Would like to convert a DPDT switch...help!

[swedespeed7]

Hi guys,

I'm kind of poking around in the dark here, but hopefully someone can help me out. Here's the deal:

I have a DPDT rocker momentary switch that controls a 12V motor. Press and hold the switch one direction, the motor opens a door until it's all the way open. Vice versa, door closes until all the way closed. Opening/closing takes about 3 seconds.

If the switch is kept depressed in either direction, the motor will continue to receive power and would most likely burn out eventually.

My goal is to convert the momentary rocker switch to a single push-button switch. For example, the switch is pushed and the motor operates until the door is all the way open. Press it again, motor closes the door all the way.

I'd like to accomplish this without having to modify the motor or door.

Is there a way to use relays to accomplish this? Something else? I'm somewhat familiar with the standard 5-pin relay but that's it.

If this is possible, what type of switch should I use?

Thank you in advance!

 

[davenn]

hi there
welcome to EP

to detect when the door is fully open or closed, you would need limit switches on/near the door frame/motor

Then the rest is relatively straight forward

Dave

 

[BobK]

You could also possibly detect the limits electronically by detecting an increase in motor current when it hits the end of travel, assuming the mechanical setup will not be damaged by doing that.

Bob

 

[swedespeed7]

You could also possibly detect the limits electronically by detecting an increase in motor current when it hits the end of travel, assuming the mechanical setup will not be damaged by doing that.

Bob

That sounds like something I'd like to do. How can I accomplish this? What parts are required?

Thanks guys!

 

[BobK]

How is your electronic knowledge and skills?

Bob

 

[swedespeed7]

It's more than average I suppose, but that's not saying much these days!

 

[BobK]

Okay, easiest way would be with a microcontroller. Do you have any experience?

Bob

 

[swedespeed7]

Okay, easiest way would be with a microcontroller. Do you have any experience?

Bob

No I don't.

 

[BobK]

How about soldering components on a perfboard?

Bob

 

[swedespeed7]

How about soldering components on a perfboard?

Bob

Soldering yes, board no.

 

[hevans1944]

This sounds like overkill for "automating" a switch that operates intermittently for three seconds! Just tell folks to release the switch after the door opens or closes, maybe upon penalty of whatever if they fail to do so.

My ancient Sears garage door opener operates exactly as you describe: push one button and the door opens. Push it again and the door stops (usually). Push it a third time and the door reverses direction and closes. No limit switches. If the door hits an obstacle it stops. I think it must have a circuit that senses motor current (AC motor though, not DC) sudden increase to detect limits of travel and obstacles.

You can do this too with a Hall-effect DC current sensor. Digitize the Hall sensor output with an Arduino or a PIC or similar microprocessor and determine what the current increase is at the limits of travel. Set a threshold somewhat less than that but greater than the normal motor current. Connect a push-button to one of the μP digital inputs, a pair of relays to two of the outputs (one for power, one for direction), add a few lines of code and you're done. There is another recent thread here that has a link to a nice Hall-effect DC current sensor. Or Google is your friend.