**Details** This Tibbit is based on the MID400 AC line-to-logic optocoupler. AC voltage detection is particularly useful when integrating old contactor-based control systems into digital management systems, such as detecting and reacting to blackouts or monitoring AC feedback lines to ensure power delivery in mission-critical applications. Tibbit #63-1 is designed for use with 110V AC lines (also referred to as 120V AC). Due to its low detection threshold, it can also monitor 24V and 48V AC voltages, which are not uncommon in contactor-based control systems. The MID400's output is exposed on the Tibbit's –DETECT pin (Line D). The line goes LOW when the AC voltage exceeds the "on threshold" (~19Vrms ±5%). The line is set to HIGH when the AC voltage falls below the "off threshold." When connected to a Tibbo Project PCB socket with interrupt capabilities, changes to the –DETECT pin can generate interrupts. The use of an interrupt line is optional — you can also poll the –DETECT line. **LEDs** There is a single green LED, which lights up when Line D is LOW (AC voltage detected). **LIABILITY DISCLAIMER** Tibbit #63-1 is designed to detect high AC voltages. Improper handling of high AC voltages may lead to property damage, injuries, and even death. By using Tibbit #63-1, you explicitly agree not to hold Tibbo liable for any damages, injuries, or death arising from the use of these Tibbits.