Electronic Projects   |   Store   |   Schematics   |   Downloads   |   Search  

Circuit-Zone.com - Electronic Projects



LM3886 Amplifier
Posted on Sunday, May 29, 2011   •   Category: Amplifiers


Several years ago, National Semiconductor came out with some very high performance, easy to use audio power LM3886 amplifier ICs. I was in need of an extra amplifier so I could biamp some of my home-built electrostatic loudspeakers so I tried the LM3886 chip. LM3886 amplifier was chosen because of the ease of use, power output, turn-on and off thump suppression, low distortion, and built-in protection against shorts and thermal runaway. There isn't much more to ask of a power amp than that. When driving electrostatic speakers, you can't have too much protection.


Field Strength Meter
Posted on Saturday, May 28, 2011   •   Category: Test and Measurement


This Field Strength Meter has been specially designed for our FM bugs. It is capable of detecting very low power transmitters and will assist enormously in peaking many of our FM transmitters that have a coil in the output stage that can be adjusted for optimum output. Up to now, field strength meters have only been able to detect transmitters with an output of 100 milliwatts or higher, and for an output such as this, a simple circuit such as a meter and a coil is sufficient. But when it comes to a low power device, a simple circuit, with no amplification, is not suitable. We spent more than 5 days building all the circuits we could find - that purported to be suitable for low-power transmitters, hoping to find one that would work. Unfortunately none came anywhere near good enough so we had to design our own. The circuit we came up with is shown above and it incorporates an RF amplifier, diode rectification, and a DC amplifier so that a movement from a multimeter (a movement is the 'meter' part of a multimeter) could be used as the readout. The heart of the design is a pair of diodes that are partially turned on via a resistor (the 100k sensitivity control) and this overcomes some of the .6v threshold of a diode. You may not think .6v is very much but when you are talking in millivolt terms, it is 600 millivolts. The signal we are attempting to pick up produces one or two millivolts on the receiving antenna and if you need 600 millivolts to turn a diode ON, the field strength meter becomes very insensitive.


Audio Volume Control Attenuator with IR Control
Posted on Saturday, May 28, 2011   •   Category: Amplifiers


The circuit provides both audio volume and input channel selection. A stepwise volume control is implemented with a set of small relays and resistors. In a high-end audio system, a noticable sound improvement over potentiomeneters can be obtained, also over 'audio grade' potentiometers. Clearly, the IR remote control provides convenience over solutions with stepped attenuator rotary switches. The sealed relays will maintain contact quality over a practically endless lifetime.


75 Meter SSB Transceiver
Posted on Friday, May 27, 2011   •   Category: RF Radio Frequency


Here's 75 Meter QRP SSB Transceiver. In general, the transceiver switches the 4-element 1500 ohm xtal BPF ends between the inputs and outputs of the two SA602s to reverse the signal flow for R/T operation. Since no IF amplifier is used in the design, 20 dB of additional receiver gain is produced by the 2N2222 receiver RF amplifier, while automatic gain control (AGC) is produced by the peak DC swing of the LM386 output passed through a rectifier and filtered by a capacitor and fed to the gate of a BS170 enhancement mode FET acting as a variable resistor across the input of the LM386. Both receive and transmit band pass filtering are done by the same half-pi BPF. The diode pair in the mic circuit reduce the "chirp" that occurs during the R/T transition. Additional BS170s could easily be used to mute both the mic and audio instead of the R/T switch directly. These BS170s would be controlled by the +R and +T voltages on their gates while their drains would be tied to 1) the mic circuit between the two coupling capacitors and 2) pin number 1 (audio in) of the LM386 (BS170 sources to ground). Additional power output (perhaps 60 mW) could also be attained by connecting the RF output transistor's collector choke (10 uH) to a 9 V supply instead of the 5 V. Additional biasing current might also be required for this change.


8W PLL Stereo Transmitter with LCD
Posted on Friday, May 27, 2011   •   Category: FM Transmitters


This is 8W PLL Stereo Transmitter with LCD. It is a stable PLL FM transmitter based on TSA5511 synthesizer. Frequency is performed with three buttons through PIC16F84 microcontroller. Frequency of the transmitter is displayed on 16x1 LCD. Transmitter oscillator is based around BF981, BFR91, BFR96 transistors. 2SC1971 RF power transistor can be replaced with 2N4427 or 2N3553 but they will provide less output power.


Page 48 of 149:   1   2   3   4   5   6   7   8   9   10   11   12   13   14   15   16   17   18   19   20   21   22   23   24   25   26   27   28   29   30   31   32   33   34   35   36   37   38   39   40   41   42   43   44   45   46   47   48   49   50   51   52   53   54   55   56   57   58   59   60   61   62   63   64   65   66   67   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   92   93   94   95   96   97   98   99   100   101   102   103   104   105   106   107   108   109   110   111   112   113   114   115   116   117   118   119   120   121   122   123   124   125   126   127   128   129   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146   147   148   149

Circuit-Zone.com © 2017. All Rights Reserved.
AC / DC Innveters
AM Radio
Amplifiers
Antennas
Arduino
Audio Attenuators
Audio DAC
AVR
Battery Chargers
CNC Milling Devices
Counters / Frequency Meters
Fluorescent Lamps
FM Radio / Receivers
FM Transmitters
Frequency Wave Generators
Headphone Amplifiers
iPOD Hacks
LC Meter
LED
Miscellaneous
Motor Controllers
MP3 Players
Oscillators
Oscilloscopes
PC Circuits
PCB
Phone Circuits
PIC
PLL Circuits
Power Supplies
RC Servo Motors
Remote Control
RF Radio Frequency
Robots
Sensors
Solar Circuits
Stepper Motors
Stereo Encoders
Test and Measurement
Timer Circuits
TV Transmitters
USB Circuts
USB Interface Adapters
USB Soundcards / USB Headphones
Video
Volume Control