Air flow detection to turn on my Arduino from sleep

Hi everyone,

I have been building a system that tracks that my heating is actually blowing hot air through vents when it is operational. Currently, I am using the ESP8266 board with the Adafruit MPRLS pressure sensor, however, this can only be installed when a power outlet is close enough to be connected to my system and then clipped onto the vent and the pressure is different in different rooms, so I have to calibrate it.

I would like to make this more portable and independent so that I could make my unit smaller, low-power, and clip it on any heating vent (ceiling, for example) thus powering a sensor with 3.3V. I think I would need to put my device in deep sleep when there is no air coming out of my vent, and wake it up using some type of sensor that detects that air is coming from the vent. I have looked and don't seem to see a sensor that could wake up my unit? I could put to sleep again a few minutes after the air is not flowing anymore, and then the cycle would repeat again.

Thank you!

Hi, @nahoku02
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".

This will help with advice on how to present your code and problems.

Why just pressure, that will tell you if you have air flow, but not if the heater burner is operational.
You need to also measure temperature.

Tom... :smiley: :+1: :coffee: :australia:

Thank you for the quick reply, @TomGeorge. I have the temperature and humidity measurements going with it, using the DHT11 Arduino.

There are pressure sensors that simply close a switch, available with a variety of sensitivities, and those can be used to wake up an Arduino from deep sleep.

The most sensitive are easily activated by breathing, and are used by disabled people for controlling equipment. Look up "sip and puff switch", for example Sip/Puff Switch

Another option would be a swinging vane in the flow stream, which closes or opens a contact. It is easy to make your own.

hot wire anemometer

Since by definition that requires significant power (notice the word "hot"?), it would be the worst choice for a battery powered application. :roll_eyes:

That said, using a battery powered devices in a fixed location in a building where power actually is available, is always a poor choice. :grimacing:

Strip of paper sellotaped to the outlet so it flaps about in the breeze.

my question would be why ? Is there a problem with the heating that needs fixing ? The heating I thought would be more reliable than a battery powered monitor ?

Anyway … how about a small fan that turns in the breeze ,maybe adapt and old pc fan

Thank you for the suggestion.
The answer to why is lengthy, but the short version is that the unit is 2.5 years old, fancy, and supposedly highly efficient, with a smart wireless sensor on the wall, while I am not on site. We have had issues with it, with four new circuit boards and a new blower motor, and I still don't think it's working right. Thus, I want to track how much time the fan is blowing as the smart thermostat shows me the unit is in heat mode while it is actually not blowing any warm air at all.

It might therefore be easier to measure the temperature in the room or the temperature of the blowing air from the outlet - that is much easier to do .
Just use a ds18b20 and send the temperature of the air coming out, and maybe a second with the room temperature, you could even subtract one from the other to prove the air coming out is warmer.

Another option is to measure heat from the furnace - likely to be accessible mains there too

All in less than 3 years? Something is very seriously wrong. The band-aid you are currently considering won't help with such major problems.

Yes, and almost certainly not those circuit boards. This smells of a technician swapping the circuit boards because they've no idea how to diagnose the problem. This is quite widespread - seen from car technicians, to watch repairers, to appliance techs.

How about a furnace pressure sensing switch, such as the "Robert Shaw 2374-510 Universal Air Pressure Sensing Switch"? This particular model can measure positive, negative, or differential pressure in range 0.10" to 10.0" W.C. This is not the cheapest way to go, but it might work. I believe the switch is set to NO. There may be cheaper switches, but not every furnace vent pressure switch will be appropriate. From a quick search, many operate on a "negative" (less than atmospheric) pressure, rather than a positive pressure.

Does you system have automated damper controls? Else why the need for testing different heat registers?

There may be other possibilities causing the problem you describe. My new/old heat pump system could also do what you describe under certain conditions.
One is the parameter the tech set was to have the fan continue for 90 seconds after the heat stopped.
Another condition is possible when the A/C temp set to cool is very close to the actual heating setting. Our thermostat insists there hast to be at least a 4 degree difference. Perhaps your thermostat allows a smaller difference.
Finally, the multispeed system fan can be set to "on" and will revert to the lowest fan speed when heat is not being supplied, instead of turning completely off.
Paul