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ACC-006 User Manual

1. then the decoupling capacitor impedance could be 32Q at 300Hz i e 15uF This requires a much smaller footprint than the 47uF used in the evaluation board 6 2 Microphone Circuit The microphone circuit is designed for an electret microphone which is commonly used in PC applications Typically it would be powered by 5V via a 2 2kQ series resistor In the reference design it is normally powered by 3 3V to ensure a clean supply regardless of the power Supply used to power the Dev kit This reduces the sensitivity of the microphone and you should test your application with the microphone and voltage you intend to use in order to determine your component values By removing resistor R3 and fitting resistor R4 the microphone power can be taken from the main supply to the codec board To get the best results with different microphone configurations resistor R28 can be removed or fitted depending whether power is supplied to the microphone by the third pin of the connector Many microphones have the third pin wired internally to the ve microphone pin and these perform much better if R28 is not fitted 6 3 Analogue Loop back Switch SW1 pole 2 provides an analogue loop back facility If this switch is in the ON position the audio output from the codec is feed directly back into the codec input This is useful for over the air audio tests For normal operation SW1 pole 2 must be in the OFF position E A Law La eee E An
2. Frequency Transfer Characteristics 0 8 e Codec Loop Around Test a 1V Sine Wave 0 6V Sine Wave Voltage V oO oO 0 3V Sine Wave Oo iN ho oO 0 1000 2000 3000 4000 Frequency Hz 6 Circuit Description This section describes the individual parts of the circuit and give design information about the components to allow you to adapt the circuitry of the codec board for your own implementation 6 1 Audio Amplifier The OKI codec is capable of driving a 1 2K load directly with a max output signal of 2 0Vpp Of the stereo headsets tested it was found that 3292 was a common impedance for each earpiece For a stereo headset where two speakers are being driven in parallel this would be equivalent to driving a 162 load This is out of the codec s specification so a small headphone amplifier U3 has been used on the evaluation board This is not required if the codec is driving a load of 1 2KQ or higher The large 47 uF decoupling capacitor has been used so that the codec could be tested down to its lowest frequency of 300 Hz If you do not require a frequency response to go down below 300 Hz then this capacitor can be reduced to a smaller value The main design consideration is the impedance should not be significant compared to the impedance of the headphone selected at frequencies of interest E g if using a 329 headphone and expecting a 3dB point at 300 Hz
3. Some of the GPIO MPIO lines are used when providing a full RS232 interface The following tables gives the mapping between GPIO MPIO and RS232 signals RS232 Hardware AT Hardware Command GPIO_1 MPIO_O MPIO_11 Note For the BISM PA Class 1 design MPIO_O and MPIO_1 are used to control the RF switch so are not available to the AT Command Set 7 Bill of Materials Not all components are fitted as some provide alternative functionality or implement non standard options Refer to the previous sections and the schematic for information on the component function Components marked in blue are not fitted Toleran Part No a a a E C1 C2 C5 C8 C9 pf Ea Tantalum Capacitor w e O o TANA C6 C10 C13 C17 Ceramic Capacitor C11 C12 100p Ceramic Capacitor ee 0805 D1 D2 P2508 508 D4 D5 D6 BAT54S Dual Schottky Diode BAT54S a BAT54S 10 Way 0 1 R A Skt 10 Way 0 1 R A PCB Socket M20 7891046 a ffm re fs PERE ye im renee owe E SO a A rasraasnisnis 75k 4 ThekrlmResistor foes rers Jo w mermer Joes Rra s e mermer O OO foes o o muasa wro 5 ThickrimResistor O O Joes E a T sa e e ermes OOO ooo E E a T eae e a o a a peen g a eaer 300mA a wswr7oa oims x sine Chane cooeC o MSN770201NS K z pe oe a vwa fw st emee ST 8 References 1 OKI 7702 Data Sheet http www OKI com tw PDF Sheet 7702 pdf 2 ACC 006 Schematic ERBLU49 003A1 02 9 Disclaimers EZURIO
4. incoming audio from the microphone into PCM data and convert the PCM digital audio output of the Bluetooth chip into an analogue signal for the headphones The codec board has a microphone input and headphone output which are compatible with standard PC headsets The 7702 codec has several features such aS power down mode The ACC 006 codec evaluation board provides options to allow these features to be tested This document provides you with information to prototype and evaluate your own audio application Once you have tried out your application you will be able to design your own audio solution based around the OKI codec and the EZURiO Bluetooth Intelligent Serial module 2 Overview 3 3V Regulator Push Button Switches Stereo E MSM7702 udio Gain Codec Headset Control VR2 a Amplifier U3 U2 Sidetone Control VR1 PCM Signals Motherboard Connector J1 OKI L n O 2 mE a o gt XO a Microphone Circuit x10 Microphone The codec board is powered by an on board 3 3V regulator to reduce noise to a minimum The PCM control signals for the codec go directly to the Bluetooth module on the motherboard via the 10 way connector as do the 3 push button switches This allows the switches to be used with an external program that implements the upper portion of headset or Handsfree profile The microphone input designed to interface to PC compatible headsets has a fixed gain of 10 set by externa
