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joe1986
Joined: 25 Jan 2008
Posts: 258
Helped: 11
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 30 Mar 2008 16:01 300 POINTS FOR good idea |
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hi friends, i am doing a project "WIRELESS TEXT MESSAGING USING MOBILE/LANDLINE PHONE"
SOFTWARE:
The msg.asm program is written in Assembly language and compiled using Metalink ASM51 cross-compiler.
HARDWARE:
1. There are 2 mobiles used one at the transmitting end and the other at the receiving end.
2. At the input a condenser microphone and an amplifier using IC LM 358 and DTMF DECODER 8870.
3. An LCD (16*2 DISPLAY) is used at the ouput along with a microcontroller (AT89S8252).
PROJECT DISRIPTION:
The message is transmitted by calling the second mobile phone and typing the desired message at the transmitter end. when the handset of the phone at the receiver end is picked up, you can type the message on the phone at the transmitting end. The receiver end comprises of input, decoder and display sections.
The input section consists of a mobile/landline phone, condenser mic and audio amplifier. For the decoder, the underlying concept is DTMF signal reception and decoding the signal to BCD format through DTMF decoder 8870. The display section consists of a microcontroller and the LCD. The microcontroller processes the decoded signal and outputs it for display on the LCD in the form of text message.
Once the connection is established between the two phones (as in normal case), whatever phone key is typed at the transmitting end, the corresponding DTMF tone is heard in the earpiece of the receiver (phone). The earpiece is connected to a microphone. The microphone (mic) picks up the DTMF tone. Its output is amplified by means of an op-amp and this output is fed to the DTMF decoder. The DTMF decoder would give the corresponding BCD value of the tone.
The LEDS acts as a visual indicator, when the valid signal is received by the system. The tone output is fed to an inverter buffer. The output of the inverter is fed to PORT 2 of the microcontroller. The microcontroller, connected to the LCD through PORT 0, reads PORT 2, processes the data and sends the output data through PORT 0 to the LCD and the message is displayed in the LCD. No separate driver is used for the LCD. It is driven directly by the microcontroller.
The microcontroller requires regulated 5V DC supply. Reset pin 9 of the controller is connected to 5V through reset switch S1. you can press reset switch two or three times for proper display of characters on the LCD.
This system can be used in noisy environments of factories as a means of communication among workers. The cursor will initially point to the first location in the LCD when power in the circuit is switched on. Conventionally you type a message on your mobile Phone as follows; To transmit character a press button 2 on the mobile only once. For character b press button 2 twice within a short time interval and for character c press it thrice. For digit 2 press button 2 four times. Each key pressed on the phone generates two tones of specific frequencies, so a voice or a random signal cant imitate the tones. One tone is generated from a high-frequency group of tones and the other from a low-frequency group.
For example , to send message efy3, press button 3 followed by button 2 to display e, press button 3 twice to display f, press button 9 followed by button 3 to display y and finally press button 3 followed by button 4 to display button 3.
i have been using PROTEUS 7.1 to check whether the program gives the desired result (i tried interfacing the microcontroller and the LCD in proteus) and tried running the code to check the output but there was no success
can anyone tell me as to what is the problem in the program or what modifications can be made in the program to get the desired output
here is the file which contains the proteus file and my assembly language program
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cherreram
Joined: 05 Mar 2008
Posts: 5
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| 08 Apr 2008 17:50 Re: 300 POINTS FOR good idea |
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Hi
Well, I can't help you totally but I think I can give you some help, because time ago I made a similar system using a voice rf link on radiocomunication equipment.
My idea was similar. I will send over a voice channel dtmf tones to represent digital data.
On the reception side, I took the signal from voice radio channel with a mic and then sent it into a standar dtmf decoder. Seems easy, but not.
The problems:
first, dtmf standar chip decoder are design to fit with the ITU-T recomendations. So they don't accept more than 2.5% signal error( check this on the datasheet). On a rf channel, signal suffers transformations and then, when we use a mic, depending its quality, the audio signal is affected again and then, on the amp stage, etc, etc. So when finally come to DTMF chip, the tone received could not fit with the original one. Consecuently, dtmf chip don't accept it.
My solution was use a pc soundcard to record signal and then using MATLAB analize it on the frecuency plane. Some DTMF tones arrives with great error, so I made a Matlab's program fast fourier transform based and used it to decode the signal. it Worked fine on PC. After that, I put this program into a dsp and run the system again. Everything works now and I can send, at low baudrate, short digital information over a voice channel on HF radioequipment.
I think you are having similar problems, try to check.
check too if when you press a key, it reproduces exactly a dtmf tone.
Hope it can help you a little.
good luck
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ashad
Joined: 28 Mar 2006
Posts: 303
Helped: 9
Location: Singapore
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| 24 Apr 2008 5:19 Re: 300 POINTS FOR good idea |
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r u still facing same problem ..... 
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king_cobraz_77
Joined: 06 Mar 2006
Posts: 18
Helped: 1
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| 27 Apr 2008 15:22 Re: 300 POINTS FOR good idea |
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| it will work fine exactly
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zuisti
Joined: 02 Jul 2004
Posts: 46
Helped: 2
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| 03 May 2008 9:38 Re: 300 POINTS FOR good idea |
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Hi joe1986,
I have downloaded and tried your project uploaded.
I'm working with Proteus, also with 51 type uCs and I'm using also assembly.
So I think I can help you, but I don't understand clearly yet what do you want.
I don't understand your asm nor your DSN. Are you sure these are related things?
I cannot see any buttons nor leds, the whole port2 is wired to the port3 ....
Please be more specific and I'll help you to making a working test program.
Cheers: zuisti
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