Texas Instruments orporated GASSENSOREVM User Manual
Gas Sensor Platform Reference Design User's
Guide
User's Guide
Literature Number: SNOA922
April 2013
WEBENCH is a registered trademark of Texas Instruments.
SmartRF is a trademark of Texas instruments.
iPhone, iPad, iPhone 4S, iPad 3 are registered trademarks of Apple Inc.
App Store is a trademark of Apple Inc. (service mark).
Embedded Workbench is a registered trademark of IAR Systems.
I2C is a trademark of NXP.
Bluetooth is a registered trademark of SIG, Inc.
All other trademarks are the property of their respective owners.
Contents
1 Gas Sensor Platform Reference Design User's Guide .............................................................. 5
1.1 Introduction .................................................................................................................. 5
1.1.1 Fundamental Blocks of LMP91000: ............................................................................. 7
1.1.2 Examples of Firmware and iOS Calculation .................................................................... 8
1.1.2.1 O
1.2 CO Sensor Example ........................................................................................................ 9
1.2.1 Postprocessing Steps as Implemented in the iOS ............................................................ 9
1.3 Supported Sensor Types .................................................................................................. 9
1.3.1 WEBENCH
2 Features ........................................................................................................................... 12
2.1 Gas Sensor Platform With BLE Design Features ..................................................................... 12
2.2 Featured Applications ..................................................................................................... 14
2.3 Highlighted Products ...................................................................................................... 14
2.4 Block Diagram ............................................................................................................. 15
3 Hardware Description ........................................................................................................ 16
3.1 Getting Started ............................................................................................................. 16
3.2 Battery Life Calculation ................................................................................................... 18
4 Antenna Simulations .......................................................................................................... 19
4.1 Simulations With the Battery Board (SAT0009) ....................................................................... 19
4.2 Summary of Findings ..................................................................................................... 24
4.3 Conclusion .................................................................................................................. 24
4.4 FCC Reports ............................................................................................................... 24
5 Schematics and Bill Of Materials ......................................................................................... 25
5.1 SAT Gas Sensor Platform With BLE .................................................................................... 25
5.1.1 Power Board Schematic and BOM ............................................................................. 25
5.2 BLE and AFE Section ..................................................................................................... 27
6 Layout .............................................................................................................................. 32
6.1 SAT Gas Sensor Platform With BLE .................................................................................... 32
6.1.1 SAT0009 (Power Board) Layer Plots .......................................................................... 32
6.1.2 SAT0010 (AFE and BLE Board) Layer Plots ................................................................. 32
7 Practical Applications ........................................................................................................ 34
7.1 iOS Application ............................................................................................................ 34
7.2 Firmware Section .......................................................................................................... 37
A SAT0009 Power Board Files ................................................................................................ 41
A.1 Gerber Files ................................................................................................................ 41
A.2 Altium Project Files ........................................................................................................ 41
Sensor Example ......................................................................................... 8
2
®
Support ............................................................................................. 11
2
Contents SNOA922–April 2013
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1-1. Sensor Design............................................................................................................... 7
1-2. CO Setup..................................................................................................................... 9
1-3. O
1-4. 3-Lead Amperometric Cell................................................................................................ 10
1-5. 2-Lead Galvanic Cell In Potentiostat Configuration................................................................... 10
1-6. WEBENCH CO ............................................................................................................ 11
1-7. WEBENCH O
2-1. Block Diagram of Gas-Sensing Platform With Bluetooth Low Energy.............................................. 15
3-1. Installing the Sensor on the Platform .................................................................................. 16
3-2. CR2032 Battery............................................................................................................ 17
3-3. System Running With LED Flashing.................................................................................... 17
3-4. Current Consumption ..................................................................................................... 18
3-5. Current Consumption-Active vs Sleep Modes......................................................................... 18
4-1. Ansoft Antenna Simulation Setup ....................................................................................... 19
4-2. Antenna Simulations With Power Board ............................................................................... 20
