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I dont have any better solution than this. Will work on it & ll post back soon.
EDIT: Sorry to whoever whose idea I just copied - I didn't see that post at the time, hopefully you can find something else that is useful in here somewhere.
You could rig a switch to the door & calibrate it to the appropriate cycle. Door open, fan on. Door close, fan stays. Door opens second time, fan shuts off. That would follow the pattern of person enter, person leave.
That is a very simple layout & obviously not foolproof. What if you're sitting in there & someone else comes in? Fan off. In which case you'd need a bypass or some sort of override.
You could use an IR motion sensor, yes. But they don't detect heat per se, because they're only set to discriminate one channel (they shoot one channel of light out and proceed to look for it, if you're looking for an active setup as opposed to passive). In order to counter the inactivity drawback, you'd need some form of a thermal imaging sensor (which with having their military applications aren't usually cheap).
Maybe this is a bit far fetched, but I'll put it out there for food for thought and to give you something to chew on:
- Have one sensor mounted outside the target room, in a hallway, other room, etc. For reference this is motion sensor #1.
- Have another sensor mounted in the target room. This is sensor #2. Route both to a logic board, programmed with the instructions and conditions:
1) If someone triggers #1 and detriggers it, and THEN triggers #2, turn fan / light on. (they have entered)
2) If someone triggers #2, detriggers it, THEN triggers #1, turn fan off (they have left). This does not occur until State 2 has EXPLICITLY occurred (fan will not turn off due to inactivity, and does not occur if State 1 has not occurred)
This would fix the first dilemma of a second person entering & accidentally deactivating the system. The issue is, the first person to LEAVE would deactivate it & shut everyone else in the room out in the cold.
That's one way I could think to solve it. A slightly more complicated way would be to have the logic board log all occurrences (say, entering is +1, leaving is -1) and the fan doesn't shut off until the net result is 0. For example, three people enter.
Log:
+3. One person leaves
+2. Fan stays on, two occurrences left.
Under this system, it would be impossible to have a negative number at rest (in a closed room, how can you have more people leave than entered if the system is working correctly?
Of course you can have a bypass or override built into the system so if you're cold, for example, you can manually bypass the sensor & logic control.
You might also have to tune the setup (sensitivity of detectors) if say, you have animals. You wouldn't want them turning on the fan inadvertently & using up power.
The feasibility of this, I'm not sure of. Again, it's more food for thought than anything else.
You could rig a switch to the door & calibrate it to the appropriate cycle. Door open, fan on. Door close, fan stays. Door opens second time, fan shuts off. That would follow the pattern of person enter, person leave.
That is a very simple layout & obviously not foolproof. What if you're sitting in there & someone else comes in? Fan off. In which case you'd need a bypass or some sort of override.
You could use an IR motion sensor, yes. But they don't detect heat per se, because they're only set to discriminate one channel (they shoot one channel of light out and proceed to look for it, if you're looking for an active setup as opposed to passive). In order to counter the inactivity drawback, you'd need some form of a thermal imaging sensor (which with having their military applications aren't usually cheap).
Maybe this is a bit far fetched, but I'll put it out there for food for thought and to give you something to chew on:
- Have one sensor mounted outside the target room, in a hallway, other room, etc. For reference this is motion sensor #1.
- Have another sensor mounted in the target room. This is sensor #2. Route both to a logic board, programmed with the instructions and conditions:
1) If someone triggers #1 and detriggers it, and THEN triggers #2, turn fan / light on. (they have entered)
2) If someone triggers #2, detriggers it, THEN triggers #1, turn fan off (they have left). This does not occur until State 2 has EXPLICITLY occurred (fan will not turn off due to inactivity, and does not occur if State 1 has not occurred)
This would fix the first dilemma of a second person entering & accidentally deactivating the system. The issue is, the first person to LEAVE would deactivate it & shut everyone else in the room out in the cold.
That's one way I could think to solve it. A slightly more complicated way would be to have the logic board log all occurrences (say, entering is +1, leaving is -1) and the fan doesn't shut off until the net result is 0. For example, three people enter.
Log:
+3. One person leaves
+2. Fan stays on, two occurrences left.
Under this system, it would be impossible to have a negative number at rest (in a closed room, how can you have more people leave than entered if the system is working correctly?
Of course you can have a bypass or override built into the system so if you're cold, for example, you can manually bypass the sensor & logic control.
You might also have to tune the setup (sensitivity of detectors) if say, you have animals. You wouldn't want them turning on the fan inadvertently & using up power.
The feasibility of this, I'm not sure of. Again, it's more food for thought than anything else.
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