Inserted into a set of closed circuit television (CCTV), or simply connected to a mini-CCD camera, this device allows to inexpensively detect an intrusion, a movement or a change in lighting in a room guarded. The Video Motion Detector (VMD) uses the images transmitted by the camera and is, therefore, an ideal sensor for controlling an alarm system or to attract the attention of supervisory personnel. It has a relay output, capable of activating a VCR on which to record images when activated or any warning system.
Electronic accessories designed to detect the presence of a person or vehicle in a surveillance zone, we all know more or less passive infrared sensors, radar, ultrasonic and laser barriers, among others. They are the most used detectors, especially the first two, which are easily installed and can cover quite extensive areas.
There is also a system for detecting presence less known to the general public but which is gaining importance in recent times. Its diffusion is closely linked with that of monitoring systems by closed circuit television (CCTV). These are the "Video Motion Detector (VMD)," which could be translated into French, oh! joys of the language of Molière, with "presence detection system by modifying the level of a video image.
These are devices that detect the presence of people or objects in a normally motionless, using the images from a camera.
The principle is simple: if you "frame" a place where everything is stationary, with a camera, when a person or an object of substantial size will enter the field, the image is clear, will not be identical , so its video signal will undergo a change.
If we have, a system capable of storing the value of the original image and compare the value of an image modified by a presence, it will be possible to control any alarm. The reasons for the VMD are now common in many companies are obvious: they can be integrated into an existing video facility without incurring large costs, while maintaining excellent reliability.
Indeed, the VMD is able to analyze the video signals from one or more cameras already in place.
They also enable security systems capable of controlling the image recording or broadcast signals warning of intrusion, without having to modify the importance already in place.
As the camera that "sees" the field to monitor and that is his signal, modified by the presence, will be used to control the alarm, it will also help the economy of conventional sensors.
All these factors led us to develop in the "video motion detector" that we propose in this article. It is simple but effective.
It will be interesting for everyone, even for readers who use electronics as a hobby that.
How does our VMD
The assembly can be connected in parallel to the cable that connects a camera to a VCR or monitor, therefore, a video installation on existing and without interference or signal degradation (see Figure 8).
On a purely technical level, we can say that our device is analog, in the sense that it does not digitalized images that are analyzed in real time to monitor changes in the composite video signal.
VMD in digital, the frames are periodically sampled and digital information is compared with that of the previous sampling.
Ours, is limited to detect amplitude variations of the video signal. Variations that are confirmed so obvious, because the change of an image due to the entry of a person, for example, has a more or less marked alteration of the luminance component of the signal.
So if we have adequate filters and a comparator precise, it is possible to do at least as well as sophisticated digital circuits.
Thus, we reach our goal with a relatively simple, such as you can see in Figure 1.
The circuit includes an amplifier section input, a half-wave rectifier, a dual amplifier with filters, a window comparator and a time-controlled relay aimed at achieving the aler you.
Let's see what each of these blocks is by imagining you have connected the points VIDEO IN to the output of a camera or in parallel to a video line.
Technical Features
Adjustable sensitivity and amplification.
Opportunity to work with any video standard (PAL, NTSC, SECAM, color, B / W).
Insensitive to slow variations in brightness.
Insensitivity to variations in brightness caused by frequency.
Alarm relay contacts.
Activation time of the alarm relay adjustable from 1 to 60 seconds.
Figure 1 : Wiring diagram of the Video Motion Detector (VMD).
Figure 2 : The Video Motion Detector once assembly is complete. The device can be connected to any monitoring by installing closed circuit television (CCTV), already existing. It is also possible to create from scratch his own surveillance system in a simple and inexpensive. The alarm output can be used to activate an automatic registration system.
Figure 3 : Installation diagram of components of the Video Motion Detector. Remember to solder the 3 straps to the right of C19 and C20 above.
Figure 4 : Photo of the prototype VMD. Do not electroplate R1 soldered to the circuit but the bias in order to cut it if it becomes useless.
Figure 5 : Scale drawing of a printed circuit of Video Motion Detector.Component List
R1 = 100 Ω
R 2 = 47 kilohm
R3 = 47 kilohm
R4 = 1.5 kΩ
R5 = 1.5 kΩ
R6 = 4.7 kΩ trimmer horiz.
R7 = 2.2 kΩ
R8 = 330 kΩ
R9 = 330 kΩ
R10 = 330 kΩ
R11 = 100 kΩ
R12 = 4.7 kΩ
R13 = 33 kΩ
R14 = 330 kΩ
A15 = 1 kΩ
R16 = 4.7 kΩ trimmer horiz.
