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Sound based Data Transmission

DTMF have been used to transfer data through sound, however it limits the data rates. In this project they have used a speaker and a microphone system to transmit the data generated. The data is generated using a PS/2 remote which is then processed by the microcontroller and the audio signal is fed to a speaker. The sound is detected by the microphone attached on the user side which is then processed and displayed on the LCD attached to the receiver side. The TX-MCU samples DATA on the falling edge of CLK to build a data packet representing the key that was pressed, then transmits the packet as a combination of two alternating on/off tones (one at 8 kHz, another at 5 kHz) over the speakers, where one tone represents CLK and the other represents DATA. The current design uses a very simple protocol called On-Off Keying on two tones. Upgrading the code to use a more sophisticated protocol would increase the data rate. The change in speaker and microphone specifications might also increase the range of the system. Continue reading

Give a cellphone Land Rover ride

Well this is actually a toy Land Rover which is adopted to be controlled with cellphone. Malik decided to use a cellphone as remote controller instead any other RF solution because of one major reason – the distance limitation. In fact using mobile phone you are only limited by GSM coverage which is almost everywhere. But for this there are two mobile phones needed and both with active SIM cards. This way one mobile becomes a remote controller and another receiver. While in call sender can press any button on keypad and this way generate DTMF tone that can be decoded in receiving side. More complicated things are on Rover. First of all DTMF tone is decoded with MT8870 decoder and then signal goes to Atmega16 microcontroller which controls two motors via motor drivers L293D. So as a result you may end up with rover wandering far away from you blindly. Logical next step is to add some tracking solution. Continue reading

DTMF extension for microcontroller system

Telephone lines that maybe found in your house may be used not only for making calls but also for other purpose like home automation, remote device control. To make it possible there is an interface between phone line and microcontroller system needed. This DTMF extension is universal module that can be connected to any microcontroller platform. It detects DTMF tones and decodes them to binary digits that can be easily read by microcontroller, which can decide what tasks to perform. DTMF decoder is based on CM8888 chip which is ideal for interfacing with MCU. Here is an example source code for interfacing with AVR ATmega8535 microcontroller which is written for WinAVR compiler toolset. Continue reading