The ELM337 provides a convenient means to interface standard photocells or light dependent resistors (LDRs) to digital logic circuits. It provides an input comparator with hysteresis, line frequency filtering, digital delays, and high current output drivers all within the one 8 pin package. Three mode setting pins configure the ELM337 for pulse or continuous output and for a delay on change of from 1 msec to 10 minutes. The transition threshold is set with a single external resistor, simplifying designs and minimizing costs. Applications need not be limited to those employing photocells, as the Example Applications section shows. The Schmitt trigger input provides a convenient way to interface to virtually any input signal, whether from digital logic or from a slowly varying analog source. The remainder of the ELM337 can simply be thought of as a time delay on pickup and dropout type circuit - very useful for sequencing processes.