Jump to content

Leaderboard


Popular Content

Showing content with the highest reputation on 08/07/21 in all areas

  1. 1 point
    Hi, As some of you are aware, I was making LED trigger boards. Sadly, I've been super busy with my day job, and haven't really had much time to make them any more. Sorry to those that may have tried to contact me in regard to them. In true Wetpixel form, here is the basics of how I have been making them, and how they work. The core of the circuit involves some simple logic gates, a RC timer circuit, and a NPN transistor. Plus resistors, caps, and a diode. This design, provided the right components are picked, will work for years, and take tens of thousands of photos off a single set of button cell batteries. There are plenty of schematics out there that simply hook a hotshoe output to a transistor to drive the low side of the LEDs. However, there are some serious downsides to doing that. If you pick a shutter speed of say 1/200th of a second, the LEDs will light for 1/200th of a second - let alone if you pick an even longer shutter speed. This is incredibly wasteful of valuable battery energy. Far far shorter LED pulses are enough to trigger a fibre optic based strobe, and set it off, making for far far more efficient use of the small amount of energy in button cell batteries. Into the nitty-gritty. If you look at the drawing, there are two types of logic gates used. One is a schmitt inverter - these simply invert a signal. If the input is high, the output will be low. If the input is low, the output will be high. To note though - is the schmitt trigger on the input. This causes the detected input threshold from low to high to take place at quite a specific voltage, and the transition from high to low to take place also at quite a specific voltage. The other is an AND gate - if both inputs to this gate are high, the output will be high. In all other input scenarios (either is high, or both are low), the output will be low. Some basics... D1 provides input polarity protection for if some numpty puts the batteries in back to front. C1 and C2 provide some input voltage stability. After the hotshoe, you have R3. This is a pull down resistor. It simply makes sure that the input to R4 is pulled to ground if the hotshoe contacts are open. R4 simply provides a bit of resistance to the input to Schmitt inverter #1. It is probably not needed, given the incredibly high input impedance of the Schmitt inverter. Should the hotshoe be open, the input to SI#1 will be low, and due to how the gate works, SI#1 output (labeled as Point#1) will be low. The opposite is true. Should the hotshoe close, SI#1 input will be high, and SI#1 output (Point 1) will be low. R5 and C3 form the heart of how this circuit works. They form what is known as an "RC Timer." If the output from SI#1 goes high, it takes a while for C3 to charge through the resistance of R5. Likewise, if SI#1 output goes low, it will take a while for C3 to discharge through R5 to ground through SI#1. Thus, there is time lag between SI#1 output and what is happening at C3, and in turn the input of SI#3. This time lag is defined by the choice of values of C3 and R5, and can be finely tuned. SI#3 and SI#4 were used simply to get a non-inverting output output off the RC timer circuit. Two inverters = a non-inverter. But, in this case... with a schmitt trigger. I went this way, because I already needed to order schmitt inverters for SI#1. If you want to use a non-inverting schmitt buffer in place of SI#3, and SI#4, that will do the exact same thing. Sooo... actual operation. If the hotshoe is open, SI#1 output will be high. Provided enough time since the last shot, C3 will be fully charged. SI#3 and SI#4 will be providing HIGH to one side of the AND gate. Bam! A photo is taken. The hotshoe contacts close. SI#1 input goes high. S#1 output goes low. At the same time, the RC timer starts discharging, and SI#2 input goes low. SI#2 output goes high, and VOLIA, both inputs to the AND gate are high! The NPN transistor turns on, and the LED turns on! Once this has been in this state for long enough, C3 will have discharged enough for SI#3 input to go low, and in turn through SI#4, for the AND gate lower input to go low. This means LEDs will turn off, even before the hotshoe opens, and after an amount of time defined by the selecton of R5 and C3! When the hotshoe opens again, if you chase the logic, the upper side of the AND gate will instantly go low. The RC filter will take a while to charge (plenty before a camera is ready for another shutter actuation). The lower output to the AND gate will be HIGH, and we are ready to take another photo! How cool is that? The flash time of the LEDs can be fine tuned down to microseconds simply by the choice of resistance of R5, and the capacitance of C3. Provided you pick the right logic gates that have incredibly low quiescent current, and are 6V tolerant, along with the right type of capacitors that have low leakage, this circuit can sit dormant on a set of batteries for YEARS with no use! Hopefully this is useful to somebody! Happy photo taking, Bevan For those interested: https://en.wikipedia.org/wiki/Schmitt_trigger https://en.wikipedia.org/wiki/RC_time_constant EDIT: I'll scan the drawing when I have access to a scanner.
  2. 1 point
