Download Sommar Lighting

Joule Thief Technology
The Contemporary Home
Free standing Lamp/Light
Brian P Smith
Embedded Electronics Designer
The Task
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You are asked to design and develop either a freestanding lamp, a wall lamp or a
hanging lamp suitable for either indoor or outdoor (patio/garden) use.
The lamp should utilise LEDs and a USB or solar cell power source. We are particularly
keen to see ideas which explore different ways of controlling lights from simple on/off
to more complex remote control.
We would like this new range to be called “SOMMAR” which translates to “Summer”
and will need to be available for our summer 2019 season.
This range will need to be fresh and vibrant and appeal to a wide number of customers
both in this country and abroad.
We would also like your students to consider packaging in a typical IKEA style as well as
any necessary assembly instructions.
LEDs (Light Emitting Diodes) - 1
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LEDs are available in a wide range of colours, formats, and sizes
Single colour LEDs
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Bicoloured LEDs
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Red, Green, Blue, Yellow, Orange, Amber, Pink, Lilac and White
Red/Green, Green/Yellow
Tricoloured LEDs
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RGB (Needs a microcontroller), Rainbow (contains a simple colour sequencing chip)
LEDs (Light Emitting Diodes) - 2
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LEDs are available in a wide range of colours, formats, and sizes
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LED formats – LEDS are available in a range of ‘packages’
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PTH – Pin thru hole
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SMD – surface mounted device
LEDs (Light Emitting Diodes) - 3
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LEDs are available in a wide range of colours, formats, and sizes
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PTH – Pin thru hole
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2mm, 3mm, 5mm, 8mm, 10mm diameters
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SMD – surface mounted device
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2mm x 1mm, 3mm x 2mm, 4mm x 3mm, 5mm x 5mm
LED Arrangements
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LEDs are incredible versatile and often available in pre-made arrangements
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LED strips – these are made using
SMD LEDs (single colour or RGB)
along with protective resistors, they
are powered by 5V or 12V.
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LED ‘Bulbs’ – these are made using
SMD LEDs (single colour or RGB)
along with protective resistors, they
are powered by 12V or 240V (mains).
Powering LEDs
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LEDs need a particular voltage and
current for them to work correctly.
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Too little voltage and they don’t light up.
Too much current and they ‘burn out’
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LEDs needed a voltage between 1.8V
and 2.2V, white LEDs need at least 3V
to operate, and between 5mA to 30mA
to light up correctly, any more than that
and they ‘burn out’.
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To protect the LED from too much
current and to set the correct working
voltage we use a SERIES RESISTOR , the
value of which is found using OHMS
LAW
Power Supplies
USB Power supply
Solar Cell power supply
• The cheapest Solar
Cells generally only
produce about 3V and
100mA of current
under full sunlight.
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operate LEDs.
Storing Electricity
Rechargeable cells
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Simple AA (1.5V) cells can be charged
up using a Solar cell, using a simple
circuit:
Super capacitors
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A simple 3V power supply that doesn’t
use a rechargeable cell, but uses a
SUPERCAPACITOR
Cells vs Super-capacitors
Rechargeable cells (£2.00)
Super-capacitors (£0.80)
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Positive points
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Positive points
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Negative points
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Negative points
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Which Technology would you choose and why?
What options are there?
Power Supply
LEDs
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You have two power supply options
1. USB
2. Solar Cell
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Which type of LED will you use:
1. Coloured LED 5mm, 8mm, 10mm
2. White LED 5mm, 10mm
3. Rainbow cycling LED 5mm, 10mm
You will need to select an appropriate power supply and LED for your particular
situation
Once that is done you will need to select a suitable storage system – super-capacitors
are the recommended solution
For white and colour cycling LEDs some extra electronics will be required
For automatic switching on, when dark some extra electronics will be required
Automatic light switching
USB powered
Solar cell powered
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To automatically switch on/off the
lighting circuit, a light sensor circuit and
transistor will be required:
To automatically switch on/off the
lighting circuit, the solar cell is the
sensor and a transistor is required:
Elec-trickery
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One of the issues for low voltage systems such as 1.5V AA batteries and 3V Solar Cells is
that they cannot supply enough voltage to operate White or Blue LEDs effectively or
efficiently.
To over come that problem we can use a Joule Thief circuit, which uses
electromagnetic induction to generate a high voltage from a low one – this was
discovered by Michael Faraday.
The basic circuit is:
STEM How it works
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When powered up the transistor is switched on by a current flow through the left
hand coil, and creates a magnetic field.
When the transistor turns on it causes the right hand coil to switch the transistor
off, as a result the magnetic field collapse very quickly
This causes a large induced voltage to be produced which powers the LED, that
voltage only lasts a short time
The transistor can now switch on again and so the process repeats many times a
second.
As a result the LED is lit for a short time, but 100’s of times per second, and to us it
appears to be on all the time.
Lets make one!
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The first task is to wind our own
inductor, to do this we need a small
ferrite core and two 200mm length of
solid insulated wire – Cat5 network
cable is the best to use.
1. Take the two strands of wire through the
centre of the core
3. Keeping the two wires together, make a few
more turns through the centre
4. Keep winding until you fit as many turns as
will fit in a single layer around the core,
typically 8-10 turns with thin insulated wire
2. Keeping the two strands together, wrap
them around and through the core again
5. Clip the wire leads down. Note that we have
two pairs of wires: one coming out the front,
and one coming out the back, and strip off
the insulation
Building the circuit board 1
1. Solder on AA Battery holder
3. Solder on the 2N4401 transistor
2. Solder on the 1K resistor
4. Solder on the LED ( two types of
white available )
Building the circuit board 2
5. Solder in place your inductor coil, ensure
the correct ends go into the holes marked 1
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6. Add a switch to your circuit using two lengths of
wire into the holes marked SW
7. Add your 1.5V battery, press the switch
and we have light!!!
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A 3V LED powered from a 1.5V
battery – thanks Michael Faraday
More Elec-trickery
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The Joule Thief circuit will work fine with White or Blue LEDs and all the other colours
as well BUT it will not operate colour cycling LEDs
This is because the need 3V DC and the Joule Thief circuit produces a pulsing DC,
which flashes the LEDs 1000 time per second (1KHz) approx.
We can fix that problem by replacing the LED with the following circuit:
The combination of the capacitor and diode smooth and rectify the pulsing DC to DC
that the colour cycling LED needs to operate.
Where next?
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Using this information you now should be able to start to work out which systems you
need to create the electronics for your “Sommar” light.
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You need to write up that information that is key to your particular idea along with any
other requirements so they can be investigated.
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If anyone is considering the use of remote control you need to let me know so I can
provide specific guidance on this method.