Simple delay for a relay.

[Yort]

Hello,I know this question has probably been answered a hundred times but I'm having trouble finding a simple solution. I've designed an apparatus that uses a 12v dc motor to open and close a sliding door for our dog. I'm using a DPDT relay that reverses the motor when it reaches the end of it's stroke to then close the door. What I need though is a simple delay, around 10 to 20 seconds before the relay switches the motor to reverse. Thanks for your help in advance.

 

[Dr_Doggy]

.......and maybe some trip sensors, so it don't catch his tail?

 

[KeepItSimpleStupid]

You should consider making sure the dog isn't in the doorway. I'd hate to see a squished dog.

A reliable way to do this is to use a delay on make relay. See SSAC Timers & Controls Home Page

 

[Yort]

Yes. I designed it with a load sensor (it's actually just a spring attached to a microswitch) that is sensitive to any obstruction as the door is closing, it works pretty good actually. I also put soft foam along the door and the jam just in case.

 

[KMoffett]

What starts the door opening?

Ken

 

[KeepItSimpleStupid]

Your supposed to put an RFID sensor on the dog/cat <G>

I think that's cool that you automated the door. Way back when, my dog had a brick archway for his entrance on the porch. Inside there was a door with a small window and a key lock. The flap was Ozite indoor/outdoor carpeting.

 

[KMoffett]

I think this will work. The RFID sensor will need to provide switch closure for Start. But, if the pooch sits within the range of the RFID sensor the door would keep cycling, up-pause-down-up-pause-down.... Then it would require a non-retriggerable monostable (another 555) between the sensor and the start switch.

But we're getting ahead of YORT's spec's.

Ken

 

[Yort]

What starts the door opening?

Ken

What I need is a sensor that is sensitive to a very defined area, about a 6 inch perimeter around the door.
I considered a lot of proximity sensors. My first thought was to use a IR motion detector, but then realized that it's range would be too wide, also they tend to be inconsistent. I also considered using a laser pointer and some reflectors pointing to a photo sensor, but decided that would be a little too complicated. I also was thinking about RFID which is almost a perfect solution, but since I'm trying to do this on the cheap i'm going to hold off right now for something simpler.

One thing about our dog is that whenever he wants in or out he will use his paw against the door - so I've decided to go with a vibration sensor. I haven't tried this yet, but we'll see how it works.

 

[Yort]

Ken,

thanks for this. I'm a mechanical engineer and have never made a circuit before but I'm eager to give it a try. In fact this little project of mine has got me so interested in electronics I'm thinking about going back to school. After spending a few weeks reading through this forum I have become fascinated with all of it.Two questions about this circuit, what is the delay? and what would I have to do to adjust the delay if necessary?


I appreciate your help.

 

[KMoffett]

Love to encourage enthusiasm!
A problem with proximity or beam-break sensors for "dog doors" is that any dogs...or cats...or raccoons!...would appear the same as your dog. I saw on a forum where a person made a 2-door "man trap" with a camera and image recognition software for their dog door. I would think there would be some minimal RFID hardware out there. I'll have to look.
The time delay is adjusted by the "potentiometer" R5 in my schematic. It's a variable resistor...like a volume control.

Ken

 

[Dr_Doggy]

what about a door mat that is sensitive, along with the rfid tag, it would be safe and secure and only open for the dog!