AN4041 Application note APWLink+ microphone USB demonstration 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 digital 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 brief 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 'VMMCPBSEWJFX 5PQ WJFX #PUUPNWJFX .JDSPQIPOFTFDUJPO[PPNWJFX .1%5 . 1%# .1%5 5PQWJFX September 2012 Doc ID 022706 Rev 2 #PUUPNWJFX 1/14 www.st.com Contents AN4041 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 2/14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Doc ID 022706 Rev 2 AN4041 List of tables List of tables Table 1. Table 2. Table 3. Table 4. Microphone supply voltage range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 L/R channel selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Ordering information for demonstration boards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Document revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Doc ID 022706 Rev 2 3/14 List of figures AN4041 List of figures Figure 1. Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Figure 9. 4/14 APWlink+ demonstration board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 DSP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Microphone USB demonstration board (block diagram) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Windows message . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Computer management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Recording properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Board layout - top view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Board layout - bottom view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Doc ID 022706 Rev 2 AN4041 1 Software description 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 G1 = 7.8125. As a result, the output of the filter pipeline is a 16-bit pulsecode modulated (PCM) signal. For further information, please refer to application note AN3998, “PDM audio software decoding on STM32 microcontrollers” available on www.st.com. Doc ID 022706 Rev 2 5/14 Hardware description 2 AN4041 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) APWlink connector APWlink+ L/R J1 Mic_Vdd SDO56 SDO34 BICK SDO12 MIC_DATA12 Clk LRCK Vdd SDA SCL Mic_Vdd Vdd Out Clk Out gnd I2C I2S L/R gnd µC_Vdd STM32F107RC SEL SPI 12.288 MHz SPI_CK Mic_Vdd SEL J5 Mic_Vdd Timer MIC_CK MIC_CK J4 USB I/F 8 MHz OSC SEL µC_Vdd Mic_Vdd 2.5V Regulator 2.5V 3.3V Regulator 3.3V 5V USB Connector D1 D2 D3 D4 D5 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 digital microphone voltage ranges are given in the following table. 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 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 highfrequency 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 singlechannel configuration or stereo configuration by setting the LR pin. This pin sets the validity 6/14 Doc ID 022706 Rev 2 AN4041 Hardware description of the output data on the high level of the clock or on the low level, refer to the following table. Table 2. L/R channel selection L/R Clock low Clock high GND Data valid High impedance VDD High impedance Data valid 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 the audio on the USB peripheral making this demonstration board compatible with any laptop or desktop. This streaming capability allows using any acoustic tool for the sound acquisition done by STMicroelectronics’ MEMS microphones. The demonstration board also has the possibility to manage the microcontroller registers using the I2C bus. Another important STM32 peripheral that is used is the I2S 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 Doc ID 022706 Rev 2 7/14 Getting started 3 AN4041 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 demonstration 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 USB audio device in the list below. Figure 5. 