Design Documentation

Analog Module, MBARI 101224

4:36 PM 5/29/01 Dave Wright

General:

The analog module provides 6 channels of signal conditioning for the TT8V2 or similar embedded microcontroller. Four of the channels are differntial instrumentation amplifiers with programmable gain, the fifth can be arranged as either single ended or differential, and the sixth channel provides a scaled measurement of the battery supply voltage.

A unity gain buffered copy of the A/D reference voltage is provided for offsetting or driving transducers.

Power to the module is controlled by the presence of the reference voltage. This allows the module to be powered up when the TT8V2 A/D is operating, and draw no power at other times.

A resistor array at the input of each of the intstrumentation amplifiers, U1 thru U4 allows the scaling or offsetting of the input signal as desired. Refer to the Burr Brown INA122 datasheet for the common mode signal restrictions. component. Rx05 is the gain setting resistor

A voltage output of Vbatt/4 is provided for measurement of battery pack voltage. The voltage divider is removed from the battery when the A/D reference is not present, to conserve power.

Physical:

The module dimensions are 2.200" x 3.00". Mounting holes for #2 machine screws are provided at each corner. All thruhole connectors, and mounting holes, register with a 0.1" grid. This is to facillitate mounting of the module on standard perfboard for prototyping or "one off" construction. Active components are mounted on the "top" side, and signal input connectors on the "bottom" (non silkscreen) side. When mounted to a motherboard or other substrate, the component side faces "inward" to allow access to the connectors. Connector P1 contains the signals that are routed to the host microcontroller A/D converter and power sources.


Assembly Notes:

The connectors for the analog inputs, J1 thru J5, mount on the solder side of the board. All other components, including P1, mount on the component (silkscreen) side of the board.

Components Rx01 thru Rx08, Cx02, C501 and R50x are all application dependent values, and as a result are thruhole packages. Values are selected according to the input signal, and loaded by the end user.

 END