MCP3421 Weight Scale Demo Board User’s Guide 2010 Microchip Technology Inc.
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MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Table of Contents Preface ........................................................................................................................... 5 Chapter 1. Product Overview 1.1 Overview ........................................................................................................ 9 1.2 Analog Input Configuration Options ............................................................. 10 1.3 Load Cell .................................................
MCP3421 Weight Scale Demo Board User’s Guide NOTES: DS51918A-page 4 2010 Microchip Technology Inc.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Preface NOTICE TO CUSTOMERS All documentation becomes dated, and this manual is no exception. Microchip tools and documentation are constantly evolving to meet customer needs, so some actual dialogs and/or tool descriptions may differ from those in this document. Please refer to our web site (www.microchip.com) to obtain the latest documentation available. Documents are identified with a “DS” number.
MCP3421 Weight Scale Demo Board User’s Guide CONVENTIONS USED IN THIS GUIDE This manual uses the following documentation conventions: DOCUMENTATION CONVENTIONS Description Arial font: Italic characters Initial caps Quotes Underlined, italic text with right angle bracket Bold characters N‘Rnnnn Text in angle brackets < > Courier New font: Plain Courier New Represents Referenced books Emphasized text A window A dialog A menu selection A field name in a window or dialog A menu path MPLAB® IDE User’s Guide
Preface RECOMMENDED READING This user’s guide describes how to use MCP3421 Weight Scale Demo Board. Other useful documents are listed below.
MCP3421 Weight Scale Demo Board User’s Guide NOTES: DS51918A-page 8 2010 Microchip Technology Inc.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Chapter 1. Product Overview 1.1 OVERVIEW The MCP3421 Weight Scale Demo Board works with the LabVIEW™ Graphical User Interface (GUI) PC Software. This demo board demonstrates how to use the MCP3421 18-bit Delta-Sigma ADC for weight scale applications. It uses the PIC18F4550 microcontroller for data processing and USB communication with PC.
MCP3421 Weight Scale Demo Board User’s Guide 1.2 ANALOG INPUT CONFIGURATION OPTIONS The MCP3421 Weight Scale Demo Board has an MCP6V07 auto-zeroed op amp, to investigate different signal conditioning configuration. As shown in Figure 1-2, the user can configure the input signal chain with the following three options, combining the jumpers: a) Bypassing the MCP6V07: the MCP3421 input pins are directly connected to the sensor output. In this case, the PGA of the MCP3421 is set to a gain of 8.
Product Overview TABLE 1-1: JUMPERS POSITIONS VS. FUNCTION Symbol Jumpers Positions Function xPGA(1) J4 and J5 connected to J19 This combination evaluates the ADC perforJ10 and J13 are ON mance. The on-board op amp is bypassed. J8, J9, J11 and J12 are disconnected (Figure 1-3a) xGLo(1) J4 and J5 connected to GND J9, J11 and J12 are ON J8, J10 and J13 are disconnected (Figure 1-3b) This combination evaluates the influence of the extra gain added by the MCP6V07 device.
MCP3421 Weight Scale Demo Board User’s Guide 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 performance 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.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Chapter 2. Installation and Operation 2.1 MCP3421 CONFIGURATION BIT SETTINGS AND DATA ACQUISITION The communication with the ADC is done through I2C, but the I2C peripheral port of the MCU is not being used. Instead, two pins (RA4, RA5) are being controlled from the firmware. The MCU is changing the setup of the ADC each time S3 is pressed, to change the PGA gain: 8x for PGA, 2x for GLo and 1x for GHi. The ADC always operates in 18-bit mode.
MCP3421 Weight Scale Demo Board User’s Guide A load time linking and a run time linking example, showing how to use the DLL, are included in the System Driver:\MCHPFSUSB\Pc\Mpusbapi\Example Applications directory. Note: For running this project, the USB Microchip Stack must be installed on the user’s machine. The MCP3421 Weight Scale Demo Board firmware is mainly based on the USB stack example: “Device – MCHPUSB – Generic Driver Demo”.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Chapter 3. Weight Scale PC Software Tool 3.1 SOFTWARE INSTALLATION The Weight Scale PC software is an executable file that does not require installation. But, to enable running the software, the user must first install two additional programs, in the following order: - NI LabVIEW Run-Time Engine - NI-VISA Run-Time Engine These programs can be downloaded from www.ni.com. 3.
