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september 2012 doc id 022706 rev 2 1/14 AN4041 application note apwlink+ microphone usb demons tration boards based on the mp34dt01, mp45dt02, or mp34db01 introduction the purpose of this application note is to give a brief description of the apwlink+ microphone usb demonstration boards from stmicroelectronics. these boards host the microcontroller stm32f107rc and either the mp45dt02, mp34dt01 (top-port digital microphones) or the mp34db01 (bottom-port digital microphone). figure 1 shows the capability of the board to host these microphones. these microphones are analog-to-digital transducers, in other words, they are able to sense sound pressure and convert this signal to a digi tal signal using the pulse-density modulation (pdm) technique. the stm32 microcontroller decodes the pdm signal coming from the microphones and streams the audio via the usb. this document will provide a brie f description of the software that decodes the pdm signal and also information about the hardware as well as simple steps to use the boards. ordering information for these boards can be found in appendix c on page 12 . figure 1. apwlink+ demonstration board 5pq wjfx #puupnwjfx 'vmmcpbsewjfx 5pqwjfx #puupnwjfx .jdspqipoftfdujpo[ppnwjfx .1%5 .1%5 . 1%# www.st.com
contents AN4041 2/14 doc id 022706 rev 2 contents 1 software description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 hardware description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3 getting started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 appendix a schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 appendix b layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 appendix c ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 4 revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
AN4041 list of tables doc id 022706 rev 2 3/14 list of tables table 1. microphone supply voltage range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 table 2. l/r channel selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 table 3. ordering information for demonstration boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 table 4. document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
list of figures AN4041 4/14 doc id 022706 rev 2 list of figures figure 1. apwlink+ demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 figure 2. dsp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 figure 3. microphone usb demonstration board (block diagram) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 figure 4. windows message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 5. computer management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 figure 6. recording properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 figure 7. schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 figure 8. board layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 figure 9. board layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
AN4041 software description doc id 022706 rev 2 5/14 1 software description the digital signal processing (dsp) consists of the simple flow depicted in the figure below. figure 2. dsp the pdm signal from the microphone is filtered and decimated in order to obtain a sound signal at the required frequency and resolution. the loaded firmware implements a filter pipeline that has been designed as two filtering-decimation stages. assuming an input frequency of 3.072 mhz and a desired output frequency of 48 khz, the filter stages are configured to implement a decimation factor of 64. the final gain of the pipeline is therefore g 1 = 7.8125. as a result, the output of the filter pipeline is a 16-bit pulse- code modulated (pcm) signal. for further information, please refer to application note an3998, ?pdm audio software decoding on stm32 microcontrollers? available on www.st.com .
