Model 302
24-bit USB Data
Acquisition System
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The Model 302 interconnections consist of a 14-position analog input screw terminal block, a 16-position screw terminal block for other Input/Output, a 2-terminal power connector, and a USB connector. An extension cable is available, as an option, to connect between a 4-terminal polarized header on the Model 302 board and a bulkhead-mounting USB connector. The bulkhead fitting is made to mount in a DB9 serial connector opening to aid in retrofitting existing hardware.

NOTE:   Always handle circuit cards by the edges. Static electricity can damage computer circuitry, so care should be taken to control static discharge.

For operational checks, only the power supply and serial cable need be connected. The power supply voltage can range from 15 to 30 VDC and does not need to be regulated. Power is connected to the 2-terminal block. The power terminals are labeled "+V" and "GD". The wall-mounted transformer supplied has a white stripe on the positive wire. A battery, or other DC supply (in the correct voltage range), can be substituted. The board is protected against reverse voltage but will not operate without a properly connected supply. The power can be connected before or after the serial interface connection is made.

Note that the computer chassis ground is not connected to ground at the Model 302 because of the optical isolation. We normally recommend placing a 5K to 100K ohm resistor between the two grounds near the Model 302 if there is no other common ground point.

For maximum accuracy the board should be enclosed in a shielded box. Open cell foam can be placed firmly against both sides of the board to minimize air currents. Although a copper/solder junction is not considered a good thermocouple, there are many such junctions and collectively, they can have an effect on the least significant bits.


The software drivers provided include a system-level USB driver, a DLL and sample application code, with source, in VC or VB. Win98 and Win2000 are supported. Refer to the read_1st.txt file on the disk before installing the drivers. Do not forget to follow the steps described there for adding your Model 302's ID number to the device list.

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