User manual

MCP3421 Weight Scale Demo Board User’s Guide
DS51918A-page 12  2010 Microchip Technology Inc.
1.4 UNIVERSAL SERIAL BUS (USB) AND PIC18F4550 MICROCONTROLLER
The MCP3421 Weight Scale Demo Board has a USB connector to communicate with
the PC GUI. The PC GUI allows various user options, such as calibrations and perfor-
mance evaluation of the system.
The USB communication with the PC is done by the on-board microcontroller.
PIC18F4550 is also communicating with the ADC, and controls the LCD.
The four button switches on the board have the following functions:
• S5 is the Reset pin
• S2 is used to change the LCD indication from “Weight” to “ADC code”, “ADC out-
put”, or “Calibration”
• S3 is used in parallel with the configuration of the signal conditioning chain. By
pressing this button, the LCD indication will change from 1PGA to 1GLo, 1GHi,
4PGA, 4GLo or 4GHi. PGA means that the ADCs PGA only is used at highest
gain. GLo means that the external op amp is being used with low gain, GHi means
that external op amp is used with high gain. The 1 and 4 before the letters indicate
the numbers of averages – no averaging, or averaging on four samples
• S4 is doing the zero calibration. By pressing this button, the “Weight” indication
will go to a value closer to 0g.
1.5 WHAT THE MCP3421 WEIGHT SCALE KIT CONTAINS
The MCP3421 Weight Scale Demo Board kit includes:
• MCP3421 Weight Scale Demo Board, 102-00250
• Important Information Sheet