The JED 439 is a 2-channel USB switcher typically for use in a classroom where two sources of USB signals need to control one device, e.g. an Electronic Whiteboard (EWB).
The JED 443 is a three-channel version of it.
The JED switchers are controlled remotely from an A/V controller such as JED's T430, T440 or T460, but can be controlled by any external device which can generate one, two (or three) contact closures to ground or a simple RS232 control command.
They can also be used in a manual mode via a front panel toggle switch (A/B, 439) (or Select switch, 443) or in "Auto" mode where the act of plugging in a channel B cable switches the USB output to Channel B, but it reverts to Channel A when the Channel B USB is powered down or unplugged. (In the 443, Channel C has the highest priority.) So, in a classroom, the act of plugging in a teacher's laptop steers the USB connection to that laptop.
Wiring to the A, B, (and C) and Mode pins controls and sets the operation mode. The current USB selection is shown on the front panel LEDs.
Both LEDs are OFF (or the Idle LED is lit) if there is no current USB through-connection, allowing a Whiteboard to be used as a video screen or ink-pen "old-fashioned" Whiteboards with no pickup of pen data by the computer.
Two-wire mode (or Three-wire mode, 443): With no connection to the "Mode" pin, a contact to ground or a TTL LOW signal to input "A" selects USB "Device A", and a contact to ground or a TTL LOW to input "B" selects USB "Device B". With neither A or B input LOW, there is no USB through-connection.
(This is the situation where two or three control contacts are available, e.g. out of a JED T461-R8 audio controller with relay option (using relays 7 and 8), or an AMX (etc) system using two "outputs", can directly control the 439/443. The inputs are pulled to 5V Vcc with 1KOhm resistors, so can be driven with mechanical or optical relays, open drain N-FETs or open collector NPN transistors or TTL or CMOS logic, and are ESD and series resistor and diode protected against "insults".)
One-wire mode (439 only): With a wire link connection from the "Mode" pin to "Ground", the default selection of USB "Device A" is made if there is no connection to either "A" or "B" inputs. A contact to ground or a TTL LOW to input "B" selects USB "Device B". There is no "disconnection" mode: either A or B are always connected. (The front-panel switch can over-ride the rear inputs.)
Auto mode: With wire link connections from both the "Input A" and "Input B" pins to "Ground", "Auto" mode is selected. (The "Mode" input must NOT be connected, 439.) If there are no inputs to "A" or "B" there is no USB through-connection.
Note: In Auto mode, Rev: V03 software allows the RS232 Set and Clear commands to enable or disable the USB through-connection. (In the 443, auto mode is selected by connecting the "mode" pin to ground)
If a single active USB cable with 5 volts on the power wire is plugged into the 439/443 "A-In" USB socket, this is sensed, and the system switches to connect USB "Device A" to the output.
If a single active USB cable with 5 volts on the power wire is plugged into the 439/443 "B-In" USB socket, this is sensed, and the system switches to connect USB "Device B" to the output.
If a single active USB cable with 5 volts on the power wire is plugged into the 443 "C-In" USB socket, this is sensed, and the system switches to connect USB "Device C" to the output.
If both "A-In" and "B-In" USB inputs are active, the 439 defaults to connect USB "Device B" to the output. (This over-ride mode is designed for a typical classroom situation where a room PC is plugged into "A-In" and this PC operates the Whiteboard. However, when a teacher's laptop is plugged into "B-In" it takes over control, because its USB connection is the active one. (With the 443, Channel C has highest priority.)
RS232 mode is similar to the two/three-wire mode above, except the commands are sent in via RS232 rather than contact or logic/switch inputs. Simple commands are sent in at 38400 baud 8N1:
Product:
439 command
443 command
Set channel A:
:R161<CR><LF>
:R151<CR><LF>
Clear channel A:
:R160<CR><LF>
:R150<CR><LF>
Set channel B:
:R171<CR><LF>
:R161<CR><LF>
Clear channel B:
:R170<CR><LF>
:R160<CR><LF>
Set channel C:
:R171<CR><LF>
Clear channel C:
:R170<CR><LF>
Changing channels automatically clears the previous selection. Any "clear" command leaves no through USB connection, as discussed above.
