Here’s a fun post!  Say, let’s build something cool. I’m going to detail the shutter trigger monitor/profiler that I built this week and I’m including the schematic and parts list in case you want to experiment or build your own. Just keep in mind that this device requires an oscilloscope for full functionality, or at the very least, a pulse width counter. Also keep in mind that I am not responsible for your actions and that includes plugging things you’ve made into your expensive cameras – I refer you to the disclaimer at the end of this article for clarification. Right then, this is an offshoot of my router/sequencer project, but also a handy tool in its own right.

Camera shutters are mechanical/electromechanical devices that are prone to drift and corrosion. It’s great to be able to peek at the timings and trigger contact profiles in order to diagnose and evaluate their performance.  This goes from handy to critical if you have applications that depend on the accuracy and consistency of, say, the leading edges of your shutter contact pulses. This is my situation and that’s primarily why I built this tool – but it’s a useful tool for general photography and camera repair as well. From a development point of view, this device acts as an adapter for my ScopeMeter, which I consider to be the handiest tool ever, that allows me to examine the electrical (and later, optical) performance of my shutters, etc.

This first design (Mark I) features three shutter ports, one for each of the three types of PC cable common in my kit: 1/4″ (shutter-to-generator), 3.5mm (shutter-to-radio), 2.5mm (shutter-to-back). This is purely convenience, however do note that the profiler can, with modification, act transparently and pass-through triggers to generators, digital backs, or whatever else you might connect to your shutter – this is planned for the next version (Mark II).  Right now, let’s walk through the first version of the device.

The unit automatically powers on when plugs are inserted into the input jacks. When the inputs are empty, the batteries are completely open and will not drain. Power state is indicated via the green LED on the interface panel which also serves to indicate that the correct type of cable/plug is inserted and that the device is ready to go. The BNC port is for measurement output and it’s limited, protected, and designed to link to high and very-high impedance measuring devices such as oscilloscopes, DMM’s and counters. The output state is handily indicated by the yellow LED which turns on when the output is high and remains off when the output is low; it’s included for quick, on-the-fly connection checks and chain debugging without a scope attached. Leaving the profiler attached to a scope or other measuring device will not drain the batteries as long as none of the inputs are connected.

Connection to a shutter can be via any shutter cable that sports a 1/4″, 3.5mm, or 2.5mm TS connector. Only two-conductor (mono) plugs are supported, three-conductor (stereo) types will be ignored as long as the ring and sleeve are not common – in that case the profiler will not turn on. Any shutter with a contact type trigger output can be profiled and monitored as long as a proper cable exists or can be made. Connection to the scope through the BNC port should be made via a shielded RF cable, 50 or 75 Ohms. Noise floor is not a problem for this application so cheap cables are fine but higher quality cables will always make your life work out a little bit better.

All together, the device is compact, rugged, and easily stowed in my grip kit, ScopeMeter case, or even my pocket. I’m not actually going to carry it around in my pocket, but it would fit easily! So let’s hook it up to my ScopeMeter and have a look. As shown above, we’re into channel A with nothing in, nothing out.

Once connected to a shutter, the device powers on and remains ready to send trigger measurements to the scope. In this case I’m using my on-camera trigger cable for a Leaf back which is plugged into the 2.5mm input on the profiler. All three inputs are electrically parallel and do exactly the same thing.

I’m ready to go; now to setup the scope. I should point out that I’m testing the mechanical Copal 0 leaf shutter on my Schneider Apo-Digitar M 120mm here; this could also be any electronic shutter, SLR body, medium format lens – again, any shutter or camera with a switching trigger. It could also be connected via radio; the profiler can be used to examine radio delays and timing as well. I can also use it to look at the trigger output of an electronic technical shutter, a DSLR, or a digital back. Anyway, once connected I set my scope to fit a 3VDC peak and scale the display to the anticipated shutter speed – in this case I am starting at 1/125 sec. My Fluke 124 has the cool cursor feature, so I’ve set the cursors to delineate a perfect 1/125 sec. pulse width, which is 1000 / 125 = 8ms. You can also see that I’ve set the trigger to wait at 1.5VDC, or roughly half of the ~3VDC max output of the profiler. And so the scope waits happily until the profiler sends it a shutter pulse to chew over. For convenience I’m running my scope on-trigger instead of single-shot so that I don’t have to reset the hold each time I want to read the shutter – I can just click away and always expect the latest reading to be displayed. Either trigger mode will work just fine.

A closed shutter trigger (open shutter) means high output which is indicated by the yellow LED. Above I have the shutter locked open to take the picture, but pulses as short as 1/400 sec. can be seen and verified on the LED indicator. You can see in the picture that the scope is reading a steady ~2.8VDC with the output of the profiler in the high state. This peak reading will drop as the batteries wear, but timing performance will not be affected. So let’s look at an actual reading for the 1/125 sec. shutter speed setting on this Copal o.