    I shot this tiny little guy in Lanai - Cathedral 1 dive site. Does anyone know what it is? It is tiny about the size of a grain of rice. Sent from my iPhone using Tapatalk
  3. 1 point
  4. 1 point
    I have solved my issue with a plastic food container from IKEA, a glued rubber/foam/neoprene inside, 4 small holes and a bit of bungee on 2 loops to maintain it in place.
  5. 1 point
    The AND gates I was using are NC7S08M5X The SI gates I was using are NC7S14M5X I would recommend X7R ceramic capacitors. They have very low leakage. I'll have a crack at finding some through-hole equivalents, and putting the design together for a small-ish board that people can order off Oshpark, or JLCpcb, and solder at home with basic soldering skills. Bevan
  6. 1 point
    I just got back from a trip to Bonaire with the GH5M2. The battery life is extremely more improved. With the GH5 I could get 1.5 dives out of a Panasonic battery. The new GH5M2 battery gave me 2 100 minutes dives no problem. This is great for not having to pop open the housing as often. And, in Bonaire you don't want to keep extra batteries or anything in the truck for fear of theft. So, this is a great improvement. I did three dives on one battery. But on the third dive I did shut down the camera when not using it. I have the camera connected to a small HD monitor. Focusing is much faster and more accurate. Using back button focus was very quick and I seldom had to make multiple attempts. I shot all video so nothing to report on stills. Once I review the footage and put a video together, I'll be more informed about those aspects. Attached screengrab from the video.
  7. 1 point
    Yeah I get all that was said here. But it is just such an awkward word to me. I am from the English side of the fence (if you can call Aussies from the English side lol - Well fact is we are, just that we were the riff raff they threw out - or more likely, those who were unfortunate enough to get caught for stealing a loaf of bread to survive, got caught and sent to the other side of the world for it), and to me "DOVE" is so awkward. I mean its no big deal, especially in these trying times, but I just wondered were did this come from and is it really a word in this context? - to me its not. Wondered what others thought - that's all. Another strange English word - Chemist - why is it not pronounced "Cheemist" instead of Kemist ? Our friends in the US would know a Chemist as a drug store, others might call it a Pharmacy. In Aus its called a Chemist. But I do solemnly swear that in Australia we speak the QUEENS English, not all those bastardised versions of it !
  8. 1 point
    I am a little late to this party (just returned from Croatia, where i did similar cave dives)), but here are my thoughts: The photo that I can see on the links is definitley without strobe. You could place a remote strobe somewhere in the cave to get a special light effect. Also a diving model with lamp can be nice... As Oneyellotang suggests, I would arrange with the other divers. Usually I go (with buddy!) after the others into such a cave: since the flash is not used the stirred up dust particles are not so important. You have every time of the world then if you just keep to the overall diving time limit and meet at the end at the boat (when you are first the others are waiting and will jostle, after a while, even when they are impressed by your great camera and promise to wait before the dive starts) ... Regarding WB, you do not need to care and do it afterwards, when you store your photo as raw.. In such caves I usually increase ISO dramatically, out of the comfort zone (e.g. ISO 1600, even with my EM1II MFT sensor). One can use strong noise reduction in LR and it really does not matter for such photos when you loose some detail (Do you see any detail worth working out in the photo you linked?). I also would open the aperture bejond the value that I use for well lit photos under "normal" conditions (e.g. f 6.3, sometimes even f 5.6 with my fisheye (8mm-15mm)/Nauticam 140 port combination - but I cannot say for your specific combination, best you check out yourself an a lazy day in well lit condition what apertures can be tolerated...)... Regarding exposure time, it depends whether you intend to freeze (the often "dancing") single rays within the entire beam or you want just the beam. When the latter and your camera has good IS you increase exposure as much as required, but take care not to blow out the bright cave opening too much (with the IS of my EM1II I can do 1s exposure handheld, even if I do not find support on a rock for my camera). Often the light at the opening is still blown out: then you can locally reduce color saturation and vibrance in LR (not much color in and near the blown out area anyhow), reduce the brightness of highlights and it is also o.k. If you want to freeze the rays, you have clearly an advantage with the large sensor... Good luck, eager to see your photos, Wolfgang P.S.: Here just two photos from this last trip. They show how results are alike when using similar parameters as said above (both using natural light only): ISO1600, f 8.0, 1/60s, 8mm ISO1600, f 7.1, 1/6s, 8mm

Sponsors

Advertisements



  • Newsletter

    Want to keep up to date with all our latest news and information?
    Sign Up
×
×
  • Create New...