Buildings account for 20-40% of total energy use in developed countries. Window shades (or blinds) can help to reduce building energy use and improve visual comfort (i.e., reducing glare and increasing daylighting). A recent study showed that occupants are fairly inactive when operating manual roller shades (O’Brien et al. 2013) which could lead to increased visual discomfort and increased heating and cooling energy use. With aspirations to address issues associated with human inactivity I created an automatic motorized roller shade.
The motor moves the shade position depending on the of the location of the sun and the illuminance (i.e., amount of light) hitting a workplane (e.g., your office desk or kitchen table).
One of the best parts of this instructable is that you do not need to purchase a brand new roller shade to make this work. I will demonstrate how to retrofit an existing manual roller shade into an automatic motorized one using Arduino. The project used Arduino with the Adafruit motor shield to control the interaction between a stepper motor and a digital luminosity sensor.
This Instructable is structured:
- Introduction: What is 'good' shade position?
- Required supplies
- Code explanation
Step 1: What is 'good' shade position?
As the sun moves across the sky during the day, where should the shade be positioned? What if it is a very sunny day and there is too much light entering a space causing glare? What if it is an overcast day? This step tries to answer these questions by asking: What is 'good' shade position?
In general, we want the shade position to let in as much light as possible without cause any visual discomfort (i.e., maximize daylighting and minimize glare).
The picture above was taken sitting down at my office desk. It was an example of 'good' shade position because the shade was positioned so it was blocking direct sunlight yet was still allowing maximum diffuse sunlight to enter into my workspace.
Sunlight can be broken into essentially two components: direct and diffuse. The direct component comes straight from the sun whereas the diffuse component is created when a portion of direct sunlight scatters due to molecules in the atmosphere.
This project aims to control shade position to always block direct sunlight when present and maximize the diffuse component entering the workspace.