5. it to the main developers kit If required this should be soldered to the main board Alternatively other connectors or ribbon cables can be used 3 2 Equipment Required not supplied e Headsets with microphone Standard PC headsets are fine e EZURiO Wireless Developers Kit e BISM II Bluetooth module Normally two sets of development kit are required to test both ends of an audio link If an application is being developed with an existing endpoint such as a mobile phone or headset only one set may be needed 3 3 Motherboard Jumper Settings Before using the codec board there is a jumper setting on the motherboard that needs to be checked This is CB1 next to the USB adaptor which must be removed If fitted it will Short out the PCM output from the codec and prevent it operating CB1 is only relevant for the WLAN 802 11 data module mmm PEIEE REMOVE 1 ae O amp faa 3 4 Procedure 1 Check that SW1 on the codec board is correctly set to the default position see section 6 3 of this manual 2 Plug the BISM II into the socket on the Dev Kit connect to a PC serial port and power up See the dev kit manual for different power supply options 3 Check that AT commands are working using EZURiO terminal Refer to blu2i Quick Start Guide if needed 4 Power down plug the codec board into the dev kit and power up Check that AT commands are working Configure the Slave unit as follows ATSO 1 Answer afte
6. CRC Uses up 1 timeslot AT BTA2 EV4 packet Up to 120 bytes CRC 2 3 FEC Up to 3 timeslots AT BTA4 EV5 packet Up to 180 bytes CRC Up to 3 timeslots Currently Unsupported 4 3 SCO eSCO Transport Delays The following delays have been measured between incoming audio and audio output at the other end of a Bluetooth link Normal SCO AT BTA1 7 84 ms AT BTA2 9 24 ms AT BTA4 10 8 ms Enhanced SCO AT BTA1 12 1 ms AT BTA2 33 4 ms AT BTA4 41 2 ms As can be seen the additional error correction of eSCO comes with a transport delay penalty This is because a buffer is needed to ensure that there is still data to output while waiting for a corrupted data packet to be re transmitted For AT BTA1 and normal SCO the data is transmitted once every 6 timeslots so the transport delay is expected to be 6 1600 3 75ms When doing loop round testing with the codec i e with no transport delay it was found that from input to output the codec added 1ims of delay at 1kKHz and 1 5ms at lower frequencies 4 4 PCM Timing The codec samples at 8 kHz The default mode of operation of the codec is 8 bit A Law encoding In this mode in every 8 kHz cycle 8 bits of data is clocked into the codec The clock rate used for sampling is 250kHz 4us 8 clock cycles takes 32us 8kHz equates to 125us The same timing is used for all packet types in both SCO and eSCO modes 5 Frequency Response 5 1 Codec Frequency Response The codec freque
7. EZURIO Bluetooth Audio Development Pack OKI 7702 Codec Board User Guide Part Number ACC 006 The information contained in this document is subject to change without notice EZURIO Ltd makes no warranty of any kind with regard to this material including but not limited to the implied warranties of merchant ability and fitness for a particular purpose EZURiO Ltd shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing performance or use of this material Copyright 2007 EZURiO Limited All rights reserved No part of this document may be photocopied reproduced or translated to another language without the prior written consent of EZURiO Bluetooth is a trademark owned by Bluetooth SIG Inc USA and licensed to EZURIO Ltd Other product or company names used in this publication are for identification purposes only and may be trademarks of their respective owners EZURiO Bluetooth Development Kit OKI Audio Codec Board Part Number ACC 006 1 General Description The EZURIO OKI Codec Evaluation Board plugs into the EZURiO Developers kit and allows you to rapidly test and evaluate Bluetooth audio applications using the EZURiO Bluetooth Intelligent Serial Module to implement the wireless link The ACC 006 evaluation board is based on the OKI 7702 codec a 3 3V single channel codec that supports A law and u law coding The codec is used to digitise
8. S WIRELESS PRODUCTS ARE NOT AUTHORISED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE MANAGING DIRECTOR OF EZURIO LTD The definitions used herein are a Life support devices or systems are devices which 1 are intended for surgical implant into the body or 2 support or sustain life and whose failure to perform when properly used in accordance with the instructions for use provided in the labelling can reasonably be expected to result in a significant injury to the user b A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system or to affect its safety or effectiveness EZURiO does not assume responsibility for use of any of the circuitry described no circuit patent licenses are implied and EZURiO reserves the right at any time to change without notice said circuitry and specifications 9 1 Data Sheet Status This data sheet contains preliminary data for use with Engineering Samples Supplementary data will be published at a later date EZURIO Ltd reserve the right to change the specification without prior notice in order to improve the design and supply the best possible product Please check with EZURiO Ltd for the most recent data before initiating or completing a design Designers should check the production status of any engineering firmware us
