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Power Sensing

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intermittech edited this page Sep 14, 2026 · 3 revisions

Power sensing

Boards with spare AW9523 input ports and the matching sense circuits can report the state of each output's fuse and the presence of the main supply rail. Nothing is sensed unless a port is configured, so the feature stays dormant on boards without this hardware (sensing is only available on the AW9523 expander).

Note: the AW9523 is a 3.3 V device - its ports are not 5 V tolerant (absolute maximum VCC + 0.3 V). Sense signals derived from higher-voltage rails (5 V, 12 V, 24 V ...) must be brought down to 3.3 V logic levels with a resistor divider or level shifter before they reach an expander port; roughly, 2.3 V and above reads high, 1.0 V and below reads low.

  • Fuse sense - one AW9523 input per relay (fuse-pin in the relay block, virtual pins 100-115, -1 = off) reading the voltage after that output's fuse. With the fuses upstream of the output switches, a blown fuse is detected whenever the main rail is up - whether or not the output is switched on. An input of the blown-fuse-indicator type reads high when the fuse is open: select the matching polarity on the settings page ("Fuse sense inputs are ...").
  • Main power sense - one AW9523 input (main-sense-pin) reading the main supply rail behind the Master AC relay ("Main power sense input is high/low when power is present").

Status dots: on the Info page a single Fuses dot (green when every sensed fuse is fine, grey while the main rail is down, otherwise only the broken outputs are listed in red), a Main power row, and a dot on each coupled relay's row; in the segment "Power relays" menu a dot in front of each relay name. Green = OK, red = fault (fuse: no voltage after the fuse while the main rail is up; main power: the AC relay is on but no power is detected), grey = nothing to judge (main power off). Inputs are polled 10x per second and debounced; after the AC relay switches on, the PSU stabilization time plus one second passes before a missing rail counts as a fault. In addition, for one second after any output switches on (the whole staggered bring-up included) the fuse inputs are not judged: the inrush current of an output that just powered up can briefly light its blown-fuse indicator, so indicator-type inputs keep their last state during that window and a fuse fault is only ever reported once it has passed.

Known limitation of indicator-type fuse sensing: an output that is switched on with nothing connected reports its fuse as intact, because the indicator circuit needs the load path to draw current.

This page is generated from the usermod's in-tree readme (usermods/PowerManager/readme.md) by sync_wiki.py - edit there, not here.

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