Jump to content
Electronics-Lab.com Community

Recommended Posts

Well, here are several very interesting circuits : Remote Control Blocker by IR More than once we will have spent watching the best scene of a strip and that we change the channel. To avoid these little surprises that we do not like so much we have this powerful team that will be in charge of "flooding" with IR signal the enclosure avoiding that the remote control of the TV or the equipment that was working properly. The circuit is more than simple, the PNP transistor oscillates at the appropriate frequency of the equipment to be blocked while the NPN transistor amplifies the voltage to apply it on the IR diodes. These diodes should be high performance for a better result.Adjustme

circuito.gif.40f8fb6e479ef1b38267ae063eedfd28.gif

Place yourself near the equipment to block and operate the equipment, turn the preset to find the frequency that prevents the operation of the original remote control. 

-------------------------------------------------- ---------------------------------------- 

TV transmitter 

This sensillo circuit allows to transmit the signal of a videotape or camera around the perimeter of a medium-sized house. It is very practical, for example, when you have a satellite television system and only one tuner / decoder is available. The same applies to boxes for premium channels of cable TV operators. Although it is also useful when you want to transmit the video signal from security cameras to hard-wired points. 

electronicsThe scheme is very simple. The variable capacitor acts as a tuner, allowing you to adjust the frequency (channel) where you want to broadcast. Given the low power of this system the antenna can be a simple cable about 30 cm long or a retractable antenna. The transformer T1 is formed in its primary by 7 turns of wire while its secondary is composed of 18 turns. The 220pF capacitor connected in parallel with the secondary must be incorporated into the transformer last. This type of transformer is called SIF. As for the coil L1, this should be formed on a ferrite core of 3mm and on it should wind 4 turns of wire. 

Since this system operates with a very low power license is not required to use it, but if it were to place power stages that increase the scope of the set we recommend you to become a lawyer and become familiar with the legal aspects in force depending on the region where you go to use. 

Keep in mind that a poorly calibrated power stage could cause interference in the reception equipment of neighboring houses. Be careful in the assembly and calibration of this type of equipment. 

-------------------------------------------------- ---------------------------------------- 

2w FM transmitter 

This transmitter is ideal for jealous girlfriends. Simply put it inside a teddy bear and give it to the poor boyfriend. Then, from a distance of approx. 300 meters depending on the complexity of the place, you can listen to transmissions with a conventional FM receiver. As long as the boyfriend does not listen to himself on a walkman, all is well. 

The truth is that, beyond the use that is given, this transmitter uses only two common transistors to broadcast audio through the commercial FM band. It is quite stable and the signal quality is sufficient to transmit musical or spoken audio. 

5a33878a6b482_circuito(1).gif.5fc8064cdcd73c70e1a410cfc62a0fd8.gif

30-40 MHz 
L = 8 turns on a ferrite core of 0.25 " 
Cx = trimmer of 15-20 pF 
Cy = trimmer of 10-15 pF 
Antenna = Wire of 38" 

40-50 MHz 
L = 6.75 turns on a ferrite core of 0.25 " 
Cx = trimmer of 10-20 pF 
Cy = trimmer of 10-15 pF 
Antenna = Wire of 37" 

90-100 MHz 
L = 6.5 turns on a ferrite core of 0.25 " 
Cx = capacitor of 5.6 pF 
Cy = capacitor of 3.3 pF 
Antenna = Wire of 20 " 
 

The circuit must be assembled on an epoxy printed circuit and powered with 9 or 12 v DC. It consumes 4w, of which 2w makes them irradiated power and the other two makes them heat. 
If you want to use the system with an electret type microphone, you will have to add a resistance of 1K from the positive to the negative terminal of the input capacitor (base of 2N3708), establishing the power that type of microphones require. 

