Simple circuit to switch between 5V and 1.4V for MQ-7 sensor timing (60s/90s)

The discussion addresses generating two distinct DC voltage levels—5V for 60 seconds and 1.4V for 90 seconds—applied to the same pin of an MQ-7 carbon monoxide sensor for timing purposes. A resistor voltage divider is suggested to derive the 1.4V from a 5V source. For timing control, a simple 555 timer circuit is recommended if timing precision is not critical. Alternatives include using a CD4060 oscillator with voltage divider taps and transistor buffering or controlling an LM317 voltage regulator via programmable resistors. The use of a microcontroller is discouraged by the user. Further elaboration on the 555 timer approach is requested, with hints toward circuit inversion and simplification for practical implementation.
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