Security Camera
Submitted by Brian M
For my school, level 2, science project, I decided to try an automation project that was suggested by our teacher. He had already obtained a control board (Ed: ConText board) which was considered suitable for this. The project objectives were to implement an automated security camera system which reacted to the movement of people within its range. The idea was to photograph anyone entering a room and track and photograph their movements. I had initially considered using a computer video cam with the possibility of capturing full video of any motion but this would have meant having a laptop computer running all the time. This version simply used an old digital camera which had sufficient storage capacity for several thousand photos of reasonable resolution.
The sensors that would detect human movement were PIR
(passive infrared) detectors EKMC1601111. This sensor (made by
Panasonic) is a standard detection type passive infrared motion sensor
in TO-5 package. It detects change in infrared radiation which occurs
when there is a movement by a person or object by the change in
surrounding temperature. I decided to use three of them to allow
coverage over a wide angle.
The first task was to make the outputs of the PIR sensors compatible with the inputs on the control board. Fortunately this was very easy and only involved a small transistor and one resistor as shown below...
The PIR sensors were connected in this way to inputs IP1, IP2 and IP3 on the ConText board.
The next step was to provide a rotating platform for
the camera. This was made using a small piece of MDF and mounted on to a
stepper motor as shown. The stepper motor was then wired to the ConText
board and to its 12v (battery pack) supply as shown below... (diagram
copied from Context manual)
One
output was needed to control the camera shutter. To be on the safe side
I decided to use a relay which would provide simple contacts to activate
the camera shutter. It may have been possible to connect the camera
directly to one of the Context board outputs as these are switching type
but it was unclear as to the nature of the camera shutter control and
whether this
would
be compatible. A small 5v relay was used and connected to output 1
on the ConText board. The normally open contacts on the relay were
connected to the small DIN plug which plugged into the camera remote
shutter control socket.
After some initial testing, I decided to add a small
tube collimator (modified pen top) extension to the middle PIR sensor. I
found that the PIR sensors had quite a wide angle of detection and it
was not possible to point the camera accurately enough. The collimator
on the middle PIR narrowed the detection angle down significantly. The
intention was to use the two outer PIRs to detect any initial human
movement and then rotate the camera in that direction until the middle
one also detected it. That way a more accurate pointing of the camera
could be achieved.
The next step was the most interesting. It was to create the control text that would govern how the project operated. Other control boards, which our teacher considered, meant using some form of programming language. Although I was willing to learn these it would have taken some time before I could have started on the important bit of the control logic for this project. With the "text" control option on this board I could get started on the interesting bit straight away. Although I intended to have the final version operate "standalone" I had the board connecetd to a laptop while I developed and tested the text. The first working version of my text is shown below. I have since added some more features such as an extra input which is connected to a small limit switch. This allows me to return the unit to a known "datum" point but the version below shows the most important bits.
| Text | Description |
| PLACE 10 WAIT 5 SEC IFINPUT 1 ON GOTO 100 IFINPUT 3 ON GOTO 200 GOTO 10 PLACE 100 LOOP 50 TIMES STEPMOTOR 1 FORWARD 1 WAIT 10 MS IFINPUT 2 ON GOTO 400 ENDLOOP STEPMOTOR 1 REVERSE 50 GOTO 10 PLACE 200 LOOP 50 TIMES STEPMOTOR 1 REVERSE 1 WAIT 10 MS IFINPUT 2 ON GOTO 400 ENDLOOP STEPMOTOR 1 FORWARD 50 GOTO 10 PLACE 400 OUTPUT 1 ON WAIT 300 MS OUTPUT 1 OFF GOTO 10 END |
Start line named 10 Slow down the loop to every 5 seconds if PIR 1 detects movement goto place 100 if PIR 3 detects movement goto place 200 nothing detected, go back to start (place 10) place named 100 start loop for rotating motor clockwise (toward PIR 1) rotate clockwise 1 position (1.8 degrees for this 200 ppr motor) wait 10 milliseconds for motor to complete its small step if PIR 2 detects the movement then goto photo taking (place 400) stepper motor not there yet, go back for another step nothing detected, return motor go back to start (place 10) place named 200 start loop for rotating motor anti-clockwise (toward PIR 3) rotate clockwise 1 position (1.8 degrees for this 200 ppr motor) wait 10 milliseconds for motor to complete it small step if PIR 2 detects the movement then goto photo taking (place 400) stepper motor not there yet, go back for another step nothing detected, return motor go back to start (place 10) place named 400 activate the camera shutter short wait (300 milliseconds) de-activate shutter go back to start |
Once
I had a working text version I had to configure the board to operate
without the laptop connected. This simply meant fitting a small link
(jumper) to the board and connecting a 6v battery pack. The battery
packs were eventually replaced with a DC power supply.
Now that the project has been tested, enhanced and proven to work, the school are going to provide extra bits and pieces to let me mount it better and enclose it within a dome to make it suitable for outdoor use, where another section want to use it to capture wildlife that are known to visit the school during the night. It should prove interesting !
The video below shows the initial testing of the security camera.
Ed: Thanks for the article Brian and many thanks to EGD for giving us permission to publish it on our website.
