High-rise building vents... need to automate a pushbutton

Projects General Guidance
1

Hi everyone!

I've worked with Arduinos in years past to build things like guitar pedal effect switchers, but I have a different animal this time (that is hopefully much simpler).

The ask: I would like to use a motion sensor and either a relay or optocoupler to mimic a button push that activates an automatic vent in our high-rise building kitchen. The button is a simple 2 wire pushbutton.

The full story:

The vents in our kitchen were installed by the high-rise association years ago, and they operate with a flap that opens and closes depending if you're in the room or not (this is to correct negative pressure buildup in the system or something).

Typically the vents are on the wall facing outward in the corner of the kitchen, and they have a motion sensor that opens the vent and only shuts when it doesn't sense any movement for 20minutes... UNLESS, you have cabinets that go to the ceiling (like ours do), in which case the vents are mounted to the bottom of the upper cabinets (so they face downward to the counter) and they operate with a pushbutton.

This is problematic for a few reasons, but the largest is that we just forget to push the button all the time... Since I'm going to be installing some under cabinet lights shortly, I thought I could maybe add a motion sensor near the vents and have them operate as we're in the room.

That being said, I don't know if an opto coupler or a relay is the right answer (I think the relays click noisily, so it'd be nice to not have a click).

The vents are by the microwave cabinet, which has an open outlet, as well, so I'm hoping I can use that to power the Arduino and sensor (I might even try to power the vents with it - they each take 2 AAA batteries), and I can house the arduino unit and any subsequent attachments in that same microwave cabinet.

Any thoughts or advice on this one? Is this even feasible? I can always figure out the code, but knowing what to buy would be key (power adapters, relays/optocouplers, motion sensors - are any better than others?).

Let me know, and thank you in advance!

2

Could You measure the current passing the activated button?
If it is DC You can use a logit MOSFET in case the current is higher then the 20 mA capacity of most Arduinos.

3

I can... I have a multimeter for pedal building, but mostly use it to check resistor values. I’ll see what setting I should use and report back... :slight_smile:

4

What is the power source used to open the vents? Is it direct from the AC mains or is there a DC power supply of some "safe" voltage like 12V or 24V?

My guess is that it uses a basic PIR (passive infrared) sensor like you would use for outdoor lights. Since they switch mains AC relatively easily and cheaply, the vent motor may be AC.

Do not attempt to measure mains voltage with anything less than a CAT 3 multimeter. Even if you have a "600V" range on the meter, it's not safe to connect a cheap meter to the mains without that CAT rating.

5

The vents each run off 2 AAA batteries, which is a total of 3v max. They aren’t connected to a power source at all. It should be fine - I used the multimeter I have to build a 50w tube amp, so it should be fine, hehe.

6

The vents each run off 2 AAA batteries

Are you sure? I mean, I'm not saying they don't, maybe they do, but 2 AA batteries seems to me to be far too little power for a moving a vent open or closed, not to mention powering the control system detects when they should open or close, that would eat batteries if it has to be on all the time. I'm not saying you're wrong, it just doesn't sound right to me.

7

Seems likely the pushbutton and batteries triggers a mains power circuit that actually opens the vents.

8

Hey guys! I can see why you’d think they were powered by more than batteries, but they aren’t. it’s just a plastic flap covering a 3 inch hole. Nothing too heavy or crazy. The building has fans on the roof that do the rest of the work.

These replaced the old grates from when the building was erected in each unit (there are 2 in the kitchen, and one in every bathroom). They didn’t run any power to them. Just took the old grates and fit these into the cavities.

9

Hey guys - thank you for your help so far... sorry if I’m not being detailed enough - guess I assume my situations are more common than they are.

I’m attaching pics of my findings and to give a better understanding of the situation.

There are 2 wires attached to the batteries and “motor” of the vent mechanism. When the wires touch, the vent flap opens. The motor just pushes a plastic nub over that’s attached to the flap.

It looks like the dc current is about 3v - makes sense because that’s the battery supply.

So with that info, is it possible to create something simple? One sensor that can trigger both vents open for 20min, rescan and stay open if needed? Not sure if leaving the wires connected is best, but maybe it opens and closes every 10min that the sensor picks something up.

All that being said, I’ve only ever played with an Arduino mega - would an uno or smaller unit do the trick?

Again, thank you for the help so far - it’s very appreciated. :slight_smile:

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10

What is the CURRENT, put your meter on the DC A or mA range.

11

Right! Sorry... the pictures won't upload right.

when the multimeter is set to 2000u it says 277, and when set to 20m it says .29 - so that's about 300kA, if I'm reading it right...

12

Looking at the photos...

