Contents
- Light and other loads
- LED versus bulb
- Batteries excluded
- Dynamos
- Wiring
- Configurations
- Basic configuration
- Extended configuration
- Gadget: 12 mA 3-meter band receiver (fm radio)
- Gadget: 100-500 mA USB-cable (for MP3-player)
- Current limiters for LEDs
- with integrated circuit regulator
- 20 mA AC rear light with red LEDs and regulator chip
- with discrete components
- 40 mA DC pimped headlight with white LEDs and transistors
- 60 mA DC rear light with red LEDs and transistors
- Switching LED array
- 40 mA AC switching rear light with red LEDs and transistors
- Links
- Websites
- Mailinglists
Electronics lab (breadbord, multimeter and soldering gear,
an oscilloscope is not required).
1. Light and other loads
Lighting is the first thing to consider: a white or yellow headlight and a red
rear lamp, but much more is possible: light for map- and compass-reading;
electricity for radio, MP3-player, photocamera, mobile-phone, GPS, etcetera.
Most circuitry presented here involves current- and voltage-regulation
(to protect LEDs and capacitors).
1.1 LED versus bulb
See and be seen are different things. LEDs are perfect to get noticed by
other traffic (red LEDs at rear, white or yellow ones at front).
But to see in the dark yourself, a continous spectrum from a (halogen) bulb
is much nicer than LEDs. Even white LEDs exhibit a (discontinous) peak spectrum
and many colours may appear unnatural. Especially reading a coloured map is
much easier under a bulb than under monocromatic light.
2. Batteries excluded
Try to avoid batteries as much as possible. Even rechargeble batteries
require replacement after 2 or 3 years, and when you forget this, highly
corrosive fluids may leak out and ruin your equipment. Furthermore,
many batteries don't operate well at temeratures below zero degrees centigrade.
Batteries, they will be empty when you need them the most.
On a bike, there is no need for batteries: it just takes a dynamo and some
descent wires.
And to store tiny amounts of energy, for LED-standlight for example, or to keep the
radio playing for some minutes, I prefer supercapacitors
(also known as goldcaps or ultracaps). They are a bit expensive (perhaps because of the
gold?) but they last up to 40 years; they can be charged/discharged at least a million times.
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Two 5.5 Volt / 1 Farad goldcapacitors in series,
with zenerdiodes in parallel, in an experimental
regulator / charger circuit.
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Care should be taken not to overload or overheat supercapacitors. Zenerdiodes,
transistors (or regulator-chips) and rectifier (Schottky) diodes are required
when one wants to use them.
3. Dynamos
For the following applications (DIY-projects), either a
bottle dynamo,
which presses against the sidewall of the tire, or a
hub dynamo can be used,
for allmost any bicyle-dynamo is able to generate 3 Watts / 6 Volts.
Bottle dynamo.
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Hub dynamo (SON).
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Riding a hub dynamo, however, is much
more fun. It takes some more money and effort to have it installed but, at
daytime, when less illumination is required, you will have lots electricity in
abundance, to charge your gadgets, play loud music, etcetera.
I was able to buy two SON hub dynamos and have them installed from/by the
Bikeshop in Amersfoort (the Netherlands).
4. Wiring
Use thick, strong, paired, doubly-insulated wires (the type that is normally used for 240 Volts indoors).
Don't rely on rusty nuts and bolts
and the metal frame to conduct currents. In the following two configurations,
it is left up to you whether to ground the frame or not (SON advices not to
connect the frame at all to any of the electrical wires).
Thick doubly-insulated paired wires.
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Tie-wrapped wire to rear light.
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5. Configurations
I propose two possible configurations: the simple one may take just a single day,
the second may take more than a week to build:
- Basic configuration: 2 AC lights (bulbs and/or LEDs).
- Extended configuration: Halogen and LED lamps, standlight
(with goldcaps instead of batteries), switches under the thumb
and 5 Volt / 100-500 mA auxilary output.
5.1. Basic configuration
The basic configuration simply involves tie-wrapping a thick paired wire from
front to rear light (and from front light to dynamo) and you're done.
Rear light Front light
(AC) ============================= (halogen bulb)
\\
\\
\\
Dynamo
(6V, 3W, AC)
Basic configuration: AC wiring.
Ordinary 6 Volt bulbs can be used for both front and rear lights, but, at least
the rear lamp can easily be replaced by LEDs. Here are two examples of rear LED
lamps that can be supplied with alternating current:
And, when a rectifier bridge (+ smoothing capacitor) is added, the following front and rear lamps can also be used:
5.2. Extended configuration
Battery-free, stand-light (for 1 minute) and 5 volt DC regulated auxilary output
to charge/supply your gadgets (mp3-player, photo-camera, mobile phone, GPS, etcetera).
Watertight switches under the thumb, on the steer.
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Watertight aluminium dashboard with light-switch (right, under the thumb) and 5 Volt regulated
output (left), connected to a detachable FM-receiver module with earphones (bottom).
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When upgrading from the basic configuration, most wiring
can be left in place, it only needs to be connected differently: whereas
wires from front to rear lamp conduct AC current in the basic configuration,
DC is used in the extended configuration.
Switches, gold-
capacitors and
5 volt output
\\\\\
\\\\\ green = +11 V (max.) DC to LEDs
\\\\\ brown = 0 V DC to LEDs (ground)
\\\\\ yellow = AC to bulb
\\\\\ grey = AC to dynamo
\\\\\ white = AC to bulb
\\\\\ and dynamo
Rear light Front light
(red LEDs) =========================== (halogen + white
green = DC+ (11 V max.) or yellow LEDs)
brown = DC- \\
\\ grey = AC
\\ white = AC
\\
Dynamo
(6V, 3W)
Extended configuration: AC/DC wiring. As with the basic configuration, all wires
come together in the front lamp.
Besides two switches and a cinch-connector the dashboard contains a Schottky
rectifier bridge, two voltage-regulators and some goldcapacitors. There was
absolutely no room for a circuit-board. All components were simply soldered
together, using lots of heat-shrink tubing.
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| Dashboard prototype #1: Large 50 Volt (1000 microFarad) smoothing capacitor and 2 (1 Farad) goldcapacitors (11 Volt buffer).
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| Dashboard prototype #2: Somewhat smaller 50 Volt (470 microFarad) smoothing capacitor and 3 goldcaps (11 Volt and 5 Volt buffers).
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In the first prototype there was no room for a third goldcap to buffer the 5 Volt output.
But I noticed I developed the rather dangerous habit of switching off standlights while waiting for
traffic lights to keep the radio playing a little longer,... and then of course forgetting to switch lights back
on after waiting! (Radio draws only 11 mA whereas rear- and front-standlights draw about 80 mA in total.)
This was fixed in the second prototype by choosing a somewhat smaller 50 Volt smoothing capacitor (C1) to create
space for an extra goldcap (C9) as 5 Volt output-buffer.
Furthermore, in the first prototype a LM317 voltage regulator was used for the 5 Volt output.
The drawbacks of this chip are that the input voltage must at least be 2 Volts higher than
the output voltage, and that at least 3 or 4 mA must be drawn (unnecessary draining the supercaps).
In the second prototype, a discrete voltage regulator was used and, to limit the output to 5.2 Volts
at most, an extra zenerdiode (D10) was added.
BD 441 pinout.
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Discrete 5 Volt limiter (BD441, D9, R2, C7, C8).
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Diagram extended configuration / schematics dashboard.
Only when Slight or S5 Volt is switched on (or when both switches
are on), the dynamo is loaded: its alternating current is put through a Schottky
rectifier bridge (D1-D4) and a large 50 Volt electrolytic capacitor (C1) is charged.
When (almost) no current is drawn from the dynamo, it may produce rather high voltages.