hardware description AN4041 6/14 doc id 022706 rev 2 2 hardware description the board is a sound card automatically recognized by the pc as an audio device. the connection is done through the usb cable which also supplies the board and then streams the audio collected from the microphones to the pc. figure 3. microphone usb demonstration board (block diagram) supply section the supply section of the board is made up of two voltage regulators that step down the 5 v of the usb connection to 3.3 v and 2.5 v. the solder jumper j4 gives the user the possibility to choose the desired supply voltage.the digi tal microphone voltage ranges are given in the following table. we recommend using 2.5 v to avoid supplying the microphone with a voltage that is too high. for instance, the mp34dt01 cannot support a supply voltage of 3.3 v. microphone section regarding the microphone section, the mems outputs are a pdm signal, which is a high- frequency stream (1 to 3.25 mhz) of 1-bit digital samples. according to the application hints given in the datasheets (available on www.st.com ), the microphone can be used in single- channel configuration or stereo configuration by setting the lr pin. this pin sets the validity table 1. microphone supply voltage range part number min. typ. max. unit mp45dt02 1.64 1.8 3.6 v mp34db01 1.64 1.8 3.6 v mp34dt01 1.64 1.8 3.6 v sda scl lrck bick sdo12 sdo34 sdo56 stm32f107rc 12.288 mhz sel l/r clk vdd out gnd apwlink connector i 2 s spi i 2 c usb i/f 8 mhz l/r clk vdd out gnd sel regulator 2.5v regulator 3.3v sel 5v mic_vdd c_vdd usb connector 2.5v 3.3v osc mic_vdd j4 j1 j5 spi_ck apwlink+ timer mic_ck mic_ck mic_data12 mic_vdd d1 d2 d3 d4 d5 mic_vdd mic_vdd c_vdd
AN4041 hardware description doc id 022706 rev 2 7/14 of the output data on the high level of the clock or on the low level, refer to the following table. on this board the microphones are used in stereo configuration, so the two digital outputs are shorted (mic_data12, refer to the schematic) and the two mems lr pins must be set one to gnd and the other one to vdd. on the board, the resistors r1 and r13 have already set the lr pin of the microphones. in order to change the mems polarity, the user must unsolder these resistors and manually set the lr pin using the solder jumper j1 and j5. note that the pcb section mounting the mems microphones is detachable. this option has been implemented in order to let the user put the microphones in the desired position (i.e. for display applications in which the microphones are placed at the edges of the display). microcontroller the stm32f107rc microcontroller simultaneously works as a pdm interface and also supports the usb audio streaming. the board hosts two external clocks, the 12.288 mhz and 8 mhz. the first one serves to clock an internal timer for generating both mic_ck and spi_ck. the 8 mhz is the microcontroller?s external clock connected to the osc_in osc_out pins. the stm32 samples the microphone?s output data by using the synchronous serial port (spi1). the microphone signal mic_data12 is a stereophonic signal and the spi must be able to sample both channels. since mic_data12 is synchronous with its clock, spi_ck must be doubled. summarizing, the timer generates: -mic_ck = 3.072 mhz -spi_ck = 6.144 mhz finally, the usb interface allows streaming t he audio on the usb peripheral making this demonstration bo ard compatible with any laptop or deskt op. this streaming capability allows using any acoustic tool for the sound acquisition done by stmicroelectronics? mems microphones. the demonstrat ion board also has the po ssibility to manage the microcontroller registers using the i 2 c bus. another important stm32 peripheral that is used is the i 2 s which allows exporting the audio in the most commonly used digital format. this allows the user to test the signal using audio testing equipment such as audio precision. all these signals can be monitored on the apwlink connector. leds d1-d5 the status of the board is indicated by the following leds: d1 on: usb enumeration successful d2 on: firmware correctly downloaded d3 off: firmware correctly downloaded d4: not soldered d5 on: board supplied table 2. l/r channel selection l/r clock low clock high gnd data valid high impedance vdd high impedance data valid
