We often look poorly recorded video tapes, full of interference with pictures and some ill-defined net.
To improve image quality it is useless to amplify the signal to the VCR output. Everything would be then amplified, flaws included. It should, instead, a device for re-order timing and burst, separately restating the pure video. The installation that we offer in these pages is intended to accomplish this task.
How many times have you happened to see some poorly recorded tapes, with variations in brightness, color faded or very annoying horizontal stripes?
Often the problem occurs on videotapes recorded by amateurs using two VCRs.
As for audio cassettes, signal degradation occurs during the transition from one device to another. For once, it's even more unpleasant, the original tapes of the trade, bought and paid a high price have the same defect. This comes just system protection against copying that degrades the signal by adding noise, the sole pretext of preventing duplication.
With some high quality video, these parasites are amplified to hamper honest vision of the recording. The basic and immediate solution to improve things, while ensuring an acceptable quality, would be to connect a broadband amplifier at the output of the playback system. This amplifier should be able to raise the level to compensate for signal attenuation due to poor support, if the tape is too low end.
However, this is not always enough.
Often, however, the result is quite different than expected. A video signal can be amplified only if its timing signals, or burst interleaving are net. Otherwise, with the usual variable gain amplifier, it also increases the noise level, and instead of improving, we see that the signal deteriorate significantly
The ideal solution is to connect on the VCR output A device capable of separating the synchronization signals and control the video signal, to get rid of any unwanted noise, and then return, exit, a composite video signal practically perfect.
The implementation is obviously difficult but, fortunately, modern technology brings new electronic components regularly.
These help to develop a video signal through digitization, providing a limited and selective amplification by allowing the recovery of synchronization signals.
Our electronic filter for video cassettes uses one of these components.
Study schema
From the first look at the electronic diagram, we see some complexity due to the presence of two integrated circuits, one standard, the other individual. The first is U5, sync separator LM1881 well known, produced by National Semiconductor and used in many televisions for the start pulse line (top line sync) and the flyback. (Back of the spot light).
In our device, the component from National Semiconductor allows to extract the tops start line (every 64 ms) and pulse-end screen (every 20 ms assuming we use the PAL system at 50 Hz) and then send them to the circuit U6. This latter is a PLD (Programmable Logic Device, which is a device composed of an elementary logic programmable) of the firm Lattice type ispLSI 1016.
If the PLD is programmed correctly before use and its implementation in the circuit, it can generate pulses of horizontal and vertical synchronism with which he drives the CMOS switches present in U2. This
order to pass only the pure video signal by filtering out any peaks and making out as they once reworked and corrected.
U4 is the circuit at 24 MHz clock that drives the integrated circuit U6.
Once these initial explanations given in principle, try to deepen a little, without going into too much detail, it being understood that the purpose of this article is giving the thread to learn how to use the system.
Suppose we want to duplicate a videotape "blurred."
analyze the circuit starting from the IN.
On this input is injected into the video signal from the SCART connector (SCART) of the first VCR, the one who reads the tape to duplicate.
This signal is sent from one side through C5 and C6, the CMOS switches and U2a U2b and the other hand, is applied through C2, at the entrance of the separator U5.
Note the parallel C5/C6 constitutes an "expander" bandwidth. Same to the exit for C8/C9. Also note the presence of the bridge R3/R4, whose objective is to provide the polarization when U2b U3 is activated and carries the signal to the filter R5/C7. Obviously all
CMOS switches must first be extinguished, at least until the LDP (U6) which does not receive control signals for synchronizing the LM1881 (U5).
U5 will allow extracting video signal on its pin 2 the following four signals : The horizontal sync, vertical sync, burst and the information about the interlacing of the image on the screen.
Let's see what happens in what we regard as the heart of the digital filter: the circuit in 1016 of ispLSI Lattice. This is a PLD to 2000 doors, allowing to work at a maximum frequency of 125 MHz. This PLD is specially programmed to handle the synchronization signals from the LM1881, and for generating the logic control for CMOS switches present in U2 (CD4066) to reconstruct the sync pulses. To understand its operation, as well as that of the whole, we must first know that currently the video signal from the tape recorded in PAL is not fully visible to the user, since it is composed of 625 lines.
