There were 72 boards that individually controlled the water valves. (Two in each of 6x6 panels) Each had a PIR detector and amplifier. They were all identical, but had a bank of switches to adjust their function. Timing, sensitivity, absolute and delta levels.
The 73rd board had four RS422 output channels that were wired to blocks of valve boards and over ride the sensors to shut off the rain.
This provided 100% dry route through for VIPs and did a 'curtain effect' to part the rain in front of the screen.
A comparator input on each board was used to receive a few simple commands.