Sensor Interfacing with XE8000 Sensing Machines

Application Note AN8000.14
Semtech Sensor Demo
AN8000.14
Application Note
Semtech Sensor Demo
Rev 1 February 2006
www.semtech.com
1
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AN8000.14 XEMICS
Table of Contents
1 Introduction...................................................................................................................................................... 3
1.1
Purpose of the document ......................................................................................................................... 3
1.2
Sensor demo principle ............................................................................................................................. 3
2 Sensor board ................................................................................................................................................... 4
2.1
Pin assignments ....................................................................................................................................... 4
2.2
Applications examples: ............................................................................................................................ 4
2.2.1
Minimum system ............................................................................................................................... 4
2.2.2
Two sensors system ......................................................................................................................... 5
2.2.3
Two sensors and EEPROM system ................................................................................................. 5
3 Demo board..................................................................................................................................................... 6
3.1
Bloc diagram ............................................................................................................................................ 6
3.2
Schematic................................................................................................................................................. 6
3.3
Hardware layout ....................................................................................................................................... 7
3.4
Electrical specifications ............................................................................................................................ 7
4 Embedded software......................................................................................................................................... 8
4.1
System default values .............................................................................................................................. 8
4.2
Noise cancellation .................................................................................................................................... 8
4.3
Flowcharts ................................................................................................................................................ 9
4.4
Flowcharts Continued ............................................................................................................................ 10
5 Zooming ADC ................................................................................................................................................ 11
5.1
Bloc diagram .......................................................................................................................................... 11
5.2
ZoomingADC™ Registers...................................................................................................................... 11
6 SEMTECH ZoomingADC™ Excel sheet ....................................................................................................... 13
7 GUI Software description .............................................................................................................................. 14
7.1
Installation .............................................................................................................................................. 14
7.2
Description ............................................................................................................................................. 14
7.3
Main screen............................................................................................................................................ 14
7.4
Display settings (Span) .......................................................................................................................... 15
7.5
Advanced Settings ................................................................................................................................. 16
7.6
About Box............................................................................................................................................... 16
8 Hyperterminal Alternative .............................................................................................................................. 17
8.1
Configuration .......................................................................................................................................... 17
8.2
Usage ..................................................................................................................................................... 17
8.3
Commands ............................................................................................................................................. 18
8.3.1
Reset............................................................................................................................................... 18
8.3.2
Version ............................................................................................................................................ 18
8.3.3
Read Address ................................................................................................................................. 18
8.3.4
Write Address.................................................................................................................................. 18
8.3.5
Configure the averaging.................................................................................................................. 19
9 Sensor Demo files ......................................................................................................................................... 20
9.1
Database structure................................................................................................................................. 20
10
Conclusion ................................................................................................................................................. 20
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1
1.1
INTRODUCTION
PURPOSE OF THE DOCUMENT
Sensor interfacing with XE8000 Sensing Machine is quite easy. The ZoomingADC™ adapts easily to most types of
sensors. However one must have good understanding of the microcontroller basic features such as programming,
usage of the RC oscillator and of the UART serial interface, in order to first have operational software. These are
all things that may not be the first priority when one wants to have a quick overview of the Sensing Machine
possibilities with a selected sensor.
In this context, Semtech provides a demonstration system that gives access to the sensor through the
ZoomingADC™ using a predefined graphical user interface (GUI) that requires a minimum of work in terms of
software and hardware.
This document describes the sensor demo and its graphical user interface developed by Semtech for
demonstrations purposes.
All the files necessary to reproduce this board and use the GUI are available on Semtech web site in ZIP format.
1.2
SENSOR DEMO PRINCIPLE
Sensor Demo bloc diagram
GUI
Serial
cable
Demo board
Sensor
Dedicated
connector
ZoomingADC™™ Excel
sheet
SEMTECH
Sensing Machine
RS232
Level
Shifter
XE8805A
Or
XE8801A
Or
XE8802
Power
supply
32k XTAL, Vreg cap
3xAAA
batteries
PC with a serial COM port
As shown in the figure above, the sensor demo is split into three different parts:
The sensor board: the sensor board holds the sensor and eventually its external components; this board has a
dedicated connector that connects to the demo board.
The demo board: this PCB has the minimum components necessary to run the XE8000 microcontroller and to
communicate with a PC through serial communication. The microcontroller has embedded software that enables
the access to the ZoomingADC™ registers from the PC.
The PC with a dedicated graphical user interface that allows one to read and write ZoomingADC™ registers,
displays it’s output on a chart and the Semtech excel sheet that allows one to compute the values to set in the
ZoomingADC™ registers.
