The silicon-controlled rectifier as an input latch for digital laboratory computer interfaces

Several standard solutions have been developed for problems encountered when monitoring laboratory response sensors with microcomputers. These problems include voltage-level translation, power-supply isolation, contact debouncing, and temporary data storage. Data storage has typically been accomplished through the use of edge-sensitive devices, which introduce difficulties when a researcher wishes to monitor the duration of a response. A circuit is described that includes an optoisolator with a silicon-controlled rectifier at its output stage. The circuit acts as a latch for the detection of brief responses, and, because it is not edge-sensitive, it can also be used to record the duration of sustained responses.