In fact the first 19 lines contain synchronization signals and the burst, possibly teletext and the copy-protect. Only 583 lines are actually created for display on the screen. The latter are eliminated, even if they contain useful video information.
The goal of the LDP is to separate the first 19 lines by synchronizing with the " composite sync. "Coming out of the LM1881. Then counted and the LDP filtered composite video signal for the corresponding period in order to eliminate interference and the impulse to protect the duplication that alter the signal. The signal is then returned, once cleaned. In practice, the circuit of the firm Lattice done that from the first horizontal pulse detected on the falling edge after a positive transition of the vertical impulse. It has peaks from pin 1 of U5 to the nineteenth. Then with a logic 1 (pin 26 of U6 and pin 5 U2b) CMOS switch activates the U6 U2b. The video signal
arriving at the input IN, then passes through the filter that removes R5/C7 each synchronization (peak brightness, etc.). This filter restores well the output of U3, mounted in non-inverting amplifier, a level which corresponds to black, and, therefore, obscures the top of the TV screen.
U2c u2d and, in parallel to reduce series resistance, are activated by the pins 25 and 27 of the LDP.
Once past the 19 lines mentioned above, U6 suspends counting and resets. He puts the pin 26 to logic low, thereby triggering the switch U2b. U6 via its pin 28 set to logic high, the switch will activate U2a.
Thus the video signal avoids the filter and amplifier U3 to arrive directly to the capacitors C8/C9 and at the base of output transistor T1.
In this case, it is assumed that there is more interference peaks or protection and, consequently, the video signal can pass cleanly.
From the emitter of the transistor, the signal reaches the output connector via C3/C4, (for which we find the same considerations as for the C5/C6 in terms of bandwidth), where it can be taken and sent to the input video recorder in charge of re-registration.
The circuit can be fed continuously (9 V to 25 V) or alternating (8 V to 18 V), without addressing the polarity Val through diode bridge PT1. The capacitors C10 and C12 filter and smooth the voltage. The diode LD1 indicates, lighting up, the presence of food. U1 is a classic controller built 7805. It delivers the required 5 volts to integrated circuits.
Figure 1: Diagram. 
Figure 2: PCB-wide 1. 
Figure 3: Components layout. 
Iist
R1: 3.3 kΩ
R2: 82 Ω
R3: 4.7 kΩ
R4: 4.7 kΩ
R5 R6 1.5 kΩ
: 680 kΩ
R7: 470 Ω
R8: 3.3 kΩ
R9: 1 kilohm
R10: 1 kilohm
R11: 68 Ω
C1: 100 nF multilayer
C2: 100 nF polyester
C3: 100 nF multilayer
C4: 47 uF 16 V electrolytic
C5: 47 uF 16 V electrolytic
C6: 100 nF multilayer
C7: 100 nF multilayer
C8: 47 uF 16VL
electrolytic C9 100 nF multilayer
C10: 100 nF multilayer
C11: 100 nF multilayer
C12: 470 uF 25 V electrolytic
C13: 470 uF 16V electrolytic
C14: 100 nF multilayer
C15: 100 nF multilayer
C16: 220 uF 16 V electrolytic
LD1: 5mm Red LED
PT1: 1 A diode bridge
U1: U2
7805: Integrated circuit U3
4066: Integrated Circuit LM358
U4: 24 MHz oscillator
U5: U6 LM1881N
: Lattice PLD ispLSI 1016 (MF282 software)
T1: BC547B NPN Transistor
Miscellaneous:
- Taking Power ICs
- RCA jack for CI (2)
- Support 44-pin integrated circuit
- Support integrated circuit
2x7 - 2x4 Support integrated circuit (2)
- PCB Ref. S282.
(All resistors are 1 / 4 W 5%)
The chip ispLSI 1016 of Lattice.