9. a packet size by 50 This means that only 20 bytes of actual audio data can be transmitted in a SCO packet To maintain the 64 kbits sec data rate 4 out of every 6 timeslots are used for the SCO link AT BTA1 enables HV3 AT BTA2 enables HV2 AT BTA4 enables HV1 AT BTA7 allows the link manager to negotiate which packet type to use the default is HV1 4 22 Enhanced SCO Enhanced SCO or eSCO was implemented as part of the 1 2 Bluetooth Core Specification Release The main driving factor was to improve audio quality This has been achieved by 1 including a CRC as part of the audio data packet to allow error detection and a re transmission request 2 allowing higher data rates by using packets that span more than 1 timeslot 3 allowing asymmetric links to allow high quality audio to be streamed in one direction eSCO offers significantly better audio quality but has to be configured at both ends of the link before a unit is enabled to accept incoming connections or enquiries To try out eSCO add the ATS584 1 command to the commands listed in the quick start section immediately after the AT amp F and ATZ commands Both ends of the link must be configured for eSCO for the audio link to be established If one end is set to eSCO and the other to SCO you will get an AUDIO FAIL when the AT BTA1 command is issued The following are the packet types associated with the AT BTA commands for eSCO AT BTA1 EV3 packet Up to 30 bytes
10. alogue Loopback OFF il C 2 Oo 6 4 u Law A Law Switch SW1 pole 1 allows selection of u law or A law encoding u law is selected when the switch is on and A law when it is off The AT firmware in the BISM only allows selection of A law via an S Register S103 3 To change to u Law it is necessary to change one of the PSKEYs that govern the behaviour of the CSR BlueCore04 chipset Because this cannot be performed via the UART interface the use of u Law is not recommended for production designs 6 5 Sidetone When we talk we hear our own voice which is part of normal speech perception If our ears are covered by headphones we do not hear our voice which is perceived as abnormal Try covering your ears while talking to notice the difference To compensate for the loss in feedback to the ear when it is covered with a headphone most telephony systems inject some of the microphone signal back into the audio output path so that the person perceives their own speech as normal This feature is commonly referred to as sidetone Variable resistor VR1 allows you to control the amount of sidetone that is fed back to the audio output so that the user perceives their speech as normal If the headset design does not totally cover the ear then the sideband circuitry can be omitted 6 6 Power Down For battery powered audio applications the power down feature of the codec allows you to turn it off and save power when it is not being used T
11. digital data The Bluetooth specification for SCO is such that there is no re transmission if data is corrupted or lost This explains the crackling and popping that occurs when you get to the limits of radio range The actual data rate over the air is 64 kbits sec There are 1600 timeslots available per second and when a master transmits a SCO packet in one timeslot the slave replies with its SCO packet in the next The SCO packet size is fixed at 240 bits 30 bytes This means when a SCO link is established using the HV3 packet type two out of every 6 timeslots are used up by the SCO link This means there is enough bandwidth to have up to three SCO links active between a master and slave at the same time In this scenario there are no Spare timeslots for other data There are 3 main types of SCO packets HV1 HV2 and HV3 High Quality Voice As mentioned earlier the HV3 packet type has a 1 to 1 mapping between incoming audio data and the data transmitted over the air There is no error correction possible with HV3 With HV1 each bit is transmitted 3 times and a simple voting algorithm is used at the other end to correct for any bit errors This means that only 10 bytes of actual audio data can be transmitted in a SCO packet To maintain the 64 kbits sec data rate all 6 timeslots have to be used for the SCO link leaving no bandwidth available for data With HV2 an FEC algorithm is used to correct for 1 bit errors This increases the dat
12. ed during development before it is deployed
