The hat lamp
I previously designed had 3 brightness settings. I thought including a PWM dimmer would make it useful for dark adaptation and extending battery life. Using a dim setting for a warm color would be melatonin friendly when reading at night.
In this circuit, I used SMD components which allowed the board to be glued to a battery slot of a 4 AA battery holder. The small switch of the holder was used to power the 7555 timer. Because we needed more current for the LED, I soldered ground directly to the source of the MOSFET.
Since only low power components were used, the battery can last for months if you accidentally left the switch on with the LED disconnected or dimmed to zero percent brightness. That's if low self-discharge batteries were used. Only 250 uA is used on standby.
- IRLM6402 or AO3401 SMD P-channel MOSFET (SOT-23 package)
- Copper clad board
- 7555 timer (SMD package)
- 2.2nF, 100 nF, and 10 nF capacitors (0805 package)
- 10k and 10M resistors (0805 package)
- 2-1N4148 diodes
- 500k potentiometer with dial
- 4 AA battery holder
- 2 core connector
- 3W LED (any color) with heatsink
- LED lens (optional)
- Velcro (to attach heatsink to a hat)
- 2 ohm 2W resistor (needed if using red or yellow LEDs)
- heatshrink tubes
- 2 core wire (3 to 4 ft)