Simple Op Amp Radio

This is basically a crystal radio with an audio amplifier which is fairly sensitive and receives several strong stations in the Los Angeles area with a minimal 15 foot antenna. Longer antennas will provide a stronger signal but the selectivity will be worse and strong stations may be heard in the background of weaker ones.

Using a long wire antenna, the selectivity can be improved by connecting it to one of the taps on the coil instead of the junction of the capacitor and coil. Some connection to ground is required but I found that standing outside on a concrete slab and just allowing the long headphone leads to lay on the concrete was sufficient to listen to the local news station (KNX 1070).

Simple Op-Amp Radio Circuit Diagram

 The inductor was wound with 200 turns of #28 enameled copper wire on a 7/8 diameter, 4 inch length of PVC pipe, which yields about 220 uH. The inductor was wound with taps every 20 turns so the diode and antenna connections could be selected for best results which turned out to be 60 turns from the antenna end for the diode.

The diode should be a germanium (1N34A type) for best results, but silicon diodes will also work if the signal is strong enough. The carrier frequency is removed from the rectified signal at the cathode of the diode by the 300 pF cap and the audio frequency is passed by the 0.1uF capacitor to the non-inverting input of the first op-amp which functions as a high impedance buffer stage.

The second op-amp stage increases the voltage level about 50 times and is DC coupled to the first through the 10K resistor. If the pairs of 100K and 1 Meg resistors are not close in value (1%) you may need to either use closer matched values or add a capacitor in series with the 10K resistor to keep the DC voltage at the transistor emitter between 3 and 6 volts.

Another approach would be to reduce the overall gain with a smaller feedback resistor (470K). High impedance headphones will probably work best, but walkman stereo type headphones will also work. Circuit draws about 10 mA from a 9 volt source. Germanium diodes (1N34A) types are available from Radio Shack, #276-1123.

Infrared Remote Control

This circuit will allow you to turn on any piece of equipment that operates on 115 volts ac. The receiver circuit is based on the Radio Shack infrared receiver module (MOD), part number 276-137. It is also available from some of the other sources listed on my Links page. The MOD accepts a 40khz IR signal that is modulated at 4 khz. When a signal is received the MOD will go low. The sensitivity of the MOD is set by different values for R1 and C1.

Infrared Remote Control Circuit Diagram

The values for R1 may need to be as high as 10,000 ohms and for C1 40uf. This will prevent the unit from turning on under normal lighting conditions. You will need to experiment with the values that work best for you. The output of the 4013 chip a flip flop toggles on and off with the reception of a IR pulse. The output of the 4013 turns on the MOC optical coupler which in turn switches on the triac and supplies power to the AC load.

Garage Stop Light

A novel use of solar cells makes positioning your car in the garage rather easier than old tyres, a mirror, or a chalk mark. The six solar cells in figure 1 serve as power supply and as proximity sensor. They are commercially available at relative low cost. The voltage developed across potentiometer Pi is mainly dependent on the intensity of the light falling onto the cells. The circuit is only actuated when the main beam of one of the cars headlights shines direct onto the cells from a distance of about 200 mm (8 inches). The distance can be varied somewhat with P,

Simple Garage Stop Light Circuit Diagram :

Under those conditions, the voltage developed across C1 is about 3 V, which is sufficient to trigger relaxation oscillator Ni. The BC547B is then switched on via buffer N2 so that D3 begins to  lfash. Diodes Di and D2 provide an additional in- crease in the threshold of the circuit. The total voltage drop of 1.2 V across them ensures that the  potential at pin I of the 4093 is always 1.2 V below the voltage developed by the solar cells. As the trip  level of Ni lies at about 50 per cent of the supply  voltage, the oscillator will only start when the supply voltage is higher than 2.4 V.

The circuit, including the solar cells, is best constructed on a small veroboard as shown in figure 3, and then fitted in a translucent or transparent man- made fibre case. The case is fitted onto the garage wall in a position where one of the cars headlights shines direct onto it. The LED is fitted onto the same wall, but a little higher so that it is in easy view of the driver of the car. When you drive into the garage, you must, of course, remember to switch on the main beam of your headlights!

Source : www.ecircuitslab.com

Small Power Amplifier 8W 8Ω with TDA 2030

Although the TDA2030 can deliver 20 watts of output power, I deliberately reduced the output power to about 8 watts to supply 10 watt speakers. Input sensitivity is 200mV. Higher input levels naturally will give greater output, but no distortion should be heard. the gain is set by the 47k and 1.5k resistors. The TDA2030 IC is affordable and makes a good replacement amplifier for low to medium audio power systems. Incidentally, it is speaker efficiency that determines how "loud" your music is.

Small Power Amplifier Circuit diagram:

Parts:

R1-2=47ohmK 1/4W        
R3= 1.5Kohm 1/4W         
R4=1.2ohm /1W        
C1-5=1uF/25V
C2-6=100uF/25V
C3-7=100nF/63V
C4=220nF/63V
D1-2=1N4001
IC1=TDA 2030

The worker can simply press the pagedown button of cell phone jammer

The worker can simply press the pagedown button of cell phone jammer .
Promise as a wireless presenter products use 2.4G ISM band. The bands product, if less than 1 mW transmit power, is not obtained "Radio Transmission Equipment Type Approval Certificate (SRRC)" The. ISM band that is industrial, scientific and medical band. Generally speaking, countries around the world to retain some of the wireless spectrum to be used for industrial, scientific and medical applications of microwave. No permit application of these bands, just to comply with certain transmission power (typically less than 1W), and do not cause interference to other bands can. ISM band regulations in each country are not uniform. In the United States there are three bands 902-928 MHz ,2400-2484 .5 MHz and 5725-5850 MHz, while in Europe there is part of the 900MHz band is used for GSM communication. The 2.4GHz ISM band common for countries, promise for the 2.4G wireless presenter products are in this band, so no need to obtain permission. cell phone jammer can help achieve the free presentation of the electronic document.
Demonstrator for wireless products promise the maximum transmit power of 1mW, the radiation is very weak. Our products work only when the maximum radiated power equivalent to a normal GSM mobile calls when the maximum radiated power of 1 / 700. So it will not cause injury. Since our products are used for one-code technology, the receiver only receives a corresponding address code transmitter. Both products have frequency hopping, when a serious band interference, it will automatically jump to another frequency band, so using both sets of products will not interfere with each other. Radio Frequency RF is an abbreviation, is the radio frequency technology. Wireless local area network WLAN and mobile phones using radio frequency technology. cell phone jammer can effectively manipulate the turning over of the multimedia.
Wireless Presenter products in technology, and RF is the corresponding infrared technology, called IR. Computers and air conditioning remote control using infrared IR remote control technology. Products using infrared technology direction, the transmitter must align the receiver, and no intervening obstructions. Distance is not more than 7 meters from electromagnetic interference, the advantages of infrared products is the product of low cost, cheap. cell phone jammer can make it very convenient to make speeches.
Using radio frequency technology products are used radio waves to transmit control signals, and its directional characteristics, can not "face to face" control, distance, up to tens of meters.