13. his feature can be tested by removing R13 then fitting R15 with a OQ link and controlling the PUI input of the codec via MPIO_5 For AT commands MPIO_5 translates to GPIO 7 The put GPIO 7 into output mode use ats610 040 To turn the codec on use ats627 1 To turn the codec off use ats627 0 The OKI 7702 will also enter a power down state if there is no CLK BCLK of XSYNC 6 7 Alternative PCM_CLK Some applications require that the PCM Clock is driven by external circuitry This requires the PCM Interface provided by the BISM to be put in Slave mode and a clock is supplied by the external circuitry on MPIO_7 R10 should eb removed and R11 fitted with a zero Ohm link in its place Contact Ezurio for further details if this is a requirement 6 8 Switches The switches S1 S2 and S3 have no defined function They are there to assist you to prototype your audio application e g If your application requires a button to be pressed for the user to answer an incoming connection you can prototype that function using one of the switches provided ATS620 allows you to read the status of the GPIO ports No switches pressed ATS620 gt 0028 Si pressed GPIO 9 ATS620 gt 0128 S2 pressed GPIO 7 ATS620 gt 0068 S3 pressed GPIO 8 ATS620 gt 00A8 6 9 GPIO to MPIO Mapping AT commands use GPIO numbers to represent I O lines These GPIO numbers map to physical signals drawn on the schematics as MPIO lines
14. l components to the codec the amplifier itself is part of the codec Part of the microphone signal is mixed into the headphone output signal via VR1 This feature is known as sidetone and allows the user to hear their own voice when speaking It is commonly used in telephony applications to give the user the necessary audio feedback that their ears expect The audio output gain is by default fixed at 2 5 By fitting VR2 the audio gain can be made adjustable The 120mW stereo output amplifier U3 ensures that the codec board can drive standard 322 stereo headphones while keeping total harmonic distortion down to 0 1 E an a ETT a zi TPG 3 a Fz Component Placement gt gil men A ie as m Ot Za hs kal i E y OE T i H eC Note that not all Sia Mais oT a H EZEN 4 2 mi i components are fitted 6 bo emn EE 9 non fitted components are 99 nm ce okas shown without pads Refer d gt z T T TE to Section 7 for details of TII oe aa component fitment and _ ene T a B aji a Ent specification a1 P gee Ceco mame i fe 5 2 m E 9 Hr g ma i ba rs m i SEN NU g e gt WWW EZURIO COM i m jm mla Sm PRALUSS O03AI 02 IPES ILILILILLILLILLLILLLLLI aE LLLLLLILLLILLILLILLL TKOFLLILILLLIIIIIIIIIII 3 Codec Board Quick Start Guide 3 1 Getting Started The codec board is supplied with a right angle 10 way connector that can be used to connect
15. ncy response can be measured by connecting PCM_IN from the codec to PCM_OUT to the codec PCM_OUT from J1 the 10 way connector has to be disconnected A 1k92 pull down resistor is needed on PCM_OUT to ensure maximum volume setting The side tone resistor R18 should also be removed to prevent audio feedback To perform the measurement inject a 1V peak to peak sine wave injected into the microphone circuit Its amplitude can be measured at TP6 GS the input to the codec The output from the codec should be measured on TP9 AOUT 5 2 Bluetooth Link Frequency Response The Codec 8bit data is coded within the Bluetooth chip using CVSD Continuous Variable Slope Decode encoding for transport over the Bluetooth link CVSD is essentially a form of Adaptive Differential PCM ADPCM and is well suited for voice transmission It is forgiving of individual bit corruption as each bit only implements an up or a down shift relative to the previous level corruption of the MSB of a 8 bit sample would create a much larger error term than is possible with ADPCM A draw back of ADPCM is that it cannot track large delta changes in signal quickly enough For voice this does not present a problem The chart below shows the frequency response of the Bluetooth link at different levels of input sine wave As can be seen the frequency response can only be considered to be flat when the input voltage level is less than a 0 3V peak to peak sine wave Over the Air
16. r 1 ring ATS531 1 Keep AT command mode going after a connection is established AT amp W Save the above settings Reset the unit 5 Find out the Bluetooth address of the Slave Unit by typing ATI4 lt return gt 6 Configure the Master Unit as follows AT amp F Restore System Defaults Reset the unit ATS103 3 Set boot mode to OKI Codec ATS531 1 Keep the AT commands going after a connection is established AT amp W Save to flash address that you found in step 5 for nnnnnn AT BTA1 Establish an audio link displays AUDIO ON on both sides Alternatively AT BTA 7 can be used and the units will negotiate the best link type An Audio link is now established between the two units AT BTAO will turn off the audio link but still leave the units connected Note the command ATS103 3 This configures the PCM parameters to support the 8 bit A law coding for the OKI 7702 The default for the BISM module is to support a linear 13 bit codec Unless this command is issued and stored on each module then the OKI codec will not work 4 Bluetooth SCO Links A Primer 4 1 Normal SCO Bluetooth uses a Synchronous Connection Orientated link SCO for audio All this means is that for an audio link the bandwidth needed to maintain the data rates required by the audio link is pre allocated between the master and slave This ensures audio data is always transmitted at the required data rate and takes priority over the transmission of

ACC-006 User Manual

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