The PLD (Programmable Logic Device - Programmable logic circuit) used in the device is fully programmed to generate pulses of horizontal and vertical synchronization, with which he drives the CMOS switches in order to pass a video signal pure, cleaned of all parasites. The video protection system anticopying
protection inserted in some videotapes to prevent the reproduction is nothing but interference in the "invisible" in the video signal. In practice, we have peaks of very high brightness (up to 10 volts) in the first lines of the signal are usually placed where the teletext data. In this way, the output signal is saturated in an area where there should be no embarrassment. 
The problem arises when the signal in question is sent to devices equipped with the AGC (automatic gain control). As peak brightness are important, the MCO (thinking offset) will decrease the signal level and will result in a darker image.
Of the most recent video, the gain control is crucial when it is used to balance the loss due to deterioration of magnetic tapes and recording heads clogging. The video signal level is considerably reduced, it follows a loss of synchronization and the colors, resulting in considerable deterioration of the image on the copy. Practical realization
Well, now we know the theory, we can begin to build the video filter. First prepare the printed circuit of which we find the photo side slopes at scale 1 in Figure 2. By making a copy on tracing paper, film for photoengraving is immediately ready. Once the circuit
cut and drilled, one goes first resistance and support for integrated. Pay attention to U2, U3 and U5 requiring carriers normaux (respectivement 2x7, 2x4 et 2x4 broches), alors que U6 a besoin d’un support PLCC à 44 broches.
Après cela, passons aux condensateurs en accordant une attention toute particulière à la polarité des chimiques, à l’oscillateur à quartz U4 (utiliser un modèle à 24 MHz), ainsi qu’au régulateur 7805 qui doit être monté à plat avec la partie métallique bien en contact avec le circuit imprimé.
Puis c’est au tour du pont de diodes (regardez la disposition des composants sur la figure 3 pour son orientation) et de la diode LED LD1. Pour cette dernière, rappelez-vous que le méplat indique la cathode et doit être tournée vers U1.
Remember the little jumper located near the U3 support. For this you must use a piece of copper wire from 0.6 to 0.8 mm in diameter or a tail resistance. For connections of input and output, it is preferable to solder RCA mono at 90 ° to the PCB. It should also provide a plug weld on CI.
This being done, the electronic filter for video cassettes is ready. Insert one by one the integrated circuits in their sockets, taking care not to bend the legs and in the correct direction (see the pan assembly of Figure 3), then check well all.
In use, remember that the only video signal must be applied to the filter without the audio. Several solutions can be implemented:
- Extract the video signal from the SCART / SCART (SCART) that connects the two VCRs. To do this, simply cut the soul of small shielded cable soldered to pin 19 (VIDEO OUT) jack on the VCR side "reader" as well as its mass soldered to pin 17 (GND VIDEO). Then be transplanted on two pins with a small shielded cable terminating on an RCA jack and we have our video IN. For our OUT video, we will manufacture the same cable screened beginning with RCA but that will connect the video input from the SCART connector (pin 20) of the VCR "recorder" and the corresponding weight (still pin 17).
- If you have video recorders equipped with RCA inputs and outputs, everything is much simpler. In this case, simply use one (case of audio in mono) or two (the case of stereo audio) Cable RCA / RCA to connect with one another both audio inputs and two video cables Connect the one hand, the video OUT on the VCR " player "on the IN video filter and, secondly, OUT video filter input IN VCR video" recorder. "
Everything should work properly since there is no adjustment to make. If a discrepancy should arise, it should check the assembly and welds with the utmost care.
Similarly, it is important to put the video recorder set to "registration" from the channel SCART (or RCA) and not from the internal tuner.
To test the connections, it is sufficient to link the two cards are intended to be connected on the IN and OUT of the filter. In doing so, we must see the video signal through the VCR recording.
connection diagram between two VCRs in order to make a backup "clean" of your favorite movies. 
view of the prototype once assembly is complete Our prototype can operate in either DC or AC, with values between 9 and 25 VDC or 8 to 18 VAC.
If desired, supply the system with a 9 volt battery, replace the outlet with a a power-button.
This device is a re-timer and a video stabilizer whose goal is to improve the quality of the reproductions that you own the rights to use. Using this device should be strictly reserved for private use and in strict compliance with laws governing copyright.
The publisher, the manufacturer and distributors disclaim any liability in the event that misuse would be done by the user or by third parties.
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