JED Microprocessors Pty Ltd. 173 Boronia Rd Boronia 3155, Vic, Australia. +61 (03) 9762 3588  Home/Contact > Projector_Controllers > T439 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 439 is 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 or two contact closures to ground or a simple RS232 control command. The JED 439 can also be used in a manual mode via a front panel toggle switch (A/B) 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. So, in a classroom, the act of plugging in a teacher's laptop steers the USB connection to that laptop.

The unit can be controlled from the front panel toggle switch, or from the rear control inputs. Wiring to the A, B and Mode pins controls and sets the operation mode. The current USB selection is shown on the front panel LEDs.

Both LEDs are OFF if there is no current USB through-connection, allowing a whiteboad to be used as a video screen or ink-pen "old-fashioned" whiteboard with no pickup of pen data by the computer.

Two-wire mode: 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 a pair of control contacts are available, eg 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. 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: 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.) 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.

If a single active USB cable with 5 volts on the power wire is plugged into the 439 "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 "B-In" USB socket, this is sensed, and the system switches to connect USB "Device B" 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.

RS232 mode is similar to the two-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:

Changing channels automatically clears the previous selection. If both are "cleared", there is no through USB connection, as discussed above.

Downloads

A data sheet/user manual in PDF form: JED 439 V03 Manual

If you are interested in the JED 439, call one of the distributors on the main JED projector control page: JED projector controllers

Distributors worldwide ... if you are interested in the JED 439, call/email Ed Schoell at +61 (0) 3 9762 3588 to be added to the list and to our direct mail distributor recommendations: eschoel@jedmicro.com.au