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Circuit Description

This circuit demonstrates the use of a 4-bit Hamming code for error detection and error correction. Use the four input switches on the left to set the 4-bit input value for the encoder, which calculates three parity bits and transmits these together with the four data bits.

The seven switches and XOR gates in the middle of the circuit allow to insert faults into the transmitted data. If the switches are off, the corresponding data bit is transferred normally. If a switch is on, however, the XOR gate inverts the corresponding data bit, which is equivalent to a transmission error for that bit.

The decoder block on the right takes the seven code bits and tries to reconstruct the original information, that is, the original four data bits.

First, set all seven error switches to off. Then select a few input values for the encoder with switches on the left and observe the generated parity bits and the operation of the deocder. Next, play with the 'error switches' to insert bit faults into the transmitted data and again observe the operation of the decoder. What happens if you activate more than one 'error switch'?