getting started AN4041 8/14 doc id 022706 rev 2 3 getting started the demonstration board is very user-friendly and is ready to use. after connecting the micro usb cable to the laptop or desktop, the message shown in figure 4 below appears. this is possible since the firmware loaded into the stm microcontroller allows the operating system to recognize the peripheral as an audio device. the version (in this case v1.0) indicates the firmware loaded. the version v1.0 refers to a software decimator of 48 khz as the sampling frequency and 64 as the decimator index. figure 4. windows message the user can also check if the usb demonstrat ion board is recognized as an audio device by accessing the computer management and then clicking on the device manager. the demonstration board appears as a u sb audio device in the list below. figure 5. computer management
AN4041 getting started doc id 022706 rev 2 9/14 since the firmware is able to let the operating system recognize the peripheral as an audio device, it is possible to set the "st 2uphone s evb_v1.0" evaluation bo ard as the recording device. in this configuration, the demonstration board can be used to record the input of general-purpose acoustic tools. figure 6. recording properties
AN4041 schematic doc id 022706 rev 2 10/14 appendix a schematic figure 7. schematic 1 vbat 2 pc13-tamper-rtc 3 pc14-osc32_in 4 pc15-osc32_out 5 pd0_osc_in 6 pd1_osc_out 7 nrst 8 pc0 9 pc1 10 pc2 11 pc3 12 vssa 13 vdda 14 pa0-wkup 15 pa1 16 pa2 17 pa3 18 vss_4 19 vdd_4 20 pa4 21 pa5 22 pa6 23 pa7 24 pc4 25 pc5 26 pb0 27 pb1 28 pb2 29 pb10 30 pb11 31 vss_1 32 vdd_1 33 pb12 34 pb13 35 pb14 36 pb15 37 pc6 38 pc7 39 pc8 40 pc9 41 pa8 42 pa9 43 pa10 44 pa11 45 pa12 46 pa13 47 vss_2 48 vdd_2 49 pa14 50 pa15 51 pc10 52 pc11 53 pc12 54 pd2 55 pb3 56 pb4 57 pb5 58 pb6 59 pb7 60 boot0 61 pb8 62 pb9 63 vss_3 64 vdd_3 u5 stm32_lqfp64 1 2 r7 0r0 1 2 r9 0r0 1 2 r10 0r0 1 2 r11 0r0 1 2 r2 10k 1 2 r3 10k 1 2 r4 10k 1 in 2 out1 3 out2 4 adj 8 7 out4 6 out3 5 u6 lm317lm c49 1uf 1 2 r44 1k 1 2 r47 1.6k 12 l3 inductor2 bead 12 d5 led-1 c41 10nf 1 2 r38 27 c39 100nf + c40 33uf 12 l1 inductor2 bead c1 100nf 1 2 r5 10k c4 100nf 12 but1 tact2 c5 100nf 1 2 r6 22 1 2 r12 22 1 2 r15 10k 12 34 56 78 910 11 12 13 14 15 16 j15 1 2 jp1 jp 1 2 r19 100 1 2 r20 100 c6 ns 1 2 r21 0r0 c7 10pf c8 10pf 12 l2 820nh c9 100nf c10 10uf c11 100nf c12 4.7uf c13 100nf c14 4.7uf c15 100nf c16 4.7uf c17 100nf c18 4.7uf 1 2 r8 1.5k e b c q1 e b c q2 1 2 r22 36k 1 2 r23 10k 1 2 r24 1k 1 2 r25 47k 1 2 r26 180 1 2 d1 led-1 1 2 r27 0r0 nc 1 gnd 2 lr 3 gnd 6 vdd 5 dout 4 clk u1 mp45dt01 c21 100nf c22 10uf 1 2 r29 100 c19 15pf c20 15pf 1 gnd 2 lr 3 gnd 6 vdd 5 dout 4 clk u2 mp45dt01 c23 100nf c24 10uf 1 2 r28 100 c25 15pf c26 15pf 1 2 r30 100 12 d2 led-1 1 2 r31 100 12 d3 led-1 1 2 r32 100 12 d4 led-1 12 l4 inductor2 bead 1 2 r34 1k 1 2 r35 1k 12 34 u3 xt_active 1 2 r37 10k c27 100nf 1 2 3 j5 jumper_3p 1 2 3 j1 jumper_3p 1 2 r33 10k 1 2 r36 0r0 1 2 r39 0r0 nc c28 2.2uf c29 2.2uf 1 2 jp4 jp 1 2 3 j3 jumper_3p 1 2 3 4 5 6 7 8 9 10 j2 5x2_header 1 2 jp3 jp c3 330nf c30 4.7uf 1 2 3 j4 jumper_3p 12 l5 bead 1 2 3 4 j6 con4 1 2 3 4 j8 con4 1 2 3 4 j9 con4 1 2 3 4 j10 con4 1 i/o1 2 gnd 3 i/o2 4 i/o2 5 vbus 6 i/o1 u8 usblc6-2 tp1 spi1_cl ock 1 vbus 2 d- 3 d+ 4 id 5 gnd j7 mi ni typeb c2 18pf c31 18pf 1 vin 2 gnd 3 vinh 4 bypass 5 out u4 lds3985xx 12 3 4 y1 8.000mhz r1 0r0 r13 0r0 tp2 tp3 tp4 1 2 r14 0r0 1 clk 5 gnd 3 vdd 4 data 2 l/r u7 mp34db01 1 clk 5 gnd 3 vdd 4 data 2 l/r u9 mp34db01 3 clk 4 data 2 l/r 1 vdd 5 gnd u10 mp34dt01 3 clk 4 data 2 l/r 1 vdd 5 gnd u11 mp34dt01 i2s_bick i2s_lrck i2s_dat_12 i2s_dat_34 stm32_i2s_data34 stm32_i2s_data12 stm32_i2s_bick stm32_i2s_lrck vcc_usb vcc_usb a_vdd uc_vdd uc_osc_in uc_osc_out uc_vdd uc_vdd scl sda usbdm usbdp nrst i2s_dat_12 i2s_dat_34 i2s_dat_56 i2s_bick i2s_lrck scl 3.3v reset stby sda mclk mute fail reset a_vdd uc_vdd uc_vdd vcc_usb uc_vdd uc_vdd usb_disc uc_vdd mic_data12 uc_vdd mic_vdd mic_data12 mic_ck mic_vdd mic_data12 mic_ck led1 mic_ck led2 uc_vdd led1 led2 led3 mic_vdd uc_vdd uc_vdd uc_vdd stby mute fail uc_vdd 12.288_ck mic_vdd mic_vdd 12.288_ck led3 vss_cap vss_cap vss_cap 12.288_ck stm32_i2s_mclk jtms stm32_i2s_bick stm32_i2s_lrck nrst jtck 2.5v 3.3v uc_vdd mic_vdd mic_data12 mic_ck mic_vdd mic_data12 mic_ck stm32_i2s_lrck stm32_i2s_bick stm32_i2s_data12 stm32_i2s_mclk mco usb_disc usbdm usbdp jtms mco jtck jrst stm32_i2s_lrck stm32_i2s_bick stm32_i2s_data34 uc_osc_in uc_osc_out jrst mic1ck mic1lr mic2ck mic2lr mic_vdd mic_vdd mic1lr mic1ck mic_data12 mic_data12 mic_vdd mic_vdd mic_data12 mic2lr mic2ck
