The main objective of this system is to transmit message or text through ordinary Land Line Telephone/mobile from one end (source) to another end (designation). This is get achieved by the DTMF technology. It has two sections one for editing the text and to transmit the edited text and the other section consist for receiving the text message. The system works on the DTMF technology. (Dual Tone Multiple Frequency).
It involves several steps. They are
DTMF decoding/Encoding process
ON/OFF hook detection
Displaying the message in LCD
The above process is get achieved by the microcontroller AT89S8252/AT89C51/52.Thus Microcontroller controls the whole system.
As the title “wireless messaging via mobile/landline phone” itself indicates that this project deals with the transfer of message from one mobile to another or one landline to another without using wire connection.
The DTMF tones sensing circuit display the message at LCD as sent by other end by means of tone transmission.
Applications: DEFENCE, FUN & ENTERTAINMENT, GAMES & SPORTS, SURVILLANCE
Project Title: MICROCONTROLLER AT-89S8252 BASED WIRELESS MESSAGING VIA MOBILE/LANDLINE PHONE (SMS) Category B. TECH PROJECTS ENGINERING DIPLOMA Technologies Used: MICROCONTROLLER (EMBEDDED) BASED Subjects: ELECTRONICS & COMMUNICATION, ELECTRONICS & ELECTRICALS, HOBBY KITS ELECTRONIC HOBBY KITS Modules Used: DTMF ENCODER/DECODER , REGULATED POWER SUPPLY
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MICROCONTROLLER AT-89S8252 BASED WIRELESS MESSAGING VIA MOBILE/LANDLINE PHONE (SMS)
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Long Range FM Transmitter 1
How to make a long range FM transmitter at low cost
The use of transmitters which have a more powerful output than the ‘flea-power’ are sometimes required when there are many obstacles in the path of the surveillance transmitter and monitoring station receiver, or the distance between them is too far so as to make a low powered device feasible. Whereas a typical microtransmitter will produce an RF power in the order of just a few milliwatts, i.e. a few thousandths of a watt, the VHF-FM transmitter described has a power output of between around a half and 2 watts, depending on the power source, which may be anywhere between 6 volts and 30 volts d.c. The battery or batteries should be of the alkaline high power type, since the current drain will be found to be relatively higher when compared to microtransmitter current drain. The power output of this device is somewhat proportional to the current drain and so therefore both may be decreased by altering the value of R6 to a higher resistance, or a variable resistor with a value of around 1k may be introduced in series with the existing R6, so as to give a variable power output. The variable resistor must not be a wirewound device because this would act as an inductor which will cause feedback problems.The audio input to the power oscillator, which incidentally is formed by TR2 and associated components, is derived from a piezoelectric microphone which drives the simple audio frequency amplifier TR1. The input of the audio amplifier is controlled by the gain pot R1, which selects the correct amount of voltage that is generated by the piezoelectric microphone, then connects this signal to the base of audio amplifier TR1 via C7. It may be found that there is insufficient housing space for a bulky piezoelectric microphone, so with a slight modification to the circuit, it is possible to employ an electret microphone insert as shown. Since the RF field that is generated by this transmitter is relatively large, the problem of RF feedback may very well be encountered. This may be overcome by placing the transmitter inside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.
Component listing for 1 watt transmitter
Resistors Semiconductors R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heatsink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R
L = 6 turns 22 gauge enamelled wire wound on 3⁄16″ former
C1, 2, 3, 8 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF
C7,C8 = 40uF/25V Electrolytic
Circuit diagram for Long range FM Transmitter
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Remote toggle switch circuit
In application level this circuit is similar to that of the circuit given previously. The only difference is in the approach. This circuit is designed by using another method. Using this circuit you can toggle any electrical appliance between ON and OFF states by using your TV remote. The only requirement is that your TV remote should be operating in the 38 KHz.
The IC1 (TSOP 1738) is used to receive the infrared signals from the remote. When no IR signal from remote is falling on IC1, its output will be high. When the IR signal from the remote falls on the IC1, its output goes low. This triggers the IC2 which is wired as a monostable multivibrator.The output of the IC2 (pin6) goes high for a time of 1S (set by the values of R2 and C3.This triggers the flip flop (IC2) and its Q output (pin 15) goes high. This switches on the transistor, which activates the relay and the appliance connected via relay is switched ON. For the next press of remote the IC1 will be again triggered which in turn makes the IC2 to toggle its output to low state. The load will be switched OFF. This cycle continues for each press of the remote. The pin 6 and pin 4 of IC1 are shorted to avoid false triggering.The diode D1 can be used as a freewheeling diode.
Circuit diagram with Parts list.
- Assemble the circuit on a good quality PCB or common board.
- The circuit can be powered from a 5V DC regulated power supply.
- The capacitors must be rated 15 V.
- The IC1&IC2 must be mounted on holders.
- The current capacity of relay determines the load circuit can switch.Use a high amperage(`10A or above) relay for driving large loads like motor,heater etc.
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Here is a versatile remote controlled appliance switch that can ON or OFF any appliance connected to it using a TV remote.
IR remote sensor IC TSOP 1738 is used for recieving the signal. Normally when no signal is falling on IC3 the output of it will be high.This makes Q1 OFF.When a signal of 38 KHz from the TV remote falls on the IC3 its output goes low.This makes Q1 conduct and a negative pulse is obtained at pin 2 of IC 1 NE 555.Due to this IC1 wired as a monostable multivibrator produces a 4 Sec long high signal at its out put.This high out put is the clock for IC 2 which is wired as a Flipflop and of , its two outputs pin 3 goes low and pin 2 goes high.The high output at pin 2 is amplified to drive the relay .For the next signal the outputs of IC2 toggles state. Result, we get a relay toggling on each press on the remote.Any appliance connected to this circuit can be switched ON or OFF.
Circuit Diagram with Parts List .
- Before wiring the circuit make sure that the carrier frequency of the TV remote you have is 38 KHz.For that wire the sensor part only ,point your remote to the TSOP1738 and press any switch.If out put of TSOP1738 goes low them ok, your remote is of 38Khz type.Nothing to worry almost all TV remote are of this type.
- You can use any switch because for any switch the code only changes,the carrier frequency remains same.We need this carrier frequency only.
- Assemble the circuit on a good quality PCB or common board.
- The appliance can be connected through NO or NC and contacts of the relay .
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The above project uses two nos transreceiver modules ,and the circuit communicates at 9600 kbps. ‘c’ codes comes with along with project