Solenoid breakout board V2

I am now starting to built a version 2 solenoid breakout board. While the first one works I have learnt a bit more about controlling the valves.

Here is the diagram from Fritzing.

Added resistors in line with the diodes. The flyback diode may cause the the solenoid to release too slowly. Adding the resistor speeds up the current decay and causes the solenoid to release/close more quickly.
Using 12V 250mA solenoids with TIP121s, the resistor should not exceed 220 ohms.

Added a small bypass capacitor connected between the TIP121 emitters and the solenoid +ve terminals. The capacitor can be connected across the power in lines which is connected to the TIP121 emitters and the solenoid +V.



Connecting a photo interrupter/optoisolator to an Arduino

In an early version of the camControl device (before the dropController) I used an interrupter/optoisolator to detect the water drops. The plan was to detect the water drop, wait a little bit and then activate the shutter.

There are various different kinds of photo interrupter, different shapes and different sizes but all do the same job.
Photo interrupter

A photo interrupter has a LED at one side (normally IR) and a photo transistor at the other. When the LED in emitting light the photo transistor allows a current to flow. Remove the light and the current stops.
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Photographing Water Drops Using An Arduino Controller

I started creating a controller using a single Arduino Nano on a breadboard. Although it was very basic it worked fairly well. It allowed me to control a solenoid valve and trigger the camera shutter. I also added basic camera control and a timelapse function (intervalometer). This part worked well. I could set the frequency and the number of shots and the Arduino did the rest.

Initially had the Arduino controlling the solenoid and then triggering the shutter after a delay. I later added an interrupter sensor and a laser beam sensor to detect the water drop and activated the shutter based on a delay after the sensor was tripped. As the controller developed more the breadboard became very messy and this started to annoy me.

I separated the functions in to two units; a drop controller and a camera controller.










Photographing Water Drops: Second Go

I had another session photographing water drops. The idea is to create two drops slightly apart. The first drop hits the water, rebounds and creates a column and then the second drop collides with the column. Sounds a lot easier than it really is.

Here are some of the results.

Water Drop Water DropWater DropWater DropWater DropWater DropWater DropWater DropWater Drop

These are from plain water. Next step is to add washing detergent to the water in the bowl and add a thickening agent like guar gum to the drops.



First Proper Try At Water Drop Photography

I wanted to try taking water drop photos and see what worked and what didn’t. Overall the results were better than I expected but not as good has I had hoped. Lighting is not good but I knew this from the beginning and concentrated on the drops and the timings. Working on the lighting can de done later once I have the other things sorted out.

I noticed that I got different results even when using the same timings. All the below had exactly the same settings.
Same settings - different results

The only difference was the time between shots. I suspect that as you wait water in the bottom nozzle moved towards the exit hole and you get a cleaner drop. Couldn’t really tell and I may be completely wrong.

Here are some of the better shots

Water DropWater DropWater Drop



Controlling a Solenoid Valve from an Arduino

There is now an updated and more detailed post. See Controlling a Solenoid Valve from an Arduino. Updated.

Using the Arduino to control the solenoid valve is simply a case of setting a pin high for the appropriate amount of time. There is, however, a caveat, the solenoid works at a different voltage to the Arduino and you cannot directly connect the two. In this case a TIP120 transistor is used as a bridge.


The TIP120 allows a small dc voltage (from the Arduino) to switch a larger dc voltage (12V to the solenoid). It can be thought of as a switch, applying a current to  B allows current to flow between C to E.

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Using an Arduino and a optocoupler to activate a camera shutter

There are several ways you can connect an Arduino to a DSLR so that you can use the Arduino to activate the shutter. I chose to use an optocoupler, sometimes called an optoisolator.


There are many types of optocoupler and you chose one based on the requirements of your circuit. My circuit is a 5V Arduino and a Canon 40D which has about 3.2V on the shutter release. Due to the relatively low voltages there are many suitable optocouplers to pick from. I already had a Fairchild 4N26 so this is the one I used.



Optocouplers are digital switches.  They work by using an LED emitter paired with a photo detector transistor. This means they can be used to allow one circuit to switch a separate circuit without having any electrical contact between the two. Basically, if you put a current through pins 1 and 2 and light the LED the photo detector transistor detects the light from the LED and allows a current to flow through pins 5 and 4. No current on pins 1 and 2 means current does not pass through pins 5 and 4.

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Photographing Water Drops

For quite a while I was looking at water drop photos and thinking about trying to do them myself. I finally gave it a go. My first try was simply making drops and trying to capture the splash. Everything was manual; the water drop, the shot, and it was very hit and miss. Mostly miss…

Early attempts at photographing water drops
I did get some shots I liked but these are nothing compared to the shots from other people.

When researching online it quickly became apparent I wasn’t going to get better shots with the setup I had; which was a plastic bag with a small hole and hitting the shutter release like a maniac.

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