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

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.

Thatâ€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.

USB Printer Switch Circuit Design

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.

USB Printer Switch PCB Design

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.

Assembly this USB printer switch in a box with total six holes: two for USB-B (CON1 & CON2), one for USB-A (CON3), two for LED indicator, and one for the switch selector.

This is the circuit diagram of USB power booster, expecially to strength the power capability of USB port from PC / laptop / notebook. USB from PC can supply only a limited power to the external devices connected through its USB port, when too many devices are connected simultaneously, there is a possibility of power shortage. Therefore an external power source has to be added to power the external devices.

In USB, two different types of connectors are used: type A and type B. The circuit presented here is an addon unit, designed to add more power to a USB supply line (type-A). When power signal from the PC (+5V) is received through socket A, LED1 glows, opto-diac IC1 conducts and TRIAC1 is triggered, resulting in availability of mains supply from the primary of transformer X1. Now transformer X1 delivers 12V at its secondary, which is rectified by a bridge rectifier comprising diodes D1 through D4 and filtered by capacitor C2.

Regulator IC 7805 is used to stabilise the rectified DC. Capacitor C3 at the output of the regulator bypasses the ripples present in the rectified DC output. LED1 indicates the status of the USB power booster circuit.

Construct the circuit on a general purpose PCB and mount in a suitable box. Bring out the +5V, ground and data points in the type-A socket. Connect the data cables as assigned in the circuit and the USB power booster is ready to use.

At the heart of the circuit is IC TDA2822M. This IC is, actually, monolithic type in 8-lead mini DIP (Dual Inline Package). It’s designed for use as a dual audio power amplifier in battery powered sound players. Features of TDA2822M are very low quiescent current, low crossover distortion, DC source voltage down to 1.8 volts and minimal output power of approximately 450 mW/channel with 4 ohm loudspeaker at 5V DC supply input.

An ideal power amplifier can be basically described as a circuit which can supply audio power into external loads without having producing substantial signal distortion and without having consuming extreme quiescent current.

This circuit is powered by 5V DC source obtainable from the USB port of the Computer. When electrical power switch S1 is turned to “on” position, 5V power supply is extended towards the circuit and power indicator red LED1 illuminates immediately. Resistor R1 is actually a current surge limiter and capacitors C1 and C4 work as buffers.

How the USB Powered, Stereo Computer Speaker Circuit Works

The operation of the circuit is very simple. Audio signals from the Computer audio port or headphone port are fed towards the amplifier circuit via R2 and C2 (for left channel), and R3 and C3 ( forright channel). Potensiometer VR1 used as the volume controller for left (L) channel, while potensiometer VR2 used to control the volume level of right (R) channel. Pin 7 of TDA2822M receives the left channel sound signals and pin 6 receives the right channel signals by way of VR1 and VR2, correspondingly. Amplified signals for driving the left and right loudspeakers can be obtained at pins 1 and pin 3 of IC1, correspondingly. Components R5 and C8, and R6 and C10 form the classic zobel network.

Construct the stereo computer speaker circuit on a medium size, general purpose PCB and enclose inside a appropriate case. It really is recommended to utilize a socket for IC TDA2822M. The external connections ought to be made working with suitably screened wires for improved result.

You may download the tutorial of RJ45 LAN tester building include the schematic diagram, circuit explanation, project preview and program source code from the following link:
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Schematic Diagram:

Components List:

PCB Layout:

The PCB layout using double layer design. You may create your own design using single layer board, but it will be resulting larger size of PCB.

Technical Specifications:

• Supply Voltage: 5V
• Interface: USB 1.1, USB 2.0
• Output Interface: Headphones, S/PDIF
• Sampling Rate: 32KHz, 44KHz, 48KHz
• SNR: 98dB
• THD: 0.006%
• Headphone Output Power: 12mW
• Power Consumption: 35 – 45mA
• OS: Windows 98, ME, 2000, XP, Mac OSX

Source: http://electronics-diy.com/PCM2706_USB_Soundcard.php
Visit the page for more detail of PCM2706 USB Sound Card circuit explanation.

About PCM2706:
The PCM2704/5/6/7 is TI”s single-chip USB stereo audio DAC with USB 1.1 compliant full-speed protocol controller and S/PDIF. The USB-protocol controller works with no software code, but USB descriptors can be modified in some parts (for example, vendor ID/product ID) through the use of an external ROM (PCM2704/6) SPI (PCM2705/7) or on request. The PCM2704/5/6/7 employs SpAct architecture, TI”s unique system that recovers the audio clock from USB packet data. On-chip analog PLLs with SpAct enable playback with low clock jitter.

Download PCM2706 datasheet from the following link:

PCM2706 Datasheet

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