CO Sensor Output to Microcontroller: ADC vs Comparator for 1.5V Supply, 0.5-1V Vout

A CO sensor powered by 1.5 V outputs a voltage between 0.5 V (no CO) and 1 V (CO detected). Directly connecting this output to a microcontroller input pin causes constant triggering due to the baseline 0.5 V output. Two main approaches were discussed to interface the sensor output with a microcontroller: using an analog-to-digital converter (ADC) or a voltage comparator. A voltage comparator with a reference voltage set midway between 0.5 V and 1 V (approximately 0.75 V) provides a simple go/no-go detection method. Microcontrollers with built-in comparators, such as the PIC12F683, can simplify implementation by using internal voltage references and comparators or ADCs. For discrete solutions, a transistor buffer stage (e.g., using a PN2222A NPN transistor) can level-shift and condition the sensor output. Adding a resistor (e.g., 33 kΩ from base to ground) improves noise margin by raising the low trip point above 0.5 V. Discrete comparator circuits can achieve precise 0.75 V trip points but may require additional stages to output TTL-compatible logic levels. Using just a diode for level shifting is insufficient to meet microcontroller logic high thresholds. Overall, a comparator-based solution with proper reference voltage and output conditioning is recommended for reliable CO detection with low supply voltage sensors.
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