1980s computer controls Grand Rapids Public School heat and AC
I remember a conversation I had with a friend's father, an HVAC engineer. He brought home a control board one-time, showed me the sensor inputs and control outputs. I don't remember how many there were, but let's say a dozen of each.<p>He described how a sensor in would connect to this spot and feed the system temperatures from a sensor in some remote part of the building. The control output would then go to the appropriate HVAC system and turn on/off A/C, heat or whatever to get the temperature to what it needed to be at.<p>The system would spider out around the building with these sensors and regulate the building's temperature.<p>At the heart of the board (which looked like a PC motherboard) was the CPU, a z80, already hilariously ancient when he showed this to me. So I asked him "why not use a more modern CPU?"<p>He responded, "why? This z80 can control an office building's entire HVAC system, and poll each sensor 200 times a second, how many times per second do you need? Temperature in a zone doesn't change that fast."<p>It was my introduction to the concept of "Lateral Thinking with Withered Technology" <a href="https://en.wikipedia.org/wiki/Gunpei_Yokoi#Lateral_Thinking_with_Withered_Technology" rel="nofollow">https://en.wikipedia.org/wiki/Gunpei_Yokoi#Lateral_Thinking_...</a>