AN4041 layout doc id 022706 rev 2 11/14 appendix b layout figure 8. board layout - top view figure 9. board layout - bottom view
ordering information AN4041 12/14 doc id 022706 rev 2 appendix c ordering information the apwlink+ demonstration boards mentioned in this document are available on www.st.com referenced by the ordering codes listed below. table 3. ordering information for demonstration boards order code board description steval-mki116v1 mems microphone demonstratio n board based on the mp34db01 and stm32f107rc steval-mki117v1 mems microphone demonstration board based on the mp34dt01 and stm32f107rc steval-mki117v2 mems microphone demonstration board based on the mp45dt02 and stm32f107rc
AN4041 revision history doc id 022706 rev 2 13/14 4 revision history table 4. document revision history date revision changes 30-jan-2012 1 initial release 06-sep-2012 2 updated maximum supply voltage for mp34dt01 in ta b l e 1 added appendix c: ordering information
AN4041 14/14 doc id 022706 rev 2 please read carefully: information in this document is provided solely in connection with st products. stmicroelectronics nv and its subsidiaries (?st ?) reserve the right to make changes, corrections, modifications or improvements, to this document, and the products and services described he rein at any time, without notice. all st products are sold pursuant to st?s terms and conditions of sale. purchasers are solely responsible for the choice, selection and use of the st products and services described herein, and st as sumes no liability whatsoever relating to the choice, selection or use of the st products and services described herein. no license, express or implied, by estoppel or otherwise, to any intellectual property rights is granted under this document. i f any part of this document refers to any third party products or services it shall not be deemed a license grant by st for the use of such third party products or services, or any intellectual property contained therein or considered as a warranty covering the use in any manner whatsoev er of such third party products or services or any intellectual property contained therein. unless otherwise set forth in st?s terms and conditions of sale st disclaims any express or implied warranty with respect to the use and/or sale of st products including without limitation implied warranties of merchantability, fitness for a parti cular purpose (and their equivalents under the laws of any jurisdiction), or infringement of any patent, copyright or other intellectual property right. unless expressly approved in writing by two authorized st representatives, st products are not recommended, authorized or warranted for use in milita ry, air craft, space, life saving, or life sustaining applications, nor in products or systems where failure or malfunction may result in personal injury, death, or severe property or environmental damage. st products which are not specified as "automotive grade" may only be used in automotive applications at user?s own risk. resale of st products with provisions different from the statements and/or technical features set forth in this document shall immediately void any warranty granted by st for the st product or service described herein and shall not create or extend in any manner whatsoev er, any liability of st. st and the st logo are trademarks or registered trademarks of st in various countries. information in this document supersedes and replaces all information previously supplied. the st logo is a registered trademark of stmicroelectronics. all other names are the property of their respective owners. ? 2012 stmicroelectronics - all rights reserved stmicroelectronics group of companies australia - belgium - brazil - canada - china - czech republic - finland - france - germany - hong kong - india - israel - ital y - japan - malaysia - malta - morocco - philippines - singapore - spain - sweden - switzerland - united kingdom - united states of america www.st.com

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