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OML-L3 : the open hardware project to build an inexpensive and customizable infrared remote control for Nikon cameras
Designed for Nikon D70, it works with every camera supported by ML-L1 and ML-L3 such as D40, D40X, D50, D60, D70, D70s, D80, D90, D5000, D3000, Coolpix 8400, 8800, P6000
The story
Searching for an alternative to buying an expensive remote
control for my Nikon D70, I found a small program for the Palm. It works well,
but the Palm isn’t really comfortable for that kind of use.
At this point I decided to build a pocket circuit, using a micro-controller, to
release the camera’s shutter. The choice of which processor to use was simple:
I’ve been working for many years with the ST6 family, but recently, I discovered
the AVR micro-controllers. Why not use one of these? It would be a great way to
learn how to create a real application with these amazing chips.
Some theory
Using an infrared demodulator and a digital oscilloscope I captured the wave
generated by the Palm. Fortunately the waveform is quite simple, so hardware and
software are easy to develop. The captured data was something like reported in
figure 1
03/2006 : the waveform in figure 1 has been updated. Mikey sent me the data recorded directly from the original ML-L3. To see the original diagram with the data recorded from the Palm, click here.
Figure 1
Note: High levels show when the transmitter’s led is on, low levels when the led
is off. The same waveform is repeated a second time after about 63,2 msec. The
diagram is not in scale.
I think that the receiver of the DSLR is built with software and not with some
hardware decoder, and it should work as follows:
- Wait for a start pulse (2000 usec)
- There must be no pulse for 27830 usec (pause)
- Receive a pulse (390 usec)
- Pause (1580 usec)
- Receive a second pulse (410 usec)
- Longer pause (3580 usec)
- Receive the last pulse (400 usec)
If one step fails, reception is aborted.
Before concluding this paragraph, I must say a few words regarding the
transmitter. Most infrared transmissions operate by modulating the led with a
relatively high frequency (in most cases 38 or 40KHz). This means that when we
have to send a bit value “1” the led is turned on and off 38000 or 40000 times
in one second. When we have to send a bit “0” the led remains turned off. My
Palm uses a frequency of 40KHz, but I don’t know what frequency the original
Nikon ML-L3 uses. In this case however, it isn’t really a problem: everything
works fine!
Now that we know how the remote control works, we are ready to start the developing phase.
03/2006 : Mikey reported that the frequency is 38,4KHz. All subsequent info has been updated to match this frequency. To view the original page with previous values, click here
Hardware
As mentioned above, I decided to use an AVR 8-bit RISC MCU. I chose the
ATTiny2313 model for various reasons: low cost, easy to find, and I have it in
my toolbox. If you prefer, you should be able to use every AT90, ATMega and
ATTiny simply recompiling the software. An SMD version of the chip would help
reduce dimensions, but I wanted to keep the circuit simple to build, so my
design uses a DIP version.
To be compact a small battery must power the circuit: a lithium battery like
CR2032 could be a good choice. A battery holder like the one I used is easily
found on most old PC motherboards.
We will see in the next paragraph that we need a precise clock to generate a
good 38,4KHz square wave, so a quartz crystal is needed as oscillator. I have a
lot of 8MHz, so I selected this as clock frequency. Someone could think that
this “high” frequency causes too much battery consumption, but we must remember
that transmission is very short and the power absorbed by the led is much higher
compared to the MCU. By the way, it’s possible to reduce the frequency carefully
reading the next paragraph.
Hardware details outlined; it’s time to write down the program.
Software
First of all, we need a precise time-base reference to make the led blink at
38,4KHz. This implies that the led is powered on for 13usec (13.0208 to be precise) and then turned off
for the same time. To do this, we need to know exactly the processor’s clock
frequency and how many clock cycles are needed to reach the 13usec. The clock
frequency is 8MHz, so every clock cycle requires 125 nanoseconds or 0,125usec.
Obviously, after 104 clock cycles the requested time has been reached.
Considering that the “CALL” instruction, “RET”, “SBI” (led on) and “CBI” (led
off) spend cycles, we can write the following routine:
delay130:03/2006 : the delay routine in version 2.0 of the program has been altered to obtain maximum precision. The basis however, remains the same.
; This is a 13.0 uS delay (104 cycles @ 8MHz)
;
; sbi/cbi = 2 cycles
; rcall = 3 cycles
;
ldi DelayReg,32 ; 1 cycle
delay125_0:
dec DelayReg ; 1 cycle
brne delay125_0 ; 2 cycle if jump to label, 1 if not
ret ; 4 cycles
Now, with this routine, it’s as if we had a clock with a period of 13
microseconds: why not use this for the global waveform generation?
I can explain the idea with an example: the start pulse needs the led blinking
for 2000usec or in other terms, approximately 154 * 13usec. If we count 77 times “led on
for 13usec, led off for 13usec” the start pulse has been generated!
Here’s the code:
;(Start pulse)03/2006 : version 2.0 is different to obtain maximum precision.
ldi R17,77 ; (13.0 uS * 2 ) * 77 = 2002 uS
startpulse:
sbi PORTD,0 ; Led on
rcall delay130 ; Wait 13 uS
cbi PORTD,0 ; Led off
rcall delay130 ; wait 13 uS
dec R17
brne startpulse
After writing a few more loops like the one above, we’re done.
Remember, the
processor must send a complete “train” of pulses twice, and then stop. For
battery saving, use the “SLEEP” command.
For the complete, operational, source code, take a look at the download section.
Final considerations
In the title I wrote “inexpensive and customizable”. Why? Well, “inexpensive” is
easy to explain: with only 10 USD (about 10 Euro), maybe even less, you can build
a perfectly functional remote control for your Nikon.
For “customizable” imagine the following situations:
- You’re a few meters behind your camera, maybe hidden by a tree or a wall.
- Your camera is mounted on a tripod and you want to take a shot without
touching the equipment. It’s uncomfortable having to stretch your arm to the
front of the DSLR.
- You want to stay 50-100 meters away from the apparatus and the IR led doesn’t
have such a long range (make sure no one can steal your jewel).
- You want to take a picture every 1, 2, 5 or 10 minutes automatically.
You have the hardware (with schematics), you have the software (with source
code), you have a brain (with some neurons): use them and you will find a
solution for all your needs!
If you have no ideas, here are some suggestions:
- Connect a long, flexible, electric cable from the pcb to the pushbutton switch
and position the remote control somewhere in the front of the camera.
- Connect a very supple, not too long, electric cable from the pcb to the IR led.
Fasten the led (maybe using the camera’s strap) to the front and take the box
with the pushbutton in your hand.
- Use a radio remote control to activate the IR remote control. An NPN
transistor in open-collector mode can be used to simulate the switch press.
- Build a programmable timer with relay or open-collector output. Remember that
after 15 minutes of inactivity the camera deactivates the IR receiver. An even
better alternative is modifying the micro’s software allowing it to send
two-pulse sequences at regular intervals. The latter requires a superior-quality
battery.
- You can also connect a second switch to the micro and altering the program,
send a non-stop sequence. This way the camera operates in continuous mode until
you release the button.
Special thanks:
- Gerhard Schmidt (DG4FAC) – AVR tutorial - http://www.avr-asm-tutorial.net/index.html
- Brian Hammill - Basic idea for 40KHz routine - http://www.ipass.net/~hammill
- Pitronics - SP12 AVR programming software - http://www.xs4all.nl/~sbolt/e-spider_prog.html#programmer
- Mikey for original Nikon ML-L3 data
- Tamiko for english document revision
For any question, send a message to : ir-control [NO] @ [SPAM] bigmike.it
(remove [NO] and [SPAM])
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