Sundial for the Visually Impaired

Blind & visually impaired individuals develop acute auditory and tactile senses which helps them interpret their surroundings in place of visual input.  Although they are quite rare, sundials adapted for use by the blind have been proposed and even built in the past.  This design attempts to rejuvenate this application by delivering a modern & 3D printable adaptation.  Note that this version of the design only applies to users in the northern hemisphere.  A southern version will follow at a later date.

History

17th-century proposal by Jacques Ozanam
In his 1694 Récréations mathématiques et physiques, French mathematician Jacques Ozanam posed “Faire un cadran solaire auquel un aveugle puisse connaître les heures”.  His ingenious solution was a heliocaustic clock: a glass sphere filled with water focuses sunlight into a caustic curve, heating successive metal strips arranged around the sphere. A blind user could feel which strip was warm and thus tell the time by touch cnum.cnam.frCommission des Cadrans Solaires.

Modern realization by Claude Guicheteau
Drawing on Ozanam’s idea, Claude Guicheteau built a “cadran solaire pour aveugles” in April 2003. This stained-glass sundial is inscribed with raised Braille hour-markers on its dial plate. A user or guide can orient the gnomon by feel, and then read the hour by running a finger over the embossed Braille dots https://slideplayer.fr/slide/1157660/ 

Beyond these, most assistive time-telling devices for the blind are based on talking clocks or vibrating watches, rather than classical sundials. 

My Application - Summary

My design goal was to keep the solution as simple as possible & in keeping to a sundial's traditional function, without compromising on accuracy or ease of use.  I therefore opted not to use an Arduino or any complicated electronics.  The design only consists of a simple light sensor which activates a power gate to drive an active piezo element beeper.  The circuit is also cordless & battery-free, only utilizing a small 52x52mm solar panel as a power source.

Note that this design is essentially built upon two of my previous heliochronometer sundials which consist of the following main features:

1. an audible alignment alert which activates when the sun is properly aligned, as described in reference 1 (below);
2. a planetary gear system with a secondary minute dial, as described in reference 2. 

The position of the “sunspot” projected from the analemma slit determines the time & it is done without any visual confirmation, relying entirely on auditory and tactile feedback.  Braille is provided on both the main hour dial & secondary minute dial instead of standard numerals.

How was it Designed & how does it Work

Refer to references 1 & 2 for details.

A photo-transistor light sensor is located at the nodus reception point, with the analemma plate positioned at the opposite end of the alidade.  Note that this is not a typical configuration as far as most heliochronometers go since the analemma is directly facing the sun instead of the nodus.  Additionally, the alidade, nodus & analemma are completely shielded from any stray light, except for narrow slits which forms the shape of the analemma curve.  When properly aligned, sunlight will pass through these slits & reach the nodus sensor, which in turn activates a P-channel MOSFET to deliver power from the solar panel to the beeper. 

Parts to Print

You will need to download & print all parts in reference 1, but minus:

•  alarm_sundial_alidade_shielded.stl

You will also need to download & print all the parts in reference 2, but minus:

• Sundial-Clock-Hybrid_Hour_Dial_PartA.stl
• Sundial-Clock-Hybrid_Alidade_Disc_PartA.stl
• Sundial-Clock-Hybrid_Alidade_Disc_PartB.stl
• Sundial-Clock-Hybrid_Minute_Dial_PartA.stl
• Sundial-Clock-Hybrid_Minute_Dial_PartB.stl
• Sundial-Clock-Hybrid_Minute_Dial_PartC.stl
• Sundial-Clock-Hybrid_Hour_Dial_PartB.stl
• Sundial-Clock-Hybrid_Alidade.stl
• Sundial-Clock-Hybrid_Analemma.stl
• Sundial-Clock-Hybrid_Nodus_Arm.stl
• Sundial-Clock-Hybrid_Nodus_Hole.stl
• Sundial-Clock-Hybrid_Nodus_Tilt_Knob.stl
• Sundial-Clock-Hybrid_Alidade_Disc.stl
• Sundial-Clock-Hybrid_Alidade_Spacer.stl
• Sundial-Clock-Hybrid_Planet_Gear_Carrier.stl
• Sundial-Clock-Hybrid_Sun_Gear_v2.stl
• Sundial-Clock-Hybrid_Inner_Ring_Gear.stl
• Sundial-Clock-Hybrid_Hour_Dial.stl
• Sundial-Clock-Hybrid_Minute_Dial.stl
• Sundial-Clock-Hybrid_Minute_Dial_Larger_Text.stl
• Sundial-Clock-Hybrid_Planet_Gear.stl

You will finally need to download & print all the additional parts provided in the file section of this design. 

Assembly

Refer to the file sections under References.

Alignment

Refer to the file sections under References.

References

1. Alarm Sundial with an Audible Time Alignment Feature by 3DMason | Download free STL model | Printables.com
2. Heliochronometer Clock Hybrid Sundial - with Reading Accuracy Optimization by 3DMason | Download free STL model | Printables.com