Given its reduced power this type of devices do not require state authorization to operate. -------------------------------------------------- ---------------------------------------- 55w car amplifier

Up to now, all the auto power circuits required a voltage source since these devices needed more than 40 volts. This circuit breaks with that tradition making it possible to manufacture a good quality audio amplifier for the car with only one integrated circuit per audio channel. In this way to make a stereo unit will suffice with two integrated and to make it quadraphonic will have to use four. 
5a3387bd26ca3_circuito(2).gif.45b20c95d99732c0aaae7b9fa7229aef.gif

As you can see in the diagram, the chip has everything necessary in its capsule, so it only remains to place the capacitors and filter and control resistors. Since the system is of the bridge type, the two speaker terminals are amplified, so none of them should be placed to ground. In any case, the circuit is protected against costs at the start, in addition to a long list of other protections. It is configured in class H. For more information about this chip connect to the page of Philips electronics, whose link is available in another section of this portal. 

The audio output does not require DC blocking capacitors as well as typical RL sets in these projects. 

It is possible to add a MUTE function which we omit in the diagram to simplify it to the maximum. If you want to do it, you have to place a 1K resistor between the ground and terminal 4, leaving the components that are as is. Thus the circuit goes into a mute state. By removing said resistor, the circuit returns to normal operation. Consult the specification sheet for more information about it. 

As in all these projects, heat sinks are extremely critical. Poor dissipation will cause the circuit to overheat and this will cause the system to shut down. It is not going to ruin because the chip includes internal thermal protection, but it will shut down causing it to stop amplifying. A Slot-1 or Slot-A microprocessor and fan (such as the AMD K7 or Intel Pentium III) is suitable, as long as the fan motor is running. In the case of using this type of forced cooling, it is important to design a good air channel since the fan is useless if it has no fresh air inlet and outlet. Another way to get good heatsinks is by making the sides of the cabinet the same heatsinks. In this case the size will be adequate and, in addition, 

It should be noted that this small "eats" 10 amps at maximum power so the power cables must be of adequate section. Otherwise they could be cut causing short circuits in the electric circuit of the vehicle. If you are going to mount four of these modules take into account the following: A medium vehicle has a 63 amp battery. This circuit multiplied by four consumes 40 amps. It is necessary to make a simple division to determine that it is capable of unloading the battery of the car in only two hours of use at maximum power. Therefore you will have to take special care as to see where the unit is connected. Another important factor is the ignition and fuel injection system. These circuits are usually somewhat sensitive to voltage drops so this amplifier can impair its operation. An alternative (very common in these cases) is to place a second battery housed in the trunk of the vehicle, which is charged through a diode from the voltage regulator of the alternator. Even the most expert of the engineers should take a tour of an installation house for this type of equipment because "the best hunter will miss a hare" and a mistake in the installation can leave it on foot. 

Do not even think about connecting the amplifier's power cord to the ignition key of the vehicle directly. Not even the key of a large truck could withstand the current. The way to connect it is simple, although it requires a relay. The contacts of the relay coil go in parallel with the current radio or pass tapes of the car, while the contacts of the mechanical key of that relay go in series with the cable (thick) that brings power to the amplifier from the battery. In this way the relay makes the brute force and the ignition key must only move the coil of the electromagnet. The relay should be able to handle up to 50A. It is possible to get one like this in the auto parts houses, asking for the one that switches the general power supply of the motor or the one that drives the starter motor. 

Another important point of the installation is the input signal. If the tape device you have installed in the car does not have line output, you will have to make an impedance adaptation and a power reduction to be able to connect the speakers' outputs to the amplifier's audio inputs. A good way is to buy a passive equalizer which modifies the tone of each band to equalize "attenuating" the others. It is important that this equalizer does not have an amplified output, because we would be at the starting point again. Although today most CD car kits have output without amplification. Another very common way is to place audio output transformers with the 8 ohm winding connected to the stereo output and the 2000 ohm winding connected to the amplifier input. 