R17 = 220 Ω
R18 = 1 kΩ
R19 = 22 kW
R20 = 1 kΩ
R21 = 470 kΩ trimmer horiz.
R22 = 39 kΩ
R23 = 1 kΩ
R24 = 10 kilohms
R25 = 1 kΩ
C1 = 10 uF 25 V electrolytic
C2 = 100 uF 16 V electrolytic
C3 = 2.2 pF ceramic
C4 = 100 nF multilayer
C5 = 47 uF 25 V electrolytic
C6 = 1 uF 63 V polyester 5 mm pitch
C7 = 1 uF 63 V polyester 5 mm pitch
C8 = 10 uF 63 V electrolytic
C9 = 47 nF 63 V polyester 5 mm pitch
C10 = 33 uF 16 V electrolytic
C11 = 1 uF 63 V polyester 5 mm pitch
C12 = 33 uF 16 V electrolytic
C13 = 1 uF 63 V polyester 5 mm pitch
C14 = 100 nF multilayer
C15 = 10 nF 63 V polyester 5 mm pitch
C16 = 100 uF 16 V electrolytic
C17 = 100 uF 16 V electrolytic
C18 = 100 nF multilayer
C19 = 220 uF 25 V electrolytic
C20 = 100 nF multilayer
C21 = 1000 uF 16 V electrolytic
D1 = 1N4148 diode
D2 = 1N4148 diode
D3 = 1N4148 Diode
D4 = 1N4007 diode
D5 = 1N4007 Diode
T1 = BC547 NPN Transistor
LD1 = Diode LED 5mm Red
U1 = TL082 Integrated
U2 = LM324 Integrated
U3 = Integrated NE555
Regulator U4 = 7809
Relay RL1 = 12 V 1 RT to this
Others:
2 Brackets 2 x 4-pin
1 Supports 2 x 7-pin
2 2-pole terminal blocks
A 3-pole
1 RCA jack for it
1 PCB ref. S347
An Analog Video Motion Detector
The Video Motion Detector that we propose, is an analog version of digital business models.
The products commercially available to perform the analysis of each frame, digitize the information and compare with previous. If a difference is found, there are trigger alert.
Our VMD control the envelope of the analog signal coming out of the camera, detecting variations.
If these changes exceed a preset limit, the system goes into alarm. This is possible because the video signal generated by any camera has an average value closely related to the degree of illumination of the full field, regardless of whether the image transmitted either in color or black and white.
Black and white, each frame consists of a number of points more or less illuminated by the sun or artificial light source.
Thus, the signal representing information on the brightness of each line (luminance), resulting in a full screen, an average value that changes between two different images.
This is the same for color images because the luminance component and the video carrier determines a video signal, whose mean value changes significantly from one image to another. If you have any doubts regarding this concept, consider that each color is perceived not only as a function of the wavelength of light it reflects, but also by the amount of reflected light. It is no coincidence that the body clear (white, yellow) back a good portion of light radiation incident on their surface while dark bodies (blue, purple, black) tend to absorb it. Variations in average value produced by the change of the images are, for that extremely small, around 1 Vpp. These are a few millivolts. For this reason, our system carries out a strong signal amplification in order to easily identify these variations. A window comparator voltage is accurate to detect the oscillations from 800 to 900 mV.
Figure 6: Operation of the window comparator. TV on the left, the camera transmits the image of the room to monitor the signal is at rest. On the TV center, the camera transmits the image of the intruder, the signal rises above the threshold, it is detected. On the TV right, the camera transmits the image of the brightly lit room monitor, the signal drops below the threshold, it is detected. R16 adjusts the gap between the thresholds.The input gain
Between the signal and, through the capacitor C1 reaches the input of the first operational amplifier U1A, wired as non-inverting amplifier.
This makes the signal amplification based on the position of the trimmer R6, a minimum of 2 times to a maximum of 7 times.
The amplification is used not only to compensate for any attenuation suffered by the signal along the line but also losses in the stages that follow, especially in the filters.
Some readers will have noted that the first two operational amplifiers, is contained in a TL082, an integrated circuit normally used to treat AF signals and certainly not ideal for use in video, where the bandwidth stretches of 5, 5 MHz. As strange as it sounds, it behaves very well and in no way alter the functioning of the circuit.
