Electric roller blinds

Not with window blinds, but on my motorised projector screen I cut off the controller and replaced it with a Sonoff Dual, with open-source ESP8266 wifi firmware. I'm very pleased with how that turned out.

No direct experience but traditionally such things just had a reversible motor with limit switches at each end. Obviously you *could* use stepper motors, or have an encoder somewhere.

I think the ones I've seen either have limit switches, or you 'train' them to know when the top and bottom is. I assume they just dead reckon based on a timer to go to a position between fully open and closed.

Tempted to give the 35 quid pulley a go, just to see...

Theo

I think my mains-powered projector screen has a synchronous AC motor, so to move it to a desired mid-position could be very accurately done using a timer. (It has limit switches for top and bottom). I don't know whether any window blinds have synchronous AC motors...

Another way is to measure current and use a motor that can be stalled without damage for a few seconds. A lot of car windows use that system. Its cheaper than limit switches...

or stepper motor and count the steps?

FAR more expensive

a cheap DC can motor can be had for a dollar. And the cheaper they are the better as that kind don't show massive stall currents.

A resistor and a simple current sense chip is way cheaper than counting pulses.

Yes. Although if you have invested in any domestic blinds recently, a £50.00 adaptable control system, with potential for remote armchair operation is peanuts:-)

That's how our Swish electric curtains work.

Motor with pulley on one end of the track, timer-unit tells the motor to go the other way, it slowly drives it that way till the curtains stop and then the unit stops driving.

The only time it gets confused is if the track gets damp somehow (humidity / condensation?) and the friction goes up and it can then stop before the curtains are fully open / closed. Leave it a while and it has (so far, over 20 years), cleared itself.

I have repaired the main unit once, replaced the main smoothing cap but now the display has failed so we can't reset the time / open / close times but we just override it as required.

Apart from the partial opening option (that could be done manually?), I can't see why such a solution couldn't also work horizontally, although you may have to add some hard stops in the cord to stop it at the right points (automatic on a conventional curtain pair).

Cheers, T i m