4-3. Antenna Simulations Matching With Power Board.................................................................... 20
4-4. Antenna Simulations Electrical Field Propagation With Power Board.............................................. 21
4-5. Antenna Simulations Setup Without Battery Board................................................................... 21
4-6. Antenna Simulations Matching Without Battery Board ............................................................... 22
4-7. Antenna Simulations Field Propagation Without Battery Board..................................................... 23
4-8. Improved Antenna Matching............................................................................................. 23
5-1. Power Section.............................................................................................................. 25
5-2. BLE Section ................................................................................................................ 27
5-3. AFE Section................................................................................................................ 28
5-4. CO - O
5-5. Filter......................................................................................................................... 31
6-1. Power Board ............................................................................................................... 32
6-2. BLE and AFE Board ...................................................................................................... 33
7-1. Application Icon............................................................................................................ 34
7-2. Locating the Sensors ..................................................................................................... 35
7-3. Updating the Sensors..................................................................................................... 35
7-4. Connecting to a Sensor................................................................................................... 36
7-5. Main Menu.................................................................................................................. 36
7-6. CC Debugger .............................................................................................................. 37
7-7. Launching IAR ............................................................................................................. 37
7-8. IAR Version in Use ........................................................................................................ 38
7-9. Main Loop .................................................................................................................. 38
7-10. Communication Settings.................................................................................................. 39
7-11. Sensor Section............................................................................................................. 39
7-12. CO Settings ................................................................................................................ 40
7-13. Adding New Sensor....................................................................................................... 40
A-1. Power Board ............................................................................................................... 41
A-2. AFE and BLE Board ...................................................................................................... 42
List of Figures
Setup...................................................................................................................... 9
2
............................................................................................................. 11
2
..................................................................................................................... 31
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List of Tables
4-1. Antenna Simulations Results Without Battery Board ................................................................. 22
5-1. Power Section BOM ...................................................................................................... 26
5-2. BLE Section BOM ........................................................................................................ 29
4
List of Tables SNOA922–April 2013
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Gas Sensor Platform Reference Design User's Guide
1.1 Introduction
The intent of this user's guide is to describe in detail the Gas Sensor Platform with Bluetooth®LowEnergy Reference Design from Texas Instruments. After reading this user's guide, a user should better
understand the features and usage of this reference design platform.
Chapter 1
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Introduction
The Gas Sensor Platform with Bluetooth low-energy (BLE) is intended as a reference design that
customers can use to develop end-products for consumer and industrial applications to monitor gases like
carbon monoxide (CO), oxygen (O2), ammonia, fluorine, chlorine dioxide etc. . BLE adds a wireless
feature to the platform that enables seamless connectivity to an iPhone®or an iPad®. Customers can
easily replace the targeted gas sensor based on their application, while keeping the same analog frontend (AFE) and BLE design. The system runs on a CR2032 coin-cell battery. AFE from TI — LMP91000 —
interfaces directly with the electrochemical cell. The LMP91000 interfaces with CC2541 which is a BLE
system on a chip from TI.
An iOS application running on an iPhone 4S®and newer generations or an iPad 3®and newer
generations lets customers interface with this reference platform. Customers can use and customize the
iOS application, the hardware files and firmware source code of CC2541, which TI provides as an open
source. The Gas Sensor Platform with BLE provides customers with a low-power, configurable AFE and
the option to integrate wireless features in gas-sensing applications. This platform helps customers access
the market faster and helps differentiate from performance, power, and feature sets.
The platform complies with the below certifications on wireless:
• EN 300 328 compliant
• FCC 15.247 compliant
• IC RSS-210 compliant
The platform complies with the below certifications on EMC:
• FCC – FEDERAL COMMUNICATIONS COMMISSION Part 15, Class B
• IC – INDUSTRY CANADA ICES-003 Class B
• EN 301 489-17
The heart of this reference platform is the AFE from TI, the LMP91000. The LMP91000 is perfect for use
in micropower, electrochemical-sensing applications. The LMP91000 provides a complete signal-path
solution between a sensor and a microcontroller that generates an output voltage proportional to the cellcurrent. This device provides all of the functionality for detecting changes in gas concentration based on a
delta current at the working electrode.
