4. MCU reads ID card (hardware debugging and code reading)-EEWORLD

Collect

1. Power amplifier circuit and 125Khz carrier measurement

Point A is the measurement point of the oscilloscope, and the signal carrier is the 125KHz waveform generated by the microcontroller.

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Actual waveform

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2. LC resonant circuit and sine wave measurement

Point B is the oscilloscope measurement point

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3. Envelope detection circuit and detection waveform

Point C is the oscilloscope measurement point

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4. Amplification and shaping circuit and output waveform measurement

The measurement point is OutSignal.

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5. Waveform analysis and code reading

Through the final output waveform above, the microcontroller can already recognize the output Manchester code.

First, we use a commercially available card reader to read the ID card number used in this test.

1 E 0 0 6 8 B 0 9 8

We disassemble the data format of EM4100 according to the format in the article, as shown in the following figure

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Below is a randomly selected output waveform. Let's analyze it.

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11111111111100110111001000, comparing the data in the list above, I found that they don’t match at all.

Now let's take a look at the format of Manchester code.

A transition from low to high indicates "1", and a transition from high to low indicates "0". (Baidu Encyclopedia)

At this time, we invert the code obtained above.

0000000000011001000110111 (Now it can be matched~~~~~)

Now let's take a look at the relevant pictures on Wikipedia, and I believe it will become clear at a glance.

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