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Reverse polarity switch with delay for DC motor

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Postby bad coffee » Fri Mar 05, 2010 8:15 pm

So I finally built a prototype door, with everything included.

Sometimes the circuit works.

Door closed -> door open works. Sometimes. (see below)

Closed-> open.

If full travel (8seconds,) The door ping-pongs 100% Open-close-open-close until I power the circuit down.

If short travel (~4 or less) the door stops closed most of the time. The rest it goes into ping-pong.

Sometimes if I start it with the door open, it closes, and immediately opens, then stops when it hits the limit switch.

I swapped out the "closed" door switch, and nothing changes.

Do I have a bad component?

Do I have something wired incorrectly going into the 556 chip?

Could it be the switch? It's an Omron NO limit switch.

Do I need to change the cap to a different value?

Thanks
B
Last edited by bad coffee on Fri Mar 05, 2010 8:48 pm, edited 1 time in total.
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Postby pebe » Fri Mar 05, 2010 8:33 pm

You are using a NC switch, and that's the wrong type. As I said in the description:
This is how it operates. Assume the arm is at the top. The limit switch S4 was closed when the arm hit the top stop.

So you need a Normally Open type.
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Postby bad coffee » Fri Mar 05, 2010 8:41 pm

Pebe,
It's a SPDT, NC. I'm wired to the NO side. Sorry, that's a typo.

Any other ideas?

If the switch ALWAYS ping-ponged, I'd say I got somthing wired wrong. But if I set the door halfway closed, then hold the full open limit switch and release once I start it, the door hits the close limit switch and shuts off. So the circuit is almost working.

B
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Postby pebe » Sat Mar 06, 2010 3:45 pm

If you set the door at mid position and switch on the motor will not move because both 555s will have triggered and there will then be 12V on each end of the motor. That is not a condition one would normally encounter in the real world and I have added nothing in the circuit to guard against it. If it happens, just close one of the limit switches, and the motor will start.

Regarding the 'ping pong' ing. It sounds like you have static pulses from the motor leads being picked up on the Trigger pins. Make sure the 100nF caps are fitted as close as possible between Trigger and Vss (0V) pins.
Also keep the motor leads well away from the Triggers.

How have you constructed the circuit? Can you supply a photo?
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Postby bad coffee » Sat Mar 06, 2010 4:46 pm

Here's the setup, sorry for the awful phone pictures.

Door opener:(pics really big so I didn't want to link them)
http://www.bad-coffee.com/pics/door1.jpg

Top side of board
http://www.bad-coffee.com/pics/door2.jpg

Bottom
http://www.bad-coffee.com/pics/door3.jpg


Here's my ghetto drawing.
It's bottom view, Solid black lines are jumpers underneath, dotted lines are jumpers topside.
The relays at the top, the coil is on the right, contacts on the left (top connectiors are common)

Circles are solder 'glob' pads underneath.

Image

The motor is really close to a switch, so that might be the problem. I'll try moving the switch and see if it helps. However, it was the switch far away from the motor that wouldn't actually trigger the limit stop.

Thanks for the help.
B
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Postby pebe » Sat Mar 06, 2010 5:21 pm

There is a small change I would make to the wiring layout. But first.
What are you using for a power supply? Is it well smoothed?
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Postby bad coffee » Sat Mar 06, 2010 5:36 pm

I'm using a 1200MA wall wart I had around. I thought it was regulated, but I just checked and it's not.

I'll look around and see if I can find a regulated one.

What change to you propose?
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Postby pebe » Sun Mar 07, 2010 11:50 am

A likely cause is false triggering of the 556. As the board is wired at the moment, pin7 of the 556 receives its supply via the long wire from X to –Battery. The wire also feeds the relays and the motor. The ‘earthy’ end if the cap C1 is taken into the middle of that wire at Y. The higher impedance of the wire at that point makes the Trigger pin more susceptible to voltage spikes on that wire and from capacitive pickup from the O/P pin next to it.

You should provide a more direct connection for C1, and feed the –ve supply direct to pin7 by wiring it as shown.

The circuit is not fussy about a stabilised supply provided it is reasonably steady. If there is still a problem, fit a 470µF 25V capacitor as close to pins 7 and 14 (supplies) as possible.
Attachments
556 mod.GIF
556 mod.GIF (25.36 KiB) Viewed 124775 times
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Postby bad coffee » Mon Mar 08, 2010 1:43 am

Pebe,
Thanks for the help. I'll do the mod when I get back into town (I'm away on business this week,) and let you know how it goes.

B
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Project related to Reverse polarity switch with delay for DC

Postby afif3011 » Sun Mar 14, 2010 1:44 pm

Pebe,

Im trying to do the same project Reverse polarity switch with delay for DC motor but I need to change the 555 timer to 8051 microcontroller to program the delay rotation. Can i simply replace the 555 timer to 8051 microcontroller based on the circuit that you post.

