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Happy Birthday Detector

How it works

This project implements a Happy Birthday Detector — a digital system that continuously transmits a looping serial bit stream and detects a hardcoded 9-bit birthday pattern within it.

Birthday Pattern

The birthday date is March 7 (03/07/2005):

Field	Value	Binary
Month	3	`0011`
Date	7	`00111`
Pattern	—	`001100111`

System Architecture

The design has five sub-modules integrated into project.v:

TX Generator — A 10-bit counter (0–1023) that produces data words, incrementing only after the serializer finishes sending the previous word to prevent overlap.

TX Serializer — Takes each 10-bit word and transmits it one bit per clock cycle, LSB first, producing a continuous serial stream at the 10 kHz system clock rate.

RX Detector — A 9-bit shift register that captures incoming serial bits and compares the last 9 bits to the birthday pattern every clock cycle, asserting a match pulse for one cycle whenever the pattern is found.

Hit Counter — Accumulates match pulses. Every 10,000 clock cycles (1 second at 10 kHz), it latches the running count, resets it, and pulses hit_count_valid to notify the display.

7-Segment Driver — Converts the latched 8-bit binary count into two active-low 7-segment display codes (tens digit and units digit), supporting display of values 0–99.

Timing

Parameter	Value
Clock frequency	10 kHz
Bits per frame	10
Frame rate	1 kHz
Display update	Every 1 s (10,000 clocks)
Pattern length	9 bits

Pin Mapping

Pin	Direction	Description
`ui_in[0]`	Input	`TX_ENA_N` — active-low transmit enable
`uo_out[6:0]`	Output	Units digit 7-segment code (active low, gfedcba)
`uo_out[7]`	Output	`HIT_COUNT_VALID` — pulses HIGH each second
`uio_out[6:0]`	Output	Tens digit 7-segment code (active low, gfedcba)

How to test

Apply reset: Hold rst_n LOW for at least 10 clock cycles, then release HIGH. All internal counters and state machines will initialise to zero.
Enable transmission: Drive ui_in[0] (TX_ENA_N) LOW. The serial bit stream begins immediately on the next clock cycle.
Wait for display update: After 10,000 clock cycles (1 second at 10 kHz), uo_out[7] (HIT_COUNT_VALID) pulses HIGH for one cycle. At this moment, uo_out[6:0] holds the units digit and uio_out[6:0] holds the tens digit of the birthday hit count for that second.
Read the 7-segment display: Decode uo_out[6:0] for the units digit and uio_out[6:0] for the tens digit. Both use active-low encoding: 1000000 = 0, 1111001 = 1, 0100100 = 2, and so on.
Verify non-zero count: The birthday pattern 001100111 (decimal 103) falls within the 0–1023 counter range, so the detector finds at least one match per counter cycle. The display should show a non-zero value after the first second.
Test disable: Drive ui_in[0] HIGH to stop transmission. The display will show 0 hits/sec after the next update interval.
Test reset recovery: Assert rst_n LOW mid-operation, then release. The system restarts cleanly and resumes display updates after another 1-second interval.

7-Segment Encoding Reference (active low, gfedcba)

Digit	Code
0	`1000000`
1	`1111001`
2	`0100100`
3	`0110000`
4	`0011001`
5	`0010010`
6	`0000010`
7	`1111000`
8	`0000000`
9	`0010000`

#	Input	Output	Bidirectional
0	TX_ENA_N - Active-low transmit enable (0=transmitting, 1=off)	SEG_A - units digit segment a (active low)	SEG_A - tens digit segment a (active low)
1	unused	SEG_B - units digit segment b (active low)	SEG_B - tens digit segment b (active low)
2	unused	SEG_C - units digit segment c (active low)	SEG_C - tens digit segment c (active low)
3	unused	SEG_D - units digit segment d (active low)	SEG_D - tens digit segment d (active low)
4	unused	SEG_E - units digit segment e (active low)	SEG_E - tens digit segment e (active low)
5	unused	SEG_F - units digit segment f (active low)	SEG_F - tens digit segment f (active low)
6	unused	SEG_G - units digit segment g (active low)	SEG_G - tens digit segment g (active low)
7	unused	HIT_COUNT_VALID - pulses high each second with new count	unused (input)

321 IEEE Happy Birthday Detector