Here's our 3 hens (Edna, Dora and the bantam Dotty). Click for more photos.
Here's the chicken coop, with the addition of an automatic door opener. The chicken coop was purchased from Pets Station.
There are some (expensive) automatic chicken doors that are available for purchase, but I decided to design and make my own. You are welcome to copy or adapt the design to suit your own requirements.
Our chicken coop has a sideways opening door - this design could be applied to a vertical opening door. My plan was to use an alarm clock as a timer to trigger opening of the door. I found a suitable (cheap) clock at a home wares store. My requirements were simply that it was battery operated, and had a mechanical alarm - that is, it must physically ring bells. I assumed I could modify the mechanical mechanism to release a spring loaded door.
On opening the clock, I find that it uses a motor with an off-centre axle to actuate the bell ringer.
The alarm clock used two 1.5V AA batteries, one was for the clock, the other was used to drive the alarm motor (obviously switched by the alarm activation). Since there was switched power source, maybe I could replace the motor with a solenoid. It turns out that the available solenoids (e.g. this one) require a higher voltage (12V) and this would complicate things.
Instead I decided to go with a motor, and have it pull the door open using a string. The existing motor was suitable, but would require a gearing system to reduce the speed and increase torque. The gears I found already include a motor - which coincidentally is exactly the same model. Apparently it can operate at 3V or 1.5V - so I have the option of putting the batteries in series if I require more power. I decided with a bit of re-engineering the clock body could be used to house the automatic door opener. Here's the motor and gears attached to the back panel of the clock (note the gearing ratio needed some later mods).
The alarm clock rings the alarm for a very long time (an hour or so), and normally you would manually switch the alarm off. I'll add a micro switch to stop the motor once the door has opened fully. This shows the micro switch attached to the back panel.
That will cover opening the door, but how do I close the door. Due to the motor gearing it will be near-impossible to physically close the door. Instead I'll add a switch to reverse the motor. Taking it further, I add a three position switch, with manual open, close and auto (open) positions. This photo also shows the opening for the micro switch, and the door string.
Now it was ready to be wired up, here's the before and after shot. Not exactly neat, but it works.
Here's a circuit diagram showing what I've done - click to access a PDF version.
Update 5/9/10: The diagram now shows the wiring of the rotary switch.
I also modify the gearing ratio since the string was being pulled too fast. When the micro switch activated to stop the motor, there was too much travel and the switch would have been damaged. This image also shows mounting holes that will be used to attach the clock to the chicken coop.
This shows the door opener attached to the front of the chicken coop.
The string attaches to the door as shown. I've also got an adjustable screw to press the door stop micro switch.
This shows the door stop activated.
To protect from weather, I've modified a plastic container to fit snugly around the clock.
I've also added a large shield to prevent water getting down the back, or through the holes I use to mount the plastic container. Here's the completed door opener.
This video shows the door opener active. I'm starting it manually here, but under normal operation it will be triggered by the alarm timer.
We've currently set the door to open at 5:30AM. We did an investigation shown in the following video and found that the chickens are waking before 5AM - when it is still very dark. They don't seem too fussed with being forced to sleep in a bit longer. They also don't mind the sound of the motor.
Update: The wooden door frame has been replaced with aluminium to reduce the sliding friction (and avoid risk of the door expanding due to rain). I also intended to replace the door with a plastic one, but have not yet done so. The wooden door seems to slide alright, even with the dirt and muck that can collect there.
This photo also shows how I've spring loaded the door. This reduces door bounce when opening, plus helps when closing the door. The springs are only light, since I don't want to strain the motor. Battery life seems good so far, with 2 months on the same battery.
Update 1/4/10: I've replaced the first AA battery after almost 4 months of operation. The battery wasn't flat, I just didn't want to risk it not opening in the morning. Of course, I've only replaced the door motor battery, the clock is operating on the other battery.
Update 12/6/10: This chicken coop has now been replaced with a larger one. We're still using the same automatic door opener however it now operates vertically, see this posting for more details.