Cool. Just hope the chickens aren’t coming.
Many thanks to David for last week’s very informative discussion of his highly innovative and flexible mini-modular clixx_io system.
It would be good to have a command (double-press?) so that the door can be frozen at its current position.
For the mechanics of my sliding-door opener, I will try a standard curtain track, even if it needs some reinforcement to withstand the forces: it has a pulley at each end, and rope enclosed within the track (which will need to be cut and tensioned - maybe with an idler wheel as on a car’s fan-belt) . The rope would wind once or twice round the drive-shaft, or around a pulley on it).
Hi Michael,
Sounds like a good idea. I’ll come back next wednesday and we can keep going on it.
What are the dimensions of that bigger motor?? I guess it will fit easily
in a space of about 100mm between window and curtain. btw, you will have
noticed that curtain-control may be a very popular application, quite apart
from sliding doors.
Two buttons are needed - one inside, one out. Are there spare pins or
solderable-points?
An alternative to buttons, or maybe an extra, may be detecting
interruption of light-path near the door, as in entry-alert devices. That
may conflict with the double-click idea for arresting the motor. The
light-path would need to be a plane over the full 1500mm or so of the door,
so that at least foot, hand or head is detected. An audible beep would be
wise too - the screen door can be invisible, people do sometimes try to
walk through it. Very hard on the nerves, the head, and especially on the
screen door. (Are we re-inventing the logic here??)
I will be there Weds.
@PaulG will you open?? One does need to check 
@Michael and @clixx_io - I can open the Space tomorrow evening from 6.30 to around 8.30. Please let me know if you cancel.
Paul: I can’t make it tomorow night.
Michael: Not sure. They are not so big from memory 10x6x3cm
I can come back wed 22nd.
Paul, can you open for the 22nd? Who can put it in the calendar?
The type of motor that I was suggesting is here. It’s an automotive window regulator. (Sadly the engine in this isn’t working - maybe it can be fixed - it was in the throwout bin at a friends business).
The good thing about it is that it drives a cable in a push/pull arrangement. Which could easily be adapted to a sliding door.
Here’s a link to a (new) (cheap-chinese) (maybe-3-uses-only) one: http://www.aliexpress.com/item/Universal-power-window-motor-for-auto-electric-window-regulator-EQ153-motor-Free-Post/2018648292.html
As OP have mentioned, Oatley-Electronics also have suitable parts.
I will bring the one that I have along on wednesday anyway. I’m sure we will get something working.
“Here’s a link to a (new) (cheap-chinese) (maybe-3-uses-only) one.” … well it expired before it was linked?! 
Yes, car window motor is a clever option. Inconveniently - there are no car-wreckers nearby.
I will bring a curtain-rail for
Two buttons are needed - one inside, one out. Are there spare pins or solderable-points?
Always 
An alternative to buttons, or maybe an extra, may be detecting interruption of light-path near the door, as in entry-alert devices. That may conflict with the double-click idea for arresting the motor. The light-path would need to be a plane over the full 1500mm or so of the door, so that at least foot, hand or head is detected. An audible beep would be wise too - the screen door can be invisible, people do sometimes try to walk through it. Very hard on the nerves, the head, and especially on the screen door. (Are we re-inventing the logic here??)
I will bring some PIR movement sensors tonight. I think they would be what you want.
I will be there Weds.
Same. Seeya’s tonight.
Update on my project to automate a very heavy (double-glazed) sliding-door. I found a car nicely nearby, kept for parts by the owners. So I have a nice free shiny automotive window regulator now, with three more there if this works out. It is worm-drive, may not open the door fast enough without modification.
Another option is a battery drill. Noisy and large, and less convenient, but good torque.
I need to decide on mechanics and then move to the logic and safety issues.
I’ve been slowly writing a function to control the motor using software PWM (Pulse Width Modulation).
None of the functions that I could find would allow me to turn on a motor for a percentage of power for a given number of seconds+1/10ths of a second so I wrote something myself that hopefully can make it easier to control.
Anybody know a good way to insert debug/test hooks in the code?
/**********************************************************************
* PWM write to a GPIO Pin
*
* This is software PWM function that oscilates a pin at a particular
* percentage value for a time measured in 1/10ths of a second.
*
* @param onpercentage - A value between 0 - 100 representing the number
* of on cycles in 100 for the pin to pulse. A
* value of 10 will give a 10% duty cycle.
*
* @param seconds - number of seconds for the function to run
* @param deciseconds - number of 1/10th second units to run.
*
**********************************************************************/
void clixxIOGPIOPin::pwmWrite(short onpercentage,int seconds, int deciseconds)
{
const short skip_marks = (100 / onpercentage) - 1;
unsigned long ds = (seconds * 10) + deciseconds;
for (unsigned long dc = 0; dc < ds; dc++)
{
short e=skip_marks;
for (short d=0; d<100; d++)
{
this->digitalWrite(true);
delay_ms(1);
if (e > 0)
{
if (e-- != 0)
{
this->digitalWrite(false);
}
delay_ms(1);
} else
{
e = skip_marks;
}
}
}
}
The main reason is that you might want to start the motor at 30% for 1 second, increase the speed to 60% for three seconds and then slow right down at the end to 10% for the last two seconds.
fwdpin.pwmwrite(30,1,0);
fwdpin.pwmwrite(60,3,0);
fwdpin.pwmwrite(10,2,0);
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I am negotiating a proverbial bump in the road, having forgotten that, because the wire rope to open/shut my sliding door would need several turns around shaft, to gain traction for accelerating the rather heavy door, the rope has a helical path on its drive shaft, and moves back and forth on the shaft as door opens / closes. Thus the car window mechanics is not suitable, as it cannot be adapted for a 1200mm movement of the door, being set up for the 450-or-so mm span of a car window at most. Maybe I print a drive-pulley for the Toyota window gear, about 80mm diam. Is it feasible to print it with a helical groove with pitch of 1.7mm and depth 1mm or so on the pulley? A drill may be a more suitable motor, including the chuck, it has a slip-mechanism that would be useful as a safety feature. I will come tomorrow anyway.
Hi Micheal,
btw, Here’s a picture I found of a commercial unit that uses rubber-timimg-belts as a mechanism.
I found a candidate for the rubber-timing belt on an asian website: http://www.aliexpress.com/item/free-shipping-10meters-GT2-Rubber-Timing-Belt-6mm-width-10m-length/1487697793.html
See you tonight.
EDIT: 6mm probably won’t be wide/strong enough.
I suggest going to 15mm or more: