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3 LED
Bike Light
for PIC10F200
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Description
Buy
3 pre-programmed PIC's in 8-pin PDIP package for £2.75
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This project is a
multi-function LED bike
(cycle) light using 3 LEDs.
It is based on a PIC10F200
baseline microcontroller, running from a supply voltage
of 2 to 5 volts. In standby mode it consumes a current of
less than 1µA making it perfect for battery powered operation.
It uses three individually
driven high brightness LEDs, and a single push button switch for
turning the light on/off and changing operating modes when on.
The features written into the program
for this project address what I consider to be three
shortcomings of LED bike lights on the market today.
- they can easily be turned
on accidentally
- they require you to cycle
through all the modes to turn them off
- you may have to cycle though
several modes to get the one you want after switching it on
To deal with point 1
this light requires the mode button to be held for >2
seconds to enter / exit standby mode. This helps
prevent it from being accidentally turned on when removed from the
bike and stowed in a pocket or bag.
When the light is powered-on, a
short press of the mode button cycles through all available
modes. The default firmware supplied features seven modes and as
long as the power to the circuit isn't removed, it will come out
of standby and run the last selected mode.
Disclaimer:
The legality of this bike light for on-road use depends on the
laws and regulations in the country of use. It
should be assumed it is not legal to use it on the road unless
you have establish yourself that the use of such a device is
permitted.
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Schematic
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schematics are shown, one for the PIC10F20x 8-pin PDIP
package, the other for the 6-pin SOT-23 package.
The two parts have different pin outs.
Resistor values are shown
as 100R and these are conservative values for use from a 3
to 4.5 volt battery supply and high brightness red LEDs.
The actual value used should be selected based on the
supply voltage, the type of LEDs used and if powered from
a battery the desired battery life.
Running from a 3 volt
supply (2 x AAA batteries) you could use 68R resistor
with red LEDs and 10R with white LEDs.
Resistor value
notation.
100R means 100 ohms, 4K7 would be 4,700 ohms |
Download
schematic in PDF
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Circuit
/ Firmware Description
There are two functionally
identical versions of the project presented on this page; a
small easy to assemble version using the 8-pin PDIP version of
the PIC10F20x and a very small version based on the SOT23
package PIC and surface mount components.
The circuit drives 3 LEDs from the I/O pins of the PIC microcontroller. A
single push button switch provides standby/power-on function as
well as mode selection.
The circuit can operate from a
voltage in the range 2 to 5 volts although you will need to take
into account the forward voltage drop of the LEDs used; red LEDs
typically need at least 2 volts, white LEDs 3 volts. Current consumption in
operation depends on the LEDs used and the choice of current
limiting resistors. Typically it will be in the range of
10 to 30mA. In standby current consumption drops to less
than 1µA making it well suited to battery operation. The
100nF capacitor is used for decoupling of the power supply to
the PIC.
The LED functions are
defined by a lookup table in the PIC's program firmware.
If you have access to a PIC programmer and want to edit or
modify these you can download the source code (see bottom of this page).
The default modes supplied are:
- All LEDs constant on -
power save mode
- All LEDs constant on -
full brightness mode
- All LEDs blink at 2.5Hz -
power save mode
- Single LED walking
- All LEDs strobe mode 40mS
on / 600mS off
- All LEDs short flash, long
hold
- All LEDs burst strobe mode
6 x 20ms on / 60mS off followed by 1 second off.
To reduce power consumption the
firmware can drive each LED sequentially at very high speed so
only one LED is on at a time; because it does this around 1300 times
per second persistence of vision makes all the LEDs appear to be on
at the same time. This
reduces power consumption to that of a single LED, increasing
battery life. This feature can be selectively disabled,
providing slightly higher brightness at the expense of increased power
consumption when all LEDs are on. The operating mode is
defined in the mode sequence data table so if you're creating your
own sequences you can pick and choose how this feature is used.
LED / current limit resistor
calculation
To calculate the resistor needed
for a particular LED/ current requirement check out the website
below.
http://led.linear1.org/1led.wiz
PCB Layout
There are two sets of artwork
provided for the bike light.
a) Through hole design for the
PDIP version of the 10F20x
b) Part-surface mount design for the SOT-23 version of the
10F20x
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The
SOT-23 package has a small laser etched dot in the
corner nearest pin 1. You'll need
exceptional eyesight or a good bench magnifier to see
it. |
Download PCB
artwork in PDF
The artwork here is just a
starting point. You can design alternative layouts,
assemble it onto strip-board, or even take an existing bike
light and hack it to use the PIC from this project to control
it.
Construction photos
DIP and SOT PCB's straight
from etching before the boards have been separated or
drilled.
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It's tiny!
The PIC SOT-23 package measure 2mm x 3mm
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Both the
DIP and SOT-23 version of the bike light are very simple
to build with minimal number of components. The PDIP version while less compact is the easier to
construct. Use
the photo's here and reference the PCB overlay and
schematic diagram during assembly. Click on the
photos for hi-resolution versions.
The switch
can be bought from
Rapid Electronics and is supplied with a number of
different button lengths. The one shown in the
photo's is the 9.5mm type.
Description and Rapid part # are listed below:
TACTILE SWITCH 6X6MM HEIGHT 5MM (RC) 78-0621
TACTILE SWITCH 6X6MM HEIGHT 7MM (RC) 78-0622
TACTILE SWITCH 6X6MM HEIGHT 9.5MM (RC) 78-0625
TACTILE SWITCH 6X6MM HEIGHT 13MM (RC) 78-0626
DIP
Version
Buy 3 x programmed 10F200 PDIP
PICs for £2.75 - visit the
online store here
You can
fit the switch to either side of the PCB depending on
how you intend to use the bike light and the case you
want to fit it in.
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Switch mounted on front of
PCB |
Switch mounted on
underside of PCB
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The
resistor used are 1/8 (0.125) watt carbon
film, 5%, making them a bit smaller and shorter than the
regular 1/4 watt resistor. Rapid Electronics sell
them and the 100R resistor is part # 64-0044 for a pack
of 100 resistors. If you can't get them then you can just about squeeze a 1/4 watt resistor in.
The PIC is
fitted with pin 1 at the end nearest the switch.
I've used a socket for the
PIC on this prototype so I could swap the PIC when
testing the code. If you're building this into a
light I would suggest you leave the socket and
solder the PIC directly to the PCB. This keeps the
profile of the finished board lower. |
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To keep the PCB as compact
as possible, the battery wires are soldered directly to the solder pads of the
PICs power supply pins. Pay
careful attention to the polarity when connecting the
wires. Red
wire + / Black wire - |
SOT-23
Version |
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Fit the surface mount
components first. The resistors and capacitor are
0805 package size.
You'll need to pay careful
attention when placing and soldering the PIC to make
sure it is aligned over the solder pads. Also
check that it is oriented correctly (with pin 1 top
left in photo below)
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Program the PIC before the LEDs are fitted.
Programming the SOT23
version of the PIC is not easy because of its size.
I've tacked some short wires to the PCB then hooked them
up to the PICkit2 programmer. Once the PIC is
programmed the wires are removed. |
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Take
note when fitting the LEDs on the SOT-23 version of the
bike light. The square copper pad is the LED cathode connection and the LED nearest the switch is
fitted the opposite way round to the other two LEDs.
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On the
SOT23 version, two solder pads are provided for the
connection of the battery leads. |
Firmware
The HEX file is ready to
program straight into the PIC 10F200. The asm file is the
source code which you can modify or just view to see how it
works.
Buy
3 pre-programmed PIC's in 8-pin PDIP package for £2.75
See the
Programmed
PICs section in the Picprojects
On-line store
now.
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Description |
Filename |
Download link |
| Source
code for 10F200 / 10F202 |
bikelightv2.asm |
download |
HEX file
ready to program into the PIC
for use with 10F200 only |
bikelightv2.HEX V1.0.0 17/09/2009 |
download
Checksum 402B |
If you need a PIC Programmer I
strongly recommend the
Microchip PICKit 2,
this is available from suppliers world wide or direct from
Microchip. It's reasonably cheap to buy and reliable.
Contact us:
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