The LMP91000 is programmed to support multiple electrochemical sensors, such as 3-lead toxic gas
sensors (see Figure 1-4) and 2-lead galvanic cell sensors (see Figure 1-5) with a single design as
opposed to multiple discrete solutions. The AFE supports gas sensitivities over a range of 0.5 to 9500
nA/ppm. It also allows for an easy conversion of current ranges from 5 to 750 µA, full scale.
The adjustable cell-bias and transimpedance amplifier (TIA) gain are programmed through the I2C™
interface. The I2C interface can also be used for sensor diagnostics. An integrated temperature sensor can
be read by the user through the VOUT pin and used to provide additional signal correction in the µC or
monitored to verify temperature conditions at the sensor. The AFE is optimized for micropower
applications, and operates over a voltage range of 2.7 to 5.25 V. The total current consumption can be
less than 10 μA. Additional power-saving capabilities are possible by switching off the TIA and shorting the
reference electrode to the working electrode with an internal switch
The LMP91000 supports many different toxic gases and sensors, and is configured to address the critical
parameters of each gas.
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Introduction
Figure 1-1. Sensor Design
1.1.1 Fundamental Blocks of LMP91000:
Transimpedance Amplifier — TIA provides an output voltage that is proportional to the cell current. TIA
provides seven programmable internal-gain resistors and allows the external-gain resistor to
connect to the LMP91000.
(V
ref_div–Vout
V
out
Input — The LMP91000 provides a 3-electrode solution — counter electrode (CE), reference electrode
(RE), working electrode (WE) (see Figure 1-4), as well as a 2-electrode solution — short the CE
and RE (see Figure 1-5).
Variable Bias — Variable bias provides the amount of bias voltage required by a biased gas sensor
between RE and WE. This bias voltage can be programmed to be 1% to 24% of the supply, or it
can be VREF. The bias can also be negative or positive depending on the type of sensing element.
V
Divider — This is the voltage at the noninverting pin at TIA. This voltage can be programmed to be
ref
either 20%, 50%, or 67% of the supply, or it can be VREF. The V
of the full-scale input range of the analog-to-digital converter (ADC) and sufficient headroom for the
counter electrode of the sensor to swing in case of sudden changes in the gas concentration.
• How to select the appropriate V
– If the current at pin WE (Iwe) is flowing into the TIA, then the V
of V
– If Iweis flowing out of the TIA, then the V
• Assume V
• Assume Variable Bias is set to 2% of V
• Assume V
= (V
ref
The V
) / (RTIA) = I
) – (RTIA × Iwe) (2)
ref_div
.
divider in that case would be 0.82 V. The noninverting input to A1 woul;d be
ref
ref_divider
= 4.1V.
ref
we
is set to 20% of V
0.902 V, which is 22% of V
divider:
ref
ref
(1)
Divider provides the best use
ref
divider should be set to 67%
ref
divider should be set to 20% of V
ref
.
ref
.
ref
.
ref
.
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Introduction
Control Amplifier A1 — A1 is a differential amplifier used to compare the potential between WE and RE.
The error signal is amplified and applied to the CE. Changes in the impedance between the WE
and RE cause a change in the voltage applied to CE in order to maintain the constant voltage
between WE and RE.
Temperature Sensor — An on-board temperature sensor provides a ±3˚C accuracy. The sensor can be
used by an external µC to correct for performance over temperature.
Serial Interface — Calibration and programming is done through the I2C digital interface. Calibration and
state-of-health monitoring is enabled by the I2C interface. As mentioned before, health monitoring
is very important because chemical cells can degrade over time.
1.1.2 Examples of Firmware and iOS Calculation
This section explains the signal path and signal processing as implemented in the Gas Sensor Platform,
from the sensor to LMP91000, to CC2541 and to the iOS application.
1.1.2.1 O2Sensor Example
The following example uses the O2sensor from the Alphasense A2 series (see Section 1.3.1).
