Reversing switches

[mikemwa]

I have a string on 2 pullies with a stop attached to it. There are 2 switches or some kind of sensors in the path. There is a gear motor attached to one pulley. I want to push the button and the stop will travel to one switch then stop. When the button is pressed again I want the stop to go to the other switch and then stop and so on. How would I wire something like this up?

I have attached a simple drawing of what I'm trying to do.

[mikemwa]

Any ideas out there? I didn't think it would be that difficult.

[redwire]

How far apart are the pullies?  Just thinking about using one motor with a lever attached to the outer hub and the  stop could be located in a slot that travels back and forth driven by the lever. 

The way I would approach would be to use a small microchip programmed to do the following:
1. with a button push send power to motor by making one of the output pins high and one low. May need to use 2 transistors with diodes to power motor.
2. When sensor 1 or 2 is tripped the microchip set the output pins low; set a condition i.e. "daylight"
3. When a button pressed, check condition if "daylight" power one direction if "night" set output pins opposite
4.  When sensor 2 is tripped stop power to motor; change condition to "night".
5.  Go to 3

[Hero999]

Any ideas out there? I didn't think it would be that difficult.

If it's that easy than why haven't you figured it out for yourself yet?

I don't know how you can do it because you haven't provided enough information.

What kind you motor are you using: DC, AC shaded pole/synchronous?

What components do you have at your disposal? This requires a state machine which isn't easy to implement with relay logic but is trivial with logic ICs or a microcontroller.

[mikemwa]

The pullies are about 5-6 feet away from each other.
The motor is a micro DC gear motor I just happened to have on hand. It also has an encoder which I haven't checked out yet. It is a motor from http://www.faulhaber.com/uploadpk/EN_1624_S_DFF.pdf. I think I got it from BGMicro. Any gear motor should work. This one is supposed to work on 6 to 18 volts but I've run it on as little as 1.5 volts. Takes very little current. It has a 141 to 1 gear ratio.
The project I want to work on is just to open and close long living room drapes with the push of a button. I can think of many other applications this would work on.
With the push of the button the drapes would open and stop when the one micro switch was pushed. Then when you push the button again the drapes would close.
In the attached drawing I just mentioned switches but I was thinking of micro switches.

[Hero999]

On second thoughts this is easy with switch/relay logic.

The motor can be reversed by exchanging the positive and negative connections. The simplest way to do this is with a DPDT switch. Normally closed limit switches can be used to disable the forward/reverse direction appropriately, so when the motor reaches the end of its travel it shuts off.

The trouble is a latching DPDT push-button switch doesn't seem to be a common part. If you can find one then good but you may have to combine a DPDT relay with a standard SPST latching push-button, although it's not ideal is it does draw a lot of power, even when the motor isn't running so is useless in a battery powered application.

[redwire]

What Hero999 described using the DPDT switch is about the simplest method to hook this up.  Of course you will need to hold the switch while it closes but hey, perhaps there are days when you only want the curtains partially closed.  Using your button method you could only be full open or closed.

[Hero999]

What Hero999 described using the DPDT switch is about the simplest method to hook this up.  Of course you will need to hold the switch while it closes but hey, perhaps there are days when you only want the curtains partially closed.

I suggested using a latching push-button so that wouldn't happen. A non-latching push-button would be no good here because the curtains would draw when it's pressed and open as soon as it's released or vice versa, if it's wired the other way round.

 Using your button method you could only be full open or closed.

No, to do that you need two SPDT push-button switches: one for open and the other for close or you could use a rocker swithc with a spring return to the centre position, like a car's electric window switch.

[mikemwa]

Thanks for the help. I will get a few parts and give it a try. I'll let you know how it goes.

[lyndon]

I designed this for someone who wanted to control the door to a chicken coop:


Now in his case, he had two timers, one to open the door (left) and the other to close it (move right) so I did this with two inputs. But you can use a toggle flip-flop to turn the inputs on alternately.

Switches LEFT and RIGHT are the limit switches at end of travel. They are normally closed and open when the door touches them.

It could be done easily with a microcontroller, but the gentleman I did this for could only wire up switches and relays, so that's what I did. I never built one, but he did and was happy with it.

Hope that helped.

[Hero999]

Thanks for posting your circuit.

Just a few suggestions:

Why use relays? Surely it'd be better to use DPST switches instead. Maybe if it's a large motor relays are the best way to go but in this case it's a small motor so could be switched directly. You could then use normally closed limit switches.

[lyndon]

If you're referring to my circuit, the reason for relays instead of a switch was the signal to start the motor came from an external timer; there was no person present to throw a switch.

If it was being manually controlled, the entire circuit could be simplified to a single DPDT-center off switch.