(*click*) There we go. Instantly I can see that the trigger contacts close cleanly. I can also see that the trigger opens before the expected 8ms has elapsed. This is due to a combination of shutter mechanics and probably a slightly fast shutter. Note that any pre-delay is not recorded because the scope is triggering off of the shutter contacts, so presumably the shutter has opened fully before the initial trigger and will finish closing after the contacts break open. In order to get the actual photo-time of the shutter being tested for comparison I would need to use an optical sensor – this will be covered in Part II. For detailed analysis, I can upload any of the captures into FlukeView.

Here I can look closely at the rising edge characteristics and determine how my sequencer inputs will trigger from this shutter. And after looking at a few shutters I’ll have a better understanding of how to develop the input buffer sensitivity. Okay, but this is really unnecessary for most applications. I would like to point out the glitch that is seen just after the peak settles – this is probably due to cable capacitance or some other electrical aberration and it is seen on every shutter I’ve tested. It would be fun to track it down, but honestly, who cares. I’m hooked up, so let’s look at a few other shutter speeds while we’re at it.

(*reeclick*) (*reeeeeeeeeeeeeeeeclick*) These are readings for 1/8 sec and 1 sec shutter speeds on the same shutter. In each case I can see a crisp leading edge and constant output throughout the pulse. I have also verified perfect consistency over multiple actuations, and that’s exactly what I’m looking for.  This shutter is electrically healthy and it will be perfectly compatible with my sequencer trigger inputs. I will cover more in-depth shutter performance testing once the optical section is completed – at that point I will be able to record the actual photographic performance and also see where in the shutter cycle the trigger is switching.

BIT OF A WARNING! The schematic above is updated from the wiring shown in the pictures. It has been modified so that the shutter inputs are tip-positive. The pictures in this post show wiring for tip-negative. Not a big deal at all; the reason is to provide broader compatibility with transistor switching in electronic devices. Build from the schematic, not the pictures. Also, I do not advise connecting this circuit as a pass-through to other devices. Wait for the second version which will feature a safe opto-isolated pass-through.

Moving on, and as promised, the schematic is given above. The circuit is basically a DC power supply working against a small load balance with a standard flyback and a series protection diode guarding the output which is designed for very-high impedance measuring tools. Noise can be a problem when reading peaks. The load resistor (R3) fills two shoes: sinking the scope input when the output is low and acting as a stabilizer when the output is high. The shunt diode (D3) is there to protect sensitive transistor logic on triggers such as digital backs, DLSR’s, and radio transceivers. The protection diode (D4) is provided as a matter of course to protect everything from wayward output connections. I am using stereo TRS jacks to control the power via the plug sleeves.

As to the power supply, I like the convenience of 3V power from two AA batteries, but this could easily be a 9V battery with adjustment to the resistor values. I know that 3V is safe for all modern shutter devices that I use as it is well below the standard sensing voltage. A Profoto D4 generator, for instance, listens with a > 10V potential.

So let’s open the hood and take a quick peek.

The Hammond enclosure that I am using is perfect for this application. The top panel is removable and easily machined with a drill press to take the connectors and LED’s. I’ve tightened all the nuts snug and set them off with a bit of Loctite to keep them from changing their minds.

What you see is mostly interconnect, with all of the business happening in the diode/resistor group soldered to the output jack. Very easy stuff. Solder cleanly and solidly and protect component leads with heat shrink for durability. Solder flux should be removed. In this case I’ve used Kester 331 organic core, so a warm water rinse took care of that. Keep water out of the 2.5mm jack if you do this and dry completely with warm air before setting the heat shrink and installing into the enclosure.  A no-clean solder/flux could be used and the rinse could be avoided, but that’s no fun.

A nice fit with room for the future. Not shown are the two open-cell foam sheets that slip below and above the circuit in order to hold everything secure and provide plenty of shock protection. Expect a much shorter service life if everything is left to flop around.

Finally, here is a parts list for Mouser Electronics – the exact parts you see above, in fact. If you do decide to build one of these or experiment with shutter measurements, please share back. Lots of room for improvement here and, like I mentioned, stay ready for Mark II with simultaneous optical measurement, a safe pass-through, and more.

As always, thanks for reading and happy building. Remember to share a link to this post when you can, it sure helps me out! Also, make sure to check out some of my recent posts for some pretty sweet images, projects, and builds.  Cheers!

If you decide to build the device that I outline herein, that’s great, but you do so at your own risk. I cannot be held responsible for any damage to yourself or to your equipment that may result from the use or misuse of the electrical equipment that I describe in this article. I advise you to consult a professional regarding the specific equipment to which you intend to connect any device that you make.