A change in µA current of the sensor indications a change in gas concentration. The LMP91000
processes the current and uses the linear TIA stage to convert the current to analog voltage (see
Figure 1-1). The analog voltage is then sent to CC2541. The CC2541 then converts the raw analog
voltage to a digital signal through a 12-bit ADC and transmits the signal through the Bluetooth radio to an
iOS device. The iOS device then performs postprocessing.
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1.1.2.1.1 Postprocessing Steps as Implemented in the iOS
• Covert voltage (binary to decimal).
– In this example, we assume that CC2541 transmits 0348h in its VOUT field. iOS software converts
this hexadecimal voltage into a decimal value:
0348h = 840 (3)
• Since the ADC is inside the CC2541 is a 12-bit resolution (2s complementary).
– Thus the ADC resolution inside CC2541:
2.5 V / (211-1) = 0.001221 (4)
– Note: LM4120 provides a fixed 2.5V precision reference to both LMP91000 and CC2541 in this
reference platform and thus we have used 2.5 V above to calculate the ADC resolution inside
CC2541 .
• Multiply the decimal value from Equation 8 with the ADC resolution:
840 × 0.001221 = 1.025 V (5)
(V
ref_div–Vout
) / (RTIA) = I
• V
• RTIA above is set to 7000.
• Thus current at pin WE (Iwe) flowing into the TIA is ~91 µA (fresh air calibration). (6)
here is 67% of V
ref_div
we_fresh air
.
ref
• To change the O2concentration, if you exhale (breathe out) on the O2sensor; the VOUT would
increase. Let's assume that CC2541 transmits 03B0h in its VOUT field. 03B0h will translate to 944 in
decimal. (see Equation 8).
– 944 × 0.001221 = 1.152 V
• Thus current at pin WE (Iwe) flowing into the TIA in this case would be: (1.667– 1.152) / 7000 =
73.5 µA
• In Equation 11, the calibrated fresh air WE (Iwe) value is 91 µA. For calibration, this can be set to
correspond - 20.9%.
• When we exhale (breathe out) on the O2sensor; the normalized O2percentage would then be:
(73.5 × 20.9) / 91 = 16.88% (7)
8
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1.2 CO Sensor Example
The following example uses the CO sensor from the Alphasense CO-AF series (see Section 1.3.1).
A change in µA current of the sensor indications a change in gas concentration. The LMP91000
processes the current and uses the linear TIA stage to convert the current to analog voltage (see
Figure 1-1). The analog voltage is then sent to CC2541. The CC2541 then converts the raw analog
voltage to a digital signal through a 12-bit ADC and transmits the signal through the Bluetooth radio to an
iOS device. The iOS device then performs postprocessing.
1.2.1 Postprocessing Steps as Implemented in the iOS
• Covert voltage (binary to decimal).
– In this example, we assume that CC2541 transmits 019Fh in its VOUT field. iOS software converts
this hexadecimal voltage into a decimal value:
019Fh = 415 (8)
• Since the ADC is inside the CC2541 is a 12-bit resolution (2s complementary).
– Thus the ADC resolution inside CC2541:
2.5 V / (211-1) = 0.001221 (9)
– Note: LM4120 provides a fixed 2.5V precision reference to both LMP91000 and CC2541 in this
reference platform and thus we have used 2.5 V above to calculate the ADC resolution inside
CC2541 .
• Multiply the decimal value from Equation 8 with the ADC resolution:
415 × 0.001221 = 0.506 V (10)
(V
ref_div–Vout
• Based on the CO-AF specification, the sensitivity of the sensor is 55-90nA/ppm. In the iOS software,
the sensitivity is set to 70nA/ppm (~average of the range).
– 857nA × 70nA/ppm= ~12ppm
• Note: The RTIA for the CO-AF sensor is set to 7000. This ensures that the full range of the CO-AF
sensor (0-5000ppm) can be utilized without clipping.
) / (RTIA) = - I
• As Iweis flowing out of the TIA in case of CO sensor, then the V
• RTIA above is set to 7000.
