Bike Blinker +Plus+
Revised 06-18-10


Photo #1

Introduction
As a cyclist I frequently start bicycle rides long before sunrise.  This has motivated me to have an interest in lightweight and efficient bicycle lighting systems.  I also have an interest in LEDs and microcontrollers as they relate to my model railroading endeavors (see:  http://trainelectronics.com).  I recently combined both interests and developed what I feel to be a unique helmet mounted LED lighting system that not only alerts drivers to my being on the road but provides me and my fellow cyclists with some useful information as we ride.

In order to give motorists the best chance of seeing my lights I like to have at least some illumination on my helmet.  This is usually the highest point on a cyclist and the most likely to be noticed.  The first version of this lighting system was made by mounting three bright white LEDs on the front of my helmet and three bright red LEDs on the back.  A simple flashing circuit used a PIC 12F683 microcontroller.  A single push button switch allowed for the selection of a number of different flashing modes and sequences.  While this worked well it did little more than what was available with many commercial units. 

Something More than Just Illumination!
I live in Pittsburgh and do a good bit of my bike riding in the winter.  As you can imagine temperature is always of interest and a topic of conversation before, during and after each ride.  I normally carry some sort of digital thermometer on my bike rides and I frequently hear another member of the Mt. Lebanon Cycling and Caffeine Club yell out "Dave, what is the temperature now?  It must be well below freezing!"  I don't mind being the resident temperature reporter in the peloton but it occurred to me that the flashing lights on my helmet could be used to relieve me of this duty.  By incorporating a thermal sensor into the circuit and coming up with a way to report its output with the helmet lights I would have an automated system that would take care of continuously reporting the temperature.  Thus was born the "Bike Blinker +Plus+".

Objectives
My years as a classroom teacher proved to me the value of setting objectives before starting a lesson or any other project.  The objectives for the bike blinker include that the unit will:

LEDs
The three white LEDs that I placed on the front of the helmet are 1/2 watt devices that are unusually bright.  (see Photo #2)


Photo #2

Each 5 mm LED enclosure contains three discrete LEDs.  Photo #3 was taken through a red filter and shows one of the LEDs operating at a very low voltage.  Because the intensity of the LED's light has been dramatically diminished you can clearly see the three points of light from each of the LEDs and the wires that are connected to them.


Photo #3

These LEDs provide a very bright light and each one only draws about 60 ma.  They can be clearly seen in  photo #1 which shows the front of the helmet.

The red LEDs for the rear are also rated at 1/2 watt.  They are 10 mm units that throw a bright directed beam.  One red LED faces straight back with the other two being aimed a bit to the sides.  This arrangement gives maximum visibility.  The vent to the right in photo #4 houses the circuit board and the sensor.

 
Photo #4

Temperature Sensor
Temperature readings come from a Dallas Semiconductor DS18B20.  This device uses a 1-wire protocol to communicate with the microcontroller and is factory calibrated to an accuracy of +/- 0.5 degrees C.  Routines to read these sensors are readily available on the Internet and I had no difficulty interfacing it to the PIC controller. 

Getting Power to the LEDs
The LEDs that I am using draw much more current than the microcontroller can supply from its output pins.  A transistor is inserted between the microcontroller's output pins and the LEDs to provide the necessary current.  Any general purpose NPN transistor should work.  My first design used two 2N2222 transistors.  I could have gotten away with using only one transistor but decided that it would be simpler to use one transistor to drive the three front LEDs and another to drive the three rear LEDs.  This effectively doubled the current handling capacity and saved me from experimenting with series resistors that were needed to match the different LEDs so that they could be operated by a single transistor.  This arrangement worked quite well and was used for several months.  I continued to experiment with the circuit and discovered that I could improve battery life and LED brightness by replacing the 2N2222s with n-channel Mosfets.  The 2N2222 transistors have a fairly high internal resistance and dropped the voltage to the LEDs by well over 0.5 volts.  Mosfets, on the other hand, have a very low internal resistance and there was very little voltage drop through them.  I was also pleased to find that the Mosfets worked well when substituted for the 2N2222s without any changes to the circuitry (See Figure #1)

.
Figure #1

Microcontroller
A PIC 12F683 microcontroller ties the hardware together by reading the temperature sensor and a single pushbutton switch while operating the flashing LEDs.  I have used this chip for a number of model railroading projects and knew that it had more than enough capability for this endeavor.  I also knew that the 8 pin 12F683 was available in a surface mount package that would go a long way towards meeting one of the objectives, making the unit as small and light in weight as possible.

