Snowy handed me a couple of solar water controllers dating from the early 1980's. Let's see what the technology was 20 years ago.
741 op-amp with a 4069 high voltage hex inverter driving the relay
This controller has a couple of TL062 op-amps. The TSC 7107CPL drives the three seven segment displays - My guess is that the TSC 7107CP is a "voltmeter" device.
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