Optical Measurements Using LED Discharge Photometry (PEDD Approach): Critical Timing Effects Identified & Corrected

The light-emitting diode (LED) photometry using the paired emitter detector diode (PEDD) strategy has been demonstrated to be a viable sensing method for analytical measurements. Timing of the LED discharge is one of (if not “the”) primary factors in this approach and can have a significant impact on sensing characteristics, such as resolution or the limit of detection (LOD). Details of these timing implementations have not appeared in the literature so far, making reproducibility and comparisons between systems challenging. This study investigates a number of timing implementations and demonstrates that the difference between these methods can impact resolution by up to 68%. Specifically, the three methods are based on a variety of Arduino functions and base C registry readings for the logical operations (comparison and reading the digital I/O status), i.e.: 1) “Wiring: digitalRead(), if()”; 2) “C: Register, if”; and 3) “C: Register, switch().” In addition, during a deeper analysis, it was found that employed methods are not based on a constant measurement sampling frequency as software execution times differ upon discharge logic threshold crossings, meaning that consequent time-based analysis may be impacted. This is explored in detail with respect to controlled incident light intensity. Finally, an approach is presented that corrects this and is subsequently verified—one capable of resulting in a constant measurement sampling frequency allowing for a greater estimation of the photocapacitance accuracy by up to 29%.