Construction
Solder the 12F683 microcontroller to the circuit board being sure to align pin 1 properly.  To check the wiring I like to program the chip as soon as it is mounted.  Just connect power (3 to 5 volts DC) to the board and plug in a four pin header to the I.C.S.P. (in circuit serial programming) connection.  Successful programming will confirm that the chip has been installed correctly.


Photo #5

Next add the 4.7 K resistor and DS18B20 temperature sensor.  Note the pin position of the sensor.  The flat side of the device goes towards the center of the board.  (See Photo #5)

Attach the resistors (1 K or 1.5 K) and Mosfets to the board.  There is a spot on the board where a resistor can be added for each LED.  This set of pads is jumpered by a small trace (circled in Photo #6) in the event that you don't need a current limiting resistor.  If one is to be used you must cut that connecting trace before adding the resistor.  I have run the unit using the LEDs shown here without current limiting resistors and have had good results.  If you increase the input voltage to 5 volts you would surely need to add 50 or 100 ohms in series with the LEDs to keep from damaging them.


Photo #6

The push button switch needs to be oriented with its longer axis in line with the longer axis of the board.  If you choose to use an external switch its wires connect to the upper left pad (the one with the hole in it) and the one in the lower right (next to the "1" in "sw 1"). 

Connect your LEDs to the board and apply power.  The current Fahrenheit temperature should begin to flash out.

Using the Serial Output for Testing
Pin 7 and ground can be connected to a PC's serial port for testing.  The PIC's Pin 7 goes to pin 2 on the PC's DB9 serial port connector and ground goes to pin 5 on the DB9.  On your PC set HyperTerminal for 9600 baud, 8 bits, 1 stop bit and no parity. When power is applied to the completed Bike Blinker the version number and current Celsius and Fahrenheit temperatures should be displayed.  (See Figure #2)

The comments in the PicBasic Pro program listing explain why the  "Min/Max" temperatures shown on the HyperTerminal screen are 100 more than their actual values.  They are stored on the PIC this way to accommodate negative temperatures on a device that does not normally understand negatives.


Figure #2

Software
The program for the 12F683 is written in PicBasic Pro.  The code is well documented and should be fairly easy to follow.  You will also note that there area a number of "SEROUT" commands.  These send information to the device's serial port and were used for debugging as they give information on the program's operation.  If more program space is needed for additional modes or features the serial commands can easily be removed.

Software
'd. bodnar 12-26-09 0 fixed error between 15 and 8 F
'1998 bytes of 2048 before text strings removed
INCLUDE "modedefs.bas"
ansel=0                 'use pins as digital rather than analog
DEFINE OSC 8            'use 8 mhz oscillator
OSCCON = $70            'set clock speed 
option_reg.7=0          'turn on weak pull ups
wpu = %00100000         'weak pull ups on pin GPIO.5 only 
INTCON = %00001100      '00xx11xx to be CCP1 mode

SerialOut       VAR GPIO.0      'pin 7
NotUsed1        VAR GPIO.1      'pin 6
LED             VAR GPIO.2      'pin 5 
NotUsed3        VAR GPIO.3      'pin 4
DQ              VAR	GPIO.4      'pin 3 One-wire Data-Pin "DQ"
ChangeSwitch    VAR GPIO.5      'pin 2
R_Temp          VAR	WORD        'RAW Temperature readings
C_Temp          VAR WORD        'Celsius Temperature
Decimal_C_Temp  VAR WORD        'store just the decimal C temperature
F_Temp          VAR WORD        'Fahrenheit Temperature
G_Temp          VAR WORD        'Generic Temperature for report (either C or F)
NEGPOS          VAR BYTE        'Sign char "-" or "+"
C               VAR BYTE        'Status of I/O port bit
Minimum         VAR BYTE        'minimum temperature (store as C or F)
Maximum         VAR BYTE        'maximum temperature (store as C or F)
Mode            VAR BYTE        'branch variable
Y               VAR BYTE        'for/next variable
Z               VAR BYTE        'temporary variable
Ones            VAR BYTE        'ones
Tens            VAR BYTE        'tens
Hundreds        VAR BYTE        'hundreds
Scale           VAR BIT         '=0 if Fahrenheit / =1 if Celsius
SleepCounter    VAR BYTE        'count times mode shown before sleep
C_neg           VAR BIT         '=1 if cold bit for C set
MinMaxReptFlag  VAR BYTE        '0=temp, 1=min, 2=max- order of minmaxreport

