ATTiny2313 AnalogRead Not Working for LDR and PIR Sensor Project—Why?

The discussion addresses an issue with using analogRead on an ATTiny2313 microcontroller for a night-activated project involving an LDR and a PIR sensor. The project works correctly on an Arduino but fails on the ATTiny2313, where analog inputs do not function as expected, causing the LED and buzzer to activate immediately upon powering the IC. Troubleshooting steps included verifying circuit connections, testing with and without the PIR sensor, changing resistor values, and trying alternative code. The key insight revealed is that the ATTiny2313 lacks a built-in Analog-to-Digital Converter (ADC), so it cannot perform analogRead operations directly. This limitation explains why analog input readings fail on the ATTiny2313. Suggested solutions include adding an external ADC via SPI, switching to a microcontroller with built-in ADC like an ATmega, or using the PIR sensor as a digital input since it typically outputs digital signals. The LDR readings referenced (values around 500) correspond to digital bit values from ADC conversion on Arduino platforms, which the ATTiny2313 cannot replicate natively.
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