bluetooth low energy keyboard reference design - ti. · pdf filekeyboard to try and connect...

TI DesignsBluetooth Low Energy Keyboard Reference Design

TI Designs Design FeaturesTI Designs provide the foundation that you need • Low power, 3 mW average when typing at 300including methodology, testing and design files to characters per minute speedquickly evaluate and customize the system. TI Designs • Designed with TI Bluetooth Low Energy (BLE)help you accelerate your time to market. protocol stack, including HOGP implementation

• Full feature keyboard support of up to 128 keys (16Design Resourcesx 8 matrix) without PCB modification

Tool Folder Containing Design FilesTIDM-BLE-KEYBOARD • Turnkey solution for BLE keyboard applicationsMSP430G2444 Product Folder

Featured ApplicationsCC2541 Product Folder• Keyboard for tablet PC and Smart Phone

ASK Our E2E ExpertsWEBENCH® Calculator Tools

An IMPORTANT NOTICE at the end of this TI reference design addresses authorized use, intellectual property matters and otherimportant disclaimers and information.

All trademarks are the property of their respective owners.

1TIDU548–October 2014 Bluetooth Low Energy Keyboard Reference DesignSubmit Documentation Feedback

Copyright © 2014, Texas Instruments Incorporated

http://www.ti.com/tool/TIDA-00xxX

http://www.ti.com/product/MSP430G2444

http://www.ti.com/product/CC2541

http://e2e.ti.com/

http://e2e.ti.com/support/development_tools/webench_design_center/default.aspx

http://e2e.ti.com

http://www.go-dsp.com/forms/techdoc/doc_feedback.htm?litnum=TIDU548

System Description www.ti.com

1 System DescriptionThis solution uses the MSP430G2444 and CC2541 to implement a Bluetooth Low Energy keyboard.

1.1 MSP430G2444The Texas Instruments MSP430 family of ultra-low power microcontrollers consists of several devices,featuring different sets of peripherals targeted for various applications. The architecture, combined withfive low-power modes, is optimized to achieve extended battery life in portable measurement applications.The device features a powerful 16-bit RISC CPU, 16-bit registers, and constant generators that contributeto maximum code efficiency. The digitally-controlled oscillator (DCO) allows a wake-up from low-powermode to active mode in less than 1 µs.

The MSP430G2x44 series are ultra-low power mixed signal microcontrollers with built-in 16-bit timers, upto 32 GPIO, and a built-in communication capability using the universal serial communication interface. Inaddition, the MSP430G2x44 family members have a 10-bit A/D converter. Typical applications includelow-cost sensor systems that capture analog signals, convert them to digital values, and then process thedata for display or for transmission to a host system.

Figure 1. Functional Block Diagram, MSP430G2x44

2 Bluetooth Low Energy Keyboard Reference Design TIDU548–October 2014Submit Documentation Feedback


http://www.ti.com


www.ti.com System Description

1.2 CC2541The CC2541 is a power-optimized, true system-on-chip (SoC) solution for both Bluetooth Low Energy andproprietary 2.4 GHz applications. The CC2541 enables network nodes to be built with low total bill-of-material costs. The CC2541 combines the performance of a leading RF transceiver with an industrystandard-enhanced 8051 MCU, in-system programmable flash memory, 8-KB RAM, and other powerfulsupporting features and peripherals. The CC2541 is highly suited for systems requiring ultralow powerconsumption. This is specified by various operating modes. Short transition times between operatingmodes enable low power consumption.

Figure 2. CC2541 Simplified Block Diagram



http://www.ti.com


Block Diagram www.ti.com

2 Block Diagram

Figure 3. Hardware Block Diagram

3 System Design TheoryFor this keyboard to work properly, the host operating system must support a BLE-enabled keyboard.Windows 8.1 can be used as the host, as it already supports BLE keyboards through a HID over GATTprofile. The HID over GATT profile defines the procedures and features used by Bluetooth Low EnergyHID Devices using GATT, and Bluetooth HID hosts using GATT. As shown in Figure 4, the keyboard isthe device and Windows 8.1 is the host in this solution.

