Have you ever wanted to take cool splash photos with your DSLR?
Yes?
Well, me too, and that was exactly the moment I started looking for a light barrier camera trigger, which allows you to just simply throw some objects into liquids like water, milk etc. and trigger your camera at the exact same spot – over and over again till you got the perfect shot.

On doing some research, I found out that there are some decent ones on the market, but they are kind of expensive. There are some cheaper ones as well, but they don’t have a feature to set a time-delay, which, in my opinion, is very important. Of course, you could buy a cheap one, alter the sensor’s height and fiddle around to simulate a delay – but there must be a better way, and there is: You can easily and inexpensively build one by yourself in just a few hours.

I had a light barrier sensor lying around which doesn’t need a reflector (type: LTK-1180-104), but you could just as well take any other sensor that trigger on small objects and is fast enough. The sensor I used has a switching frequency of 1kHz according to its data sheet, so the maximum response time should be approximately 1ms.

A hint for those who don’t have an appropriate data sheet: Connect a simple LED to your sensor’s output and use the slo-mo camera function of your mobile phone to check the response of the sensor. This turned out to work surprisingly well.

Now you need to find out how your camera trigger mechanism works. The remote trigger device I’ve been using for some years now includes an adapter cable from Nikon’s own connector to a more common 2.5mm 4-pol audio jack, which is very neat. After doing some testing, it turned out that the last ring is Ground, the first one is the camera’s shutter in open-collector mode and the second one is the focus, also in open-collector mode. Simply connecting them to Ground activates the corresponding functionality. If you want to take a picture, you have to trigger *both* at the same time. 

Alright, let’s face the circuit: To put it in a nutshell, you just have to delay the sensor’s signal and, afterwards, fire a transistor to pull your focus- and shutter-signal to ground. My first thought was to use an Arduino as everything works with an Arduino nowadays. Then you can add a display, some GUI and Bob’s your uncle. When doing this, you have to use an external interrupt to keep your reacting time short. Even if your delay is short enough, you don’t know whether or not it is going to be the same length each time triggering the sensor by using the Arduino language. Coding in C or, even better, in assembly language might solve this issue. But why wasting a micro-controller when you can build an even more reliable circuit in hardware?

The basic idea is to use two monostable flip-flops built with reliable and easily available NE555 timers. The first one determines the delay between triggering the sensors and triggering the camera. The secondone determines the pulse time for the trigger signal to your DSLR.

Now, let’s have a look at it in more detail: As the flip-flop is falling edge-triggered, the first NPN transistor is used for a phase shift of the signal of 180 degrees. You can get rid of this transistor by using a low-active sensor. Then the collector is AC-coupled to the first NE555 timer. The RC circuit of this timer is used to set the important delay time. So, I soldered terminals to replace the capacitor, in case a higher delay is needed, and used a 10-turn potentiometer to precisely set the interval. Again, the output is AC coupled to the second stage timer. This one fires on the falling edge of the delay-pulse and stays high for an internally set time (length of trigger signal). In my case this pulse is approx. 150ms. The output of this stage separately pulls down the camera’s signals by using two NPN transistors.

In the upper half of the circuit diagram you can see the USB connector for powering the circuit as well as a step-up module to provide 12 volts needed for the light barriers sensor. You should also use some polyswitch fuses to protect the power source. 

Finally, put everything in a stable case that is as small as possible, and have fun taking unique pictures in a way you’ve not been able before. Also, make sure to use the MOP function on your DSLR to avoid delays by moving the cameras mirror. 🙂