FABLAB Delhi
Dhananjay V. Gadre
List of Projects
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Flickering Candle
Electronic Batteryless dice
Led Pen
Electronic Birthday Blowout Candles
Audio Spectrum Analyzer
Twilight Switch
Flickering LED candle
Flickering Candle
• An LED can be used to mimic candle light.
• The trick to mimicking a candle lies in recreating
the way a candle flickers.
• The candle flame sways randomly (or so it
seems) and sometimes the intensity of the flame
seems to vary with air currents.
• While using an LED to behave like a candle, it
may not be possible to make the ‘flame’ sway,
but what can certainly be achieved is the
random variation of intensity
Concept – Theory of Operation
• For randomization, a particular type of
pseudorandom generators known as linear
feedback shift registers (LFSRs) have
been used.
Concept – Theory of Operation
(contd…)
• An LFSR is a shift register the input to which is
the exclusive-or (XOR) of some of the bits of the
register itself.
• The bit positions that are used for the XOR
operation to yield the input bit are called taps.
Implementation
• The pseudo-random number generator and the
intensity control of the LED have been
implemented using AVR ATiny13 microcontroller.
• The circuit has been split into two boards: the
controller board and the LED holder board.
• The LED holder board is placed on top of the
controller board so as to minimize the footprint of
the circuit board. This way it occupies less space
and can easily be packaged in a tube to give a
feel of a candle.
The Project Hardware
Electronic Batteryless dice
Electronic Batteryless dice
• There has been a lot of interest in muscle
powered electronic devices.
• The muscle powered voltage generator is based
on Faraday's law, consisting of a tube with
cylindrical magnets. It is also called Faraday
generator.
• Instead of a traditional dice, it is nice and cool to
use an electronic dice that is powered from
faraday generator.
• Moreover, since the faraday generator produces
power only when it is shaken, it mimics the
shake of real dice.
Concept – Theory of Operation
• Faraday Generator produces AC output
voltage. So, it is rectified and then filtered
by a capacitor.
• The capacitor voltage is then regulated
and used to power the electronic circuit
required for the dice.
• The dice is mimicked by seven 3mm LEDs
arranged in the traditional pattern of dots
on the dice.
Concept – Theory of Operation
(contd…)
• The pulsed output from the generator is
also fed to the microcontroller to determine
whether the tube is being shaken or not.
Implementation
The Project Hardware
LED pen
LED pen
• You might have seen advertisements by battery
manufacturers in which images are drawn in the
air and captured by a long exposure camera
• Now imagine, instead of a flashlight, you have a
multicolor LED pen with which to draw these
pictures and image?
• This is exactly what this project achieves.
• Such images and pictures are called light
doodles.
LED doodles
Concept – Theory of Operation
• The LED used is a RGB LED.
• By the use of PWM on each color component, It
can be used to generate multiple colors.
• Sixteen colors have been selected in this project.
• There is an on-off switch to change the state of
the LED and a potentiometer to change the color
of the LED.
• The output of the potentiometer is fed to the ADC
input channel of the microcontroller.
Implementation
The Project Hardware
Electronic Birthday Blowout
Candles
Electronic Birthday Blowout
Candles
• The Electronic Birthday Blowout Candles
emulate the conventional candles (arranged on
a birthday cake)
• LEDs have been used as small candles.
• They flicker randomly to give the appearance of
real candles.
• Moreover, they also go off in a random fashion
when someone blows air on them.
• When all the LEDs have been extinguished, a
tone of “Happy Birthday to you” is played.
Concept – Theory of Operation
• 20 LEDs have been connected in a
multiplexed fashion.
• Their intensity is varied to give a flickering
effect.
• The sensor part consists of a thermistor in
series with a resistor.
• The thermistor is also in thermal contact
with a high power resistor(1/2W) which
raises its temperature above room
temperature.
Concept – Theory of Operation
(contd…)
• When user blows on it, the thermistor gets
cooled which increases its resistance.
• This is detected by the microcontroller and
random number of LEDs are extinguished.
• The controller used is ATmega8.
The Project Hardware
Audio Spectrum Analyzer
Audio Spectrum Analyzer
• Spectrum Analyzer made is based on 5
FIR filters implemented in ATmega88
microcontoller.
• The audio range from 200 Hz – 9600 Hz
has been broken down into 5 subbands.
200 – 600 Hz
600 – 1200 Hz
1200 – 2400 Hz
2400 – 4800 Hz
4800 – 9600 Hz
Twilight Switch
What is the Twilight Switch?
• An AVR implementation of a fully
autonomous sensor-less switch for
outdoor artificial lighting that operates at
twilight time
• Project addresses the twin concerns of
road safety and energy conservation
• After one-time configuration, automatically
calculates and operates a relay/switch at
twilight times.
Concept – Theory of Operation
• The current locations geographical coordinates
and local time are required. These are
configured one-time.
• A clock is maintained with the AVR’s 16 bit timer
and crystal oscillator.
• Twilight time is calculated with precise formulae
– a modified form of the Sunrise Equation.
• A switch is operated to turn on lighting at end of
twilight time and turn it off at beginning of twilight
time.
Implementation
• The Twilight switch code, consisting of precise
twilight time calculations, UART configuration
interface and onboard timekeeping, fits on an
Atmega8
• A configuration and display terminal (via UART),
also on Atmega8, with LCD and keypad
interface, eliminates the need of a PC for
configuration.
• A working prototype is in operation at CEDT,
New Delhi
The Project Hardware
The
Configuration
Terminal
Configuration
Keypad
Backup
Battery
Twilight
Switch
Review of Salient Features
• Calculations happen once a day; ‘tick’ is recorded every
8 seconds and switch is operated twice a day. The kit
stays in power-save mode rest of the time.
• The formulae are accurate to within  2 minutes for any
geographical location and time of the year. Maximum
error at poles.
• Crystal used for timekeeping gives a drift of 1 sec/day
because of temperature effects. We are investigating use
of a temperature-controlled RTC that gives a max error
of 2min/year.
• A transistor driver/relay may be used to operate a lamp
drawing power from a higher voltage source.