In fact, as we shall see later, the video signal will be filtered to obtain a nearly continuous component which represent the envelope.
Thereby losing the signal characteristics (timing, etc..) poses no problem.
This applies to the four operational amplifiers contained in U2.
Figure 7: Diagram of connections and settings. Through trimmers R6 and R16, it is possible to adjust the sensitivity of the complete circuit, and thus its ability to discern more or less important variations of the received image. The maximum sensitivity is achieved by rotating the two trimmers clockwise. R21 determines the activation time of the relay alarm. In our case, this period is between 1 and 60 seconds.Connections with the outside
The drawing shows how the VMD is inserted in a typical installation of CCTV. In this case, the camera that monitors the site, is powered by 12 volt output (MAC) provided on the PCB. The control line REC (recording) VCR is controlled by the relay to our track.
In any installation of closed circuit video surveillance, a fundamental parameter is the impedance of the line camera and monitor are connected using a 75 ohm coaxial cable, because all of these devices has such an impedance.
With a video source, it is possible to drive multiple receivers as monitors, or VCRs. However, a normal camera, finds it difficult to send its signal to more than two devices, without being significantly degraded. This is because two VCRs and two monitors in parallel determine unusually low impedance (75 / 2). At the entrance of our circuit (VIDEO IN) was provided a resistance of 100 ohms (R1) that serves to match the impedance depending on the type of installation. It will be mounted or not depending on the configuration which is inserted in the GDV.
During a typical installation of CCTV, with a camera that controls a single monitor or single VCR, resistance R1 can be left in its place or even removed, depending on the quality of the image. In practice, if the vision offered by the screen is good, there is no need to change. By cons, if the image is poorly defined, or dark with snow, disconnect R1.
For an installation with a VCR and monitor, the resistor R1 must not be mounted.
In fact, the camera is already two loads of 75 ohms in parallel and it is enough.
Finally, if you plan to use a camera as a sensor only (no VCR and no monitor) and if you connect the outgoing part solely on the VIDEO IN of our device, the resistor R1 must be in place.
Figure 8 : Interconnection scheme of the various elements required to operate the VMD.The single-wave amplification
After U1a, the composite video signal passes a second operational amplifier referenced U1b mounted as half-wave rectifier. The purpose of this section is to charge the capacitors C6 and C8 with the pulses that follow the video signal, leaving only the discharge through R11.
In this way, we get a unidirectional voltage that varies in correspondence of significant variations in brightness of the image transmitted by the camera.
Variations that occur when the image changes following the entry of a new item in the field. If the situation does not change or after a return to normality of the observed field, the difference in potential across R11 becomes practically constant and does not pass to next stages because it is blocked by capacitor C7.
In short, the cell comprising U1b, D1, R7, R11, C6 and C8 behaves like a filter with very low cutoff frequency that allows only very slow changes, those arising precisely the modification of images transmitted.
Selective amplification Such voltage fluctuations, and only those, are applied (by the capacitor C7) to the next block, consisting of two active filters, amplifiers that reduce the frequency selective over their limit cut while amplifying the rest.
The first low-pass is made with U2a. This operational amplifier is working in non-inverting configuration with capacitor C9 in parallel with the resistor R10 cons-reaction, to reduce gradually the other frequencies, from about 15 Hz
This is necessary to eliminate interference caused by electrical and optical frequency of the sector: something we can not see with our eyes, but there is.
To understand this, consider a lamp powered by the 220 volt area. If we look, we see illuminated uniformly and therefore we believe it emits a constant light, but this is not true. In fact, being driven by an alternating current, the filament pulse at the same frequency (50 Hz) of the sector, therefore, it restores a luminous radiation, whose intensity is modulated by the envelope of the sinusoid sector.
This is invisible to the eye does not escape the camera and translates into a pulse of light.
In fact, a ripple at 50 Hz component of light.
The interference is present in the composite video signal. If this signal was not filtered, the interference would be detected by our system.
Cascaded U2a, is a second crossover, too type lowpass, but operating on a lower frequency: he cuts, in fact, 0.5 Hz therefore leaves that go very, very slow signal variations.
Practically, only those determined by a significant change images.
The window comparator
Now we can see the power voltage comparator. The latter adopts a configuration known as "Window". In practice, the potential is applied to compare two operational amplifiers. The one on the inverting input of the first (U2c) and the other to the non-inverting input of the second (u2d). The entries of these two operational amplifiers are biased left free with two voltages whose difference is a function of the desired sensitivity.
