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Source:Http://blog.csdn.net/xl19862005
By xandy)
I. Demodulation Circuit
In my design, the demodulation end uses the MSP430 single-chip microcomputer, because the power consumption of Ti series single-chip microcomputer is very low, in sleep state, the current can reach UA level, under normal operation, the current can also be kept at several Ma levels.
Connect the right channel of the mobile phone to the p2.3 foot of the MSP430 microcontroller.CodeSet and activate the forward input of the second feature (comparator 0) of this pin, and configure the reverse input of the comparator 0 to the internal VCC/2 reference voltage ,, VCC is divided by two K Resistors on the right channel of the mobile phone. As long as the voltage of the right channel changes within the range of the comparator's conduction, the comparator can capture the signal on the right channel of the mobile phone! Is the output feature of the comparator:
The following figure shows the output waveform of the modulated signal following the comparator in the previous section:
Ii. demodulation principle
Since the modulation signal is represented by waveforms of different frequencies, the output waveform after the comparator is shown in, it is easy to find that, these wide, narrow, and continuous square waves carry the information we want, and then capture these square wave signals through the capture device in the MSP430 microcontroller.
The timer is used to calculate the time of these square waves, so as to call out the previously modulated signal and obtain the code element.
The demodulation diagram is as follows:
