This mini transmitter is on a printed circuit of just 4 x 9 cm which take up a high sensitivity electret microphone and a camera CMOS ultra miniature black and white. This is a transmitter and its image no bigger than a cell phone. Depending on the type of RF module that is chosen and that depends on the free channel available where one does operate, it may issue either UHF or VHF. Its range is between 50 and 100 meters.
The "soap opera" Loft Story challenges us, it's the least we can say!
What's more, some less, sometimes we look at some passages of "Loft Story", the new television show aired on M6, presented by Benjamin Castaldi.
Eleven young people, including six boys in the middle of five daughters whose names are singing for a long time haunt our memory: Delphine, Kenza, Loana, Julie and Laura.
Eleven young people chosen from a crowd of candidates, who agreed to live together for 70 days, locked in a common room (the loft), constantly monitored by 24 cameras (including some infrared, which can operate in the dark) which existence is known of the candidates but not the specific locations where they are hidden.
They occur together in the dining room or alone in the bathroom, they can be a sudden zoom at any time in any situation.
Thus, for example, we have witnessed a flirt live between Loana and Jean-Edouard.
These same images being broadcast over the Internet and satellite, which was a secret between two people becoming - the minute - known to everyone.
We do not know what to think of this new use that is made cameras and transmitters.
Yet we had had the premises, there are a few years now, watching the astronauts trapped in a spaceship, too, constantly filmed by a camera installed on board, which broadcast their actions, live, worldwide .
Does filming and continuously transmit images of an astronaut locked in his combination is good, while filming and continuously transmit the actions of eleven young people living together and forming - all in all - a group of friends is wrong? Everyone will answer these questions according to his own sensibility.
We just want - from this incident - a declaration that the things that were unthinkable a few years ago are now becoming not only possible, but legal.
Mores seem to evolve under the pressure of technological advances.
Thus, nowadays it is well recognized in the city we are filmed on average seven times a day, according to some statistics.
Besides the visible cameras, for example, on motorways and major roads allow staff to monitor road safety and relieve traffic in the most difficult moments, we meet at any time, on our way, a multitude of cameras .
There at the entrance to metro stations, banks, in supermarkets, train stations, airports, in jewelry stores, offices ...
And if the front door of the building where you live is protected by a video entry, you start the day by being filmed ... by yourself ... to your own knowledge!
On the other hand, why prohibit a person to keep under surveillance the door of her building's garage or the shop?
Hence we see that according to which side one takes, the decision that may relate to the use of broadcasting stations that can be installed anywhere, is not the same.
You just realize that these systems are becoming widespread, and if the need arises, we should protect themselves or protect themselves.
Advantages and Disadvantages
This generally discourages people to make an installation of closed circuit video surveillance, it is inevitable that these facilities bring inconvenience. Namely: the dirt and disorder.
In fact, surveillance cameras are installed at specific locations and units of viewing and recording are generally at a distance. In conventional systems, to route signals to each other, it uses cables. And to get these cables we are led to sometimes break, sometimes to make slits and for that we must move the furniture, where dirt and mess!
The system we present here removes these drawbacks and gives everyone the chance to make easy to install remote monitoring at low cost.
This is a complete system, in that it makes shots and passes with the sounds that accompany them.
The transmitted signal can be received by any television, could be the one you have in your kitchen, your bedroom or your living room.
In other words: no cables needed to connect the camera shooting the reception system, let alone a system for receiving specialist (monitor).
However, since nothing is perfect in this world and that every coin has two sides, if such facility has an unbeatable price and can be done without drilling, it has two drawbacks you should know admit it.
First, the signal can be received by anyone as easily as you: just make it lighter its position on the TV channel you are using. Secondly, the issue may be disturbed by other transmitters can operate in the vicinity on the same frequency.
Choice between UHF and VHF
If nothing can be implemented to overcome the first drawback, there is a way to limit the consequences of the second.
Indeed, since in the catalog of the manufacturer of hybrid modules include two similar models operating on different frequency bands, it is possible to mount the transmitter on either one or the other.
The show can be done either by VHF on channel H2 is UHF band on channel 22.
Presentation of the issuer
We have already had occasion to talk of hybrid modules manufactured by AUREL Corporation.
Whereas previously it was piecemeal applications, this time we have implemented a complete transmitter on a single small circuit board, comprising an ultra-miniature camera black and white set to solder directly on the PCB, and a electret condenser microphone, highly sensitive amplifier incorporating a field effect transistor.
Locked in a small plastic box and powered by four AA 1.5 volt stick, the transmitter - which, recall, requires no wired connection - can serve as visible or hidden camera because, due to its compact dimensions, there was no trouble to conceal it. Nobody would turn to a housing bore no resemblance to a camera shooting and even less a miniature TV transmitter.
The scope of this transmitter varies between 50 and 100 meters, depending on the obstacles between the transmitter antenna and the TV aerial on which we receive the images. Based on the experiences we do, we can say that it is VHF version that you get the best results. This is not about power, because the scope is the same regardless of the type of module used. The best results come simply from the fact that the UHF band is often crowded (especially on channel 22).
In short: it is particularly suitable for a transmitter to be monitored (by the image and sound) a room of small dimensions, or objects located not too far from him.
wiring diagram
Figure 1: Diagram of the complete transmitter. The presence of four components at very high level of integration (operational amplifier, microphone electret amplifier incorporating a FET, CMOS camera special PCB module and hybrid HF) lead to a very simple scheme. 
Figure 2: The electret condenser microphone, although having only two legs, incorporates an amplifier transistor field effect gives a sensitivity as he arrives to pick up even whispers the weakest. Through the use of four components at very high level of integration already sold assembled (including the electret condenser microphone cartridge incorporating a FET amplifier, the operational amplifier, CMOS camera special ultra miniature PCB alone accounting a complete system of shooting, and the hybrid module RF transmitter), the electrical circuit (Figure 1) of this transmitter is extraordinarily simple. For starters, there is no AC power to predict.
To leave all the necessary mobility to this mini TV transmitter, it uses batteries, not excluding - of course - the possibility of adopting a 6 volt power supply.
While we are talking about power to 6 volts, the circuit sees in reality only 5.4 volts, due to the presence of two silicon diodes in series (D1 and D2) located at the entrance, which while providing protection against short circuits, introduce, with their tensions of waste, the voltage drop necessary.
Indeed, the integrated components, including the operational amplifier U2, the CMOS camera module and the hybrid U1 require a voltage of 5 volts, within plus or minus 5%, which is the case here.
The two silicon diodes introducing a drop of 1.6 volts, the voltage reaches the circuits is, in fact, 5.4 volts.
The operational amplifier U2 is used to amplify the signal from the electret microphone MIC, whose role is, of course, to capture the sounds.
Despite its small size (Figure 2) and the fact that he has only two connectors, this microphone includes an amplifier transistor field effect which gives a sensitivity as he arrives to pick up even whispers .
The radio signal from the operational amplifier arrives, via the capacitor C7, the input "IN A" (A as Audio) hybrid module, corresponding to the leg 2.
The video signal to be transmitted, collected on leg 1 of the micro CMOS camera, which you can read the features in Figure 3, goes directly to the input "IN V (V as video) of the hybrid module, corresponding to the leg 4.
The leg 3 is connected to positive supply, while pin 2 is the general mass and at the same time the mass of the video signal.
As for leg 4, corresponding to the AGC (Automatic Gain Control), it leads to a rider whose implementation is optional.
By inserting this jumper, you can activate the automatic gain control, which is actually a system that addresses changes in video signal level. Although micro CMOS camera has six legs, only four are used.
The arrangement of these six-legged moreover, was designed by the manufacturer so that we can not take the wrong direction when it is implanted on the PCB.
The module of the micro-camera-flat soda, all against the printed circuit board (see detail in Figure 4).
For the rest, there is no provision for adjustment or development.
The values of each component were calculated to obtain the tiny transmitter the best results in terms of image quality.
With regard to the sound, the only thing we could possibly adjust to the sensitivity of the microphone (MIC).
To increase or reduce this sensitivity, simply change the value of the resistor R6, whose role is to determine the gain of the operational amplifier.
The output level of the video signal from the micro-camera is standard and automatically adjusts the input level of the hybrid module transmitter. The latter comes in the form of a small printed circuit board equipped with 8-pin (see Figure 5) as solder any component.
Once the welds are complete, it must be folded horizontally. So, the module lies flat on the PCB, occupying the site reserved for him, and whose ground plane is a kind of shield HF.
Specifications
Sensor: ...................................... Omnivision 1 / 3 "CMOS Standard: ..................................... CCIR Resolution: ................................... 240 TV lines - 288 x 532 pixels Sensitivity: .................................. 2 lux Electronic Shutter: ...................... 1 / 50 - 1 / 6000 AGC (AGC): .................................... ON / OFF Optics: ...................................... pin-hole f = 7.4 mm F = 2.8 Opening angle: ............................ 30 ° Food: ................................. 5 Vdc ± 5% Consumption: ................................. 10 mA
Figure 3: This new type of camera, called to spread, has everything to seduce. We mention its low price, its extremely small size (21 x 21 x 15 mm), sensitivity and the possibility of flat solder directly on the PCB. It can enter into systems of shooting very compact and easily concealable. Its resolution is not very high.
It is only 240 lines. But that does not prevent him from providing images to perfectly identify individuals. Do not even lose when sight of the fact that this type of camera is designed primarily for film closely.
Pin
1 = Video
2 = Ground video - alim.
3 = + alim.
4 = AGC (AGC)
5 = NC
6 = AGC (AGC)
Figure 4: The module containing the micro CMOS is a model for PCBs. It is welded directly to the pellets provided to receive it. Only 15 mm high, it does not exceed the other components. Its six legs, only four are used. The legs 5 and 6 are not welded because the former is not connected inside the module (NC), and second because the function to which it leads (AGC) was taken from the leg 4 (also connected to the AGC). Aurel modules TXAV UHF and VHF versions
Both modules have the same pinout and are pin compatible.
Their technical characteristics are identical in all, excluding the value of the output power available on the antenna in the UHF version is half that provided by the VHF module. But, in fact, since the transmission frequency in the UHF band is higher (479.5 MHz 224.5 MHz cons) and therefore more penetrating, it has no significant impact on the staff, which remains the same . It varies between 50 and 100 meters, depending on possible obstacles between transmitter and receiver.
It is the use of this type of modules that makes it so easily for the realization of a TV transmitter.
With dimensions of just 28 x 25 x 8 mm and with only eight legs, these hybrid modules, made using SMD components and powered at 5 volts, which include all elements necessary for obtaining a high quality emission .
It includes a crystal oscillator, amplitude modulated by the video signal that enters the foot 4, and a modulator driven by the audio signal between the tab 2, which modulates the frequency of a subcarrier at 5.5 MHz.
The input sensitivity of the sound stage is 1 Vpp (350 mVrms) at an impedance of 100 kilohms, which represents a value high enough not overloading any possible source (mixer, amp, cassette recorder, camcorder).
Figure 5a. 
Figure 5b. 
Figure 5c. Figure 5: Aurel modules TXAV version UHF and VHF.
Figure 6: Diagram of component layout of the mini TV transmitter. 
Figure 7: Here is how to present the issuer, complete the achievement. Note that the microphone and the hybrid module of the prototype pictured here have been slightly increased for illustration purposes only. 
