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A Low-Cost Video Security System Would you like to have a video security system but can’t afford the high cost of professional equipment? If so, take a look at this low-cost build-it-yourself setup. It’s based on a compact CCD camera together with a PC board to convert the composite video output to drive a surplus computer monitor. By LEO SIMPSON In these days of super VGA computer monitors, it is rare to find the old TTL monochrome “green screen” monitors being used at all. So what happens to them? Well, they’re not much use as boat anchors but they do have potential for use in a small closed circuit television security system such as the one presented here. The video security system described here consists of a small CCD camera, a monochrome monitor and a small PC board. The board takes the composite video signal from the camera and sepa­rates the horizontal and vertical sync signals to drive the monitor. The board also amplifies the video signal by a factor of about two to three. Finally, there is a small audio amplifier on the board to allow a microphone to monitor any sounds that might occur in the area under surveillance. The high resolution video camera employed in this project produces a standard “composite” 1V p-p signal that combines video, vertical and horizontal synchronisation. This output can be connected to a black & white or colour video monitor, a tele­vision receiver which has a direct video input, or the video input on a VCR which can then drive a TV set. Computer monitors, on the other hand, usually require sepa­ rate video, intensity, horizontal and vertical synchronisation signals and these are produced via a 9-pin D-socket from the computer’s video drive card. By the way, these monochrome video monitors, usually used with IBM PC or compatible computers but also with much larger computer systems, were referred to as “TTL monitors” because their drive signals came from 5V logic circui­try (eg, TTL). Fig.1 shows the 9-pin D-socket of a typical TTL monitor and the signals present at each pin. Note that for our applica­tion, the intensity modulation signal at pin 6 is not required. Typical TTL monitors as used by IBM computers had a verti­ cal horizontal line frequency of 60Hz, a horizontal line frequen­cy of 18,432Hz and a video bandwidth of 15MHz or more – far superior to a typical monitor intended for use with VCRs and TV signals. Now while the text display typically used on computer monitors normally involved a 5V signal, the video signal required in our application is analog in nature (ie, it is a picture with a wide range of contrast rather than the on-off format of text displays). Hence, the video signal level required by these moni­tors is around 3-4V p-p. By contrast, the CCD camera featured in this article pro­ duces a 1V composite video signal to the CCIR standard; ie, 50Hz vertical line and 15,625Hz horizontal line frequency. The dispar­ity between the horizontal and vertical line frequencies does not cause a problem though, as typical TTL monitors will work quite happily at The interface board has provision for both positive & negative sync pulses, as well as an audio monitoring facility. 56  Silicon Chip Above: our photographer, Stuart Bryce, has been captured by the CCD camera as this photo was taken. The CCD camera functions well even in very low light conditions. the lower frequencies, provided their horizontal and vertical hold controls are adjusted for a locked picture. The camera is on a small PC board measuring 54 x 38mm. It has a 582 x 512 pixel CCD image sensor with a wide angle f1.8 lens and an auto iris rated for a minimum illumination of only 0.1 Lux. At this very low light level, supplementary illumination is provided by six on-board infrared LEDs. So what is needed to match the video signal from the CCD camera is a circuit to extract the horizontal and vertical sync signals, amplify them to the correct level and boost the video signal to about 4V p-p. The circuit is shown in Fig.2. How it works Incoming video is applied via trimpot VR1 and the paral­leled 100Ω resistor R2. VR1 is used to adjust the video input level while R2 in parallel with VR1 sets the input impedance to about 70 ohms. From there, the signal is coupled to the input of the first amplifier stage via C4 and C3. C4 is a 0.47µF mono­lithic capacitor which exhibits low inductance; it GND 1 GND 2 NC 3 NC 4 NC 5 6 (+) INTENSITY 7 (+) VIDEO 8 (+) H-SYNC 9 (-) V-SYNC Fig.1 this diagram shows the 9-pin D-socket for a typical TTL monitor & the signals present at each pin. Note that for our application, the intensity modulation signal at pin 6 is not required. was included to compensate for the inductance of the 100µF electrolytic capacitor C3. This inductance could otherwise reduce the amplitude of the higher video frequencies. The first common emitter amplifier stage, based on NPN transistor Q1, has a gain of about 2, determined mainly by the ratio of R6 to R7. The output from this stage is directly coupled to a second common emitter amplifier stage based on PNP transis­tor Q2. This stage also has a gain of approximately 2, mainly determined by the ratio of R9 to R8. Q2 is directly coupled the base of NPN transistor Q3 which functions as an emitter follower to give the amplifier a low output impedance. It is capable of providing an output swing of about 4V p-p. The output of Q3 is AC coupled by C7 and C8 