1.
Take a cigarette lighter with LED

2.
Take it apart

3.
Take an ATMEL ATtiny13, DIP8 capsule, and squeeze it into the batteries holder. Also, replace the original white LED from the lighter with an IR (Infra Red) LED

4.
Wire everything as in the schematic diagram. The LED does not need a series resistor. Internal resistance of the cell batteries are doing a pretty good job in limiting the LED current.

5.
Program your microcontroller with the following BASCOM code:

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' Infrared Remote Control Transmitter for Nikon D90
' -------------------------------------------------
'
'  v0.2
'  Written by RoGeorge
'  2010.01.03
'  Compiler BASCOM-AVR v1.11.9.1
'
' Description:
' DIY replacement for Nikon ML-L3 Infra Red (IR) Remote Control
'
' After power up the microcontroller send a
'  "TAKE PICTURE" IR command to a Nikon camera
'  then enter in powerdown mode.
'
' It should work with:
'  Nikon N65, N75, Coolpix 8400, 8800, Pronea S, Nuvis S & Lite Touch Zoom,
'  Nikon D40, D40x, D50, D60, D70, D80 & D90 Digital SLR Cameras
'
' It works (tested) with:
'  - Nikon D90
'
' Schematic:
'  - 1 x ATtiny13
'  - 1 x normal open microswitch between batteries (push button)
'  - 3 x 1.5V SR41 (AG3) button cells as power source
'  - 1 x IR LED between OC0B (PIN 6 = LED anode) and GND (PIN 4 = LED cathode)
'  - NO curent limiter resistor is necessary for the IR LED
'
' IR LED waveform out (100% modulated with 38.4 KHz carrier):
'  -  2000 us on
'  - 27830 us off
'  -  390 us on
'  -  1580 us off
'  -  410 us on
'  -  3580 us off
'  -  400 us on
'  - 63200 us off
'  - repet once again the whole sequence
'
' Fusebits:
' Low: -1101010
'  ??????++-- CKSEL[1] Clock selection
'  ????++-- SUT[1] Startup time selection
'  ???+-- CKDIV8 Clock division ratio (1:1/1, 0:1/8)
'  ??+-- WDTON (1:WDT normal, 0:WDT always on)
'  ?+-- EESAVE (Retain EEPROM at chip erase 1:No, 0:Yes)
'  +-- SPIEN (1:Disable ISP, 0:Enable ISP) *Available only HVS mode

' High:---11111
'  ????+-- RSTDISBL (RESET pin 1:Enable, 0:Disable(PB5))
'  ??++-- BODLEVEL[1] (BOD 11:None, 10:1.8V, 01:2.7V, 00:4.3V)
'  ?+-- DWEN (On-Chip Debugging via RESET pin 1:Disable, 0:Enable)
'  +-- SPMEN (SPM instruction 1:Disable, 0:Enable)
'
' Cal: 75
'
' Bill of Materials:
'  - 1 x Cigarette Lighter with white LED for case, batteries and power switch
'  - 1 x IR LED
'  - 1 x ATtiny13
'
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 $regfile = "attiny13.dat"
 $crystal = 9600000

 $swstack = 8
 $hwstack = 2
 $framesize = 0

 $noramclear

'initializations
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

'select clock prescaller to 1/1 (9.6 MHz)
'''''''''''''''''''''''''''''''''''''''''
 Clkpr = bits(7)
 Clkpr = 0

'Ports init
'''''''''''
 Config Portb = Output

'TIMER init
'''''''''''
 Config Timer0 = Counter , _
  Edge = Falling , _
  Compare A = toggle , _
  Compare B = toggle , , _
  Clear Timer = 1

 ocr0a = 13
 ocr0b = 0

'Other peripherals init
'''''''''''''''''''''''
 stop adc
 stop watchdog
 stop ac

'main
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 declare sub pulse1

  waitms 63

  call pulse1
  call pulse1

  portb = 0
  disable interrupts
  powerdown

 end
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

 sub pulse1
  start timer0
  waitus 2000

  stop timer0
  waitms 28

  start timer0
  waitus 390

  stop timer0
  waitus 1580

  start timer0
  waitus 410

  stop timer0
  waitus 3580

  start timer0
  waitus 400

  stop timer0
  waitms 63
 end sub

'EOF
'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

6.
Mount everything back into the cigarette lighter and put your Nikon camera into remote controlled mode. Each time you try to turn on the LED lighter, the lighter will send an IR set of pulses. Your camera will receive these infrared pulses and take a picture.

After taking the picture, switch off the lighter switch.

7.
Enjoy this imitation of ML-L3 IR remote control for Nikon photo cameras.
Tested with a Nikon D90, works great, firing range tested up to 7 meters.

8.
Remember, smoking is bad, photo shooting is good!