The peculiarity of the window comparator is the output, obtained by mixing the levels of each of the outputs of two operational amplifiers, can not take a high level only if the potential continues to look inside the "voltage window" and therefore to a value below the threshold and the highest above the lowest threshold.
The gap between the upper and lower thresholds can be adjusted with trimmer R16 which allows you to adjust the sensitivity of the entire circuit.
To understand this, let's see how our window comparator.
The diagram in Figure 6 gives a good idea of the thing.
Suppose that the video input, there is a composite signal from a camera transmitting a still image (that of a closed room, for example). We see that the filter made with U2b can reproduce on its output, the resting potential (half of 9 volts supplied by the regulator U4).
Thus, the pin 10, non-inverting of U2c is more positive than pin 9 thus, the pin 8 output, provides a high level.
It is the same for u2d whose non-inverting input (pin 12), is more positive than the inverting input (pin 13). For this reason, its output (pin 14) is in the same state as the output of U2c (pin 8), that is to say high.
The presence of the resistance R19 is the common anodes of D2 and D3 is at high logic level.
If now we suppose to put something in front of the camera or turn a person really changes the frame captured and with him, the composite video signal that reaches the IN VIDEO circuit.
It follows a slow change of amplitude of the rectified voltage by U1b, passing through C7 and through the low-pass filters that amplify them, determining an oscillation between pin 7 of U2b and ground.
If the amplitude of this oscillation is more or less than the difference between one-half the supply voltage comparators and threshold imposed by R16, at least one or two comparators U2c u2d will switch, making, thereby , its outgoing part at both low and por the resistance R19 to ground.
It becomes obvious that the gap between the two thresholds will determine the level of change required to flip the comparator. By reducing the value of the resistor R16, the voltage difference between pins 10 and 13 of U2 decreases.
Thus, the circuit will switch to small changes in luminance. For cons, the reverse occurs by increasing the value of the resistor R16. In this case, only an image change resulting from the presence of a large object will switch the circuit.
Yes, it's a little difficult but it is difficult to get any easier! Can be summarized bluntly, the purists will forgive us, saying that the purpose of this window comparator is to obtain a high level output when an image is fixed and a low level when the image changes, the sensitivity is adjusted by R16.
The relay control output
When the window comparator switches, determines a negative pulse to the trigger input of circuit U3, the popular NE555, mounted in monostable configuration.
Whenever his pin 2 of the NE555 is brought low (to ground), its output (pin 3) produces a positive pulse whose duration depends on the value of the components used in the circuit. In our case it varies from 1 to 60 seconds depending on the position of the trimmer R21.
To summarize the operation of the circuit, we can say that following a change of the image captured by the camera, the shot receives an impulse that sets its output high, thereby activating the relay RL1.
The relay contacts can be used to control an alarm buzzer sound from the siren, a flashing light from a desk in the ignition of a large bulb, or any other warning system. The relay contacts can also be used to activate a VCR or TV monitor. Of course, all these systems can be operated simultaneously, provided that the relay of VMD is limited to controlling power relays suitable warning systems ordered.
Power supply
The circuit is fully powered with a voltage between 12 and 15 VDC, applied at the points + and - Val.
To provide this voltage, we can use what you n'impor power source (even non-stabilized), capable of delivering at least 150 milliamps.
The diode D5 is used to protect it against any accidental polarity reversal and the electrolytic capacitor C19 filters out any kind of impulse noise and residual ripple.
The section of the relay, including LED, works in 12 volts. For cons, the rest work in 9 volt stabilized, obtained from the integrated controller U4, 7809 in a TO220 case. This choice is dictated by a desire for stability.
By separating the relay circuit of the other sections of the assembly we avoid any brownouts. Many capacitors placed on the positive supply line of 9 volt, contribute, too, to stability.
In the circuit, we also provided an output of 12 volts (CAM) to power the camera used to capture images. Before using this output, check carefully that this tension is well suited to the camera that will be connected.
The load resistance R1
Before proceeding with the construction, we want to stop briefly on a previously overlooked component but decisive: the resistance R1 of 100 ohms.
This resistance, used as impedance matching, is or is not necessary according to the type of installation.
If the camera for the device only serves as a sensor directly connected to the VIDEO IN, it is necessary to load the line with the resistance R1.
In the case where the system would be inserted in parallel in a facility existing video, consisting of a camera and a video monitor or VCR, the resistance R1 is not used.
In other words, if the video line is not charged, the resistor is used, otherwise it may be deleted.
