Passive RIAA Preamplifier

There are two types of pre-amplifiers for magnetic phono cartridges. An example of the most common type is the one described in the March 2002 issue of SILICON CHIP. It has the RIAA equalisation network in the feedback loop. The second type was previously used in valve circuits which typically had no feedback loop and used passive RC networks to provide the phono equalization. This experimental preamp was put together using inexpensive FETs to compare the performance of these two types of preamp. The first stage, consisting of Q1 and Q2, is a simple FET audio amplifier, where the FETs are connected in parallel to reduce noise. This is followed by a passive RIAA network consisting of 240kO and 15kO resistors and the associated 0.1OF .022OF and .0047OF capacitors.

Some of the gain loss in the passive network is then made up by FET Q3. It also has a 51kO drain resistor and is buffered by bipolar transistor Q4 which is connected as an emitter-follower stage. All resistors are 1% tolerance metal film type while the capacitors for equalization are MKT polyester types. Ideally, the Idss of all FETs should be matched for both channels. Resistors R3 and R8 should be adjusted so that the drain voltage in each stage is between 13V and 14V, to give symmetrical signal clipping. The power supply can be three 9V batteries connected in series. Current consumption is only 3mA for the stereo circuit.

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USB Printer Share Switch

This simple device allows two computers to share a single USB printer or some other USB device, such as an external flash drive, memory card reader or scanner. A rotary switch selects the PC that you wish to use with the USB device, while two LEDs indicate the selected PC.

The most common way to share a USB printer between two PCs is to use one machine as a print server. However, that’s not always convenient because it means that the server PC must always be on if you want to print something.

Picture of the project:

That can be a real nuisance if you just want to quickly fire up the other machine and print something out. It also means that the two PCs must be networked together, either via a hub/router or directly via an ethernet crossover cable. Another way is to use a dedicated USB print server. However, as before, this must be connected to an ethernet network, along with the PCs. Such devices also need their own power supply, generally cost well over $100 and are overkill if you just want to share a single USB printer between two computers for occasional printing in a home set-up.

Parts layout:

That’s where this simple device comes in. It’s basically a 2-way switch box that lets you manually switch your USB printer from one PC to the other, as required. The switching is performed using a rotary switch, while two LEDs on the front panel indicate which PC has been connected to the printer. This method has several advantages. First, you don’t need to network your two computers. Second, you can print from either machine with the other turned off. And third, the device doesn’t need a power supply.

Circuit diagram:

The circuit uses switch poles S1a-S1c to select either USB socket CON1 or CON2 and connect its pins through to CON3. The fourth pole (S1d) selects either LED1 or LED2, to indicate which PC has been selected.

Source: Silicon Chip14 April 2009

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Low Cost Transistorised Intercom

Several intercom circuits have appeared in www.circuit-lab.com using integrated circuits. The circuit described here uses three easily available transistors only. Even a beginner can easily assemble it on a piece of veroboard. The circuit comprises a 3-stage resistor-capacitor coupled amplifier. When ring button S2 is pressed, the amplifier circuit formed around transistors T1 and T2 gets converted into an asymmetrical astable multivib-rator generating ring signals. These ring signals are amplified by transistor T3 to drive the speaker of earpiece. Current consumption of this intercom is 10 to 15mA only. Thus a 9-volt PP3 battery would have a long life, when used in this circuit. For making a two-way intercom, two identical units, as shown in figure, are required to be used.

Output of one amplifier unit goes to speaker of the other unit, and vice versa. For single-battery operation, join corresponding supply and ground terminals of both the units together. The complete circuit, along with microphone and earpiece etc, can be housed inside the plastic body of a toy cellphone, which is easily available in the market. Suggested cellphone cabinet, with the position of switches, speakers and mike etc is shown.

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CONSTANT BRIGNESS LED AND MUTE CONTROL ELECTRONIC DIAGRAM

CONSTANT BRIGNESS LED AND MUTE CONTROL ELECTRONIC DIAGRAM

The output power of the modules are approximately 220W to 250W into 8? and 350W to 400W into 4?. Complete documentation for the amplifier modules can be found in the documents listed below. AN-1850 LME49830TB Ultra-High Fidelity, High-Power Amplifier Reference Design Although the power supply design is specific to the amplifier modules the concepts and circuit design may be used for any power supply purpose. The power supply is an unregulated design with an option to allow connection to either 120V or 240V mains. The design uses toroidal transformers, a fully integrated bridge, and various rail capacitors for ripple voltage reduction, noise suppression, and to act as high current reservoirs. Additional circuitry to control inrush current on power up and power up/ down Mute control are also included.

The topics discussed inside the application note including the introduction, overview, schematic and design, power supply, additional circuit, inrush current control, mute control, constant brightness LED circuit, summary, and many more.

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2000 Buick Regal Wiring Diagram

2000 buick Regal Wiring Diagram

(click for full size image)

The Part of 2000 buick Regal Wiring Diagram: cruise input, vehicle speed, air solenoid relay, air pump relay, ground destribution, powertrain ctrl module, red wire, black wire, yellow wire

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Rascal Combines Linux and Arduino

Does this sound familiar to you? After spending many hours on optimizing for speed and memory your super-duper MCU application, you can only conclude that it will not run on an Arduino board. You have built the shield (the Arduino compatible extension board) with your special I/O and you wrote most of the software, but these last functions that should add that finishing touch just don’t fit in the board’s memory. Maybe Rascal can help?

Built around a 400 MHz AT91SAM9G20 ARM9 from Atmel, the Rascal is an open source Linux board compatible with Arduino extension cards or shields. Programming the board is easy thanks to a library written in Python from Pytronics that allows easy access to peripherals and shields. The Rascal’s firmware comes with a web server that can serve as a programming interface; you can write your applications directly in a web browser connected to the Rascal board.

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18 LED Dimmable LED Lamp

This circuit is a dimmable white LED lamp array with 18 LEDs. The lamp brightness is regulated as long as the input voltage is above 10.5V. A low-dropout analog voltage regulator is used for a simple and relatively efficient design. The lamp produces enough light to use as a a reading lamp or a small work lamp. 

Project Image

Specifications:

• Power Requirements
• Input Voltage: 10.5-16V DC
• Input Current: 11-150mA at 12VDC

Theory:
The 12V DC input voltage is routed through the 1A fuse and the on/off switch. The 1N4001 diode acts as a crowbar device. If reverse polarity is applied, the fuse will blow and the rest of the circuitry will be protected. Power is sent to the LM2941CT voltage regulator IC. The regulator is wired to produce a voltage range from 5.5V (dim) to 8.3V (bright).

18 LED Dimmable LED Lamp Circuit Diagram

The 4.7K resistor across the 1K brightness adjustment potentiometer produces a non-linear brightness adjustment to compensate for the eyes logarithmic brightness perception response. The LEDs are organized in six series groups of three with a 24 ohm current limiting resistor on each group. This arrangement limits the maximum current through each LED group to around 20mA.

Use:
Connect the DC input terminals to a 12V source, such as a 12V lead acid battery. Be sure to observe the correct polarity. Turn the power switch on and adjust the brightness adjustment for the desired brightness.

Parts:
    1X LM2941CT low-dropout voltage regulator
    1X aluminum heat sink
    1X 1A DC rated fuse
    1X DC switch
    1X 1N4001 diode
    2X 1K 1/4W resistors
    2X 4.7K 1/4W resistors
    6X 24 ohm 1/4W resistors
    1X 1K linear potentiometer
    18X 5mm white LEDs, 20mA max
    1X 22uF 16V electrolytic capacitor
    1X 100nF 25V monoblock capacitor
 

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