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2
SENSOR BOARD
The sensor board is made to carry the sensor; the connector of this board is a STD 1 row 2.54mm pitch connector.
2.1
PIN ASSIGNMENTS
The pin assignment is as follows:
Pin assignment
Physical dimensions
Minimum system
Two sensors with the same reference
Optionnal digital interface
VBIAS / + Power supply
2.54
AC R1,R3 / + Reference voltage
2.54
AC_A A1,A7 / + Measured signal
2.54
AC_A0,A6 / - Measured signal
2.54
AC_ R0,R2 / - Reference voltage
2.54
VSS/ - Power supply
5.08
AC_A3,A5 / + Measured signal
2.54
AC A2,A4 / - Measured signal
2.54
2.54
2.54
2.54
2.54
2.54
PC0 /
PC1 / SCK
PC2 / NSS
PC3 / MISO
PC4 / VDIG
All dimensions are in milimeters
As shown in the picture above, the board may have three sizes depending on which kind of application is being
used:
The minimum system includes the power supply, the references inputs and two analog inputs.
The next size offers two more analog inputs.*1
Then the last version offers the access to digital I/O that may allow the connection of an EEPROM or another
system that the sensor may need to work correctly.*1
*1 Note that these mode are not included in the embedded software of the Microcontroller.
2.2
APPLICATIONS EXAMPLES:
2.2.1
Minimum system
Minimum system
VBIAS / + Power supply
AC_R1,R3 / + Reference voltage
AC_A A1,A7 / + Measured signal
AC_A0,A6 / - Measured signal
AC R0,R2 / - Reference voltage
VSS/ - Power supply
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2.2.2
Two sensors system
Two sensors with the same
reference
VBIAS / + Power supply
AC_R1,R3 / + Reference voltage
AC_A A1,A7 / + Measured signal
AC_A0,A6 / - Measured signal
AC_ R0,R2 / - Reference voltage
VSS/ - Power supply
AC_A3,A5 / + Measured signal
θ
AC_A2,A4 / - Measured signal
2.2.3
Two sensors and EEPROM system
Optionnal digital
interface
VBIAS / + Power supply
AC_R1,R3 / + Reference voltage
AC_A A1,A7 / + Measured signal
AC A0,A6 / - Measured signal
AC R0,R2 / - Reference voltage
VSS/ - Power supply
SPI
EEPROM
θ
AC_A3,A5 / + Measured signal
AC A2,A4 / - Measured signal
PC0 / MOSI
PC1 / SCK
PC2 / NSS
PC3 / MISO
PC4 / VDIG
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3
DEMO BOARD
The demo board holds the XE8805A, the power supply and the RS232 transceiver. In the XE8805A, the embedded
software manages the ZoomingADC™ and the communication with the PC.
3.1
BLOC DIAGRAM
SEMTECH
Microcontroller
From The
sensor
XE8805A
or
XE8801A
or
XE8802
32k XTAL, Vreg cap
3.2
RS232
Level
Shifter
To the
PC
Power
supply
3xAAA
batteries
SCHEMATIC
XEMICS
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3.3
HARDWARE LAYOUT
Core
3XAAA Batteries
the back
on
RS232 Interface
Analog interface
Power supply
Engineering zone
On/Off switch
XE8805A Programming
Interface
digital Interface
3.4
ELECTRICAL SPECIFICATIONS
Parameter
Power supply
Main power supply
Regulated
VDIG
VBAT
VREF
Current consumption
Micro controller
Sensor
RS323 interface
Estimated autonomy
Min
Typ
Max
Units
Comment
3.6
4.5
3.3V
3.3
3.26
3.24
4.8
Vdc
Vdc
mVdc
mVdc
mVdc
Energizer EN92
2
2
3.2
100
mAdc
mAdc
mAdc
Hrs
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4
EMBEDDED SOFTWARE
The embedded software monitors the UART communication and the ZoomingADC™ handling; the source code is
available on SEMTECH web site.
This software may be considered as a base for future applications, multi sensors handling and EEPROM
management are not included in this basic version.
4.1
SYSTEM DEFAULT VALUES
Periph
Parameter
RC Frequency
XTAL 32k
UART speed
UART number of bits
UART parity
UART Stop bits
UART Flow control
Vbat = Vref
Sampling freq.