It is necessary to clarify that although 1% of total harmonic distortion seems to be too much to be in a car it is somewhat low, given that the units that are commercialized normally have indexes of 3% to 5%. Only, just as they do with power, they lie about that value. 

Since the chip has a protection circuit against shorts that disconnects the output when the impedance of the load falls below 0.5 ohms, placing 2 ohms speakers (or 2 of 4 ohms in parallel) would cause the power to rise to 75 watts, but distortion will also rise to almost 10%. This is not acceptable for musical sound, but for propaganda or publicity on the public highway is ideal. Of course, the current demand will also increase. very good 

-------------------------------------------------- ---------------------------------------- 
Electronic Charger for Car Batteries 

Whether because we leave of using the vehicle for very long periods of time or because the battery is close to running out, this circuit allows it to be properly charged and indicated by means of an LED when the process has finished. 

5a3387f26575f_circuito(3).gif.6c1608cf295415a83c9a0f9508c936c6.gif

As you can see the circuit is a conventional power supply, followed by an LM338 regulator which is controlled by means of an operational amplifier that is responsible for controlling the state of the load to detect the precise moment when it must stop and operate the LED indicator. 

The three-stage resistive divider allows, on the one hand, to take the reference voltage for the operational amplifier and, on the other, to control the LM338 regulator by means of the output of the operational one. In this way, the load cutoff occurs when the current drops below half an ampere, when the circuit begins to oscillate causing the transistor to conduct the current to the LED making it shine to indicate the end of the load. 

Note that the bridge rectifier is 10 amperes (voltage equal to or greater than 50V) so it is not for soldering in printed circuit but to screw to the metallic cabinet of the equipment and connect by means of crimped terminals. The initial filtering capacitor can be soldered on the plate or it can be enclosed in the cabinet by means of two plastic seals and soldered in parallel with the positive and negative terminals of the diode bridge. The general switch is of the type used in electric coffee machines which have inside the neon gas lamp that lights up when the equipment is turned on. Pay close attention to how this switch is connected since it is very common to confuse terminals and short the 220V line. The regulator LM338 must be mounted outside the printed circuit on a suitable heat sink of not less than 10 x 10 cm of surface. If desired, a DC ammeter can be placed in series with the positive terminal of the output to the battery to visually monitor the current status of the load. This instrument can be analog or digital indistinctly, although nowadays it is much more colorful a digital one. The positive terminal of the instrument is connected to the circuit and the negative terminal goes to the battery (towards its positive terminal). The resistance of 0.1 ohm must be mounted on the plate, but raised 2 or 3 cm from it to prevent the heat from disturbing the pertinax. It is possible to place a buzzer that sounds while the LED shines. 

To use it, just place the battery to charge, turn on the system and press the button that starts the charge. When finished the LED will light up and the system should be turned off and the battery removed from the terminals. 

-------------------------------------------------- ---------------------------------------- 

90W amplifier 

Using only four transistors in a quasi configuration -complementary this amplifier can deliver 90W of power over a load of 4 ohms and at a really low cost. 

http://pablin.com.ar/electron/circuito/audio/amp90/circuito.gif 

As you can see in the diagram, there are no expensive components in this circuit, except for the transformer of the source and the speaker. The input stage consists of two current drivers that directly excite the transistor pairs of the output stage. The latter (the 2N3055) must be mounted on generous heat sinks in order to preserve the useful life of these devices. When being fed by a simple source (of 80Vcc) to the exit of the final stage, before the speaker, a capacitor must be placed that blocks the passage to the direct current and only lets pass the audio signal. The source must be capable of providing 1.5A of current per audio channel. In this way a stereo power will require 3A to operate and one of four channels will require 6A. 

-------------------------------------------------- ---------------------------------------- 

Well, this is all, 
Note: maybe some of the circuits have not been tested. 
in case you need some other information, more circuits or something, ask for it, 
but here is the source, where there is more http://xenoa.co.uk/

 

 

 

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
  • Create New...