I am trying to build shades, which should roll up or down, controlled by a DC motor. This motor can only be turned on or off (1/0 to turn it on/off). Also, it should be noted that the microcontroller behind this is a NI-SPEEDY with a daughter board that provides relay switches (not a range from -1 to 1).
The first thought was that when given a 1, it should roll it up then stop. And when given 0, it should be turned off and let gravity pull it down.
The problem is with stopping: I can't figure out a way to make it stop when it reaches the top. So I thought I should leave it on. But since it won't be able to rotate, I guess it might be damaged. How critical can such a thing be?
This is the datasheet of the DC motor:
Matsushita Electric, Japan 13.2V DC MYT-5AC8
A 12V battery is plugged to the daughter board of the microcontroller. The motor gets 12V DC, but I'm not sure about the current that is drawn to it.
The battery specs: 12V 7.5Ah/20hr
I tried keeping it plugged to the battery for a minute, and the heat produced was negligible, but I guess keeping it for more than that will fry it.
After trying almost all of the technically possible solutions provided, it turns out all the sensors we put were mechanically not possible to set up. They either were never activated or not reliable. Also, the circuitry involved seemed too complex (you might have noticed I'm a beginner) for two states (0/1). And since the controller is a requirement, it was not possible to use PWM or any other technique to control it via software.
All in all, this was very helpful, I learned a lot. Now let's just hope the motor will not be damaged by the time it is presented to the jury.