Input impedance
Gain of PGA1
Gain of PGA2
Gain of PGA3
Total PGA gain
Offset of PGA2
Offset of PGA3
Total equivalent input offset
Oversampling rate
Elementary conversions
Resolution
Conversion time
LSB equivalent input voltage
Equivalent input noise
PGA settling time
Clock
UART
ZoomigADC
Value (typ)
1.8432
on
57600
8
none
1
no
3.26
450
170.6667
10
10
5.00
500.00
0.20
0.00
6.52
1024
8
16.0
18.22
9.94E-08
2.41E-07
1.295
Unit
MHz
bps
bits
bit
V
kHz
kohm
vref
vref
mV
bit (1)
ms
V
Vrms (2)
ms
(1) quantization noise only
(2) white noise included
4.2
NOISE CANCELLATION
In order to completely cancel the white noise generated by the ADC and PGA, we have to average the measured
value. To get a stable reading, you need to reduce the equivalent input noise to VLSB/√12. The averaging value is
calculated as follow
2
2
⎛ InpNoise
⎞
⎛ 2.41E - 07
⎞
⋅ 12 ⎟ = ⎜
⋅ 12 ⎟ = 70
⎜
⎝ LSB
⎠
⎝ 9.94E - 08
⎠
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The averaging method chosen is the sliding window method, this introduces a delay of the number of averages but
the data flow stays fluent.
4.3
FLOWCHARTS
Main
UART interrupt
Reset
InitMicro
OnCom
UART
RX int.
OnCom
Software
FIFO write
FIFO
empty ?
yes
FIFO =
R?
yes
FIFO =
v?
yes
FIFO =
r?
yes
Get average
type
FIFO =
w?
yes
Change
average
global
variables
FIFO =
c?
yes
OnCom
Mode 0
UART RX
Int. END
Mode 0
Configure
Mode 0
Configure
Start ADC
Send
Prompt
Reset
Version
Process
Send
Measurements
results
Get average
value
ReadRAM
Send
Prompt
ReadRAM
ReadRAM
Send
Prompt
Get Address
Read at
given
address
WriteRAM
Configure
Send
Acknowledge
Send Result
Other flowcharts on next page
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4.4
FLOWCHARTS CONTINUED
WriteRAM
Process
WriteRAM
Process
Send
Prompt
Std
Get Address
Send
Prompt
Sliding win
Avg
type?
Does
standard
averaging
Does sliding
window
averaging
Get data
Write given
data at
given
address
Send
Acknowledge
Reset
Reset
Reset the
micro
Send ack
Version
Version
Send Version
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5
ZOOMING ADC™
This chapter is a reminder of the main functions of the ZoomingADC™, its registers and their definitions.
It intends to avoid consulting the datasheet to fill the excel sheet described in the next chapter. However more
complete information can be found in the XE8805A datasheet on the Semtech website.
5.1
BLOC DIAGRAM
ZoomingADC™
5.2
ZOOMINGADC™ REGISTERS
Physical
Address
0x0062
0x0063
0x0064
0x0065
0x0066
0x0067
Bit Position
Register Name
7
RegACCfg0
Default values:
RegACCfg1
Default values:
RegACCfg2
Default values:
RegACCfg3
Default values:
RegACCfg4
Default values:
RegACCfg5
Default values:
6
START
0
IB_AMP_ADC[1:0]
11
FIN[1:0]
00
PGA1_G
0
0
BUSY
0
5
SET_NELC[1:0]
01
DEF
0
4
3
SET_OSR[2:0]
010
2
1
0
CONT
0
IB_AMP_PGA[1:0]
ENABLE[3:0]
11
0001
PGA2_GAIN[1:0]
PGA2_OFFSET[3:0]
00
0000
PGA3_GAIN[6:0]
0000000
PGA3_OFFSET[6:0]
0000000
AMUX[4:0]
00000
TEST
0
VMUX
0
With:
•
OUT: (r) digital output code of the analog-to-digital converter. (MSB = OUT[15])
•
START: (w) setting this bit triggers a single conversion (after the current one is finished). This bit always reads back 0.
SET_NELC[1:0]
. To compensate for offsets, the input signal
•
SET_NELC: (rw) sets the number of elementary conversions to 2
is chopped between elementary conversions (1,2,4,8).
(3+SET_OSR[2:0])
. OSR = 8, 16, 32, ...,
•
SET_OSR: (rw) sets the over-sampling rate (OSR) of an elementary conversion to 2
512, 1024.
•
CONT: (rw) setting this bit starts a conversion. A new conversion will automatically begin as long as the bit remains at 1.
•
TEST: bit only used for test purposes. In normal mode, this bit is forced to 0 and cannot be overwritten.
•
IB_AMP_ADC: (rw) sets the bias current in the ADC to 0.25*(1+ IB_AMP_ADC[1:0]) of the normal operation current (25,
50, 75 or 100% of nominal current). To be used for low-power, low-speed operation.