to a DC resto­ration stage consisting of resistor R11 and diode D1. D1 clamps the negative transition of the video signal to ground (actually to about -0.5V below 0V). D1 is a June 1995  57 R3 22k R4 18k C4 0.47 C2 100 VIDEO INPUT R1 4.7k R2 100  C3 100 VR1 200  +12V R6 1k +10.2V Q1 BC548 B +1.45V R5 8.2k R7 470  R8 C6 C5 220  100 0.47 +10.8V Q2 E BC557 C7 B Q3 0.47 2N2219A C C C B +2.6V C8 R9 100 E E +2V 470  R10 100  C1 0.47 R11 470  D1 SR103 R14 150  R12 3.3k C10 100 ZD1 10V R13 6.8k VIDEO OUTPUT +12V C9 100 C12 100 C11 0.47 Construction 2 VR2 50k ELECTRET MIC 3 C15 100 6 IC1 LM386 4 5 7 C13 100 R15 4.7  8W C14 .01 +12V R25 2.2k R21 2.2k Q4 2N2907A E B R16 3.3M C R17 1k R19 22k R22 R23 1.5k 22k Q5 BC548 C R24 B 10k R20 10k R18 3.3k H SYNC E R27 22k C16 .015 H SYNC R26 1.5k C Q6 BC548 E R28 10k R33 2.2k R29 2.2k V SYNC V SYNC R34 1.5k R30 R31 1.5k 22k Q7 BC548 C R32 B 10k B C Q8 BC548 E E B E C VIEWED FROM BELOW Fig.2: the circuit takes the incoming video & amplifies it by a factor of four using Q1, Q2 & Q3. Q4 extracts the sync signals (ie, sync separator), while Q5 & Q6 provide positive & negative sync pulses. R18 & C16 function as a low-pass filter to extract the vertical sync pulses & these are fed to Q7 & Q8 to provide both sync polarities. IC1 provides an audio monitor facility. Schottky diode which is very fast, a requirement for video signals. This means that the video signal extends from zero volts up to a maximum positive value around 4V, assuming a 1V p-p input signal. Transistor Q4 is employed as a sync separator. It is biased almost to cutoff by the 3.3MΩ resistor R16. Because of this and signal coupling via 0.47µF capacitor C1, Q4 conducts only on the negative peaks of the incoming composite video signal. This is exactly what we want, since the negative peaks correspond to the horizontal and ver58  Silicon Chip from the emitter of Q4 to a low-pass filter comprising 3.3kΩ resistor R18 and .015µF capacitor C16. The resulting low frequency signal is squared up by Q7 to give a negative-going sync pulse and inverted by Q8 to give a positive-going sync pulse. The audio amplifier is based on an LM386 IC. R12 and R13 provide the bias voltage needed for an electret microphone while C10 bypasses the electret bias line. The electret’s audio signal is coupled via 0.47µF capacitor C11 to volume control VR2 then to IC1 which has sufficient gain to drive the 8Ω loudspeaker. tical sync pulses. So the signal at the collector of the Q4 is the composite input signal stripped of video and leaving only the sync pulses. Now we have to separate the horizontal sync from the vertical sync. The recovered sync pulses are then applied to inverter stages Q5 and Q6. These produce both positive and negative horizontal sync pulses. This was done to cater for a range of monitors, some of which require positive sync pulses and others negative pulses. The vertical sync pulses are obtained by feeding the “mixed” sync Assembling the PC board is a straightforward process which will probably take most people under an hour. The board is sup­plied with a component overlay on top and has a green solder mask on the copper side to make soldering clean and easy. The parts layout is shown in Fig.3. We suggest you install all the resistors first, followed by the diodes and small capacitors. It is a good idea to check each resistor value with a digital multimeter before soldering it in. Following the small components, the electrolytic capacitors can be installed and then the transistors and trimpots. Make sure that each electrolytic and transistor is installed with the correct polarity and ensure that you don’t get the transistors swapped around – PNP transistors don’t work in place of NPN types and vice versa! Finally, you can install the LM386 IC and the board is complete. Monitor installation The next step is to install the video conversion board into a small surplus computer monitor which is supplied as part of the kit for this project. The monitor is a secondhand 12V unit with a small screen. Probably this monitor would have been used as a terminal in a bank or insurance company. First, remove the diecast metal case of the monitor which is done by undoing four screws at the rear and then sliding it off. The board is installed quite simply by attaching it to the vertical panel opposite the EHT transformer. The side panels look like cardboard but are made of a Bakelised insulating material such as Presspahn. Drill a 22k .015 Q5 10k couple of holes through this side panel so that the PC board can be attached with two diagonal screws and nuts. However, before doing that you have to make the various interconnections. The practical way to do this is to remove the edge connec­ tor at the rear of the monitor’s PC board. This duplicates the connections made to the 9-pin D socket at the rear of the chassis and has the advantage that it is much easier to solder wires to than the D-socket itself. You will now need to run hook-up wire of different colours between the video board and the 10-pin edge connector. If we arbitrarily assign the pin numbers from left to right, the con­ nections are as follows: pin 2, vertical sync; pin 3, video; pin 4, +12V; pin 5, horizontal sync and pin 10, GND. The input from the electret microphone insert should be run in audio 3.3k ZD1 1.5k 2.2k 1.5k 22k Q7 Q6 IC1 LM386 VR2 1 Q8 shielded cable while the speaker connections can be in normal hookup wire. Lace the cables