The details of my project:
1) Im using power window motor
2) The circuit is collaborated between 8051 microcontoller and potential meter.
3) Basically the potential meter function is to detect the current position,
so when the motor move in clockwise direction the potential meter will detect the degree of current.
4) It does the same thing in reverse direction

i would like to thank you for your [banned] in dealing my final year project...
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Postby pebe » Mon Mar 15, 2010 6:36 am

afif3011,
The circuit was designed around using 555 or 556 ICs. It cannot be used for an 8051 microcontroller. Using an 8051 is like using a sledgehammer to crack a walnut - it has far too many ports and it needs external program memory and a latch.

If you want to use a microcontroller I would suggest you use one of the PIC range that has a built in oscillator. If you want to use a potentiometer to measure the degree of closure, then use one with a built-in A/D converter - you cannot use an 8051 because it doesn't contain an A/D converter.

If you wanted to drop the idea of using a pot and use limit switches instead, the PIC 12F629 would be easy to program and would do the job easily.
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Postby bad coffee » Tue Apr 27, 2010 7:56 pm

Pebe,
I rebuilt the circuit today, and the same thing was happening on one side. (It would hit the limit switch and start back the other way, then stopping once the limit switch was released.)

The other side worked great. Hit the limit switch and stopped, and started back once the circuit was powered down and back up again.

I swapped to a different 12v motor I had lying around and the circuit works perfectly. I'm going to go back and try this motor with the old circuit (I build two.)

Thanks again for all the help!

B
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Modifications for chicken coop design

Postby brettgilbert77 » Tue Jun 08, 2010 4:55 pm

Hi pebe, thanks for replying.

I'm trying to create an automatic door opener for a chicken coop, but am a complete novice to electronics so am learning as I go. There seems to be lots of information out there, but nothing definitive.

I've seen some ideas fo light sensor only circuits, but am worried that during the summer months the door would open too ealy in the day/late at night.

What I'm hoping to do is have a 12v DC motor activate based on a timer, or a light sensor (photo resistor based circuit) and turn in one direction until the door mechanism reaches a limit switch which stops the motor.

Then have the motor turn in the other direction when the light sensor/timer activates it, thus closing the door. Again a limit switch could stop power to the motor allowing for the use of different sized doors.

Perhaps a 3 way switch could select timed/automatic(light sensor)/manual operations with the later being push buttons to open/close the door on demand.

I was thinking it would be good to have maybe a red LED and green LED for Open and Closed status of the door. that way I could see at night if the door has been closed.

I'd like to encorporate a solar charging unit for the battery too, so I don't have to worry about them.

I think I might have found a simple solution to the timer here http://www.reuk.co.uk/Convert-Digital-M ... oltage.htm so could use ths as the timed switch.

If you have any circuits that may be of extra help I'd really appreciate it. Any advice on the motor to be used is welcome too, I have some salavaged motors, including stepper motors.

Feel free to tell me if this is overkill/over engineering the entire thing or if I've missed something important.

Regards,

Brett
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Postby pebe » Thu Jun 10, 2010 2:32 pm

Hi Brett,

The circuit given earlier in this thread would probably be OK for you. When the timer is off no battery current is being used. But switching the supply that way needs a timer switch that is on for at least as long as the door is opening so it would be no good for a momentary manual push button.

If you want, here is another circuit that will operate at just the touch of a switch, but the switch needs to make contact momentarily when the door is opened and again when the door is closed. A two way switch is shown to select timer or manual mode – just increase the number of ways to suit the number of switch types.

Both LEDs will be off when the door is moving, and the correct one will light when the door has opened/closed.

I cannot suggest a motor to use, because it depends on the opening mechanism. C3 and R5 may not be necessary but may be needed if there is a lot of electrical noise from the motor that may cause false opening. A stepper motor cannot be used.

As far as a charger is concerned, it would probably better to buy one of the types used for trickle charging car and caravan batteries.

Best of luck.
Attachments
555 Motor reverse 2.GIF
555 Motor reverse 2.GIF (11.25 KiB) Viewed 124732 times
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Postby ---snakey--- » Tue Sep 14, 2010 10:26 pm

Pebe,

Dunno if its my computer literacy but can't seem to see your circuit for the chicken coop door. Could you point me in the right direction, I fancy some mind melding mini project work :lol:

Cheers

Nick

UPDATE ---

Somehow the clouds parted and the sun came out. All clear now :-) Could you recommend power supply and motor? Something that I can source from maplins or similar? I am too trying to do a chicken coop door opener which in essence uses a pully/string system to raise and lower a vertical sliding door (such as one of these http://www.ascott.biz/acatalog/Electron ... eeper.html )


Cheers again

Nick
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