•
IB_AMP_PGA: (rw) sets the bias current in the PGAs to 0.25*(1+IB_AMP_PGA[1:0]) of the normal operation current (25,
50, 75 or 100% of nominal current). To be used for low-power, low-speed operation.
•
ENABLE: (rw) enables the ADC modulator (bit 0) and the different stages of the PGAs (PGAi by bit i=1,2,3). PGA stages that
are disabled are bypassed.
•
FIN: (rw) These bits set the sampling frequency of the acquisition chain. Expressed as a fraction of the oscillator frequency,
the sampling frequency is given as: 00 Æ 1/4 fRC, 01 Æ 1/8 fRC, 10 Æ 1/32 fRC, 11Æ ~8kHz.
•
PGA1_GAIN: (rw) sets the gain of the first stage: 0 Æ 1, 1 Æ 10.
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•
•
•
•
•
•
•
•
PGA2_GAIN: (rw) sets the gain of the second stage: 00 Æ 1, 01 Æ 2, 10 Æ 5, 11 Æ 10.
PGA3_GAIN: (rw) sets the gain of the third stage to PGA3_GAIN[6:0]⋅1/12.
PGA2_OFFSET: (rw) sets the offset of the second stage between –1 and +1, with increments of 0.2. The MSB gives the sign
(0 → positive, 1 → negative); amplitude is coded with the bits PGA2_OFFSET[5:0].
PGA3_OFFSET: (rw) sets the offset of the third stage between –5.25 and +5.25, with increments of 1/12. The MSB gives the
sign (0 → positive, 1 → negative); amplitude is coded with the bits PGA3_OFFSET[5:0].
BUSY: (r) set to 1 if a conversion is running.
DEF: (w) sets all values to their defaults (PGA disabled, max speed, nominal modulator bias current, 2 elementary
conversions, over-sampling rate of 32) and starts a new conversion without waiting the end of the preceding one.
AMUX(4:0): (rw) AMUX[4] sets the mode (0 Æ 4 differential inputs, 1 Æ 7 inputs with A(0) = common reference)
AMUX(3) sets the sign (0 Æ straight, 1Æ cross) AMUX[2:0] sets the channel.
VMUX: (rw) sets the differential reference channel (0 Æ R(1) and R(0), 1 Æ R(3) and R(2)).
(r = read; w = write; rw = read & write)
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6
SEMTECH ZOOMINGADC™ EXCEL SHEET
In order to ease the calculation of the parameters entered in the different registers, we create an excel sheet that
implements all the formulas that can be found in the datasheet.
Using this spreadsheet allows you to trim the values to be put in registers RegACCfg0-5
The figure below shows the spreadsheet
Input zone
Place the parameters of your
application here
Hints / Optimization zone
Follow the hints in order to
reach one optimization level or
another
Results zone
This area shows the different
values calculated following
your parameters inputs
Register contents
Binary and Hex code to be
programmed in
RegACCfg0-5 registers
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7
7.1
GUI SOFTWARE DESCRIPTION
INSTALLATION
To use the GUI on a PC you simply need to launch the executable file named SensorDemo.exe. There is no need
to install anything; you can launch it from network or a CD ROM.
7.2
DESCRIPTION
This window is the main window, it shows you the data coming from the demo board, and the functions available
are described below.
7.3
MAIN SCREEN
Data display
Version of
demo board
RAW data display
COM port control
Advanced functions
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7.4
DISPLAY SETTINGS (SPAN)
This window allows the user to change the span on the chart of the main window, this window does not need to be
closed at each action on the span value, and this is useful to try several configurations.
Note that there is no signal tracking and it is possible that the signal goes out of range due to an external event (i.e.
door or window opening). The way to retrieve the signal is to do an auto scale again.
Resets the chart
to its maximum
values
Validate the current
span displayed
Close this window
Does an autoscale
based on the 100
last measurements
Value of the span where
the signal will fit.
Note that this value can
be changed by the user.
The auto scale function calculates a display range with the specified span around the average value of the last 100
measurements.
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7.5
ADVANCED SETTINGS
This window allows the user to change different configurations of the measurement such as the averaging method
and value. But the main interest of this window is that the user can change every XE8805A register on the fly by
using the read and the write functions.
Using this tool with the standard Semtech MS Excel ZoomingADC™TM calculation sheet allows the user to quickly
change the configuration of the ADC.
This window does not need to be closed at each action on the span value, and this is useful to try several
configurations.