Leftmost power transistor (BD441) limits the voltage to 11 Volts and two 5.5 Volt
supercapacitors in series (C4+C5) are charged.
When S5 Volt is switched on, the voltage is regulated down further, to 5.2 Volt
When the halogen bulb is switched off (or when it is broken or taken out), up to
500 mA can be drawn from the 5 Volt output. But with all lights switched on, the
5 Volt output can only deliver about 100 mA.
The red and white LEDs in the rear and front lamps require current-regulation,
which is discussed in the next section (6).
Below some 5 Volt gadgets are presented.
5.2.1. Gadget: 12 mA 3-meter band receiver
In a hardware-shop I found a FM-radio that costed only 3 euros. It contained
two 1.5 Volt button cell batteries. It furthermore gave monophonic output in
anti-phase on the earplugs. I tweaked it a bit: gave it a 5 Volt supply
and corrected the phase on the earplugs.
Cheap FM-receiver with new connectors and switch.
5 Volt / 11 mA FM-receiver put in a new watertight case.
The radio draws only 11 milliAmpere from the regulated 5 Volt supply. So it can
play for minutes with fully charged supercapacitors, when waiting for some
traffic-light.
5.2.2. Gadget: 100-500 mA USB-cable
...
1 red + 5 Volt
------- 2 white - data (not connected)
1 2 3 4 3 green + data (not connected)
------- 4 black ground
6. Current limiters for LEDs
When working with LEDs, it is more important to watch the current than the
voltage. Even when comparing individual voltage-drops of a large amount of
'identical' LEDs, many differences may be observed. When putting LEDs in
parallel, it is the best to choose (from a large amount) the ones that are
very close in voltage-drop.
Most red, orange and yellow LEDs need about 2 Volts, whereas white and blue ones
need 4 Volts or more. And since a bike does not produce so many Volts, I suggest
not to put white LEDs in series, but one can put 2 red and/or yellow LEDs in
series.
Below, several current regulators for LEDs are proposed and discussed.
6.1 Current limiter with integrated circuit
Voltage regulator chips like the LM317, LM150, LM350, etc. can also be used as
current regulators. One of the disadvantages of these LM-chips is that they
consume almost 2 Volt themselves.
Here is an example:
6.1.1. 20 mA AC rear light with red LEDs and regulator-chip
The following can be built quickly, merely as an emergency backlight, when you're in a hurry.
It is suitable for AC-power supply, up to 25 Volts so you can directly attach
it to your dynamo or front bulb. Schottky diodes (1N5817) are used for rectification,
because of their low voltage drop (i.e. fast switching).
You can use any of the LM150-, LM317- or LM350-regulator chips, and you can
take one, two or perhaps even 3 LEDs in series (using the same resistor R).
Cicuitry and prototype of 20 mA AC rear light with LM-regulator chip.
The LM-chip tries to maintain a voltage of 1.25 Volt over resistor R (see datasheets).
For 20 milliampere LEDs, the resistor-value is calculated as follows:
I = 1.25 / R
0.02 Ampere = 1.25 Volt / R Ohm => R = 1.25 V / 0.02 A = 62.5 Ohm
20 mA AC rear light prototype-board rear.
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20 mA AC rear light prototype-board front.
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These LM chips are heavy enough to drive more (20 mA) LEDs in parallel. Of course,
when one doubles, triples or even quadruples the total current, R has to be adapted
accordingly (divided by 2, 3 or 4). When putting LEDs in parallel, series
resistors (of let's say 1 Ohm) may be necessary to evenly divide the current, or
one has to pair/match the LEDs very well.
A disadvantage of putting LEDs in parallel is that if one of the LEDs or one of
the wires break, all other LEDs will also break, because of the double (triple, etc.)
current. So my advice is not to put LEDs in parallel when they are physically
far apart / when long wires are used to make the parallel connection.
20 mA AC LEDs quickly hacked into a 'watertight' casing.
