Automated Chicken Door

Automating the opening and closing of the chickens door reduces the mental payload and gives more freedom. It also makes the chickens more safe as humans might forget to close the door in the evening.

This is the very definition of progress: making life easier.

• http://www.instructables.com/id/Simple-Automatic-Chicken-Coop-Door/, tutorial
• http://www.chickencoopdoor.com/Products/products.html, ~200$, sash based
• https://www.chickendoors.com/, ~200$, hinge based
• And many others which can be found with your favorite search engine

As we try to reuse the tings we have and to buy as less as possible, the solution depends a lot on the material already available.

The total cost will only be around 5€ for the electronics. The drawback to this is the time demanding construction work.

The photo-resistor is a component which resistance depends on the quantity of light illuminating its sensitive area. During the day, its resistance drop to below 100ohms, while during the night, it is higher than 100Kohms.

The photo-resistor is placed in series with a fix-value resistor. The tension between both components (V1 on the schema) is higher during the day, and lower during the night.

The tension V1 is compared to two fix tensions V2 and V3. If V1 > V2, we consider the state to be “day”. If V1 < V3, the state is “night”. This is done by two comparators. Below is the output of both comparators depending on the voltages.

When the state becomes “day”, we want the door to open. This means, that the motor turns in one direction, but only until the door is open. This is why the limit switch S1 opens the circuit when it detects that the door is open. Similarly, the limit switch S2 stops the motor when the door is closed.

The H-bridge is composed of 4 BC547 transistors. It allows the rotations of the motor in both directions. When V4 = 6V, and S1 = closed, the upper left and the lower right transistors are activated, a current is flowing through the motor from the left to the right, thus making the motor turning in one direction. The two other transistors activate the other direction.

If the system is powered by a battery or a solar panel, an energy analysis can be done to be sure of the feasibility, or to be able to improve the design.

Parameters we need to know:

First we calculate the power drawn from the motor:

Then we can calculate the energy used by the motor to open the door:

This energy can be converted in W.h:

As the door needs to be closed as well, we just double this value to get an approximation of the total energy used by the motor per day.

We try to use resistors having high values to reduce the power they use (0.07mW in total). As a result, the component consuming most of the energy is the comparator. This is why we use the an ultra low power comparator draining as little as 0.05mA. More information can be found in the datasheet.

Energy used by the comparator per day:

We can see that it is the same order than the energy used by the motor. While the motor consumes 2000 times more power than the comparator, it is used only 20s a day, while the comparator is always on.

The solar garden lighting give approximately 4h of light every night. From this information, we can estimate the energy available per day.

The LED is powered with 1.2V and consumes 30mA. We can measure this with a multimeter.

The batteries of the garden lighting have a voltage of 1.2V (can be read on the package). As we want to power our system with about 6V, we have to use 5 garden lightings, and to connect their batteries in series.

Summary:

We are happy to see that more energy is available than used. The security margin tells us that after one normal sunny day, the system can work without additional energy for 59 more days, which is very good.