I can't make any sense of the battery opening one, it's just a hole. Is that where a battery box goes? Or what?
On the one with the meter you have unfortunately drawn a big circle around the display (I think you can safely assume that no one here who is trying to help you needs you to indicate where on the meter the display is), which obscures the meter setting and the scale around the setting. Also it is not possible to see which sockets on the meter the cables are connected to, and finally the scale around the dial is not properly focused and is difficult to read, even where it is not obscured.

Please take this photo again with everything visible and clear and readable and no lines or circles drawn that obscure anything.

What is the meter connected to? Where do those wires go?

That's about 300kA

Lets get this in perspective; a 500MW alternator in a UK power station has an output current of around 25kA....

13

How 'bout 300 MicroAmps? Sounds reasonable. Did the vent operate?

14

So if you trigger the flap by pushing the button, what happens to the flap if you take the batteries out while it’s “open”?

15

Man, I am not doing good here today - I swear I'm not usually this inept, but rather a bit scattered after a grueling kitchen remodel that seemingly never ends. I'm reattaching all pictures (sans circles), and explaining the building's venting system in more detail. My apologies...

This building exhaust fan system is designed to neutralize negative pressure build-up in the apartments/condos for better airflow circulation and HVAC efficiency. The building's exhaust ducts run from the first floor all the way up to the roof of our 30 story high rise condo building, and has openings in each kitchen and bathroom. There are pressure sensitive fans on the roof which suck air out from the all the condos.

The "vent" in my unit is essentially a battery powered flap that opens and closes over the openings to the building ducts. (In the picture of my "vent", the white cover with 2 thin slots toward the back left is the battery pack housing 2 AAA batteries. The larger black opening to its immediate right of it is the flap/vent opening - it's hard to get a picture of the insides that make sense, but you can kind of see the angled flap that opens/closes. The actual product is online here if you need further sense made of this: https://www.aereco.com/product/bxc/ ).

To get the flap to open, a button is pressed. The button is, as far as I can tell, a normally open momentary SPST that when pressed, connects the wires and opens the flap. The flap stays open for 20 minutes and then shuts automatically. (some units have a motion sensor built-in, but ours do not in our kitchen because they face downward to the countertop).

To mimic the button (which was lost in the remodel), we touch the red and black wires together and it operates the same way. (In the multimeter pic for DCV, you can see the wires - one red, one black - and these connect to the motor/onboard chip that says "if these wires touch, open the flap for 20min").

When I connected the multimeter to the 2 wires that used to connect to the button, here's what I got (see pictures for proof):

  • The DCV showed 2.91v, which I presume is because of the battery power.

  • The DCA showed 277u

So what do I want the arduino to do?

  1. I'd like to use a PIR motion sensor to open the "vents" (flaps) instead of a button. (we currently always forget to press it and the vents are never open)

  2. I'd like for the relay / mosfet / optocoupler to be quiet, if possible (I know that relays click).

  3. I'd like to possibly power the flaps from the arduino (they currently only need 2 AAA batteries, so I assume it doesn't take much to power them).

Does this clear up any confusion? I'm truly sorry for all the rambling and incoherence... It's really just replacing/mimicing a simple button for a battery powered device with a motion sensor.

As always, thank you in advance for the help.

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16

Slumpert:
So if you trigger the flap by pushing the button, what happens to the flap if you take the batteries out while it’s “open”?

I just tried this - it stays open... everything stays as it was, and then when I add the batteries back, it resets to closed.

17

Based on some aaa batteries as the power source.
You should be able to use a phone charger
An UNO NANO
An IRLxxx MOSFET
A mini PIR sensor
This is beginner level stuff.

Verify the switch
And motor power.

This seems like a project you can ffigure as you go Along

18

OPs question has turned into a high level intellectual debate. So many posts, so little achieved.
As OP suggested, use an Arduino and a presence detector and make a move, one relay click, ought bo be solved by now. Relay clicks can't be disturbing rather it tells that the ventilation logic is triggered.

An Arduino needs a supply of power. Can that be done in an acceptable way? Arduino battory + valve battories? As I understand one "button press" would be what the Arduino needs to produce. In that case, use a little relay in order ti awoid button current questions.

19

mikeganz:
I just tried this - it stays open... everything stays as it was, and then when I add the batteries back, it resets to closed.

Probably an H bridge
Check voltage on the motor
When opening
And closing.
Does the swswitch have 4 wires?

20

In post #10 by OP is says some 300 Micro Amps passing the button pressed. That can be switched by anything and a relay voltage loss is almost 0 volt. An NPN transistor switching that current might cause a voltage drop of some 300 - 500 mVolt. A MOSFET likely less but use a small relay. That short pulse consumes very little power compared to the Arduino and its sensor.