Figure 8: Drawing of the circuit board, a wide, our mini TV transmitter complete. Component List
R1, R3 = 1 kΩ
R2 = 3.3 kΩ
R4, R5 = 22 kW
R6 = 680 kΩ
R7 = 270 Ω
C1 = 10 uF 16 V electrolytic
C2 = 220 uF 16 V electrolytic
C3 = 100 nF multilayer
C4 = 10 uF 16 V electrolytic
C5 = 1 uF 16 V electrolytic
C6 = 10 uF 63 V electrolytic
C7 = 1 uF 16 V electrolytic
C8 = 10 uF 16 V electrolytic
C9 = 150 pF ceramic
C10 = 100 nF multilayer
U1 = Module Aurel TXAV or TXAV / UHF
U2 = LM741 Integrated
D1, D2 = 1N4007 diode
CAM1 = CMOS TV camera for this
MIC = Micro preamplified electret
Miscellaneous:
1 Support 2 x 4-pin
Band scored two pins
1 Cavalier Computer
1 Cup of enamelled wire
12/10 for the antenna (see text)
1 PCB ref. S368/369
Achievement
Like every time a circuit uses preassembled modules where the real problems are all solved in advance, the practical realization of this small TV transmitter wishes to little.
The small printed circuit board, given its actual size in Figure 7, there are no tracks fine, and the pellet size is such that they can perform welds comfortable.
Once you have purchased or have completed the circuit, begin by installing and soldering components smaller.
As you can see from the timeline in Figure 6, the circuit includes two straps: one is located next to the miniature camera, and the other above, next to the resistor R6 .
Start by these straps. Then install the 7 resistors, 2 diodes (attention to their polarity if you want the system works!) And the support for receiving the operational amplifier 741 (orienting it as shown in the screen, so you don ' have, then, no question for you about how to insert the chip).
Continue with the jumper J1 on the MCO, and the 7 capacitors chemicals (including respect for the polarities is imperative).
Then finish by installing the module and the micro hybrid HF, which must then be folded so that it occupies the entire area reserved for it on the PCB.
Regarding the antenna, the easiest way is to use a piece of stiff wire (enameled 12/10 for example), after having stripped and scraped on the end to be welded.
Its exact length depends on the type of module used.
In combination with a module UHF antenna should be 12 cm. By cons, in association with a VHF module must measure 30 cm.
In fact the length of an antenna is calculated by applying the following formula:
l = (e / f) / 4
where "e" represents the speed of light (300,000 km / s) and f the frequency of the signal expressed in kilohertz.
The result "l" (in meters) is then divided by 4 because it is on the quarter-wave frequency in agreement that gives the lowest impedance and consequently the optimal result.
But in our case, since the PCB is already a piece of track, the length of it must be taken into account in the final calculation, leading to determine the actual length of the antenna.
So that ultimately the antenna itself will measure only 12 cm in the first case and 30 cm in the second. Of course, anything that would have to extend the length of the antenna must be taken into account in calculating the actual size of the radiating wire. A banana plug for example.
Once the welds are completed, the realization takes the form of what you can see in Figure 7.
Keep it in a case of your choice, which may also contain 4 x 1.5 volt stick to be placed in a battery holder and practice the necessary openings for the camera, microphone and antenna.
From there, the transmitter is ready for use. You can install it wherever you want and how, after all, what use you want, provided to shelter from rain and moisture.
However, consider the French legislation in terms of protection of privacy, right of publicity, etc.. Moreover, as we have already written earlier this Article, the receiving of what you make will be made on any receiver tuned to your channel. So any neighbor fiddling with his TV can receive your images. Do never send pictures that might offend or endangering public morals. In a nutshell, enjoy this micro-camera according to the established terms: "prudent man".
We have already stated that this transmitter is particularly suitable to take under control audio / video of small rooms, separated by 50, see 100 meters from the receiver.
It can be used to provide visible images in real time (think, for example, monitoring the baby's room) or to feed a VCR to view the images later, after the shooting.
Depending on the use we want to make this assembly could also precede the VCR of a circuit based on motion detection (motion detector) that would drive away the VCR when something passes in front of goal the camera.
This will be the fantasy of everyone who will suggest, ultimately, the use of the mini transmitter.
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