Automate blinds (pulldown)

Projects General Guidance
1

Hello.

I'm looking to automate my blinds.


My blinds are similar to the one in the picture, the only difference is that I have 3 strings and I don't have that lift cord lock.

I'm thinking of using a stepper motor, as it's more precise and quieter(?), and some kind of pulley system, or a winch-like system.

When the blind is fully up (pulled down), it needs to stay there. The manual way of fixing it is to pull it down and then spin it around a piece of plastic, that is on the window frame. (I hung a weight in it to measure how much it would take to keep the blind fully up, a weight at 600grams was the least required weight, if that matters.)

How would I replicate that by simply pulling/winching? I'm thinking the motor might get ruined if it has to 'hold' the strings until it's set to release it(?).

I am quite unsure on what I need and I am an utter noob, so any help/advice would be greatly appreciated. Any "just google it" comments will not be approved, sadly. (I searched the forums here, but did not find any helpful information, really. The threads were old as well.)

Thank you for taking the time to read.

2

A stepper would need to be powered all of the time to hold the blind up. A motor with a worm drive gear reduction will hold position when unpowered and can give good torque for your winch. Use micro switches at top and bottom to sense full up and down. An H-bridge motor driver sized to the motor stall current to drive the motor forward and reverse. Use a fish scale to see how much force it takes to raise the blind to get a starting point for choosing a motor-gearbox.

3

https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20170423064146&SearchText=JGY370

jgy370 motor is about the right size to fit in the blind, but it will be too tall and will stick out.
if you need to get more power, you could add some belts.
AFAIK, the slowest (greatest gear reduction) is 10 rpm on the output.

4

Thank you for your replies and suggestions! I greatly appreciate it.

groundfungus, would you bother linking me a few examples of the items you listed? I'd most certainly buy the wrong things, lol.

dave-in-nj, would you happen to know how high of a sound the JGY370 gives away? I tried finding reviews about it but couldn't really find any mentioning sound... Would you say this type of motor would be best suited for my project? Because I couldn't find any videos on youtube where people used this kind of motor.

The whole thing doesn't necessarily have be within the blind itself. I thought I'd have a box on the wall somewhere where I'd stick everything into, or something...

Thank you once more.

5

I found a video of how I'd like my project to work! However, they use a DC motor rather than a worm drive.

Here's a link:

6

DC motor rather than a worm drive

Worm drive is just the power transmission and RPM reduction. Still need a power source (DC motor). Did you look at the link in reply #1?

The guy in the video uses a gearbox. If the reduction ratio is high enough, it will hold the blind up without power constantly applied to the motor. That is why I recommend the worm drive. One of the properties of the worm drive is that it will hold without power.

7

Rather than 2 limit switches (which requires wires both up and down the window), you can use a rotary encoder either on the drive shaft or the far end of whatever you are rotating. A 3rd option is a dual output worm drive since one side can be used to rotate the load and the other side spins the encoder.

I actually tried this 2 weeks ago very briefly and my problem was actually that there was no space inside the frame of the blinds to wind the strings since I didn't want to pull the cord up/down externally. I could solve the problem but I was just messing around for a few minutes. I'm going to pop the top off of the motorized blinds I do have and see how they wind the strings (they also have a lot more space).

8

when you use a gear, you change a thing called mechanical advantage. a 2:1 ration means your need half as much force to move. when you take a 1,000 RPM motor and gear it to 10 RPM you have a 100:1 ratio. that means, 1 pound could move 100 pounds. so these small gear motors do not need extra locks or brakes. a worm gear adds even more holding power as a force on the drive shaft only pushes on the worm. it does not spin it. so the worm gear adds a sort of self locking mechanism.

the video shows a simple method and one you should be able to make.
if you have any gear motors, you could test them.

9

that video shows a schematic, but only part of the schematic.
you should be able to get an LDR or light detecting resistor to detect light level. I have taken them off of failed driveway lights, but they are simple and there is a lot of help on them. goes to the analog pins for sensing.

you need to be able to sense the blind position. for this, there are dozens of ways. I would put a magnet on the blind and put in a reed switch. I bought 10 for $1.00 so I have these.
using any sort of rotary sensor would work, but IMHO, would be a bit harder to make to work at both the top and bottom. but once set, they would be reliable.

You should be able to make switches and the light sensor and play with those on the bench while waiting for your motor.

the motor will need an H-bridge. to allow you to drive it up and down as groundfungus mentioned.

The L298 is only a few dollars and can power almost any hobby DC motor as an h-bridge. VERY hard to find that have the current limiting pins brought out to jumpers.

I think this one has them on the side jumpers

you are not required to use them, but if you ever want to use them, you can.

there is a lot of examples on using this with a dc motor. make sure you google with the word arduino.

as for sound, once you put it in a box, the sound will be reduced.

I thought about the project and you could put all this into a second box that looks like the blind top box. very long and not much different in shape and color.

IIRC, these blinds have a single drive shaft. you might be able to put pulleys on that and eliminate the cord.

and that bring me to my quandary. I really like to have a manual override in case power is lost. in my perfect world, the cords would remain in place, un-touched, the motor would connect to the drive shaft AND there would be some mechanism that would allows a person to move the blinds and disengage the motor by just pulling on the ropes.

10

some project advise.

get the swiches of you your choice and get an LDR to play with.
add a few colored LED's to show you conditions and then play with lights and your hand over the sensor, etc.

get a bit familiar with the software.

keep asking questions.