Building a 4-bit shift register from 7400 NAND gates for GPIO output port expansion on a Raspberry Pi

Latches from NANDs

Flip-flops from latches

Shift register from edge-triggered flip-flops

Raspberry Pi for input

Segmented LED display

Limitations & alternatives

Not buffered/latched/tristated

Small width

  • 1: G1, 2: G2, 3: G3, 4: G4, 5: G5
  • 6: i, 7: h, 8: g, 9: f, 10: e, 11: d, 12: c, 13: b, 14: a

Complexity & cost

  • 36¢ for the ICs = 9 * 74HC00 at 4¢ surplus
  • 1.56¢ for the protoboard = $1.56/10 ea from Aliexpress
  • 10¢? for wiring, $2.50/spool black/white, CAT5 $2.49 surplus

Conclusions

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