Figure 4. Host and HID device Roles in HOGP



http://www.ti.com


MSP430 Spy-Bi-Wire Interface

CC2541 Debug Interface

www.ti.com Getting Started Hardware

4 Getting Started Hardware

Figure 5. Debug and Programming Interface

4.1 MSP430G2444 JTAG (SPY-BI-WIRE) ConnectionTo download the program into flash for the MSP430, use the connections between the PCBA and theJTAG tool shown in Table 1:

Table 1. PCBA and JTAG Connections

PCBA PIN JTAG1 VCC2 TEST3 GND4 RESET

4.2 CC2541 Debug Interface ConnectionTo download the program into flash for the CC2541, use the connections between the PCBA and thedebug or programming tool shown in Table 2:

Table 2. PCBA and Debug Tool Connections

PCBA PIN Debug I/F1 GND2 VCC3 DC4 DD5 PWR6 RESET



http://www.ti.com


Getting Started with Firmware www.ti.com

5 Getting Started with Firmware

5.1 Keyboard Work Mode State MachineFigure 6 depicts the working mode of the keyboard: this assumes that the keyboard is already paired andbounded with the host.

Figure 6. Working Mode State Machine

5.1.1 Idle ModeAfter a successful pairing progress, the keyboard enters idle mode. In idle mode, the BLE connection isestablished with the host. No data is sent by the BLE radio, but the keyboard waits for any keystroke andthe BLE radio works periodically to keep the BLE connection.

5.1.2 Active ModeWhen the user types any key on the keyboard when in idle mode, it enters active mode. In active mode,the keystroke data is sent out to the host. The keyboard returns to idle state when no data remains. TheBLE radio in this mode is on full duty.



http://www.ti.com


www.ti.com Getting Started with Firmware

5.1.3 Sleep ModeWhen there is no user input for 60 seconds, the keyboard enters sleep mode. In sleep mode, the BLEconnection closes to save power. If the user strikes any key on the keyboard, the keyboard tries to build aBLE connection and rolls into active mode if successful. In sleep mode, the BLE radio is shut off.

5.1.4 Power Off ModeThe power off mode is similar to sleep mode, other than that when in this mode, a keystroke cannot wakeup the entire system. The BT button on the bottom-right side of the keyboard is the only key able to poweron the keyboard. This mode avoids accidentally triggering the keyboard, to save power consumption.

5.2 Keyboard User’s GuideTo make the keyboard work, see Figure 7 and follow the steps:

Figure 7. BT Button and LED



http://www.ti.com


Getting Started with Firmware www.ti.com

1. Insert 2 AAA alkaline batteries by unlocking the battery case, as illustrated in Figure 7. The BT LEDwill blink two times and enter sleep mode.

2. Prepare the BLE host, which in this example is a Windows 8.1 tablet PC. Go to the Device Manager –Bluetooth and enable the BT device. The keyboard should appear in the list in the next step.

Figure 8. Enable Bluetooth Device in Windows 8.1

3. Hold the BT button until the BT LED starts blinking quickly. The keyboard should now be listed as BLEKeyboard; click on it and select Pair to pair and bind the keyboard with the tablet. The user will beprompted to input a 6 digit number. Wait until the operation is successful. The keyboard only needs tobe bound one time with the tablet; to bound the keyboard to another tablet, remove the binding fromthis tablet first.

4. After the keyboard is paired and bound to the host, any keystroke on the keyboard will cause thekeyboard to try and connect with the host (except in power off mode). If the host is ready, the BLEconnection is established automatically.

