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Sensor for heating/cooling vent suggestions please — Parallax Forums

Sensor for heating/cooling vent suggestions please

DaveJensonDaveJenson Posts: 375
edited 2013-08-15 12:29 in Accessories
In my house, we have a large room with only one heatint/cooling vent. To get more of the heat/cool into this room, I have placed a box fan in front of the vent. When the heat/cool is running, I turn on the box fan.

I had an Idea that this could be done automatically/unattended. I would need a sensor to determine when the vent is blowing, then activate a relay to turn on the box fan. I think I have all the parts to do most of this.

Any suggestions as to how to detect that the vent is blowing air?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-08-12 14:52
    Usually this is done with a vane or paddle that sits in the air flow. The air pushes against the vane and the vane moves. As the vane moves, it pushes against a microswitch which closes when the air flow is present. Alternatively, you can use an LED and photosensor so that, when the air flow moves the vane, it blocks the light beam between the LED and photosensor and this switches the power to the fan. Depending on what you use, you can incorporate a microcontroller or just use the microswitch to control a relay that switches on the fan. The microcontroller can add some time delays and hysteresis which might be useful depending on how you've got the vane / switch / sensor set up.
  • dredre Posts: 106
    edited 2013-08-12 16:47
    Hi,
    If you want to detect some parameter only when the furnace/AC is on, why not detect the change in temperature?
    Sense the ambient [room] temperature and the temperature of the air flowing through the vent. Whenever there is an absolute temperature difference, turn on the vent fan.

    Hope this helps.

    cheers, David
  • WBA ConsultingWBA Consulting Posts: 2,933
    edited 2013-08-12 17:41
    Was going to say the same in regards to a temperature sensor. When my house is at 78, the air coming out of the vent when the AC is running is about 56, so it's pretty easy to use the temperature difference as a way for a micro to drive a solid state relay (SSR) for the fan. Make sure the SSR can handle the current of the fan as well as has inputs that are a good match to your micro.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-08-12 18:26
    How about a small piece of metal foil to act a part of a momentary switch. When the foil is blown against a wire, a contact is made. Alternatively the foil could normally rest against the wire and the air movements causes a break in the circuit.

    It might be a pain keeping the foil and wire in the correct positions.

    Just another idea to throw into the pot.
  • DaveJensonDaveJenson Posts: 375
    edited 2013-08-13 08:00
    I was looking for simple, and Mike Green comes through again!

    I will try some vane/micro / switch / relay combo.

    If that proves unreliable, I will investigate the temperature difference sensing methods.

    Thanks for all the great Ideas!
  • Hal AlbachHal Albach Posts: 747
    edited 2013-08-15 10:18
    Just make sure that the box fan does not continue to operate the sensor after the heat/cool system has stopped.
  • DaveJensonDaveJenson Posts: 375
    edited 2013-08-15 12:29
    Hal Albach wrote: »
    Just make sure that the box fan does not continue to operate the sensor after the heat/cool system has stopped.

    LOL! Right! I had thought of that also...
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