screwdriver.
These are the main problems we had.
PHOTOS OF THE DEVELOPMENT OF FM TRANSMITTER
INTRODUCTION
The FM receiver is very similar to that of AM in several respects. In commercial band occupies the spectrum between 88 MHz and 108 MHz, ie, operates at frequencies above the AM receivers, which forces a more critical construction with short cables and components are mainly small.
The blocks differ in the FM receiver is the limiter, the demodulator (also known as FM detector or discriminator) and the emphasis circuit. Recall the block diagram of a monaural FM receiver.
The limiter clips the peaks of the amplified FM signal in order to submit to discriminating a signal of constant amplitude. The discriminator converts the FM signal into an audio signal and block the function of pre-emphasis to compensate for the emphasis placed on the FM transmitter.
CONCEPTS
THE SIGNS OF AM AND FM
The first commercial radio broadcasts were made to the system known as "amplitude modulation (AM) where low-frequency information varies the amplitude of a signal" carrier "frequency considerably higher.
The amplitude modulation cannot be regarded as a hi-fi system as there are limitations on the bandwidth of information that can be transmitted, which goes with the sound quality to be achieved. There will also be limitations on the dynamic range of the signal.
A very significant disadvantage in the signals is the noise that usually occurs modulation superimposed on the carrier to be confused with the information without separate prune this.
Many of these noise signals can be removed if they are placed with the receiver filter noise suppressor whose mission is to silence the receiver when the carrier has abrupt changes in level or when the frequency of information exceeds a number of kHz (4 kHz) by understood that these signals correspond to unwanted noise. The system eliminates the problems caused by signals that modify the amplitude of the carrier frequency modulated FM transmission, which has several advantages over the AM transmitters.
One of the main advantages lies in the great reduction of noise at the reception and at all times the amplitude of the carrier remains constant during transmission, then the receiver with an amplitude limiter circuit is avoided on the modulations causes noise amplitude.
An AM signal frequency and carrier phase does not vary, while the amplitude changes the pace of information, whereas in an FM signal are the amplitude and phase of the carrier which remain unchanged while the frequency amended with the changes you wish to transmit information.
In this case, the continent and frequency modulated signal is that, somehow, the oscillation frequency of a circuit increases in proportion to the increase in the amplitude of the audio signal into a positive half cycle. During the negative half cycle, the oscillation frequency of the circuit will decrease in proportion to the breadth of information.
Everything happens in a way that for small amplitudes of the audio signal corresponding small variations in the frequency of the carrier, while large amplitudes of the information would cause substantial variations in frequency. We also know that the audio signals are composed of different frequencies in the FM signal, are evidenced in the speed with which changes occur signal frequency. The following figure note that there are frequency shifts the rhythm of the frequency of information while the value of this shift depends on the amplitude of the audio signal.
It is noted that variations in the frequency of the carrier will depend on the comprehensiveness of the information.
FM RECEIVER
Basically an FM receiver is composed of the same steps as a medium wave commercial receiver, only variation is the working frequency band (and hence the provisions of circuit) and how it detects the audio signal.
We should clarify that, prior to demodulate the information, add a limiter circuit that allows the RF signal reaches the detector with constant amplitude. Therefore an FM receiver has the following block diagram:
The band assigned to the FM channel is located between 88 MHz and 108 MHz as mentioned above, among the low channels and TV channels in the high VHF band.
FM STAGE LIMITER
The FM signal has the advantage over an AM signal, that is not affected largely as impulsive noise that is added during transmission. Indeed, the limiter block serves as a trimming or eliminating the interfering signal (the impulse noise is due to changes or disruptions to air and noise introduced by man).
In fact, the FM system is not completely immune to noise. It is possible to cut or limit most of the interference and you are presented primarily as a noise pulse amplitude, but to a lesser extent also produce phase shifts which are noted in part as a frequency deviation, this effect is at least the allow a large variation in frequency by modulating the cover.
ANTENNAS USED
The role of satellite transmitters in plants is to convert the current corresponding to the frequency modulated signal into an electromagnetic wave that can travel through space.
By contrast, the receiver antenna converts electromagnetic wave emitted by the transmitting antenna in a radio frequency current to be driven to the tuner.
Of course, the efficiency of transmitting and receiving antennas depends on the quality of transmission, the transmitting antenna to determine the percentage of signal produced by the station became electromagnetic field while the receiving antenna determines the percentage of incoming signal to the tuner.
DEVICE SPECIFICATION SHEETS 2N2222
Because Microsoft Word 2009, you can not open PDF, we feel the urgent need to omit in this report, but the leaves are attached (in English) in the parent folder of the project.
TREATMENT OR CHEMICAL WASTE RECYCLING
These were placed in a plastic bottle for the conservation of this, thus avoiding contamination of the drainage and water with this agent, and corrosion of pipes.
CONCLUSION
This device is very useful to transmit to a radio station, not only creates this device, but also, you can create one with a radius of 2 km, for the transmission of a radio, a song or simple pleasure of spending a pleasant time.
This device is used in wireless microphones, but also, there are already phones that integrate, thus allowing playback of music via the computer without the need for cables.
BIBLIOGRAPHY
http://www.forosdeelectronica.com/proyectos/emisorafm.htm
http://www.webelectronica.com.ar/news13/nota07.htm
http://es.wikipedia.org/wiki/2N2222 ---> http://www.eecs.harvard.edu/cs141/resources/2N2222.pdf
THIS IS A VIDEO, MADE BY US, TO EXPLAIN THE CIRCUIT