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circuit diagram: A total of four 1.2V cells are used here. Resistor R2 limits the charging current. For charging Li-ion battery (used in mobile phones), shift switches S1 and S2 to ‘on’ position and use connector ‘C.’ Regulator IC 7805 (IC2) provides 5V for charging the Li-ion battery. Using this circuit, you can charge a 3.6V Li-ion cell very easily. Resistor R3 limits the charging current. Fig. 2 shows the circuit for a small LED-based lamp. It is simple and low-cost. Six 10mm white LEDs (LED2 through LED7) are used here. Just connect them in parallel and drive directly by a 3.6V DC source. You can use either pencil-type Ni-Cd batteries or rechargeable batteries as the power source. Assemble the circuit on a general-purpose PCB and enclose in a small box. Mount RCA socket on the front panel of the box and wire RCA plug with cable for connecting the battery and LED-based lamp to the charger.

This is a circuit of SA58672 Small Class-D Audio Amplifier. This circuit is suitable for mobile device. It has maximum output power of 3.0 W for a 4ohm load and 1.7W for 8ohm load with power supply of 5V. If we uses 3.6 V power supply, the maximum output power is 900mW with 8ohm load. Here is the circuit : Using 9-bump Wafer Level Chip Scale Package (WLCSP), the SA58672UK save space in portable designs, because it measures only 1.66 x 1.71 x 0.6 mm. This circuit produces better overall audio performance because it has improved RF rectification and immunity to noise. The SA58672UK is suitable for cellular handsets or wireless and other portable audio application because it has fast start-up time of 7 ms eliminates pop-on sounds. [Source: NXP Application Note]

When audio is detected, the output is push-pull and consumes less than 3mA (with no signal) but drives the earpiece to a very loud level. It’s extremely difficult to set up because the whole circuit is DC coupled. Basically you don’t know where to start with the biasing. 8k2 between the emitter of the first transistor and 0v rail and the 470R resistor are the two most critical component. The emitter voltage on the BC 547 is set by the 8k2 across the 47u and this turns it on. To call the driver transistor, the collector is directly connected to the base of a BC 557. Current flow through the 1k and 470R resistors so that the voltage developed across each resistor turns on the two output transistors is caused by these transistors and the output of BC 557 are now turned on. The end result is mid-rail voltage on the join of the two emitters.Major negative feedback is provided by 8k2 feedback resistor while the 330p prevents high-frequency oscillations occurring. [Source: Talking Electronics...

Researchers at MIT have designed a novel device the size of a U.S. quarter that harvests energy from low-frequency vibrations, such as those that might be felt along a pipeline or bridge. The tiny energy harvester — known technically as a microelectromechanical system, or MEMS — picks up a wider range of vibrations than current designs, and is able to generate 100 times the power of devices of similar size. To harvest electricity from environmental vibrations, researchers have typically looked to piezoelectric materials, or PZT, such as quartz and other crystals. Various designs are based on a small microchip with layers of PZT glued to the top of a tiny cantilever beam. As the chip is exposed to vibrations, the beam moves up and down like a wobbly diving board, bending and stressing the PZT layers. The stressed material builds up an electric charge, which can be picked up by arrays of tiny electrodes. However, the beam itself has a resonant frequency and outside of this frequency, the...

This is a Small Circuit Multiband Radio -Transmitter CW for who wants to learn more about radiofrequency, mainly operating principle from radios transceivers multiband, That circuit consists of a frequency oscillator RF, which is the main component us transmitters and radio receivers.  He oscillates for high frequency, he is called variable frequency oscillator or VFO, their frequency may vary of 5.2 MHz to 15 MHz, depending the coil chosen and signal can be received in the band shortwave by any receiver radio.In S1 is used a switch type bell, but can-if use a handler CW, these used by radio amateurs. How antenna should-if use a the type dipole from 1/4 wave.

The circuit above shows a 4-transistor utility amplifier suitable for a variety of projects including receivers, intercoms, microphones, telephone pick-up coils, and general audio monitoring. The amplifier has a power isolation circuit and bandwidth limiting to reduce oscillations and "motorboating". The values are not particularly critical and modest deviations from the indicated values will not significantly degrade the performance. Three cell battery packs giving about 4.5 volts are recommended for most transformerless audio amplifiers driving small 8 ohm speakers. The battery life will be considerably longer than a 9 volt rectangular battery and the cell resistance will remain lower over the life of the battery resulting in less distortion and stability problems. 4 Transistor Amplifier for Small Speakers Circuit Diagram  The amplifier may be modified to work with a 9 volt battery if desired by moving the output transistors' bias point. Lowering the 33k resistor conne...