• Thus current at pin WE (Iwe) flowing out of the TIA is ~857nA (fresh air calibration). (11)
we_fresh air
CO Sensor Example
divider should be set to 20% of V
ref
.
ref
1.3 Supported Sensor Types
The Gas Sensor Platform from TI can be used either with a 3-lead amperometric cell (not included) (see
Figure 1-4) and a 2-lead galvanic cell (not included) in potentiostat configuration (see Figure 1-5) by a
minor resistor change shown in Figure 5-4.
• For a 3-lead amperometric cell (CO), R43 must be un-installed.
• For a 2-lead galvanic cell (O2) R43 must be installed.
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I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF
VDD
AGND
CE
WE
VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
R
Load
VARIABLE
BIAS
MENB
DGND
A1
+
-
TIA
+
-
R
TIA
VE-
VE+
NC
LMP91000
2-wire Sensor
such as Oxygen
I2C INTERFACE
AND
CONTROL
REGISTERS
RE
VREF
VDD
AGND
CE
WE
VOUT
C1
SCL
TEMP
SENSOR
VREF
DIVIDER
C2
SDA
R
Load
VARIABLE
BIAS
MENB
DGND
A1
+
-
TIA
+
-
R
TIA
CE
WE
RE
3-Lead
Electrochemical
Cell
LMP91000
Supported Sensor Types
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Figure 1-2. CO Setup Figure 1-3. O2Setup
Figure 1-4. 3-Lead Amperometric Cell Figure 1-5. 2-Lead Galvanic Cell In Potentiostat
Configuration
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1.3.1 WEBENCH®Support
TI recommends that customers use WEBENCH for their sensor-type design. Refer to Figure 1-6, Figure 1-
7, and the WEBENCH open design tool at http://www.ti.com/product/lmp91000. The WEBENCH tool lists
all of the sensor types compatible with LMP91000.
NOTE: The default firmware and the iOS software in the Gas Sensor Platform from TI are designed
to support the CO-AF from Alphasense (http://www.alphasense.com/industrial-
sensors/alphasense_sensors.html) as well as the O2-A2 from Alphasense. Customers can
easily update the firmware and the iOS software to support additional sensor types. For
firmware updates see Section 7.2.
Supported Sensor Types
Figure 1-6. WEBENCH CO
Figure 1-7. WEBENCH O
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2.1 Gas Sensor Platform With BLE Design Features
• Coin-cell operation (CR2032)
• Low-power configurable AFE (LMP91000) that provides flexibility for customers to use the same AFE
for different gas-sensing platforms and configure different platforms with a simple firmware update
• Provides reference design for BLE antenna design - leveraging low-cost trace antenna
• Enables customers to use the platform to incorporate wireless features in gas-sensing applications
• TI provides BLE firmware and iOS application software as open-source to help customers get to the
market faster.
• The platform is comprised of two boards that are stacked together and are referred to as SAT0009
(power board) and SAT0010 (AFE and Bluetooth board).
LMP91000
• Supply voltage 2.7 to 5.25 V
• Supply current (average over time) <10 μA
• Cell-conditioning current up to 10 mA
• Reference electrode bias-current (85°C) 900 pA (max)
• Output drive-current 750 μA
• Complete potentiostat circuit to interface to most chemical cells
• Programmable cell-bias voltage
• Low-bias voltage drift
• Programmable TIA gain 2.75 to 350 kΩ
• Sink and source capability
• I2C-compatible digital interface
• Ambient operating temperature –40°C to +85°C
• Package: 14-pin WSON
• Supported by WEBENCH Sensor AFE Designer
LM4120
• Small SOT23-5 package
• Low dropout voltage: 120 mV Typ @ 1 mA
• High output voltage accuracy: 0.2%
• Source and sink current output: ±5 mA
• Supply current: 160 μA Typ.