5. The keyboard automatically goes into sleep mode if there is no user input for around 60 seconds, tosave power. Press the BT button to toggle Power On/ Power Off mode for the keyboard. See Figure 6for more details.



http://www.ti.com


www.ti.com Test

6 TestThis section describes how to measure the power consumption of the keyboard.

6.1 Test EnviromentTest instrument: FLUKE 287C, mA/uA

Voltage for 2 AAA alkaline batteries: 3.2 V no load

6.2 Test Mode1. Active mode2. Idle mode3. Sleep mode and power off mode

6.3 Test Data

Keyboard Work Mode Average Current CommentsTyping rate is around 300 characters perActive 1.0 mA minute

Idle 165 uASleep and power off <1 uA



http://www.ti.com


Title

Number RevisionSize

A4

Date: 2014-8-19 Sheet ofFile: Z:\shared\btkbref\BTKBREF_rev1_1.SchDocDrawn By:

DVSS1

P2.7 /XOUT2

P2.6 /XIN3

DVSS4

/RST/SWTDIO5

P2.0/A06

P2.1/A17

P2.2/A28

P3.0 /A59

SDA/P3.110

SCL/P3.211

P3.312

AVSS13

AVCC14

P4.0 /TB015

P4.1 /TB116

P4.2 /TB217

P4.3 /A1218

P4.4 /A1319

P4.5 /A1420

A15/P4.621

P4.722

TXD/SIMO/P3.423

RXD/SOMI/P3.524

A6/P3.625

A7/P3.726

P2.327

P2.428

P1.029

P1.130

P1.231

P1.332

P1.433

P1.534

P1.635

P1.736

TEST/SBWTCK37

DVCC38

DVCC39

P2.540

U2

MSP430G2544IRHA4047KR8

2.2nC7

GND

VCC

RST

1234

P3

JTAG

VCC

GNDTEST

RST

RST

VCC

VCCGND

GND

GNDKSI0KSI1KSI2KSI3KSI4KSI5KSI6KSI7

CC2541_TXDCC2541_RXD

TEST

KSO0KSO1KSO2KSO3KSO4KSO5 KSO6

KSO7

KSO8KSO9

KSO10

KSO11KSO12

KSO13

KSO14KSO15

1 23 45 67 89 1011 1213 1415 1617 1819 2021 2223 2425 26

P2

KB

KSO15

KSO0

KSO7

KSO5

KSO2KSO4

KSO8

KSO6

KSO11KSO10KSO12

KSI3

KSI0KSI2KSI4

KSI6KSI7

KSI1

KSI5

KSO13

KSO1KSO3

KSO9

KSO14

WAKE

2.2uFC6

VCC

GND

100nFC5

STAT1

SW2

VIN3

GND4

/BYP5

VOUT6

U1

tps627302.2uF

C4

GND GND

2.2uHL1 L2

Bead

2.2uFC2

2.2uFC3

VCC

3

1

2

Q12N7002

V_BAT

V_BAT

0

R5

2KR6

GND

20KR3

BAT_LVL

BAT_LVL

BAT_DET

BAT_DET

D1

D2

1K1R2

1K1R4

VCCLED_GREEN

LED_GREEN

LED_RED

LED_RED

S1

SW-PB10K

R1

VCC

GND100nFC1

GND

KEY

V+

V-

/BYPASS

CC2541 BLE keyboard

1 2

v1.1

TP4

v1.0 -> v1.1

1. Removes KEY net on P3.02. Revoves R7 and add a test point on P2.6

Design Files www.ti.com

7 Design Files

7.1 Schematics

Figure 9. Schematic 1



http://www.ti.com


Title

Number RevisionSize

A4

Date: 2014-8-19 Sheet ofFile: Z:\shared\btkbref\cc2541_rev1_1.SchDoc Drawn By:

