How to control your camera shutter release from your Ipod (r) or other MP3 player.
An "intervalometer" is a device that remotely triggers the shutter in a DSLR camera at pre-defined intervals. This can be a very useful device for shooting time-lapse video or simply a sequence of shots at regular intervals without operator intervention. Other desirable features in an intervalometer include time control for long exposures and variable delay timer for a single shot. Naturally, there are several devices available on the market that can do this but I set-out to build my own. It occurred to me that if I could use the sound output (headset output) from my Ipod this would be a very convenient solution since I typically carry it with me everywhere...
I'll show you the finished product first and then will take you on a "flash-back" trip through the details on how to build one. The following figure shows the typical setup with an iPod (I know, I'm due for an update to the iPod touch...), my DSLR and the Intervalometer (the small black box with a single switch).
I made an effort to keep the package small and power consumption to a minimum (so I could use smaller AAA batteries). As you can see, this doesn't take much space in your "camera-bag". I'm very happy with the operation of the device so far. So much so, that I'll tell you how to make your own. Stay tuned...
how it works
The idea is quite simple but very powerful. We know that the Canon cameras activate the shutter when there's a connection (low impedance) between the "tip" and "sleeve" of the 2.5mm jack connected to its control input. This was the principle I used in this article by simply connecting a push-button to these signals as shown in the figure below:
The circuit I devised for the intervalometer is fundamentally a "sound activated" switch that replaces the "push-button" above. Every time the sound from the iPod exceeds a certain level, the switch closes and triggers the shutter release. This is the "hardware" portion of the project. The "software" portion can be easily done in any sound editor. I used Cool Edit Pro but I recon other editors could be used too. I simply generated a "tone" (5 KHz sine wave) followed by "silence" to precisely control the time the shutter was "on" and "off" respectively. Very simple to do, very easy to change the timing. Each "wave" generated this way was then saved as an MP3 file that can be selected in the iPod music library. Simplicity is great...
hardware - the circuit
After some drafting and experimentation I settled on the following circuit:
The BC547C in the first stage is a pre-amplifier for the iPod audio signal. This is a negative feedback amplifier (the 56 K resistor provides the feedback) with a gain of approximately 145. If you are interested in the specs, here are the details:
Note that the biasing current in the circuit is very small: a mere 250 uA. This is important since we will be supplying the circuit from 3 x AAA batteries (4.5 V nominal) and we want to maximize battery life. Of course this is only "standby" power consumption and power will increase once a signal is applied to the input. The input impedance is relatively low at 382 Ohm but should be adequate to the iPod audio drivers that normally drive an even lower impedance (I believe most headsets are around 32 to 60 Ohm). This will save battery in the iPod itself as it will be driving a higher impedance load than it normally would.
With no signal applied, the transistor collector voltage Vc hovers around 0.7V and the gate voltage in the BS170 Mosfef is close to ground potential. As a result the N-channel Mosfet will be normally off. When the signal is applied at the input, the transistor will amplify the signal and will turn off in the negative input voltage cycles. This will drive Vc high and will forward bias the 1N4148 diode thus activating the Mosfet and the camera shutter. The capacitor and resistor in parallel with the BS170 gate keep the transistor On for about 0.2s even when the diode is off. This acts as a sort of monostable circuit and ensures there's a minimum activation time in the camera shutter for cleaner/reliable operation.
assembling the hardware
Radio Shack sells a very nice 4x AAA battery box with built-in on-switch as shown in the photo below. This is what I used as both battery compartment and circuit enclosure:
I used only three out of the four batteries (4.5V nominal supply) and used the space vacated by the fourth battery to lodge the pcb with the circuit. This is the small prototype pcb used for the project:
The assembled circuit in said pcb:
And the final circuit inside the box with batteries included:
The final circuit. I used cables from old headsets for the project. Note that the jack connecting to the iPod is thicker than the one connecting to the camera so there is no way to confuse the two...
This is a better looking photo of the device next to a quarter coin for scale:
Now on to the software.
As I mentioned above, the "software" portion of the project consists of generating sounds at the right level and cadence to control the camera as needed. This can be easily do Apply ne in any sound editor such as Cool Edit Pro. I simply generated a "tone" (5 KHz sine wave) followed by "silence" to precisely control the time the shutter was "on" and "off" respectively. The the sound level was set to maximum to ensure a good drive level from the iPod into the sound switch. The following figure shows an example of how the "wave" looks like in the editor window. This example shows 1s activations every 6 seconds.
The resulting waveforms were then saved as separate files in MP3 format to reduce space. You can determine based on your particular needs, the set of waves that are adequate for your iPod. I decided to organize mine in three broad categories: "Single Shot", "Periodic Shots" and "Long Exposures":
The file names are pretty self-explanatory. I believe this set covers most of my needs but you can easily expand it if needed. One key point in keeping the files organized as you bring them into the iPod is to consider the way you name them on iTunes. I gave this some thought. Since iTunes organizes "Artists" alphabetically, I edited all the files so that they would have an Artist name starting with 'aa'. Consequently, these are the first files to show-up on the list which is very convenient when in use:
As you can see in the figure above, I created three "Artists" so that iTunes shows me the three corresponding categories outlined above. This is the end result in the iPod window:
The iPod shows these first in the list of "Artists" and you can easily browse through your selections. In this example I first selected "Periodic Shots" and then a wave (song) that triggers the camera every 2 seconds for a total of 3 minutes:
This is the song/wave already "playing":
Now some air-time for the 'lawyer inside my head": This project is relatively simple and should be safe to your camera (I've tested it in a rebel XSI and Rebel T1i). That said, please don't do it if you are at all concerned and don't have some experience with basic electronic circuits. Proceed at your own risk.
And this is all there is to it... It was a fun project to conceive and implement I'm still "alpha-testing" the device but it has been working very well so far. If you are interested in building one (or already did) following these instructions I would love to hear from you. Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com