Oil change computer (CB6373E)

This electrochemical circuit monitors the conductivity of the oil indicating when to change it. The circuit is from an 1967 American documentation.

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Interface for resistive transducers (CB20995E)
We found this circuit in an Analog Devices documentation from the 90s. The circuit is based on a...
Triac Timer (CB24046E)
This circuit turns off a load after an interval of 8 to 80 seconds adjusted on the potentiometer. The...
Simple Alarm with SCR (CB24114E)
Found elsewhere in this section, this circuit is from the April 1971 Radio Electronics magazine. Note...