GND1

SCL2

SDA3

NC4

P1_55

P1_46

P1_37

P1_28

P1_19

DVDD210

P1

_0

11

P0_

712

P0_

613

P0_

514

P0_

415

P0

_3

16

P0

_2

17

P0_

118

P0_

019

/RE

SE

T20

AVDD521

XOSC_Q122

XOSC_Q223

AVDD324

RF_P25

RF_N26

AVDD227

AVDD128

AVDD429

R_BIAS30A

VD

D6

31

P2_

4/O

SC

32_1

32

P2_

3/O

SC

32_2

33

P2

_2

34

P2

_1

35

P2_

036

P1_

737

P1_

638

DV

DD

139

DC

OU

PL

40

U3

CC2541F128RHAR

56K

R9

2nHL5

1pFC17

18pFC15

2nHL6

1nHL3

3nHL4

18pFC16

1pFC13

GND

GND

1pFC14

GND

100nFC10

100nFC19

100nFC11

100nFC20

220pFC12

VCC

GND

VCC

GND

GND GND

1 2X1

XTAL32M

14X2

XTAL32K

12pFC21

12pFC22

15pFC23

15pFC24

GND GND GND GND

XOSC32M_1

XOSC32M_2

XO

SC

32M

_1

XO

SC

32M

_2

XO

SC

32K

_1

XO

SC

32K

_2

XO

SC

32K

_1

XO

SC

32K

_2

GND

VC

C

VC

C100nFC18

GND

1uFC9

VCC

VCC

GND

1uFC8

GND

2K7

R11

1nFC25

GND

123456

P4

CCDEBUG

GNDVCCDCDDCC-PWR

CC-RESET RSTN

RS

TN

DC

DD

0R10

Do not mount

VCCC

C2541_R

XD

CC

2541_T

XD

WA

KE

TP1

12

A1 BLE_ANTENNA

GND

TP3

TP2

/BY

PA

SS

KE

Y

v1.1

2 2

CC2541 BLE keyboard

www.ti.com Design Files

Figure 10. Schematic 2



http://www.ti.com


Design Files www.ti.com

7.2 Bill of Materials

Table 3. BOMManufacturer PartItem Qty Reference Value Part Description Manufacturer PCB FootprintNumber

1 3 C1, C5, C18 100 nF CAP CER 100 nF 6 V 10% 0402 0402

2 1 C6 2.2 uF CAP CER 2.2 uF 6 V 10% 0402 0402

3 1 C7 2.2 nF CAP CER 2.2 uF 6 V 10% 0402 0402

4 2 C8, C9 1 uF CAP CER 1 uF 6 V 10% 0402 0402

5 1 C25 1 nF CAP CER 0.1 UF 6 V 10% 0603 0402

6 2 C21, C22 12 pF Capacitor, 12p, 0402, NP0, 5%, 50 V Murata GRM1555C1H120JA0 04021D

7 2 C23, C24 15 pF Capacitor, 15p, 0402, NP0, 5%, 50 V Murata GRM1555C1H150JA0 04021D

8 2 C15, C16 18 pF Capacitor, 18p, 0402, NP0, 5% 25 V Murata GRM1555C1H180JZ0 04021D

9 3 C13, C14, C17 1 pF Capacitor, 1p, 0402, NP0, +/-0.25 pF Murata GRM1555C1H1R0CZ 040250 V 01D

10 1 C12 220 pF Capacitor, 220p, 0402,N P0, 5%, 50 Murata GRM1555C1H221JA0 0402V 1D

11 4 C10, C11, C19, C20 100 nF Capacitor, 100n, 0402, X5R, 10%, Murata GRM1555R71A104KA 040210 V 01D

12 3 C2, C3, C4 2.2 uF CAP CER 2.2 uF 6 V 10% 0402 Murata GRM155R60J225ME1 06035D

13 2 D1, D2 RED LED 0603 0603

14 1 R1 10K Resistor, 10K, 0402, 5% 0402

15 1 R8 47K Resistor, 47K, 0402, 5% 0402

16 1 R9 56K Resistor, 56K, 0402, 1% 0402

17 1 R11 2.7K Resistor, 2.7K, 0402, 5% 0402

18 1 R5 0 Resistor, 0, 0402, 5% 0603

19 2 R2, R4 1.1K Resistor, 1.1K, 0402, 5% 0603

20 1 R6 2K Resistor, 2K, 0402, 5% 0603

21 1 R3 20K Resistor, 20K, 0402, 5% 0603

22 1 R10 0 Resistor, 0, 0402, 5% 0603

23 1 Q1 2N7002 N-Channel MOSFET SOT23-3P

24 1 L2 Bead EMI filter bead, 0402 1k ohms tape Murata BLM15HG102SN1D 0603GHz Band