6.2. Current limiter with discrete components
With 2 transistors and 2 resistors, a robust current regulator that
consumes only about 0.6 Volt itself can be built, whereas regulator-chips like the LM317, 150, 350,
etc. consume almost 2 Volts themselves.
Another advantage of discrete components is the availability in the future:
transistors will always be there, but certain integrated circuits may
dissappear from the market within 20 or less years.
Furthermore, with discrete components, it is easier to scale-up or -down the
design (maximum currents and voltages) by selecting the appropriate driver
transistor, Tpower (Tp).
When a heavy (enough) type is chosen for Tp, a BD441 for example, all
following 4 configurations of LEDs (single, series, parallel or a combination
of both) can be realised with the same transistors and almost the same resistors.
Classic current-regulator applied to LEDs: 4 variations in voltage- and current-consumption.
Resistor Re senses the emitter-current through power transistor Tp:
it converts it to a voltage. When the potential over Re exceeds about 0.5 Volt,
small-signal transistor Ts will start to conduct, thus lowering the
base-potential of transistor Tp, which in turn will again decrease the current
through Re and the LED(s).
Remitter (Re):
To determine the value of current-sensing resistor Re, one must know the desired
current through the LED(s). For example, when one or more 20 mA LEDs are put
in series, approximately 0.6 Volt will fall over Re when its resistance is:
R = V / I Re = 0.6 Volt / 0.02 Ampere = 30 Ohm
But it all depends a bit on the characteristics of small-signal transistor Ts:
some types start to conduct at 400 mV, others at 600 mV. I suggest to take a
transistor with high current amplification (HFE), like a BC337 or BC547C.
It is furthermore best to select resistor Re slightly higher than calculated
and just measure the current.
Then, when necessary, slightly decrease the value of Re (for example by putting
resistors with 10 times the value of Re in parallel).
Pinout of BC337 and BC547 small-signal transistors (Ts).
When using many LEDs in parallel, or when using high-power LEDs, it may be necessary
to calculate the maximum power dissipation in Re. For example, with ten 20 mA LEDs in
parallel, thus 200 mA in total:
P = V * I P = 0.6 Volt * 0.2 Ampere = 0.12 Watt
Re
So even then, at 0.2 Ampere, a regular 1/4 Watt resistor will suffice.
When putting more LEDs in series, Re can stay the same because the same current
is running through all LEDs, only Rb may perhaps be increased a bit for efficiency.
Rbase (Rb):
To determine the value of base-resistor Rb, one must know the (minimum) current
amplification of Tp (HFETp), the desired (maximum) collector current
through Tp and the range of the supply voltage. The value of Rb is not
critical but if HFETp is too low and/or Rb is chosen too high,
the LED(s) will never glow at their full potential (the desired collector current
cannot be reached). On the other hand, when Rb is too low, the lamp becomes
slightly less efficient and there is the risk of damaging transistor Ts.
A rough estimation of Rb, for a single red (20 mA / 2.4 V) LED and a power
transistor with a current amplification of 100:
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Vsupply = 3.2 Volt (minimum)
ILED = 0.02 Ampere (maximum)
HFETp = 100 (minimum)
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We first calculate the base-current through Tp:
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IcTp = HFETp IbTp
0.02 = 100 IbTp => IbTp = 0.02 / 100 = 0.0002 A
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Which is the same as the current through Rb, so given Ohm's law and the
knowledge that both transistors exhibit a voltage-drop of 0.6 Volt between
base and emitter (VbeTp = VbeTs = VRe = 0.6 V),
we can calculate Rb:
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VRb = IRb Rb
VRb = Vsupply - VRe - VbeTp
VRb = 3.2 V - 0.6 V - 0.6 V = 2 V
2 = 0.0002 Rb => Rb = 2 V / 0.0002 A = 10000 Ohm
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So with 10 kiloOhm for Rb you are safe.
