WO2009139640A1

WO2009139640A1 - Usb switch

Info

Publication number: WO2009139640A1
Application number: PCT/NO2009/000181
Authority: WO
Inventors: Leif Vastveit
Original assignee: Vastveit Elektronikk As
Priority date: 2008-05-14
Filing date: 2009-05-13
Publication date: 2009-11-19
Also published as: NO20082211L; NO328206B1

Abstract

A USB switching device (1) and a method of using same for serial communication between a computer (PC1-PC8) and a peripheral (PU) are described, wherein the USB switch (1) is arranged for connection to the peripheral (PU) by means of a USB peripheral port and two or more computers (PC1-PC8) by-means of USB computer ports and maintaining connection for communication between one of the computers (PC1-PC8) and the peripheral (PU), the USB switch (1) being provided with an inlet for a control signal or control command to switch, and a connecting means (91-98) arranged for each of the USB computer ports, the connecting means (91-98) being arranged to establish electrical connection between four contact points in the USB computer port and four corresponding contact points in the USB peripheral port, and wherein the USB switch is further provided with a control unit (5, 7) arranged to respond to the control signal or control command to switch, by first disconnecting the connected USB computer port and then connecting a specified computer (PC1-PC8) for serial communication with the peripheral.

Description

USB SWITCH

The invention relates to a USB switching device for serial communication between a computer and a peripheral, wherein USB stands for the English term Universal Serial Bus. More particularly, it relates to a USB switching device for serial communication between a computer and a peripheral, the USB switch being arranged to be connected to a peripheral by- means of a USB peripheral port and two or more computers by means of USB computer ports and establish connection for com- munication between one of the computers and the peripheral.

The USB has made it easy to use many types of peripherals together with a computer. As examples of peripherals may be mentioned a keyboard, pointer, memory, magnetic disk storage, printer, network equipment, scanner, camera, navigation equipment, measuring equipment and instruments of many kinds. The user experiences a great advantage by peripherals being provided with the same type of port and by peripherals being pluggable to any USB port on the computer. Another advantage is that USB peripherals can be plugged into and unplugged from the computer without it having to be restarted to establish connection and communicate with the peripherals. The bus structure is also a contributing reason why the USB has gained a dominating position in the market of peripherals. By means of a so-called USB hub, several peripheral units can be connected to one USB port on the computer. Even though a USB is meant to connect one or more peripheral units to a computer, there is also the need to connect one peripheral unit to several computers. This means that several computers share a peripheral unit, for example that two or more computers share the use of a printer. Sharing a peripheral is a different task from connecting several USB peripheral units to a computer. However, the task is not more unusual than for there to be known a type of USB unit for sharing peripherals. Such units are marketed under several names, but names from the English language such as USB sharing hub and USB sharing switch are common and, in what follows, such a unit is called a USB switch.

A USB switch is connected to a peripheral and two or more computers and establishes connection for communication between one of the computers and the peripheral . The other computers which are connected to the USB switch cannot communicate with the peripheral. A user may output a switching signal to the USB switch to establish connection between the peripheral and one of the other computers. A switching signal may communicate across the USB connection between the computer, which is to use the peripheral, and the USB switch. A switching signal may also be given by means of a manually operated key or change-over switch integrated in the USB switch.

Users often experience that known USB switches lead to the computer, to which the USB switch switches, not getting a connection to the peripheral. The problem is solved by restarting the relevant computer and the peripheral. Such a restart is time-consuming and a big disadvantage to users who have a computer each and for example are to switch between using a piece of USB-connected presentation equipment in a meeting or conference. The problem seems to increase with the cable length between the computer and the peripheral, and the problem arises even if the cable length is shorter than the maximum length stated in the USB specification.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art .

The object is achieved through features which are specified in the description below and in the claims that follow.

According to a first aspect of the present invention, a USB switching device is provided for serial communication between a computer and a peripheral, the USB switch being arranged for connection to a peripheral by means of a USB peripheral port and two or more computers by means of USB computer ports and establishing connection for communication between one of the computers and the peripheral, the USB switch being pro- vided with an inlet for a control signal or control command for switching, and a connecting means arranged for each of the USB computer ports, the connecting means being arranged to establish electrical connection between four contact points in the USB computer contact and four corresponding contact points in the USB peripheral port, and the USB switch further being provided with a control unit arranged to respond to the control signal or control command to switch by first disconnecting the connected USB computer port and then connecting a specified computer for serial communication with the peripheral .

In one embodiment, the connecting means is constituted by a four-pole relay.

In one embodiment the control connector and interface for the control command is constituted by a USB type.

In one embodiment the control connector and interface for a control command is constituted by one of the RS-232, RS-485, RS-422, MIL-ST-188, EIA 530 types or other suitable types.

