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The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system. Circuit diagram : 8 Stage LED VU Meter Circuit Diagram The divider voltages are set so that each LED represents about twice the power level as the one before so the scale extends from 22 milliwatts to about 2.5 watts when all LEDs are lit. The sensitivity can be decreased with the input control to read higher levels. I have not built or tested this circuit, so please let me know if you have problems getting it working. The power levels should be as follows: 1 LED = 22mW 2 LEDs = 42mW 3 LEDs = 90mW 4 LEDs = 175mW 5 LEDs = 320mW 6 LEDs = 650mW 7 LEDs = 1.2 Watts 8 LEDs = 2.5 watts

zBot :10-A Power Stage for DC Motor Circuit Diagram . If you look at the chassis of the zBot vehicle1, you’ll find two parts requiring intelligent control: the steering servo and the DC motor . The so called H-bridge is the normal circuit for electronic control of revolution speed and direction. The DC motor of a Tamiya car is powerful enough to propel zBot at up to 20 miles per hour. . The motor then consumes more than 10 A, so we choose high-current power MOSFETs for the driver stage. There are lots of different devices to choose from. The MOSFET we require has to supply the maximum motor current and, importantly, it has to be switched with gate voltages of about 5 V. In this case, the microcontroller switches the power stage (‘low side’) directly. For high side driving level shifters are necessary. The schematic of the H-bridge power stage shows a few inverters, NAND gates and two tri-stateable drivers. These logic functions are very important as the easier way, i.e.., directly con...

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4). A condenser microphone is connected at the input of the oscillator.  Four-Stage FM Transmitter Circuits diagram : Four-Stage FM Transmitter Circuits Diagram Working of the circuit is simple. When you speak near the microphone, frequency-modulated signals are obtained at the collector of oscillator transistor T1. The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. The preamplifier is a tuned class-A RF amplifier and the driver is a class-C amplifier. Signals are finally fed to the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna. Use a heat-sink with transistor 2N3866 for heat di...