HINIL drive for light sequencer

Readers may remember that the `Discolights` featured in Elektor September 1975 used TTL shift registers to drive triac switches. This is fine so long as great care is taken with layout and supply decoupling, otherwise noise from the triac switches can interfere with the sequencing of the TTL shift registers due to the poor noise immunity of the latter. The circuit described in this article shows an application of a new family of High Noise Immunity Logic (HINI L) from Siemens. Th is has the advantage (in this type of application) that the logic thresholds are much higher. The switching speed is also lower than that of TTL, so the circuits are much less likely to be affected by short transients.