Resets the demo board
and the chart
Queries the version
of the demo board
Read the value at the
given address
Write the wanted value at
the wanted address
Applies
average
values
7.6
changes
method
on
and
Averaging value
Averaging method used.
Close this window
ABOUT BOX
This window can be displayed with a right click action on the title bar of the main window. It gives you the version of
the GUI.
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8
HYPERTERMINAL ALTERNATIVE
Since the interface between the PC and the demo board is through ASCII protocol, a simple hyper terminal
application can be used.
8.1
CONFIGURATION
The configuration of the COM port must be as shown in the picture below
.
8.2
USAGE
The HyperTerminal will display RAW data continuously, the user can log the data using the capture function, and
the user can also send the two commands offered by the GUI interface by typing the letter corresponding to the
command.
See example in picture below
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8.3
COMMANDS
The available commands are Reset and version requests,
8.3.1 Reset
To reset the demo board the user must type “R” in the hyper terminal screen (no need of a carriage return)
Note that it is a capital letter to prevent unwanted reset.
8.3.2 Version
To get the version of demo board the user must type “v” in the hyper terminal screen (no need of a carriage return)
Then the version is displayed on the screen, the user must acknowledge with a carriage return.
8.3.3
Read Address
In order to read an address the user must type “r” in the hyper terminal screen (no need of a carriage return)
Then the display will be as follow:
Read Address: 0x_
Then type the address you want to read
Read Address: 0x0064
Once the last digit is typed the result will appear as follow:
Value Read at 0x0064 : 0x31
Now acknowledge with a carriage return
8.3.4
Write Address
In order to write a data to an address the user must type “w” in the hyper terminal screen (no need of a carriage
return)
Then the display will be as follow:
Write Address: 0x_
Then type the address you want to write
Write Address: 0x0064
Once the last digit is typed the display will appear as follow:
Write Address: 0x0064 Data: 0x_
Then type the data you want to write at the address
Write Address: 0x0064 Data: 0x32
Once the last digit is typed the result will appear as follow:
Value Written at 0x0064 : 0x32
Now acknowledge with a carriage return.
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8.3.5
Configure the averaging
To configure the averaging, the user must type “c” in the hyper terminal screen (no need of a carriage return)
Then the display will be as follow:
Config: Average on (max = 0xFF) :_
Then type the value of averaging you want to use
Config: Average on (max = 0xFF) :20
Once the last digit is typed the result will appear as follow:
Now averaging on 0x20
Average type (0 :std, 1 :sliding window) :
Choose the method of averaging:
Average type (0 :std, 1 :sliding window) :1
The display will look as follow:
Average type chosen : 1
Now acknowledge with a carriage return.
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9
SENSOR DEMO FILES
This chapter explains the structure of the zip file annexed to this technical note.
9.1
DATABASE STRUCTURE
The picture below show the database once the ZIP file is unzipped.
The database is split in 3 sub folders:
•
SensorDemo Application
This folder holds the binaries and executable for the GUI and the embedded software. Source files are
available under the source folders; the embedded software is in RIDE format and the GUI under Microsoft
visual studio .net 2003.
The ZoomingADC™ Excel sheet directory contains the excel sheet described in this document.
•
SensorDemo Documentation
This folder contains
An example of application made with the pressure sensor from Motorola MPX2202AP
This document
A white paper speaking about sensor interfacing with XE8000
The Sensor Demo user’s guide (Quick start)
•
SensorDemo PCB_E068V01A
This folder all the necessary data to rebuild the PCBs, the bill of material, the schematics, the layer
description and the gerber files. The design database is available on request
10 CONCLUSION
Sensor interfacing with XE8000 Sensing Machine is quite easy. The demonstrator for the Sensing Machine makes
it possible to evaluate the ZoomingADC™ performances with a sensor without having to bother about the MCU
programming.
Customers that start their evaluation with this board can continue their development on this basis by getting all the
related technical information from the SEMTECH web site – http://www.semtech.com
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© Semtech 2006
All rights reserved. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The
information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and
may be changed without notice. No liability will be accepted by the publisher for any consequence of its use. Publication thereof
does not convey nor imply any license under patent or other industrial or intellectual property rights. Semtech. assumes no
responsibility or liability whatsoever for any failure or unexpected operation resulting from misuse, neglect improper installation,
repair or improper handling or unusual physical or electrical stress including, but not limited to, exposure to parameters beyond the
specified maximum ratings or operation outside the specified range.
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Contact Information
Semtech Corporation
Wireless and Sensing Products Division
200 Flynn Road, Camarillo, CA 93012
Phone (805) 498-2111 Fax : (805) 498-3804
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