When you put 2 LEDs in series, the minimum supply voltage almost doubles so
you can also double Rb (18 instead of 10 kOhm).
When you put LEDs in parallel, you can simply divide Rb (so for 3 LEDs in
parallel, Rb becomes 3.3 instead of 10 kOhm).
My advice is that you always measure your LED currents and that you check
HFETp. The latter can be easily done by indirectly measuring the base
current (IbTp) by putting a digital voltmeter over Rb (knowing its
value, you can calculate its current; then divide LED current (IcTp)
by this base current (IbTp) and you know HFETp).
Rseries (Rs):
When putting LEDs in parallel, series-resistors (Rs) may be
necessary to evenly distribute the current. It all depends on how well the LEDs
match: when you buy a large amount of LEDs and measures all their voltage-drops, it may
be possible to select very identical types and choose Rs 0 Ohm. In other cases,
use resistors of 0.5 or 1 Ohm.
Below, two examples of 2-transisor current-limiters.
6.2.1. 40 mA DC pimped headlight
Add a pair of white LEDs to a (halogen) bulb headlight to
create front-standlight. It is furthermore nice to
complement the 'warm' yellowish light from an incandescent bulb with the 'cooler',
more blueish light from white LEDs.
40 mA limiter circuit for 2 white 20 mA LEDs.
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| Headlight with 2.4 Watt halogen bulb and two 20 mA LEDs in
extended configuration.
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Two holes for 5 mm LEDs were drilled in the reflector of a Lumotec halogen headlight.
With a lot of glue, two 10000 mcd white LEDs were watertightly fixed.
Pimped headlight.
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No space for a circuit-board: use some glue/kit afterwards.
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6.2.2. 60 mA DC rear light
60 mA limiter circuit for 3 red 20 mA LEDs.
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| 60 mA LED lamp put inside the cheapest of cheapest red casings available.
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| Circuit board frontside. Two 22 Ohm resistors are put in parallel
to get the right Re (11 Ohm).
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| Circuit board backside.
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6.3. Switching LED array
The main disadvantage of putting more LEDs in series is that they start to
glow at a much higher voltages (higher biking speeds). And a consequence
of putting LEDs in parallel is that transistors and resistors in the rear lamp
start to emit infrared instead of visible red when biking fast.
The safety-efficency dillema --we want lamps to burn at low speeds as well,
but we don't want to turn our knees and ankles for heat dissipation in resistors
and semiconductors at higher biking speeds-- is solved in the following design:
the switching array.
Compared to just two LEDs in parallel, it is double as efficient: the two
bottom LEDs switch on at higher supply voltages (thus minimising power
dissipation in the upper BD441 transisor).
Switching LED array design.
The upper two transistors (BD441 and BC547) form a classic current regulator
for two 20 mA LEDs. As soon as the potential between collector and emitter of
the upper power transistor (BD441) exceeds a certain --adjustable-- voltage,
leftmost small-signal transistor (BC547) starts to conduct, thus lowering the
base-potential of the bottom power transistor (BD441). Bottom power transistor
(BD441), which conducts at lower supply voltages, on its turn then blocks and
the two bottom LEDs start to glow. Resistor RH
forms positive feedback which creates a hysteris to ensure less flickering when
supply voltage Vin is very near the treshold-value. Higher values
(than 1 megaOhm) for RH will decrease the hysteris-effect.
Experimental switching LED array on breadboard
(Vin = 5.62 V, Itotal = 32.1 mA).
Although LEDs could be paired (down to 1 millivolt difference), in the first
prototype (picture below), resisistors of 1 Ohm were put in series with all
4 LEDs. Furthermore, a bridge rectifier (in the form of 4 BAT85 Schottky diodes)
was added to enable alternating current (AC) supply.
6.3.1. 40 mA AC switching rear light
First prototype of a 40 mA switching LED array rear light.
Prototype-board put into a watertight casing.
7. Links
7.1. Websites
7.2. Mailinglists