MCP3421 Weight Scale Demo Board User’s Guide 3.3 WEIGHT SCALE CALIBRATION The MCP3421 Weight Scale Demo Board requires a two points calibration: one at 0g, to remove the weight scale offset, and another at a known point, for gain calibration. To perform the complete weight scale calibration the user must follow the next steps: 1. Connect the weight scale to the PC and run the software. 2. Press S3 button to select the desired option (xPGA, xGLo or xGHi). 3. Press S4 to remove the offset.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Appendix A. Schematics and Layouts A.1 INTRODUCTION This appendix contains the following schematics and layouts for the MCP3421 Weight Scale Demo Board: • • • • • Board – Schematic Board – Top Copper and Pads Board – Top Pads and Silk Board – Top Copper, Pads and Silk Board – Bottom Copper and Pads 2010 Microchip Technology Inc.
BAT1 9V C6 0.33uF VIN VOUT MCP1702 1 2 +5V_A 1 2 OUTPUT J19 EXCITATION J18 INPUT + J5 INPUT – J4 U4 C17 10nF C10 10nF R37 R38 GND D5 1N914 * Note 1: Use 9V power supply or 9V battery, but not both at the same time. 9V DC Battery * SEE NOTE 1 BELOW 9V AC Power Supply 1 J1 3 9V 2 R25 4.7K 2 1 R24 523 R35 C18 1uF 220 220 MCP6V07 R31 Extra Gain Lo J9 CELL LOAD LC1 D6 POWER ON R19 1.5K R29 R30 J10 PGA J13 PGA Extra Gain 2.2K J12 Extra Gain 2.
Schematics and Layouts A.3 BOARD – TOP COPPER AND PADS 2010 Microchip Technology Inc.
MCP3421 Weight Scale Demo Board User’s Guide A.4 BOARD – TOP PADS AND SILK BOARD EDGE DS51918A-page 20 2010 Microchip Technology Inc.
Schematics and Layouts A.5 BOARD – TOP COPPER, PADS AND SILK BOARD EDGE 2010 Microchip Technology Inc.
MCP3421 Weight Scale Demo Board User’s Guide A.6 BOARD – BOTTOM COPPER AND PADS DS51918A-page 22 2010 Microchip Technology Inc.
MCP3421 WEIGHT SCALE DEMO BOARD USER’S GUIDE Appendix B. Bill of Materials TABLE B-1: Qty BILL OF MATERIALS (BOM) Reference Description Manufacturer Part Number 6 C4, C7, C9, C11, C12, C13 CAP X2Y CER .1UF X7R 6.3V 0603 Johanson Dielectrics Inc 6R3X14W104MV4T 1 C6 CAP .33UF 6.3V CERAMIC X5R 0603 Panasonic® – ECG ECJ-1VB0J334K 2 C8, C14 CAP CER 10UF 6.3V X5R 0603 Murata Manufacturing Co., Ltd. GRM188R60J106ME47D 2 C10, C17 CAP CER 10000PF 50V 10% X7R 0603 Murata Manufacturing Co.
MCP3421 Weight Scale Demo Board User’s Guide TABLE B-1: Qty BILL OF MATERIALS (BOM) (CONTINUED) Reference Description Manufacturer Part Number 8 R13, R14, R15, R19, R27, R32, R33, R34 RES 1.50K OHM 1/10W 1% 0603 SMD Yageo Corporation RC0603FR-071K5L 2 R17, R18 RES 10.0K OHM 1/10W 1% 0603 SMD Panasonic – ECG ERJ-3EKF1002V 1 R20 RES 332 OHM 1/10W 1% 0603 SMD Panasonic – ECG ERJ-3EKF3320V 2 R21, R22 RES 24.
MCP3421 Weight Scale Demo Board User’s Guide NOTES: 2010 Microchip Technology Inc.
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