Introduction: Cheap Time Lapse
Time lapse video is a video recording done by periodically capturing the image frames. This means that the video capturing device shoots an image at much slower frame rate than live. Live speed video is considered to be at 24 frames per second (fps). The image on time lapse video is always standing still, without moving the camera around or using the zoom functionality.
Time lapse video was a solution to save space on the target media. Back in the days these were the video cassette tapes, nowadays they are computer’s hard drives. With time lapse, you capture an event, but this is done at much slower frame rate, say at 1 fps at most. This technique was mostly used in security video surveillance prior to the motion recording.
Time lapse can be used in various fields. We already mentioned security. Large scale example is construction. Time lapse is being used to record construction of a building from the very beginning, when the construction site is only being prepared, to the very end, when the building is finished and standing tall. When you put the recorded images of a 2 and more years of construction in a 2 minute video, the building seems to be literally rising of ground by itself. This technique can also be used as a project management tool to compare the project completion with planned deadlines.
Another interesting use of time lapse, small scale this time, is stop motion animation. Stop motion animation is done by taking a shot each time you make a small change of a scene setup. This can mean either small figures, toys or objects, or a small changes of a drawing. When you combine all the recorded frames into a movie, you get a cute cartoon or animation-like video.
Classic way to achieve this was to take one or more analog cameras and plug them into time lapse video cassette recorder (VCR). If you used more than one camera, you had to connect them to VCR over quad multiplexer which converted 4 inputs into single output. This divided the screen into 4 camera views. Time lapse VCR technology is very old, unreliable and gives very low quality video recordings.
A more modern approach would be to use digital network high resolution cameras. These would be connected to fast network switch. Computer server based recording device would be connected to an uplink of the same network switch. Cameras are usually mounted in a temperature controlled housings. Installation cables are FTP Cat. 6, which can carry up to 1 Gbit/s with PoE power supply. The video recording server is usually mounted in a RACK tower in temperature controlled room with access control. Needless to say, this configuration is professional but can be very expensive. Each camera can cost up to 1000$, recorders can easily reach prices over 5000$, and that’s at least 6000$ without the installation cables and work.
Step 1: Cheaper Solution
We came up with a better, simpler and significantly cheaper solution. For a couple of hundred dollars, you can get a fairly good digital camera. Their resolutions go up to 14 million pixels and more, which is way better than a security camera’s resolution (720, 1080p). These cameras can be triggered by hand with a button, but just a little more expensive models have external trigger inputs. Some of them also have a remote control.
The PoKeys controller has a wide range of timing features. There’s an on-board RTC (real time clock). Its memory is enabled by CR2032 button battery. RTC enables you to use time related features, like time, schedule, clock and various timer blocks. 55 PoKeys digital outputs enable you to control 55 output devices independently. This means that you could connect up to 55 digital cameras to PoKeys.
You can connect PoKeys output to your digital camera through external trigger.
- If you have a remote control for your digital camera, you can connect PoKeys to button on the remote.
- If your camera doesn’t have external trigger or a remote control, you can connect PoKeys digital output directly to the camera’s trigger button.
- If you don’t like the idea of dismantling your camera, you can always use servo motor to press the shoot button.
PoKeys will trigger its digital output according to a pre-set schedule. This can be done periodically, for example every 10 minutes or an hour. At night time, if no light sources are used, visibility will be low and you won’t be able to see a single thing on the recorded frames. To solve that problem, you could also use PoSensors. Among other kind of sensors, it also holds a light sensor. When setting up PoKeys, you can make a light and time conditions. For example, you can say: record a frame every 10 minutes IF the light conditions are appropriate.
PoKeys will trigger camera as scheduled. Recorded frames will be saved to SD memory card. You will have to calculate how often you will have to replace the memory card. Your calculation will be based in recording frame rate, picture resolution and size of memory card. The pictures get to be saved locally and both – the PoKeys and the camera – are battery powered, so no further cable installation is needed.
To avoid harmful weather conditions, you can put your camera on a stand in a house nearby and direct its view through the window towards the construction site. If no house is nearby, you can get waterproof housing for your type of camera. If recording will be done through winter, you can make custom housing and use temperature and humidity sensors on the PoSensors board to control the camera microclimate conditions.
Step 2: Programming
To periodically control PoKeys digital output, in PoBlocks select the following blocks:
- Clock source
- Schedule block
- AND function
- Pulse timer
- Digital output
Clock source will give pulses based on the half-period setting in the properties pane. When schedule is ON, the AND block will output the clock pulses onto the input of the pulse timer. The pulse timer will keep the Q output ON for the time set by PT. This is done to keep digital output ON for minimum time needed for the camera to take the shot. To set up the schedule, double click on it and the schedule editor will open. Just use the slides to set the ON and OFF times. Work on the construction site will be done from Monday till Sunday from 5 AM to 9 PM.
To make a light based condition, use the sensors block. If you only want to record the images when the construction site is visible enough, plug the PoSensors module into PoKeys PoNET connector. How much light is needed to make a quality photo, depends on a sensitivity of CCD / CMOS element inside your camera. You will have to make some trial & error tests to figure this out. For this example, we have set 100 for reference value. The greater compare block (GT) will compare input value with the reference value. In input value us greater than the reference value, it will output 1, otherwise it will give 0. The PoKeys digital output will go on each time clock source goes on and enough light is available. Therefore the camera will only shoot at day and all the photos will be useful to make a time lapse video.
Step 3: Further Use
This application shows you how to use PoKeys controller for small or large scale time lapse video. You can record big stuff like construction of a building or small things like how flowers grow. Especially beautiful are sunrise shots.
Since PoKeys allows you to connect large number of cameras (up to 55), that can be triggered simultaneously, you could make one of those 3D shots from different angles, seen in action movies.
Another interesting example of using PoKeys is a DIY security project. With an IR motion sensor module, avaliable on ebay for couple of dollars, you can make your camera shoot on motion. Every motion that happens in the field of view of a motion detector, can be recorded to camera's memory card.
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