TPause          CON 300
BetweenPause    CON 300
Mode            = 1             'start in Temperature reporting mode
Scale           = 0             '0 =  Fahrenheit
GPIO            = %00110000     'GPIO 4 & 5 as inputs - others as outputs
DATA @0,0,0                     'start with Fahrenheit scale (0) & mode 0
READ 0, Scale                   'read saved scale (F or C)   
READ 1, Mode                    'read mode 

SEROUT SerialOut,n9600,[12,10,13,"Ver 5.0 Bike Blinker +PLUS+",10,13]
SEROUT SerialOut,n9600,["(c) d. bodnar 12-25-09",10,13]
 
VeryTop:  
LOW LED 
PAUSE 1000
MinMaxReptFlag=0
GOSUB showscale                 'flash "C" or "F" in Morse Code
'Note that minimum & Maximum are stored as temperature + 100 to handle negatives
Minimum         = 255           'store as temp + 100 , below 100 is negative
Maximum         = 0             'gives range of 100 below to 125 above
IF ChangeSwitch = 0 THEN        'if switch held change scale
    Scale = NOT(Scale)
    GOSUB ShowScale
    WRITE 0,Scale               'save current scale to memory
    WHILE ChangeSwitch=0        'stay here till switch released
        GOSUB showscale
    WEND
ENDIF    

start:
IF ChangeSwitch=0 THEN GOTO ChangeMode
BRANCH  Mode, [Temperature, FullBrightFast, FullBrightSlow, FullOn, MinMaxReport]
GOTO start:

Temperature:
GOSUB Start_Convert
'serout serialout,n9600,[10,13,"-+= ",negpos,10,13 ]
IF Scale = 1 THEN 
    G_Temp=C_Temp        '0=fahrenheit, 1=celsius
    ELSE
    G_Temp=F_Temp
ENDIF

Report_Temperature:
IF NEGPOS = "+" THEN
    IF G_Temp + 100 > Maximum THEN    'save new max if new temperature is above old
        Maximum = G_Temp+100
    ENDIF
    ELSE
    IF 100-G_Temp  > Maximum THEN
        Maximum = 100-G_Temp
    ENDIF
ENDIF

IF NEGPOS="+" THEN
    IF G_Temp + 100 < Minimum THEN    'store new minimum temperature if lower
        Minimum = G_Temp+100
    ENDIF
ENDIF
IF NEGPOS="-" THEN
    IF 100-G_Temp< Minimum THEN
        Minimum=100-G_Temp
    ENDIF
ENDIF
SEROUT SerialOut,n9600,["Min/Max = ",#Minimum," ",#Maximum,10,13,10]
HIGH LED:FOR Y=1 TO 20:TOGGLE LED:PAUSE 20:NEXT Y:LOW LED  'fast blink @ start
IF C_neg = 1 AND Scale=1 THEN ' temperature is below zero Ceisius
    NEGPOS = "-"
ENDIF
IF (Scale=0 AND NEGPOS = "-") OR (C_neg=1 AND Scale=1)  THEN 'dim LED after rapid flash to show below zero temperature
    GOSUB minpwm:
ENDIF
IF ChangeSwitch=0 THEN GOTO ChangeMode 'watch for button press
PAUSE 400
'serout serialout,n9600,["G=",#G_Temp," +- ",NEGPOS,10,13]     'sign is for celsius!
Hundreds=G_Temp/100
'serout serialout,n9600,["Gh=",#G_Temp," ",#hundreds,10,13] 
IF Hundreds<>0 THEN ' show hundreds of degrees if temperature is >=100
    FOR Y=1 TO Hundreds:HIGH LED:PAUSE TPause:LOW LED:PAUSE TPause
    IF ChangeSwitch=0 THEN GOTO ChangeMode  'watch for button press
    NEXT Y
    PAUSE BetweenPause:PAUSE BetweenPause
ENDIF
IF ChangeSwitch=0 THEN GOTO ChangeMode     'watch for button press
G_Temp=G_Temp-(Hundreds*100)
Tens=G_Temp/10
'   serout serialout,n9600,["Gt=",#G_Temp," ",#Tens,10,13] 
IF Tens<>0 THEN ' show tens of degrees
    FOR Y=1 TO Tens:HIGH LED:PAUSE TPause:LOW LED:PAUSE TPause
    IF ChangeSwitch=0 THEN GOTO ChangeMode   'watch for button press
    NEXT Y :PAUSE BetweenPause
    PAUSE BetweenPause
ELSE 
    HIGH LED:PAUSE 40:LOW LED:PAUSE 40:PAUSE BetweenPause
    PAUSE BetweenPause
ENDIF
IF ChangeSwitch=0 THEN GOTO ChangeMode  'watch for button press
G_Temp=G_Temp-(Tens*10)
Ones=G_Temp
'serout serialout,n9600,["Go=",#G_Temp," ",#ones,10,13] 
IF Ones<>0 THEN ' show ones of degrees
FOR Y=1 TO Ones:HIGH LED:PAUSE TPause:LOW LED:PAUSE TPause
IF ChangeSwitch=0 THEN GOTO ChangeMode   'watch for button press
NEXT Y:PAUSE BetweenPause
IF ChangeSwitch=0 THEN GOTO ChangeMode  'watch for button press
PAUSE BetweenPause
ELSE 
IF ChangeSwitch=0 THEN GOTO ChangeMode     'watch for button press
HIGH LED:PAUSE 40:LOW LED:PAUSE 40:PAUSE BetweenPause
ENDIF
GOTO start
 