25 1 L3 1 nH Inductor, 1n0, 0402, Monolithic +/- Murata LQG15HS1N0S02D 04020.3 nH

26 2 L5, L6 2 nH Inductor, 3n0, 0402, Monolithic +/- Murata LQG15HS2N0S02D 04020.3 nH

27 1 L4 3 nH Inductor, 2n0, 0402, +/-0.3 nH Murata LQG15HS3N0S02D 0402

28 1 L1 2.2 uH Inductor, 2.2 uH, 0603,500 mA 30% Murata LQM21PN2R2NGC 0603

29 1 U2 MSP430G2444 MCU Texas Instruments MSP430G2444IRHA4 IC-QFN40-RHA-0R RTB

30 1 U1 tps62730 DC-DC Texas Instruments TPS62730DRYR DRY0006A

31 1 U3 CC2541F128 BLE SOC Texas Instruments CC2541F128RHAR IC-QFN40-RHA-RTB

32 1 X2 XTAL32K CRYSTAL, OSCILATOR, 32.768 Epson Toyocom 12-00422 SSP-T-32768kHz, -20PPM/ + 20PPM, -40DEGC/+85DEGC, 12.5 pF, SMD

33 1 X1 XTAL32M CRYSTAL, OSCILATOR, 32 MHz, Epson Toyocom 12-00430 XIAL4P-SMT3*2X510 pF, -10PPM/+10PPM, -40DEGC/+85DEGC, SMD

34 1 SW1 Button switch Button switch SW-PB-SMT3*4*2

35 1 P3 JTAG connector JTAG connector for MSP430 MHDR1X4

36 1 P2 Keyboard 25-pin connector FFC-25-P1.0connector

37 2 S1, S2 Connector 2-pin connector MHDR1X2

38 1 P4 CCDEBUG debug connector for CC2541 MHDR1X6



http://www.ti.com


www.ti.com Design Files

7.3 PCB Layouts

Figure 11. PCB Layouts

8 Software Files

9 References1. MSP430G2x44 - Mixed Signal Microcontroller (SLAS892B)2. CC2541 -2.4-GHz Bluetooth low energy and Proietary System-On-Chip (SWRS110D)3. HID OVER GATT PROFILE SPECIFICATION v10r00



http://www.ti.com

http://www.ti.com/lit/pdf/SLAS892B

http://www.ti.com/lit/pdf/SWRS110D


About the Author www.ti.com

10 About the AuthorNAN JIANG is an MCU Systems Application Engineer at Texas Instruments, responsible for developingsystem solutions for IoT (Internet of Things) and industrial applications.



