Need help to create safety device which will stop window blind going down if something is in the way

[KMoffett]

Just to throw a few more ideas in. I still like to keep it simple by only cutting into one cable.

BlindsStop-4 Moved D2 to make it more effective in protecting the input.
BlindsStop-5 Made Q1 do low-side switching of the motor power
BlindsStop-6 Used an optocoupler to activate the Stop function in the control cable

Ken

 

[Mindaugas]

I like blind stop 6, looks simple and not expensive to make. Good work mate now About more details. One of resistors is to drop voltage to supply chip another for getting voltage to digital signal to be able to read current, and capacitors is for levelling out jumps of starting current, diodes for not mixing voltiges. Did I get it right ? or close ? ))

 

[KMoffett]

You got the general ideas. So first you would need to find out if a transistor, as in the photo-coupler, will actually trigger the Stop function. Do you have the capability bench testing this? You would need a general purpose NPN transistor, a 10K resistor, and a 5V power supply.

 

[KMoffett]

To add a thought. I don't know the actual physical wiring or breakout box layout at each blind. You mentioned the possibility of installing this unit on each of 400 blinds. By cutting (?) and interfacing with both the two-wire 24VDC power cable "and" the 4-wire control cable, you add major time to a large installation project. When designing something you need to look at the big picture. Not only what seems simple to you on the bench, but what will be the most cost effective (labor?) in the end. This is the reason I added a diode (D1) in series with the 24V in my original circuit. It was to protect the unit in case an installer hooked up the 24V input backwards. Releasing the magic smoke. Simple to leave it out, but "stuff happens".

Ken

 

[Mindaugas]

Well its easy for me to get to control and power cabels, plus I need less components and control is 0 v so it must be ok thanks alot for your help now i just reading non stop and waiting for parts feel like electronics bug bit me thats cool project witch makes diffrence i hope that will work well

 

[KMoffett]

The electronics bug is terminal. It will keep gnawing away at you until you die. I was bitten at 12. I can't see an electronic device without wanting to know what's inside.

Ken