Start_Convert:
OWOUT DQ, 1, [$CC,$44]		  'Send calculate temperature command
REPEAT                      
    PAUSEUS 25 	  	     	  'Waiting loop until reading complete
    OWIN DQ, 4, [C]			  'Monitor for pin high transition ...   
UNTIL C <> 0 				  ' ... reading complete
OWOUT DQ, 1, [$CC, $BE]		  'Send read scratchpad command
OWIN DQ, 2, [R_Temp.LowByte,R_Temp.HighByte]	'get temperature
IF R_Temp.11 = 1 THEN          'check below zero bit
    C_neg=1
    NEGPOS = "-"
    R_Temp = ~R_Temp + 1
ELSE 
    NEGPOS = "+"
    C_neg=0
ENDIF
C_Temp = R_Temp >> 3        'Get whole # of degrees & first decimal bit
SEROUT SerialOut , n9600,["C =  ",NEGPOS,#C_Temp/2," deg. C",10,13]
F_Temp = C_Temp * 9  
F_Temp = F_Temp / 5
F_Temp=F_Temp/2 	     'remove decimal bit
IF NEGPOS="+" THEN
    F_Temp = F_Temp + 32 
ENDIF
IF NEGPOS ="-" AND C_Temp <= 36 THEN    'was 18 - caused error!
    F_Temp = 32 - F_Temp 
    NEGPOS = "+"
ENDIF
IF NEGPOS="-" AND C_Temp > 36 THEN      'was 18 - caused error!
    F_Temp = F_Temp  - 32
ENDIF
SEROUT SerialOut,n9600,["F =  ",NEGPOS,#F_Temp," deg.F",10,13]
C_Temp = C_Temp/2	
RETURN

FullBrightFast: 'full brightness - fast blink
SEROUT SerialOut,n9600,["@f",10,13] 
HIGH LED:PAUSE 60:LOW LED:PAUSE 60:GOTO start:

FullBrightSlow: 'full brightness - slow blink
SEROUT SerialOut,n9600,["@s",10,13] 
HIGH LED:PAUSE 500:LOW LED:PAUSE 500:GOTO start:

FullOn:
SEROUT 0,n9600,[10,13,"@ON",10,13]
HIGH LED
GOTO start:

MinMaxReport:   'shows current, then min, then max
MinMaxReptFlag=MinMaxReptFlag+1
IF MinMaxReptFlag=4 THEN
    MinMaxReptFlag=1
ENDIF
SEROUT SerialOut,n9600,["@MMR=",#MinMaxReptFlag,10,13]
IF MinMaxReptFlag=1 THEN
    GOTO Temperature
ENDIF
IF MinMaxReptFlag=2 THEN
    GOTO MinReport
ENDIF
IF MinMaxReptFlag=3 THEN
    GOTO MaxReport
ENDIF
GOTO MinMaxReport