In a second aspect of the present invention, there is provided a method of switching between two or more computers connected for serial communication between one of the computers and a peripheral, the method comprising the steps of: - connecting the computers and peripheral to a USB switch by means of respectively USB computer ports and a USB peripheral port ; and - outputting a control signal or a control command to switch between a first computer and a second computer to a control unit in the USB switch, the signal or command influencing a connecting means arranged for each of the USB computer ports, and the control unit disconnecting, upon receipt of the sig- nal, the connected USB computer port on all four USB conductors before switching to the second USB computer port takes place.

For simplicity, the switching means will be referred to in what follows as a relay.

Thus, in use, maximum one of the relays will be activated so that only one of several connected computers can communicate with a connected peripheral. When switching between connected computers, all relays are first deactivated so that none of the computers has connection to the peripheral, then one of the relays is activated so that connection is created between the USB peripheral port and the desired USB computer port.

The device according to the present invention solves the problems assumed to be the cause of the above-mentioned problems of known switches . The problems are assumed to be con- nected to voltage differences between the USB voltage and/or USB signals from one computer to the next. It is also assumed that the problems will be more marked with long USB cables.

The applicant does not know of any analyses having been made of what is actually causing the problems of known USB switches, but a possible explanation might be as follows: A USB assumes that there is just one computer on the bus. < Strictly speaking, this is not true; according to the USB standard there should be only one USB "host" and that is typically a PC. All communication is controlled from the computer. All units listen to the bus, but none sends anything at all except on request from the "host". The computer (host) assigns an ID number to each unit, which is stored by the individual unit. The computer starts a dialogue by sending a data package which all the units receive. The data package contains the ID number of the unit from which the computer wants a reply, and only the unit which finds agreement between its own ID number and the ID number in the data package is permitted to reply. It is assumed that switching from one computer to another leads to disorder/confusion with respect to the ID number that the peripheral has saved as its own. If a peripheral is USB unit number 1 to one computer and is switched to another computer which has earlier identified the USB unit by the ID number 20, the USB unit will not respond to the request unless it has changed its ID number from 1 to 20. Switching between computers may be said to be not accord- ing to regulations with respect to the USB standard, and it is conceivable that a full off/on sequence will be necessary for the USB unit to get a new ID. The invention solves this by breaking all four USB conductors and thereby simulate that the user pulls out the plug and plugs the unit into another computer, so that it is ensured that the ID numbering is cancelled in the computer which is being disconnected and is run from start on the computer to which the unit is being connected. The USB switch according to the invention is particularly, but not exclusively, directed towards a USB unit which is sold under the trade name "Smartboard" and which is a kind of digital board on which the writing is in imaginary ink. The writing is transmitted to the computer which receives and possibly saves and presents the writing on a display screen or on a canvas by means of a projector. The invention is particularly meant to solve switching problems in an array in which such a board is to be switched between several PCs which may be in part far apart and far from the board. Far may here mean farther than the maximum distance specified in the USB standard.

To have a longer USB cable than what is specified by the standard as the maximum, a couple of amplifiers, possibly mo- dems, are most often used on part of the cable distance. One amplifier is mounted at, for example, the board itself or the Smartboard and the other amplifier is mounted somewhat away from the board. Thereby the USB cable from the PC does not need to reach farther than to said second amplifier. The problems in switching between several computers are still pressing. An inexplicable observation is that connecting a PC to said second amplifier via the USB switch according to the present invention works better than via connecting the PC directly to the second amplifier (without the USB switch, that is) .

In what follows is described an example of a preferred embodiment which is visualized in the accompanying drawings, in which:

Figure 1 shows a block diagram of a USB switch according to the present invention; and Figure 2 shows, on a larger scale, a principle drawing of a USB switch which is arranged to connect one of eight PCs to a peripheral;

Figure 3 shows, on a larger scale, a principle drawing of one of the relays indicated in detail A of figure

2.

In the figures the reference numeral 1 indicates a USB switch according to the present invention. The USB switch 1 includes a power supply unit 3 for transistors and for a programmable integrated control circuit 5 which will be referred to in what follows also by the abbreviation PICC 5. The PICC 5 is connected to the driver circuit 7 which is arranged to control, among other things, relays 91-98 arranged for each one of a plurality of USB computer ports. The PICC 5 and driver circuit 7 together form the control unit of the USB switch 1.

Reference is first made to Figure 1 in which the USB switch is arranged to receive a control signal or control command for switching via cables 11 terminating in the PICC 5 at a control connector (not shown) . The control connector and in- terface for the control command is of the USB type or one of the RS-232, RS-485, RS-422 types or other suitable types.

The PICC 5 is arranged to communicate with the driver circuit 7 by means of communication lines as shown in figure 1 but not indicated any further by reference numerals. The driver circuit 7 is arranged to control each one of the plurality of relays 91-98 and to switch on/off each one of a set of light- emitting diodes (LEDs) 19 positioned in, for example, an indicator panel, not shown. There are one light -emitting diode 19 assigned to each relay 91-98, one for indicating voltage on the power supply circuit 3 and one for indicating that the PICC 5 is pre-programmed and ready for an in-coming command. Communication lines between the single units are shown in figure 1 but not indicated specifically.

