five different operation modes:
1. Continuously display temperature in Fahrenheit or
2. Blink rapidly (approximately eight times per
3. Blink slowly (approximately one 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; the
maximum temperature report is preceded by the
LEDs slowly going from dim to full brightness.
When the button is pressed, the LEDs flash the
number of the new mode. If the button is held, the mode
number is flashed 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 either a
Morse Code “C” [long flash, short flash, long flash,
short flash] or a Morse Code “F” [short, short, long,
2. If held long enough for the mode selection to flash
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.
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 three to five 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.
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 the front vents
with hot melt glue and the red LEDs were similarly glued
inside of the 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 a 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
ITEM DESCRIPTION/PART NUMBER SOURCE
White LEDs 5 mm 0.5W MultiChip White Flux LED 50 Kmcd eBay seller Ivehk
Red LEDs 10 mm HIGH POWER 0.5W RED LED LAMP 150,000 mcd eBay seller Ivehk
Microprocessor Digikey.com - Part #PIC12F683-I/SN-ND PIC12F683
Temperature Sensor SparkFun.com - Part #SEN-00245 DS18B20
N-Channel MOSFET Digi-Key Part #eMMBF170LT1GOSCT-ND
Switch Electronic Goldmine - Part #G13795
Resistor R1 & R2 Electronic Goldmine - Part G255R
Resistor R3 Electronic Goldmine - Part G266R
Resistors Electronic Goldmine - SMT 1206
Circuit board file Nuts & Volts website
1K or 1.5K SMT
none or to match your LEDs