Servo-blinds automation


#1

Hi, as part of my ongoing home automation project i am attempting to use a servo motor to open and close my blinds. in order to do so i need the servo to rotate for a preconfigured amount of time. i am aware that it is not the normal operation of a servo. dose anyone has some advice?


#2

Continuous servos are not fun to work with with something like that. I would suggest instead of timing it create a switch at the top and bottom so you know for sure when it is open/closed. This will keep your servos from burning out.


#3

Yep, and you’re going to want to make sure you have code underneath that quickly stops the servo when the limit switch is detected.

If you depend on Cayenne to do it, you’re going to be grinding gears for up to 5 seconds before the decision to stop is made and sent back.


#4

Servo’s are nice as they are a ‘one stop shop’ I find you can safely run a servo into the stop for a short period of time or run a CR servo until the blind is closed and let it humm for a few seconds without too much of a problem. Issue is if you Leave it there for minutes it is going to heat up burning the H bridge and or motor out. So you just need to remove the servo pulse train after x number of seconds or turn power off the servo supply.

How many rotations or what degree of a turn is needed ?
If it is a multi turn action needed then you could just use a modest powered motor gearbox, there are some great compact all in one gear head units around that are slow, almost silent and stall out at justt a few hundred mA. You could set this to ‘run’ for x number of seconds in either direction + a few seconds into stall as long as the motor gearbox is not too powerful !

I have made my own little tri state ‘H’ bridges that would run off Two IO Pins You can even use just ONE I/O pin and Hi = CW Low = CCW and Open / Hi Z = no go-stop. But I do not think Cayenne is into tri state control of the GPIO easily yet. This system is amazingly graphic and demonstrate operation of H bridge principal nicely. They light up amazingly as the LED’s are used to steer the bias current but also happen to just look cool. I even incorporated a 1 Ohm -ve return current sense resistor so this system can sense the end of the movement / cord / jam / stall by sensing the step voltage rise.

You can find these ideas as schematics and breadboard layouts in here:
https://picasaweb.google.com/113722269455296509901/OutputCircuits

~ Andrew