8/14 Computer management Doc ID 022706 Rev 2 AN4041 Getting started Since the firmware is able to let the operating system recognize the peripheral as an audio device, it is possible to set the "ST 2uPhones EVB_v1.0" evaluation board 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 Doc ID 022706 Rev 2 9/14 Figure 7. Schematic AN4041 Appendix A Schematic <Power Supply> UC_VDD VCC_USB <JTAG> UC_VDD 2.5V 1 1 D1 LED-1 1 D5 LED-1 1 C40 2 + 33uF USBDP C5 100nF <Mangusta option> 3 STM32_I2S_BICK 2 12.288_CK UC_VDD CLK MP34DB01 3 J4 4 MIC_DATA12 CLK DATA L/R VDD MIC1LR 2 C24 10uF R13 0R0 J1 2 2 LR 3 GND VDD 6 DOUT 5 CLK 4 MIC_DATA12 MIC1CK 1 MP34DT01 GND 3 1 MIC_VDD C23 100nF U2 1 MP45DT01 MIC1LR 2 1 R28 100 C26 15pF MIC_CK C25 15pF MIC_VDD C16 4.7uF 1 2 3 4 I2S_BICK JP1 JP 2 SCL 1 R20100 5 6 7 8 46 JTMS 9 10 45 USBDP 11 12 44 USBDM 13 14 43 USB_DISC 15 16 MUTE 1 VSS_CAP 2 MCLK 0R0 R21 1 42 TP4 37 STM32_I2S_MCLK 36 STM32_I2S_DATA12 1 SDA FAIL RESET 2 DOUT 5 CLK 4 2 C20 15pF R29 C19 100 15pF MIC_DATA12 MIC2CK MIC2LR MP45DT01 1 MIC_CK U11 STM32_I2S_MCLK MIC2CK U9 J10 CON4 3 VDD 4 DATA 5 3 MIC_VDD 4 MIC_VDD J8 CON4 1 MIC_CK L/R 2 CLK 1 MIC_DATA12 MP34DB01 3 4 CLK DATA L/R VDD 2 1 MIC2LR MIC_VDD MP34DT01 MIC_DATA12 1 4 3 MIC_DATA12 R14 0R0 GND C8 10pF MIC_CK 2 LR 3 R1 0R0 12.288_CK 1 2 STM32_I2S_LRCK 2 3 1 33 2 VDD 6 3 1 MIC_VDD STM32_I2S_BICK GND STBY 35 34 1 GND TP3 38 2 C21 100nF U1 J5 5 TP2 39 R19 100 J15 C7 10pF C6 NS MCO 40 C22 10uF I2S_DAT_34 I2S_LRCK GND 41 J6 CON4 UC_VDD JP4 JP 2 I2S_DAT_12 I2S_DAT_56 2 47 STM32_LQFP64 UC_VDD MIC_VDD <Connectors> 1 51 50 VSS_1 PB11 VDD_1 48 32 31 30 17 PB10 PB12 PB2 PA2 J9 CON4 12.288_CK 1 C14 4.7uF C13 100nF VSS_CAP TP1 SPI1_Clock I2S_DAT_12 I2S_DAT_34 2 1 R36 0R0 I2S_BICK I2S_LRCK 2 2 0R0 R9 0R0 R7 1 1 2 0R0 R11 1 2 0R0 R10 1 STM32_I2S_DATA12 STM32_I2S_DATA34 STM32_I2S_BICK STM32_I2S_LRCK 10/14 Schematic MIC_DATA12 C12 4.7uF MIC_VDD MIC_VDD 3.3V C15 100nF LED3 C11 100nF DATA 1 U10 MIC1CK C31 18pF C27 100nF XT_ACTIVE 49 PA14 PA15 PC10 54 53 52 PC11 PC12 56 58 57 59 60 55 PB3 PD2 PB4 PB5 PB6 PB7 BOOT0 63 62 61 PB8 PB9 PB13 2 L5 BEAD VSS_3 PB14 PA1 29 16 PA0-WKUP 28 LED2 PB15 PB1 15 VDDA PB0 C9 100nF 14 PC6 27 C10 10uF 1 LED1 MIC_CK PC7 VSSA 26 13 PC8 PC3 PC5 2 L2 820nH PC9 PC2 PA3 1 PC1 25 12 PA8 U5 PC4 11 PC0 24 10 FAIL PA9 NRST PA7 MUTE PA10 PD1_OSC_OUT PA6 9 PA5 8 STBY 23 7 RESET PA11 22 1 A_VDD C4 100nF PD0_OSC_IN 21 BUT1 TACT2 2 NRST PA12 PA4 6 PA13 PC15-OSC32_OUT 20 UC_OSC_OUT VDD_3 64 5 VSS_2 PC14-OSC32_IN VDD_4 UC_OSC_IN VDD_2 PC13-TAMPER-RTC VSS_4 4 19 LED2 LED3 3 18 2 1 R5 10K 4 JTCK VBAT 2 Y1 8.000MHz STM32_I2S_LRCK MCO 1 1 MIC_DATA12 2 SCL UC_VDD C1 100nF 3 L/R SDA 2 UC_VDD VDD 5 2 R33 10K C18 4.7uF STM32_I2S_DATA34 4 2 2 C17 100nF 1 JRST 2 UC_OSC_OUT U3 1 R34 1k C2 18pF UC_OSC_IN R37 10k J3 D4 LED-1 1 1 1 2 D3 LED-1 2 D2 LED-1 1 R35 1k JUMPER_3P BYPASS C29 2.2uF 2 2 <Microphones> 3 4 JUMPER_3P 2 1 2 2 9 J2 2 MIC_VDD UC_VDD R32 100 BEAD UC_VDD 1 R31 100 7 1 R15 10K 2 <Clock Generators> UC_VDD UC_VDD 1 5 8 JRST 2 6 1K 1 R30 100 1 C49 1uF 3 10 1 JP3 JP 1 R39 0R0 NC C28 2.2uF 1 L4 INDUCTOR2 R44 1 2 4 U7 2 VSS_CAP UC_VDD LED1 Doc ID 022706 Rev 2 <uController STM32> 2 1.6K STM32_I2S_LRCK NRST MIC_VDD 5 LM317LM R47 1 USBLC6-2 STM32_I2S_BICK 2 BEAD 6 ADJ C39 100nF 1 7 JUMPER_3P 2 I/O2 4 C41 10nF USBDM OUT3 JUMPER_3P R12 22 1 OUT4 OUT2 5X2_HEADER 2 1 JTMS JTCK 4 3 I/O2 Mini TypeB R6 22 2 OUT1 3 VBUS 5 4 2 I/O1 6 2 GND 3 UC_VDD 2 2 4 1 I/O1 8 IN 2 1 R38 27 1 D+ 3 ID 4 GND 5 1 BEAD 1 U8 R4 10K R3 10K 2 L1 INDUCTOR2 3 VBUS 1 D- 2 U6 2 1 R8 1.5K 2 J7 GND L3 INDUCTOR2 1 1 1 R2 10K A_VDD UC_VDD 3.3V GND 180 1 3 330nF VCC_USB 2 2 C30 4.7uF C3 5 R26 1 2 E VINH GND R22 36k VCC_USB 1 2 Q2 B 2 1K 2 1 USB_DISC 3 2 E 2 1 C 5 OUT LDS3985XX R27 0R0 NC Q1 B 2 R24 VIN 1 C 2 2 R25 47k 4 R23 10k 1 UC_VDD U4 AN4041 Layout Appendix B Layout Figure 8. Board layout - top view Figure 9. Board layout - bottom view Doc ID 022706 Rev 2 11/14 Ordering information Appendix C AN4041 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 demonstration 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 12/14 Doc ID 022706 Rev 2 AN4041 4 Revision history 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 Table 1 Added Appendix C: Ordering information Doc ID 022706 Rev 2 13/14 AN4041 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 herein 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 assumes 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. 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