together for a neat job and make sure that there is no chance of them coming into contact with the high voltage supply for the monitor. Camera mounting To run the camera, interface board and monitor, you will need a 12V DC supply that can provide a little over 1 amp. This will need to be reasonably well filtered and regulated otherwise hum bars are likely to be present in the picture. The CCD camera module will need to be mounted in a small plastic case so that it is protected and reasonably unobtrusive. In fact, you could mount it in plastic box with a dark tinted perspex window to make it look innocuous. You should be able to run the This scope photo shows the video output signal on the top trace (CH2) & the negative horizontal sync signal from Q5 on the lower trace (CH1). Note that the video signal is about 2V peak-peak & this can be increased as required by adjust­ing VR1. The sync pulses are close to 5V peak-peak & are spaced 64µs apart, exactly as they should be. video output cable for a few metres without noticeable picture degradation. When all the equipment is connected, you will need to adjust the vertical and horizontal hold controls for a locked picture and then adjust the brightness control for best picture quality. 4. 7  1.5k 100uF .01 1.5k 0.47 AUDIO INPUT Fig.3: install the parts on the interface PC board as shown here. Take care to ensure that all polarised parts are correctly oriented. 100uF 12k H SYNC 2.2k 10k 2.2k SPEAKER 100uF 100uF 2.2k 100  D1 V SYNC VIDEO OUT 10k 3.3k 470  22k 1k 3.3M 470  Q1 10k 0.47 8.2k 150 100uF 100uF 0.47 Q3 VR1 470 Q4 TO CAMERA +12V GND GND +12V Q2 22k 0.47 18k 100uF 100  4.7k VIDEO IN 0.47 100uF 220  22k 1k 100uF Other TTL monitors While a small monitor is provided as part of this project kit, you may want to use a larger screen TTL monitor and this will probably present some problems of incompatibility. As it stands, the video interface board will probably not work well with standard TTL monitors and there are a number of reasons for this. First and foremost, the vertical and horizontal sync out­ puts are not directly compatible with the TTL inputs on many monitors because they do not swing between 0V and 5V. This can be achieved however, by a simple modification. To convert all sync outputs to TTL levels, short out 1.5kΩ resistors R22, R26, R30 & R34, then connect a 2.2kΩ resistor across each of the sync transistors Q5, Q6, Q7 & Q8. This The CCD camera is on a small PC board measuring 54 x 38mm. It has a 582 x 512 pixel CCD image sensor with a wide-angle f1.8 lens & an auto iris rated for a minimum illumination of only 0.1 Lux. At this very low light level, supplementary illumination is provided by six on-board infrared LEDs (three to either side of the lens). June 1995  59 PARTS LIST 1 PC board, 133 x 57mm (Oatley Electronics) 1 200Ω horizontal trimpot (VR1) 1 50kΩ horizontal trimpot (VR2) Semiconductors 1 LM386 audio amplifier (IC1) 5 BC548 NPN transistor (Q1,5,6,7,8) 1 BC557 NPN transistor (Q2) 1 2N2219A NPN transistor (Q3) 1 2N2907A PNP transistor (Q4) 1 SR103 Schottky diode (D1) Capacitors 9 100µF 25VW PC electrolytic 5 0.47µF monolithic ceramic 1 .015µF 25V ceramic 1 .01µF 25V ceramic The interface board can be mounted along one side of the video monitor, as shown here. Make sure that it is properly secured. Resistors (0.25W, 1%) 1 3.3MΩ 4 2.2kΩ 5 22kΩ 4 1.5kΩ 1 18kΩ 2 1kΩ 4 10kΩ 3 470Ω 1 8.2kΩ 1 220Ω 1 6.8kΩ 1 150Ω 1 4.7kΩ 2 100Ω 2 3.3kΩ 1 4.7Ω Where to get the kit The three components of this project are the CCD camera module, video interface board kit and small video monitor. This is available as a package deal for $215 from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. The edge connector is just behind the D-socket panel. It is convenient to make all the connections to the edge connector. will result in a nominal sync voltage swing of 0-6V but this will be reduced to within TTL limits by the loading of the monitor’s inputs. Once you have the correct TTL sync levels, you should be able to obtain a stable picture on the monitor (by adjusting the vertical and horizontal hold controls) but you will then probably find that the picture has just two shades, black and bright green. The reason for this is likely to be the TTL interface in the monitor itself. This 60  Silicon Chip will effectively convert the analog video from the external interface board to two levels, on and off. Such a picture looks pretty hopeless and the way around it is to bypass the TTL interface chip and connect directly to the set’s video input. This can usually be identified fairly easily because it will have a shielded cable running from the TTL chip to the picture or brightness control. If you connect the video signal directly to this shielded cable you should then be able to obtain a picture with the full range of contrast. However, there is a further drawback to many TTL monitors and that is because of the picture phosphor. This was great for giving bright text displays but the phosphor usually has a long persist­ ence (ie, takes a significant time for an image to fade). The result of this is that each time the camera image changes, it will blur the motion. This may not be a problem for some applications but we draw it to your attention so that you are not disappointed by the results. On the other hand, the picture quality on the supplied small monitor is quite passable, especially so when the SC low price is considered.