Objective

Design an IR sensor to count the no. of pills dispensed for a smart pill dispenser. Utilize the max voltage of the MCU's ADC for the highest resolution.

Design

  • Op-amp: LM358 operation amplifier for signal amplification

  • IR Led to emit IR light and Photodiode to sense the IR light, placed parallel to each other

  • Voltage divider for feedback to set gain of 9.34, resulting in a signal of 0 - 4.667V, which utilizes 93.34% of the ADC range.

Validation

  • The circuit was designed in CircuitLab simulator, and a DC sweep of photocurrent from 0 to 50 uA results in a signal output of 0 to 4.667 V, and the relationship is linear.

Calculations