• Low temperature coefficient: 50 ppm/°C
• Enable pin
• Fixed output voltages: 1.8, 2.048, 2.5, 3.0, 3.3, 4.096 and 5.0 V
• Industrial temperature range: –40°C to +85°C
TPS61220
• Up to 95% efficiency at typical operating conditions
• 5.5-μ quiescent current
Chapter 2
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Features
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Features SNOA922–April 2013
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• Startup into load at 0.7-V input voltage
• Operating input voltage from 0.7 to 5.5 V
• Pass-through function during shutdown
• Minimum switching current 200 mA
• Output overvoltage, overtemperature, input undervoltage lockout protection
• Adjustable output voltage from 1.8 to 5.5 V
• Fixed output voltage versions
• Small 6-pin SC-70 package
CC2541
• Radio
• Layout
• Low power
• Peripherals
Gas Sensor Platform With BLE Design Features
– 2.4-GHz low-energy compliant and Proprietary RF System-on-Chip (SoC)
– Supports 250-kbps, 500-kbps, 1-Mbps, 2-Mbps data rates
– Excellent link budget, enabling long-range applications without external front-end
– Programmable output power up to 0 dBm
– Excellent receiver sensitivity (–94 dBm at 1 Mbps), selectivity and blocking performance
– Suitable for systems-targeting compliance with worldwide radio frequency regulations
– ETSI EN 300 328 and EN 300 440 Class 2 (Europe), FCC CFR47 Part 15 (US), and ARIB STD-
T66 (Japan)
– Few external components
– Reference design provided
– 6-mm × 6-mm QFN-40 package
– Pin-compatible with CC2540 (when not using USB or I2C)
– Active-mode RX down to: 17.9 mA
– Active-mode TX (0 dBm): 18.2 mA
– Power mode 1 (4-μs Wake-Up): 270 μA
– Power mode 2 (Sleep Timer On): 1 μA
– Power mode 3 (External Interrupts): 0.5 μA
– Wide supply-voltage range (2 V – 3.6 V)
– TPS62730-compatible low power in active mode
– RX down to: 14.7 mA (3-V supply)
– TX (0 dBm): 14.3 mA (3-V supply)
– Powerful 5-Channel direct memory access (DMA)
– General-purpose timers (one, 16-bit; two, 8-bit)
– IR generation circuitry
– 32-kHz sleep timer with capture
– Accurate digital RSSI support
– Battery monitor and temperature sensor
– 12-bit ADC with eight channels and configurable resolution
– AES security coprocessor
– Two powerful UARTs with support for several serial protocols
– 23 general-purpose I/O pins
• (21 × 4 mA, 2 × 20 mA)
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Featured Applications
– I2C interface
– Two I/O pins with LED-driving capabilities
– Watchdog timer
– Integrated high-performance comparator
• Development tools
– CC2541 Evaluation Module Kit (CC2541EMK)
– CC2541 Mini Development Kit (CC2541DK-MINI)
– SmartRF™ software
– IAR Embedded Workbench®available
2.2 Featured Applications
The Gas Sensor Platform with BLE Reference Platform is designed to demonstrate how a configurable
AFE can be used with a low-power wireless radio to provide a reference platform that will help customers
develop their next-generation gas-sensing solutions for:
• Industrial: gas-sensing application
• Consumer: carbon monoxide-sensing application
• Healthcare facilities: gas-sensing application
2.3 Highlighted Products
The Gas Sensor Platform with Bluetooth Low-Energy Reference Design features the following devices:
• LMP91000: Sensor AFE System: Configurable AFE potentiostat for low-power chemical-sensing
applications.
• CC2541: –2.4-GHz Bluetooth low-energy and proprietary SoC.
• LM4120: Precision micropower low dropout voltage reference.
• TPS61220: Low input voltage, 0.7-V boost converter with 5.5-μA quiescent current.
For more information on each of these devices, go to the respective product folders at ti.com.
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2.4 Block Diagram
Figure 2-1 shows the block diagram for TI's Gas-Sensor Solution with BLE.
Block Diagram
Figure 2-1. Block Diagram of Gas-Sensing Platform With Bluetooth Low Energy
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