Ceiling Projection Clock / Night light! by EDIV

Last crawled date: 3 years ago

Ceiling Projection Clock / Night Light
The idea behind this was to create a nightlight/clock on the ceiling so that my children knew what time it was in the night – and stayed in bed!
The idea is to shine an LED through a ‘cut-out’ of the time (hours and minutes) and focus this onto the ceiling to show the time. As the time changes the ‘cut-out’ is moved to show the new time.
To do this I decided to have 2 wheels, one for hours and one for minutes. Each holds 12 ‘cut-outs’/stencils, one for each hour (1,2.. 11,12) and the other for each 5 minute interval (0,5…45,55). At night it is probably not necessary to know the time with better accuracy than 5 minutes. (For smaller children who can’t read numbers then these could be changed to suns, moons and other shapes!).
Since the resolution of a (my) 3D printer is not so great I decided to make the text approx. 1 cm high on a ¬20*20mm tile which could be slotted into each wheel.
To focus/image this onto a ceiling a lens is needed above the clock. The lens must be strong enough to form an image on the ceiling – initial tests with ‘cheap’ reading glasses showed that these were not strong enough. It should be noted that here there is a trade-off between strength of lens, magnification and LED brightness. If the focal length of the lens is short then it will need to be placed nearer to the clock – this in turn gives a larger magnification and means that LED may need to be brighter as the image is bigger, but also allows a smaller lens to be used as it is closer to the clock before the light has diverged so far. Conversely, a weaker lens would give a smaller image on the ceiling, it would need to be placed higher above the clock and would need to be bigger to capture the divergent rays. (If it is too weak then there will be no image – or at least it will be above the ceiling!)
I then found some creditcard sized Fresnel lenses which were pretty good. They need to be placed ¬15 cm above the clock before the beam is too divergent and form a 10ish cm high image on the ceiling. They do however need a reasonably bright LED – I found a 1000mcd LED was easily visible at night and 10000mcd visible in the day!
To drive the clock just one motor is used. A 28BYJ-48 stepper motor chosen as it is easily and cheaply available – the advantage of a stepper motor is that you know exactly how far it is going to rotate for a given number of steps. To keep the maths easy I decided to use a gear with 36 teeth for the large wheels. Since there 12 hours in the day and 12 five minute intervals in 1 hour then it must move 36/12 = 3 teeth at the time. The gear on the motor has 8 teeth, thus it must move 3/8s of a full turn for each 5 minutes. The gear box on my stepper motor had a gearing down of 1:64 – thus the number of steps could be calculated.
For the same reason the minute wheel has 3 teeth to drive the hour wheel forward by 1/12 of a revolution for each turn of the minute wheel.
To drive the stepper motor the small Arduino Nano (clone) was chosen which would fit inside the clock. The stepper motor comes with a driver board which can be directly connected to the Arduino.
Rather than use the stepper library, the motor can easily be tested/driven by sequentially pulsing the 4 pins high. I found that the minimum pulse duration of 2-3mS was needed for smooth movement – below this the motion was erratic.
To avoid potential damage to the Arduino/PC USB port you should disconnect any external power and the power connection between the Arduino and motor driver before (re)programming the device
Assembly
Once the parts are printed and cleaned up. Slot the hour and minute tiles into the Minute and Hour wheels. Make sure they are the correct way round or the projection may be inverted!, also on the minute wheel the ‘20’ tile should line up with the 3 teeth.
The Rings then fit over the tile pegs to hold the tiles in. It may be necessary to drill the holes in the ring and use glue to stop it falling off.
The Blinkers can also be fitted at this stage. These block stray light from the LEDs reaching the ceiling.
Extension wires should be soldered to the LEDs and the LEDs slotted in to the 2 LED holders.
The circuitry should follow the attached diagram.
The bolt holes may need to drilled out with a 6.5 mm drill.
Note the is also a small (4-5mm) spacer/washers between the 2 wheels
The motor gear should push tightly on the motor shaft.
The LED holders should be pushed in last as they block the wheels.
If the plates do not fit tightly then they can be glued.
The only other noteworthy thing is the yellow peg with a piece of grey filament sticking out in the photo. This pushes against the hour wheel to hold it in position and allow it to “click” from 1 hour to the next. If it is not fitted then the wheel can spin freely and show the wrong time. Another idea was to push the filament against the blinker to stop the wheel spinning, but this has not been tested.
Additional components
2x M6 90mm long bolts
Lens approx 15cm Focal length, wd 84 cm
Arduino Nano or similar
Super/Ultra bright LEDS (5mm, 1000-10000mcd)
Stepper motor 28BYJ-48
Mini 170 Tie Point Solderless Breadboard
5V PSU (I wouldn't recommend running it from a USB port)
Alterations...
The Base can be extended upwards to hide the electronics/wires etc… Similarly a lid could be made - I intend to try it soon - now uploaded, although it is a bit bulky.
I found it is probably possible to remove the high lens holder by using stronger watchmakers magnifier -two will be needed (one for each wheel) and they can be placed much lower down. It may be necessary to change the LED angles so the 2 numbers do not overlap on the ceiling.
(The original idea was to have a projection clock onto the ceiling and a shadow clock point horizontally through the clock. The wheels were drawn up with hour numbers and minute indicators
)
Motor Info:-http://www.instructables.com/id/BYJ48-Stepper-Motor/https://arduino-info.wikispaces.com/SmallSteppershttps://grahamwideman.wikispaces.com/Motors-+28BYJ-48+Stepper+motor+notes
To create the gears I downloaded and used Gears 3D Print (https://gears-3d-printer.en.softonic.com/ ). This creates STL files of the gears which can then be scaled up/down/editted in a CAD program.
http://www.instructables.com/id/Make-an-accurate-Arduino-clock-using-only-one-wire/