MinReport:' Min report
IF Minimum-100 >65000 THEN
    Z=100-Minimum
    ELSE
    Z=Minimum-100
ENDIF
SEROUT SerialOut,n9600,["@Mn=",#Z,10,13]  
IF Minimum>=100 THEN
    G_Temp=Minimum - 100
    ELSE 
    G_Temp=100-Minimum
ENDIF
GOSUB MinPWM
GOTO Report_Temperature

MaxReport:   'Max report
IF Maximum-100 >65000 THEN
    Z=100-Maximum
    ELSE
    Z=Maximum-100
ENDIF
SEROUT SerialOut,n9600,["@Mx=",#Z,10,13]
IF Maximum >=100 THEN   'in case starting temp is below zero C or F
    G_Temp=Maximum - 100
    ELSE 
    G_Temp=100-Maximum
ENDIF
IF G_Temp >=100 THEN 
    NEGPOS="+"
ENDIF
GOSUB MaxPWM 
GOTO Report_Temperature

Changemode:
SleepCounter=0
SEROUT SerialOut,n9600,["CMd",10,13]
LOW LED
Mode=Mode+1:IF Mode>4 THEN Mode=0
StayHere:
    SleepCounter=SleepCounter+1    'count number of times reported
    IF SleepCounter >=6 THEN GoToSleep 'if held for 5 repeats goes to sleep
    FOR Y=1 TO Mode+1     'flash mode
        HIGH LED:PAUSE 100:LOW LED:PAUSE 100
    NEXT Y
PAUSE 500
IF ChangeSwitch=0 THEN StayHere:     'stay put till button released
SEROUT SerialOut,n9600,["MD=",#Mode,10,13]
PAUSE 300
WRITE 0,Scale   'save current scale 
WRITE 1,Mode    'save current mode
GOTO start:
 
ShowScale:
DIT CON 70        'Morse Code DIT
DAH CON DIT*3     'Morse Code DAH
SPACE CON DIT*5   'Morse Code space between Dits & Dahs
''serout serialout,n9600,["Sc=",#scale,10,13]

IF Scale=0 THEN    'Morse Code "F"
    HIGH LED:PAUSE DIT:LOW LED:PAUSE SPACE:HIGH LED:PAUSE DIT:LOW LED:PAUSE SPACE
    HIGH LED:PAUSE DAH:LOW LED:PAUSE SPACE:HIGH LED:PAUSE DIT:LOW LED:PAUSE SPACE
ELSE                'Morse Code "C"
    HIGH LED:PAUSE DAH:LOW LED:PAUSE SPACE:HIGH LED:PAUSE DIT:LOW LED:PAUSE SPACE
    HIGH LED:PAUSE DAH:LOW LED:PAUSE SPACE:HIGH LED:PAUSE DIT:LOW LED:PAUSE SPACE
ENDIF
PAUSE 1000
RETURN

MinPWM:
FOR Y= 255 TO 0 STEP -1
    PWM 2, Y, 3
    IF ChangeSwitch=0 THEN GOTO ChangeMode   'watch for button press
NEXT Y
RETURN

MaxPWM:
FOR Y= 0 TO 255 
    PWM 2, Y, 3                              
    IF ChangeSwitch=0 THEN GOTO ChangeMode  'watch for button press
NEXT Y
RETURN

GoToSleep:
Mode=Mode-1
WRITE 0, Scale      'save current scale 
WRITE 1, Mode       'save current mode
SEROUT 0,n9600,[10,13,"@Sleep",10,13]
FOR Y= 255 TO 0 STEP -1  'dim showing going to sleep
    PWM 2, Y,3
NEXT Y
LOW LED:
INTCON.0 = 0	'Reset the  Port change bit 
IOC=0
LongSleep:
SEROUT 0, n9600, ["Z", 10,13]
PAUSE 3000
INTCON.0 = 0	'Reset the  Port change bit
gpio.5=0        'reset switch pin
IOC = %00100000 'enable INTERRUPT ON CHANGE on gpio 5 
SLEEP 65000
IF intcon.0=0 THEN GOTO LongSleep
INTCON.0 = 0	'Reset the  Port change bit   
IOC=0
FOR Y= 0 TO 255  'brighten LED to show waking up
    PWM 2, Y,3
NEXT Y    
SEROUT 0, n9600, ["xZ", 10,13] 
INTCON.0 = 0	'Reset the  Port change bit   
PAUSE 1000
GOTO VeryTop:


 

Reading the Temperature
The objectives state that the temperature must be reported in a manner that is easily understood.  Being an amateur radio operator my first inclination was to use Morse Code for the numbers but the thought of teaching the sequence of dots and dashes to my riding comrades convinced me to search for another alternative.  The simplest code I could come up with has proven to be easily understood by everyone who sees it.

A temperature report always starts with a rapidly blinking sequence where the LEDs flicker for 1/2 second or so.  Next the number of hundreds of degrees is flashed out followed by a short pause, the number of tens, another pause and the number of ones.  The software suppresses the reporting of hundreds of degrees if the temperature is below 100.  When reporting numbers of degrees the LEDs flash at a rate of about 1/3 second on and 1/3 second off .  When reporting a zero they flash on and off much more rapidly.  These rates can easily be changed in the software but have worked well throughout a full year of testing.

To report 103 degrees
(uncommon but not unheard of in Pittsburgh!)

  • flicker

  • flash once

  • pause

  • flash once very briefly to show a zero

  • pause

  • flash 3 times

  • repeat

 

To report 48 degrees

  • flicker

  • flash 4 times

  • pause

  • flash 8 times

  • repeat

 

To report 7 degrees

  • flicker

  • flash once very briefly to indicate zero tens
    (I could suppress this but a two "digit" report seems to work best)

  • pause

  • flash 7 times

  • repeat

 

To report 0 degrees

  • flicker

  • flash once briefly (zero)

  • flicker

  • flash once briefly (zero)

  • repeat

 

 

To report 7 degrees below zero
(the coldest Fahrenheit ride we have ever done!)

  • flicker

  • LEDs gradually go from full bright to dim to off to indicate a negative temperature

  • flash once very briefly to show zero tens

  • pause

  • flash 7 times

  • repeat

 

The Minimum / Maximum temperature reports (mode 5) work as follows:

  • current temperature is reported as above

  • LEDs gradually go from full bright to dim to off to indicate that the minimum temperature is coming

  • flicker

  • minimum temperature is reported as above - note that a negative minimum temperature would again be preceded by dimming LEDs

  • LEDs gradually go from off to dim to full bright to indicate that the maximum temperature is coming

  • flicker

  • maximum temperature is reported as above

  • repeat

The temperature reports are the same whether they are reporting Fahrenheit or Celsius temperatures.  You must remember which scale you have the unit set to report.

One Button Does It All!
A single SPST momentary switch takes care of all mode and configuration changes.  The unit currently has five different operation modes:

  1. Continuously display temperature in Fahrenheit or Celsius

  2. Blink rapidly (approximately 8 times per second)

  3. Blink slowly (approximately 1 time per second)

  4. LEDs on (no blinking) - great for fixing flats in the dark, not so good for battery life

  5. Display the current temperature then the minimum temperature that has been seen since the unit was turned on then the maximum temperature that has been seen since it was turned on.  The current temperature is shown in the normal manner.  The minimum temperature report is preceded by the LEDs slowly going from full brightness to dim and the maximum temperature report is preceded by the LEDs slowly going from dim to full brightness.

When the button is pressed the LEDs flash out the number of the new mode.  If the button is held the mode number is flashed out repeatedly.  Releasing the button initiates operation using the newly selected mode.

There are several other functions that the button controls:

  1. If the button is held for a few seconds as the unit is turned on the temperature reports change from Fahrenheit to Celsius or from Celsius to Fahrenheit.  The current mode is reported by flashing out either a Morse Code "C" [long flash, short flash, long flash,  short flash] or a Morse Code "F" [short, short, long, short]

  2. If held long enough for the mode selection to flash out five times the LEDs will slowly dim and go out and the unit will turn off.

  3. Pressing the button while the unit is off will turn the unit back on, indicated by the LEDs slowly going from off to full brightness

The blinker doesn't fully turn off when the button is held down as described above.  It enters a very low power sleep mode.  An on/off switch can be added to the circuit to completely turn the power off.  This may be desirable as the batteries will slowly be exhausted if the unit is left in sleep mode for weeks or months.

If you do not install an on/off switch you can still change the Celsius / Fahrenheit scale by putting the unit to sleep then holding the button down when you turn it back on.  The current temperature scale will be displayed after the unit awakes.  Continue holding the button and it will change to the other scale.

The mode is saved when the unit goes to sleep or is turned off so that it returns to the last selected mode when it restarts.

A video is available on the Nuts & Volts web site that shows the operation of the unit in its various modes.

Battery Choices
I operate my helmet lights with 3.7 volt rechargeable lithium ion batteries that were designed for cell phone or PDA use.  The circuit will also work well with any power source that supplies from 3 to 5 volts.  Three rechargeable NiHM AA or AAA cells in series work well.  If you opt to use a voltage greater than 3.7 volts you may need to add current limiting resistors in series with the LEDs.  Their value will vary depending on the LEDs you choose and the voltage of the batteries. 

Mounting Options
As you can see from the photos I mounted the LEDs and blinker circuit inside of the vents of my helmet. The three white LEDs were mounted inside of front vents with hot melt glue and the red LEDs were similarly glued inside of rear facing vents.  The circuit board was mounted with double sided foam tape inside of a top vent and the battery was mounted with Velcro to the top rear of the helmet.  This arrangement works very well and gives the system a nice integrated look.

I put the DS18B20 on the end of short piece of three conductor ribbon cable so that it is a few inches from my scalp.  Even then the temperature tends to go up when I stop at a traffic light on cold days as it senses my body temperature.

The mode button is also mounted externally by wiring a second SPST momentary switch at the end of the vent.  This makes it much easier to change modes while riding.

For those of you who would like a less permanent installation or who would like to have the option of moving the light from helmet to helmet you can easily mount the circuit board, battery and LEDs in a small box as shown in photo #7.  The DS18B20 is in the lid just left of center and the yellow and orange wires go to an externally mounted mode button.  You will also note that the positive lead from the circuit board goes directly to the metal case as do the anodes from the six LEDs.  This simplifies wiring as the only leads that come back from the LEDs to the circuit board are those from the cathodes.  The SPDT toggle switch turns the unit on and off.  When the switch is off the rechargeable battery connects to a charging plug (hidden from view in this photo) so that you cannot inadvertently apply charging voltage to the circuit.


Photo # 7

Enhancements
The next revision of the circuit board will control each of the two Mosfets with a separate pin on the PIC processor.  This will allow independent control of the front and back LEDs.  This would allow a mode, for example, that would leave the back red LEDs flashing while the front white LEDs could be on constantly so that you could read a map or perform repairs.  I am sure that additional modes of operation will come to mind as well.

I am also considering, at the request of a non-cycling friend, making a solar powered unit with only one LED.  It will be placed in his garden to continuously report the outdoor temperature.  He reasons that it will give a better outside reading that a thermometer close to the house and he will be able to read it without putting on his glasses!

Conclusion
I have made a number of Bike Blinker +Plus+ units for personal use and for friends.  I encourage you to do the same!  I think that you will find that it can add to your visibility and may provide some fun as well. 

Try this:  leave your helmet flashing on the bike when you go into the local coffee shop.   Invariably someone will tell you that you forgot to turn the light off.  Watching their reaction as you relate how it is giving you temperature reports is an added benefit that is sure to make you smile!

Parts List
White LEDs - eBay seller Ivehk - 5mm 0.5W MultiChip White Flux LED 50Kmcd
Red LEDs - eBay seller Ivehk - 10mm HIGH POWER 0.5W RED LED LAMP 150,000mcd
Microprocessor - 12F683 - Digikey.com - Part # PIC12F683-I/SN-ND
Temperature Sensor -DS18B20 - SparkFun.com - Part # SEN-00245
N-Channel Mosfet - Digikey.com - Part # eMMBF170LT1GOSCT-ND
Switch - SPST momentary - Electronic Goldmine - Part # G13795
Resistor R1 & R2 - 1K or 1.5K SMT - Electronic Goldmine - Part # G255R
Resistor R3 - 4.7K SMT -  Electronic Goldmine - Part # G266R
Resistors  - none or to match your LEDs - see text - Electronic Goldmine - SMT 1206
Circuit board & complete kit of parts available from the author (dave@davebodnar.com)