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

[Mindaugas]

hello all i am trying to create safety device witch will stop blind from going down if something is in the way
motor i use is somfy 30rts 24v dc dry contact control i did some test connected motor with dc current tester and check current then blind going down it was 160 mA then blind going up it was 540 mA and then blind going down and hits chair and all blind weight held by chair not motor current goes up to 250 mA so i think how to get it once current goes to 250 mA from 160 mA blind to drive up instead material overlapping and damaging everything another idea is to try use FSR resistor
to measure blind and bottom bar weight and get it to switch up once blind weight resting on any optical

 

[Alec_t]

IdmountabaralongthebottomedgeoftheblindwitheachendofthebarsupportedbyarespectivemicroswitchwelcometoEPpleaseuseproperpunctuationinanyfurtherposts

 

[Osmium]

Safety edges = rubber strip which acts like a switch when compressed: http://www.edata.omron.com.au/eData/Safety_Edges.html

 

[KMoffett]

IdmountabaralongthebottomedgeoftheblindwitheachendofthebarsupportedbyarespectivemicroswitchwelcometoEPpleaseuseproperpunctuationinanyfurtherposts

OMGLOLROTFL!

Ken

 

[Mindaugas]

I don't like safety edge or micro switches because you need wiring and is difficult to hide it, I am thinking of using something witch works from electrical current
because then blind not going down because let say someone leave chair on the way, all weight of the blind is held by chair so motor runs free of load and current goes up because weight of the blind is not helping for motor to go down. I was looking in using smart load switch with current limit of 220 mA ,but problem is then blind goes up it takes 500 mA so I need this device to go on and of then blind goes up or down I think is about using same resistor diods and transistors with smart load switch but as I am new to electronics don't have idea how to put it together but I believe if I get it right it will be cheap and easy to install in my work place I have 1500 blinds and let say for 400 blind I need this protection and its 5 star hotel its have to be not visible

 

[Mindaugas]

then blind goes down it takes only 160 mA I believe is possible and not that hard to develop this safety future using this current differents because we know that weight of the blind drops current of motor then is going down weight of it helping motor to spin and we now what blind motor runs free of load takes 250 mA
because no weight is helping for it to go down

 

[KMoffett]

Can you provide a wiring diagram of the shade control? Are there automatic full-open and full-closed limit switches?

Ken

 

[Mindaugas]

here is picture from data sheet dry contact controlled motor you can set top and bottom limit with programing tool 24 v dc

 

[Mindaugas]

how do you think can it be done ? I already spend a lot of time staying up till 3 am thinking how to get it done but am short of electronics knowledge but as I can see separate components dose job witch I need just still hitting the wall

 

[KMoffett]

This is the switch you're using?: http://www.automatedshadestore.com/...Button_Decora_Wall_Switch_-_White-pid454.html
Looks like the "third party control" input terminals on the switch might be the way to interface a "shade-blocked" circuit.
I noticed on the data sheet that the start current is 1.8A, so this would have to be ignored in monitoring the motor current.

Ken

 

[Mindaugas]

no we use room control unit witch controls blind with relays is about 4 blind on one control circuit hmmm how about this electronic smart load switch http://electronicdesign.com/power/use-smart-load-switches-current-limit-protection it used to shut fan off then its blocked simular situation

 

[KMoffett]

Besides detecting and interpreting the motor current levels, you have to have your detector interface with the system. Could you point out what units you are using in your systems: https://www.somfysystems.com/file.cfm/Sonesse_30_Databook_newest.pdf?contentid=153429

Ken

 

[Colin Mitchell]

How dos the circuit detect end-of-travel?

 

[Mindaugas]

Hello Ken we don't use any of the interfaces from somfy. Motor is dry contact controlled, we control it with third party room control unit we have switches on the wall connected to room control unit modulator witch sends signal to something like Building management system controller and that controller controlling relays and relays controlling blind motors in this way we have extra functionality like let say guest is not in the room so we close blinds to prevent heat coming in he room from sun light

 

[Mindaugas]

Hi Colin I think its detects it from time lets say 10s going down will be bottom limit

 

[Mindaugas]

and Ken I take blinds apart have good access to motor connections so we can do it just before motor instead of switch because power and controls coming separate to motor

 

[KMoffett]

Yes you can sense the current just before the motor...but where do you get the power for the detector? And once detected what do you do?

Ken

 

[Mindaugas]

ok I think can be done using transistors if control side common is 6v dc and some one press button down its activates power for motor were in series lets say we put constant current diode then blind hits something current go up and diode cuts power or some other element and when we press up we activate another way for power to go without current limiting just need to find way to work with pulse signal

 

[Mindaugas]

another problem is how to get one transistor to switch another of so you don't have to ways power can reach motor

 

[KMoffett]

OK. Last night I thought that I would take a shot at a circuit. So bit by bit I add stuff.

Attach are two possible designs. Both untested, except in my late-night head.
Not knowing what your local and building automation interface is with the blinds, I use 24V battery and a DPDT/Center-Off switch for UP/OFF/DOWN control.

First is how to power a detection circuit. D1/C1/R1/C2/U1/C3 supply a DC voltage only in the DOWN function because of D1.

Second is how to detect the current. Obviously, voltage drop across a series resistor (R6) would do it.

Third is what to do with the detected voltage level. Since I've played with microprocessors, one with ADC inputs would do it. One ADC (R5/C4/ Pin 5) for the detected voltage and another ADC to read a reference voltage (R2/R3/Pin 6) to set the trip level. The micro could also implement averaging out noise and set time delays.

Fourth is how to cut off the motor in case of a blind jam. One solution (first schematic) was to use a relay with normally-closed contacts (RLY1). The micro could drive the relay with a N-MOSFET (R4/Q1). Second solution (second schematic) was a P-MOSFET (Q1/R7) driven by the micro.

D3 and D4 in the first schematic are steering diodes for the UP voltage configuration. D3, D4, and D5 do that in the second schematic.

Again, this is just my thoughts and in no way tested.

Ken