http://www.ti.com


IMPORTANT NOTICE FOR TI REFERENCE DESIGNS

Texas Instruments Incorporated ("TI") reference designs are solely intended to assist designers (“Buyers”) who are developing systems thatincorporate TI semiconductor products (also referred to herein as “components”). Buyer understands and agrees that Buyer remainsresponsible for using its independent analysis, evaluation and judgment in designing Buyer’s systems and products.TI reference designs have been created using standard laboratory conditions and engineering practices. TI has not conducted anytesting other than that specifically described in the published documentation for a particular reference design. TI may makecorrections, enhancements, improvements and other changes to its reference designs.Buyers are authorized to use TI reference designs with the TI component(s) identified in each particular reference design and to modify thereference design in the development of their end products. HOWEVER, NO OTHER LICENSE, EXPRESS OR IMPLIED, BY ESTOPPELOR OTHERWISE TO ANY OTHER TI INTELLECTUAL PROPERTY RIGHT, AND NO LICENSE TO ANY THIRD PARTY TECHNOLOGYOR INTELLECTUAL PROPERTY RIGHT, IS GRANTED HEREIN, including but not limited to any patent right, copyright, mask work right,or other intellectual property right relating to any combination, machine, or process in which TI components or services are used.Information published by TI regarding third-party products or services does not constitute a license to use such products or services, or awarranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectualproperty of the third party, or a license from TI under the patents or other intellectual property of TI.TI REFERENCE DESIGNS ARE PROVIDED "AS IS". TI MAKES NO WARRANTIES OR REPRESENTATIONS WITH REGARD TO THEREFERENCE DESIGNS OR USE OF THE REFERENCE DESIGNS, EXPRESS, IMPLIED OR STATUTORY, INCLUDING ACCURACY ORCOMPLETENESS. TI DISCLAIMS ANY WARRANTY OF TITLE AND ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESSFOR A PARTICULAR PURPOSE, QUIET ENJOYMENT, QUIET POSSESSION, AND NON-INFRINGEMENT OF ANY THIRD PARTYINTELLECTUAL PROPERTY RIGHTS WITH REGARD TO TI REFERENCE DESIGNS OR USE THEREOF. TI SHALL NOT BE LIABLEFOR AND SHALL NOT DEFEND OR INDEMNIFY BUYERS AGAINST ANY THIRD PARTY INFRINGEMENT CLAIM THAT RELATES TOOR IS BASED ON A COMBINATION OF COMPONENTS PROVIDED IN A TI REFERENCE DESIGN. IN NO EVENT SHALL TI BELIABLE FOR ANY ACTUAL, SPECIAL, INCIDENTAL, CONSEQUENTIAL OR INDIRECT DAMAGES, HOWEVER CAUSED, ON ANYTHEORY OF LIABILITY AND WHETHER OR NOT TI HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, ARISING INANY WAY OUT OF TI REFERENCE DESIGNS OR BUYER’S USE OF TI REFERENCE DESIGNS.TI reserves the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services perJESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevantinformation before placing orders and should verify that such information is current and complete. All semiconductor products are soldsubject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s termsand conditions of sale of semiconductor products. Testing and other quality control techniques for TI components are used to the extent TIdeems necessary to support this warranty. Except where mandated by applicable law, testing of all parameters of each component is notnecessarily performed.TI assumes no liability for applications assistance or the design of Buyers’ products. Buyers are responsible for their products andapplications using TI components. To minimize the risks associated with Buyers’ products and applications, Buyers should provideadequate design and operating safeguards.Reproduction of significant portions of TI information in TI data books, data sheets or reference designs is permissible only if reproduction iswithout alteration and is accompanied by all associated warranties, conditions, limitations, and notices. TI is not responsible or liable forsuch altered documentation. Information of third parties may be subject to additional restrictions.Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirementsconcerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or supportthat may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards thatanticipate dangerous failures, monitor failures and their consequences, lessen the likelihood of dangerous failures and take appropriateremedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components inBuyer’s safety-critical applications.In some cases, TI components may be promoted specifically to facilitate safety-related applications. With such components, TI’s goal is tohelp enable customers to design and create their own end-product solutions that meet applicable functional safety standards andrequirements. Nonetheless, such components are subject to these terms.No TI components are authorized for use in FDA Class III (or similar life-critical medical equipment) unless authorized officers of the partieshave executed an agreement specifically governing such use.Only those TI components that TI has specifically designated as military grade or “enhanced plastic” are designed and intended for use inmilitary/aerospace applications or environments. Buyer acknowledges and agrees that any military or aerospace use of TI components thathave not been so designated is solely at Buyer's risk, and Buyer is solely responsible for compliance with all legal and regulatoryrequirements in connection with such use.TI has specifically designated certain components as meeting ISO/TS16949 requirements, mainly for automotive use. In any case of use ofnon-designated products, TI will not be responsible for any failure to meet ISO/TS16949.IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265Copyright © 2014, Texas Instruments Incorporated

bluetooth low energy keyboard reference design - ti. · pdf filekeyboard to try and connect...

Documents