The relays 91-98 are arranged for a USB termination 21 of a kind known per se.

In figure 2 is shown, on a larger scale, a simplified view of the USB switch 1 shown in figure 1. In figure 2 is shown only eight relays 91-98 which are arranged to connect one of eight PCs indicated as PC1-PC8 to a peripheral indicated as PU. However, it will be understood that the power supply 3, PICC 5, driver circuit 7 et cetera shown in figure 1 are also included in the USB switch 1 shown in figure 2.

Each of the cables 11 (only one indicated by reference numeral) connecting each one of the PCs PC1-PC8 to the individual relay 91-98, as described above, consists of four conduc- tors as indicated in figure 2. Correspondingly, the cables 12 connecting each single relay 91-98 to the peripheral PU consist of four conductors as indicated.

Figure 3 shows, on a larger scale and in further detail, the relay 91 which is arranged to establish electrical connection between four contact points in the USB computer port arranged for PCl to four corresponding contact points in the USB peripheral port arranged for the PU. The relays 92-98 shown in figure 2 are identical to the relay 91.

As shown in figure 3, the relay 91 is arranged to disconnect each one of the four USB conductors 11, 12. The relay 91 is controlled, in a manner known per se, by means of a coil 21 receiving power from the driver circuit 7 via a cable 23.

Thus, the disconnected computer ports are galvanically isolated from the connected computer port and from the periph- eral port at all four USB conductors 11, 12. Reference is again made to figures 1 and 2. When the PICC 5 recognizes a control signal or control command received through the cable 11, 13, the PICC 5 will output commands for switching to the driver circuit 7. As a first step, a possi- ble electrical connection, for example between PC2 and PU, will be disconnected by means of the breakers in the relevant relay, which would be, in this case, the relay 92. As mentioned above and as shown in figure 3, all four USB conductors are disconnected. As a second step, another PC, for ex- ample PC5, is then connected to the peripheral PU by means of a relevant relay, which would be, in the example, the relay 95.

The LEDs 19 will indicate which one of the PCs PC1-PC8 is possibly connected to the peripheral PU.

Even though many types of relays 91-98 could be used in the present invention, experiments have shown that relays of the high-frequency type, that is relays that give little signal loss at 500 MHz, are preferred. The relays should also be of a so-called screened type and exhibit little noise or so- called "bounce" at the moment of connecting.

Claims

C l a i m s

1. A USB switching device (1) for serial communication between a computer (PC1-PC8) and a peripheral (PU) , the USB switch (1) being arranged for connection to the peripheral (PU) by means of a USB peripheral port and two or more computers (PC1-PC8) by means of USB computer ports and maintaining connection for communication between one of the computers (PC1-PC8) and the peripheral (PU) , c h a r a c t e r i z e d i n that the USB switch (1) is provided with an inlet for a control signal or control command for switching, and a connecting means (91-98) arranged for each of the USB computer ports, the connecting means (91-98) being arranged to establish electrical connection between four contact points in the USB computer port and four corresponding contact points in the USB peripheral port, and that the USB switch is further provided with a control unit (5, 7) arranged to respond to the control signal or control command to switch by first discon- necting the connected USB computer port and then connecting a specified computer (PC1-PC8) for serial communication with the peripheral.

2. The device in accordance with claim 1, wherein the connecting means (91-98) is constituted by a four-pole relay (91-98) .

3. The device in accordance with claim 1, wherein disconnected computer ports are galvanically isolated from the connected computer port and from the peripheral port .

4. The device in accordance with claim 3, wherein the electrical isolation comprises all four USB conductors .

5. The device in accordance with claim 1, wherein the control connector and interface for the control command is of the USB type.

6. The device in accordance with claim 1, wherein the control connector and interface for the control command is one of the RS-232, RS-485, RS-422 types or other suitable types .

7. The device in accordance with claim 2, wherein the relays (91-98) are of a type that gives little noise on the contacts at the moment of connecting.

8. The device in accordance with claim 2 or 7, wherein the relays (91-98) are of the high-frequency type.

9. A method of switching between two or more computers

(PC1-PC8) connected for serial communication between one of the computers (91-98) and a peripheral (PU) , c h a r a c t e r i z e d i n that the method in- eludes the steps of :

- connecting the computers (PC1-PC8) and the peripheral (PU) to a USB switch (1) by means of USB computer ports and a USB peripheral port, respectively;

- outputting a control signal or a control command to switch between a first computer (PC1-PC8) and a second computer (PC1-PC8) to a control unit (5, 7) in the USB switch (1) , the signal or command influencing a connecting means (91-98) arranged for each of the USB computer ports, and the control unit (5, 7) discon- necting, on receipt of the signal, the connected USB computer port on all four USB conductors before switching to the second USB computer port takes place.

10. The method according to claim 10, wherein a four-pole relay (91-98) is used as connecting means.