With lower prices on laptop computers became affordable sailer acquisition and the average Greek. Getting two computers, however, automatically generated and the need to link them with the most common peripherals already available, such as a printer, a scanner , the WEB Camera , the ISDN netMod and more. To select the type of interface with computer peripheral into account that we have the most modern peripherals are interconnected USB , leading us to this choice. As regional USB to mention the USB printer. The position may well be a scanner , a camera or other device is USB , preferably low-speed USB 1.1 (01/05 Mbps ), this does not mean it can not work with devices and USB 2.0. Since we manufacture include mechanical parts, you may create problems in some regional communication through the floor construction, because of both high speed as this USB 2.0 (480 Mbps ) and "noise" generated in the contacts of the relay. According to the block diagram of Figure 1 , the printer is connected to computer # 1 and the No. 2 microprocessor computer. When given the mandate by the software to manufacturing ( USBswitch . exe ), is the cross-switching devices and the printer is now No. 2 on the computer and the microcontroller to the computer # 1.

The theoretical circuit The circuit consists of a few parts of the microcontroller IC 1 to take control of where it is attached printer, and is responsible for communicating with software on the computer through the port USB . The supply of construction made ​​from doors USB and two computers, as well as provide voltage 5 V with a maximum current of 500 mA each, capable of not only the power of our workmanship but also the peripheral to be connected. Moreover, this ensures the smooth operation of our manufacturing where we have a single computer. The data signals D + and D - channel USB are level 0 and +3.3 V . The IC 1 levels but works with TTL 0 and five V . So there are two ways to adapt: ​​either to build a converter station from the five V to 3.3 V and back to the data bus D + and D - or down the voltage supplied to the IC in the 1st 03/03 V when the signal level is between 0 and 03/03 V . The Atmel We guarantee that the operating voltage of a ATtiny 07/02 is between 2 313 V and 5.5 V , so we chose the second way, namely the operation of the IC on the 1st at 3.3 V . Instead of a stabilizer in 3/3 V chose three routes the 1st N 4 001 ( D five - D 7) are in the right time creates a voltage drop .7 V so VCC = five - (0.7 * 3) = 2.9 V . This in theory because in practice the tendency is almost on the 3rd V . The specification of the channel USB devices for low-speed 07/02 - 03.06 V so that the three V is enough. The R is the 6th load resistance to ensure the circuit always 3 V . The relay RE 1 and RE on the 2nd take the link IC to the first one, and the printer to the second computer. The RE 1 working backwards from RE 2. That is reinforced when the RE a, the RE is disarmed two, and vice versa. When the base of the T on the 1st we have 0 V , the transistor will not conduct a collector and thus will have 5 V winding through the RE an. This trend is on the 5th of V led to the base of T2 putting a state conductivity. By the same logic when the base of T1 will have the 3rd V , will pass a state conductivity dropping the voltage of the collector to 0 V and thus drive the RE two disarm. The diodes D 1, D 3 are used to protect the T1 and T2 of the reverse currents generated in the windings of RE 1 and RE on the 2nd. The LEDs D the 2nd, D the 4th is indicative of the status of each relay ( ON - OFF ). The relays have a rated voltage of 6 V DC and consumption is a ~ 20 mA . For this reason we chose to arm only one at a time and not to arm or disarm both simultaneously, thus reducing the overall power consumption of the circuit. The R 7, R 8 is terminating resistors channel USB . In R the 9th Poles D - port of USB in the three V thereby indicating the existence of device USB low speed (5/1 Mbps ). Construction of the circuit The construction of the circuit will not be a problem because of its simplicity. Little attention should be paid to the polarity of the materials (diodes, capacitors, integrated). Glue the first shorter and smaller components and then the bigger and taller. The black lines connecting the holes in the plan of placing materials are wire bridges on top of the board. The LEDs D 3, D the 4th and resistors R an, R two can not be placed on reducing the power consumption at 6 mA . If you can not find ATtiny 2,313 on the market, you in position to schedule the same files . hex and . EEP an AT ninety S two thousand three hundred thirteen and put on the same basis as they have the same layout on the pins. If, after connecting the peripheral to the computer, show you the message that found an unknown device and you've already installed drivers will need to remove one of the diodes D 5 and D the 6th or D and the 7th position of sticking a wire bridge. With this conversion will increase the voltage VCC of the three V to 3.7 V , sufficient for the proper functioning of AT ninety S two thousand three hundred thirteen. The AT ninety S two thousand three hundred thirteen can operate from 2.7 V - 6 V . Then what is the reason to move up the voltage to 3.7 V and can operate with 02.07 V ? The reason is simple. The operating voltage of 2.7 V applied as the maximum operating frequency, which is the 10th MHz . In our case, however, the operating frequency has increased on the 12th in MHz or 20% more ( overclocking ). For this reason we can not work at lower voltage. On the other hand, ATtiny two thousand three hundred and thirteen is the maximum frequency of operation on the 20th MHz so we can comfortably operate at 2.7 V . Programming IC1 The microcontroller IC 1 should be programmed with two files. The memory flash you should plan to file USBswitch . hex and internal memory eeprom to file USBswitch . EEP . If you do choose ATtiny two thousand three hundred and thirteen against AT ninety S will have two thousand three hundred thirteen of the area < Fuses > programmer you can be sure that option is checked < Ext . Crystal OSC.? eight Frequency - MHz? Start-up Time fourteen CK + sixty-five MS? (CKSEL = 1,111 = the 11th SUT) >. This will have to check because this microcontroller has the ability to activate the internal oscillator 0.128 - 8 MHz , and should make sure that is selected using the external crystal frequencies on the 8th of MHz and above. Operation When connected to our building a free port USB computer through the door K1, the computer will recognize a new device and will ask drivers ( Drivers ). The driver for device ' USB Switch 'is in the folder' Driver 'and consists of three files: AVR three hundred and nine. DLL , AVR 309. INF and AVR 309. sys . After installing the drivers, the device will be ready for use. And both computers must have installed the drivers and the program ' USBswitch . exe '. When you connect both computers to our device, install drivers and run the program USBswitch . exe , we see that in a computer would see the message of Figure 3 and in another the message of Figure 4 . One that will display the message in Figure 3 will be connected to the printer. In this case, as you can see the button "Connect to a common regional" is disabled because we have already connected the printer to this computer. In the case of Figure 4, the program informs us that the device " USB Switch " that is essentially the IC one, has been found and you can press the button "Connect to a common regional USB 'to the IC on the 1st to change the status of relay switched to the printer on this computer. If you do not install the driver, can not run the program.

MATERIALS

C1: 100nF
C2: 470mF/16V
C3: the 22nd pF
C4: the 22nd pF
D1, D3: an N 4148
D2, D4: LED
D5, D6, D7: 1N4001
IC1: ATTINY2313 ( see text )
K1: plug board USB-B
K2: Connector board USB-A
K3: plug board USB-B
R1, R2: 1k
R3, R4, R5, R6: 10K
R7, R8: 56R
R9: 1k5
RE the 1st, RE 2: Relay on the 6th V , duplicate contacts.
T1, T2: BC547
X1 : the 12th MHz

Cost of materials: 20 €
Difficulty of manufacture: *Inaccessible materials: *

Download code of the program management and driver (driver) of the USB Switch below.