For details, see the sidebar "The connections with the outside. "
The achievement and adjustment
We will now explain the construction of our VMD and how best to adjust.
As usual, you should first create or obtain the circuit given in Figure 5 and all components.
By helping the layout diagram of Figure 3 and the photo of the prototype in Figure 4, mount all the components starting with the lowest and ending with the highest. Ensure correct orientation of polarized components.
Place the two terminals to two PCB pads with a pitch of 5 mm, consistent with the marked holes VAL and CAM, in order to provide connections for system power and the binding power for the camera.
Do the same with the three pin terminal block provided for the use of the relay contacts on the location marked OUT.
As for the video input, you should use an RCA jack PCB in order to connect a camera or a video source directly with a standard cable.
Last of all, place the IC on their support in ensuring, again at their orientation.
At this point, carefully check the installation and welding, making sure not to forget the three straps (made with cascading tails resistors). We can not stress enough, a very thorough inspection of components and welds is guaranteed operation from power up.
A method among others
Here is one method we use for years and has always proved flawless. Get a box of 12 eggs.
It is economic and unless you have high cholesterol, your wife will always make a big omelet! Cut the lid and you have a storage for 12 different types of components.
In each compartment, place the resistors, ceramic capacitors, multilayer, chemical and so on.
Make a copy of the list of components if you have a photocopier or keep the list near you.
As always start with the resistors, Tez-sor of the compartment and place them on your desktop (we use a clear plastic cover to do this).
Mount these resistances in the order of the list of components, and every time check on the list, the resistance mounted.
Continue this and you will reduce to virtually zero risk of error.
Settings
To apply the settings, get a camera CCD or CMOS, operating preferably at 12 volts. Connect the son of feeding terminal provided for this and the video signal to the RCA. A glance at Figure 7 is worth to fix ideas.
When everything is in place, you can connect to the VMD power can provide 12 or 13 volts with a current of 150 mA, more than required by the camera (eg 400 mA, if the camera application ... 250 mA). Nevertheless, expect to connect it to the area or to turn it on.
Should be remembered that the polarity indicated. However, do not fear any more mistakes, because there is always D1 protects all components in case of accidental reverse connections.
Move the cursor to the end R6 fully connected to R5 that is to say up right, that of R16 at halfway and that of R21 to R22 therefore entirely up to the right as well. This way, you have predisposed the device to gain entry to the minimum, average sensitivity and the shortest period for controlling the output relays.
Turn on and get ready to make necessary adjustments.
Point the camera in that direction after attaching a firm using the method that suits you. If the relay is already activated, wait until it is deactivated. Thread a person before the camera at a distance of several meters and check that the relay RL1 is activated again. If this does not happen, we must slightly increase the gain of the amplifier input, to the maximum possible. At this point, slowly turn the cursor trimmer R6 clockwise, stopping at a position, repeat the passage before the camera until you get the activation of the relay.
At this point you may adjust the sensitivity adjustment (R16) by turning his cursor clockwise, it makes the most sensitive VMD; in the opposite direction, obviously, we desensitized.
The concept of sensitivity is related to the size of the object that is expected in the field of the camera, so the image and determine a perceptible change, sufficient to control the activation of the relay.
Therefore, the greater the sensitivity of the system, the more it becomes capable of detecting changes in the field of the camera more and more minimal.
Conversely, the more we diminish the sensitivity of the system, changes or more objects in the field of the camera will be important.
To conclude
After making sure that the VMD is working well, you can think of its placement on the site to watch.
If you connect to an existing installation of closed circuit television, you must extend the line that connects the video camera to monitor and / or VCR, interrupting the driver at a point that is most convenient. Figure 8 shows you how.
The system installed and the camera to its final location, you must verify that everything works according to your desires. The VMD should detect intrusions without occasional false alarms. To do this, you can repeat the steps described in the preceding paragraphs, setting R6 and R16.
As we have already said, the alarm output (RL1) can be used to control various alarms. Contacts with C / NO (normally open), you turn the monitor circuit when the CCTV VMD detect the entry of an intruder. You can also let it run continuously monitor and activate it, always with the same contact, a buzzer to attract the attention of the safety supervisor.
In a system that allows recording of video, the relay will be useful to allow a band of economy, by recording only when appropriate. To do this, simply connect the contacts C / NO to the eventual decision Remote Control, allowing the video recording and making contacts C / NC (Normally Closed) parallel to the control REC (record = record ).
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