Hello, I would like to automate the switching on and off of an extractor fan. It is currently done by pulling a chord. The mechanical part is needed to open/close the shutter. I am considering using a MG996R servo or similar to do so. Is it the good track? I was tempted to push the mechanism from the inside at first, but that prevents any manual override.
Since I am totally new in this area (both mechanical and ESPHome), I helped myself with ChatGPT. My shopping list would resemble to:
If the pull-cord is on/off only (not several apeeds), you can use a shelly relay and set it intro “edge” mode so that if wired properly, both the shelly can turn it o or off and pulling the chain will change it to the other state it is currently “not” in if on, pulling the chain would turn it off, if off, pulling the chainwould turn it on. (This is not complicated to do. It can be done with a multi-speed pull chain switch as well but that would be much more involved.)
Thanks, but that would be missing the mechanical part to open/close the shutter (is that the correct word?). I just added pictures to the original post.
The pull cord does both the switching and the opening of the shutter. The micro switches that you identified on the first picture are there for security only. They prevent the fan from switching on when the cover is not there. There is another micro switch (red) below the lever on the second picture, switching the fan on.
So then have the shelly turn the fan on and open the shutters, or turn off the fan and close the shutter, at the same time. If you are looking for a shelly that can treat them as separate so you can add some logic into the activities they perform, them get a shelly which can control two switches independently. However the pictures are confuising. YOur finger on a triangular piece of plastic near the vent doesn’t help (?)
That makes it simple and leaves manual operation available. Only disadvantage is that esp doesn’t know the actual state if operated manually (some sensor needed). Get beefy power supply, at least 3A.
Now I understand, there is no simple answer but below is a suggestion.
No matter the solution, you do need a servo motor, to be able to remotely open and close the vent.
However you have one issue that people also have with automating window shades: even though a servo would physically move the object - you need to move it quickly by hand without messing up the servo itself (or the connection to it)*. One way to remove that concern is just to have the string instead disconnected from the fan and the vent, and instead connected to a smart switch that can be controlled by HA.
Set up a switch with a mechanism to handle the vents and the fan. Then, you can turn that switch on and off by both the string* or remotely.
*Note where I put the asterisks above. A requirement for both of these (or anything controlled by HA) is that when the state of anything physically changes, HA needs to be kept updated on whether or not the vent and fan are open or closed/on or off - so it always shows the correct state within HA.
In your design to make sure it is bullet proof, you’ll have to take into consideration scenarios such as someone changing their mind and pulling the string again to close the vent when it is still in the process of opening, etc.
I guess you mean the issue is to allow for a manual override. I can simply do that by having the string split in two parts between the fan and the horn attached to the servo. That way, the override doesn’t move the servo. Does that indeed respond to your concern?
It wouldn’t move the servo anyway, you wrote it’s pull-and-release.
Servo returns to release position (loose cord) and cord is available for manual pull.
If you want to keep it in synch without sensor, add a push button for “manual” use, so esp doesn’t loose the position.
