Mains Power Failure Detection
The objective of this project is to allow our Home Control System (HCS) to know if the mains power has failed, so that it can raise an alarm and act accordingly. The type of alarm raised will depend upon the alarm status and the house status.
Design
There are lots of ways to detect mains power and translate the presence or absence into a safe and meaningful level, to feed into an I/O board. Optical isolation is essential as you don't want to risk putting 240V AC onto a computer circuit board.
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A typical method to achieve this optical isolation is to use a neon lamp and a phototransistor to detect the output light. For 240V mains operation use a series 270kΩ 1/4W resistor in series with the neon bulb.
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Our design should be much simpler because by piggy-backing off of another project. Our 12V UPS project uses a mains PSU to provide a 16V DC power source and we have taken a feed off of this supply and fed it into our optically-isolated input board, to detect both failure of the mains supply and failure of the UPS power supply unit.
Progress
This is down as a live and completed project.
