# STM32 Surface EMG

## Description

Single\-channel surface\-EMG acquisition board with a protected 3\.5 mm electrode input, driven reference, 20–500 Hz analog filtering, and STM32F401 recording\. External USB power/data isolation is required and must be verified before any human connection\.

## Project Details

- **Owner:** dantheman
- **Created:** 10/23/2026
- **Last Updated:** 10/28/2026
- **Visibility:** Public

## Key Components

### D1 — [TPD2E2U06DRLR](https://flux.ai/lcsc/tpd2e2u06drlr~uy6h.md)

- LCSC Part Number: C1972959
- Package or Case Code: SOT\-553\-5\_L1\.6\-W1\.2\-P0\.50\-LS1\.6\-TL\-1
- Manufacturer Name: TI\(德州仪器\)
- Manufacturer Part Number: TPD2E2U06DRLR
- Part Type: TVS
- JLCPCB Part Class: Extended Part
- Functional Group: IO J2 USB\-C
- Role: Protection
- Role Details: USB D\+/D\- ESD clamp at connector \(2\-ch, no VBUS rail pin\)
- Design Note: TI TPD2E2U06DRLR \(LCSC C1972959\) replaces USBLC6\-2P6 \(TECH PUBLIC VRWM 5\.0V\)\. DRL pinout per TI DS p3: pin3 IO1=USB\_DP\_CONN, pin5 IO2=USB\_DM\_CONN, pin4 GND, pins1/2 NC\. VRWM 5\.5V; IO cap 1\.5pF typ/1\.9pF max; leakage 10nA max; clamp 9\.7V typ @1A, 12\.4V @5A TLP\. No rail pin, so no VBUS steering into D\+/D\-\. VBUS has separate D4 TVS\. Clamp voltages EXCEED STM32 absolute maximum; MCU internal ESD structures are NOT relied on or claimed to guarantee survival beyond abs max\. Residual ESD clamp coordination \(D1 vs MCU, with R4/R5 currently 0 ohm\) is UNVERIFIED \- bench/ESD test required\. Not a surge\-qualified port\.

**Pins:**
- GND [pin 4]
- IO1 [pin 3]
- IO2 [pin 5]
- NC [pin 1]
- NC [pin 2]

### D2 — [BAV199LT1G](https://flux.ai/lcsc/bav199lt1g~4rlm.md)

- Design Note: BAV199: pin1 anode\-\>GND, pin3 common\-\>EMG\_P\_PROT, pin2 cathode\-\>3V3A \(onsemi datasheet style 11\)\. IR 5nA max at 70V\. Clamp current limited by R6 \(180k\) from the jack; R7 \(180k\) isolates the AD8232 input\. Leakage flows into electrode impedance; characterize on bench\.
- JLCPCB Part Class: Extended Part
- Role Details: EMG\+ low\-leakage clamp to 3V3A/GND between series resistors
- Role: Clamping
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2410010303\_onsemi\-BAV199LT1G\_C145516\.pdf
- Part Type: Diodes \- General Purpose
- Manufacturer Name: onsemi\(安森美\)
- LCSC Part Number: C145516
- Package or Case Code: SOT\-23\_L2\.9\-W1\.3\-P1\.90\-LS2\.4\-BR
- Product Info Url: https://lcsc\.com/product\-detail/Diodes\-General\-Purpose\_ON\_BAV199LT1G\_BAV199LT1G\_C145516\.html
- Functional Group: SENSE U3 AD8232 EMG Front End
- Manufacturer Part Number: BAV199LT1G

**Pins:**
- A [pin 1]
- C [pin 2]
- C/A [pin 3]

### D3 — [BAV199LT1G](https://flux.ai/lcsc/bav199lt1g~4rlm.md)

- Design Note: Matched to D2: clamp at EMG\_N\_PROT between R8 and R9 \(180k each\)\.
- JLCPCB Part Class: Extended Part
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2410010303\_onsemi\-BAV199LT1G\_C145516\.pdf
- Part Type: Diodes \- General Purpose
- Manufacturer Name: onsemi\(安森美\)
- Functional Group: SENSE U3 AD8232 EMG Front End
- LCSC Part Number: C145516
- Package or Case Code: SOT\-23\_L2\.9\-W1\.3\-P1\.90\-LS2\.4\-BR
- Role Details: EMG\- low\-leakage clamp to 3V3A/GND
- Product Info Url: https://lcsc\.com/product\-detail/Diodes\-General\-Purpose\_ON\_BAV199LT1G\_BAV199LT1G\_C145516\.html
- Manufacturer Part Number: BAV199LT1G
- Role: Clamping

**Pins:**
- A [pin 1]
- C [pin 2]
- C/A [pin 3]

### D4 — [SMF6\.0A](https://flux.ai/lcsc/smf6p0a~gud9.md)

- Pin Type: Passive
- Role: Protection
- Design Note: Liown SMF6\.0A \(LCSC C2990428\), unidirectional: VRWM 6\.0V, VBR min 6\.67V @10mA, Vc max 10\.3V @Ipp 19\.4A \(10/1000us, 200W\)\. POLARITY VERIFIED from library part \(partUid aa1ebf14\): symbol pin 1 sits on the bar/cathode end of the TVS glyph \(triangle apex points to pin 1\); footprint pad 1 is on the side of the silkscreen cathode bar and pin\-1 dot\. Datasheet: cathode identified by marking band\. Assembly: band aligns with silk bar = pad 1 = VBUS\_CONN\. RESIDUAL: Vc 10\.3V exceeds TPS7A20 6\.0V rec/6\.5V abs max; TVS\+PTC limit energy but do not guarantee LDO survival for surge/ESD; full protection NOT claimed\. Defined normal supply range is 4\.75\-5\.25V \(USB nominal\); 6\.0V VRWM is only standoff margin, not an extended operating range\. Unspecified\-pin\-type ERC warning is a library symbol limitation \(pins named 1/2\)\.
- JLCPCB Part Class: Extended Part
- Manufacturer Part Number: SMF6\.0A
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/C2990428\.pdf
- Manufacturer Name: Liown\(里阳半导体\)
- Package or Case Code: SOD\-123FL\_L2\.8\-W1\.9\-LS3\.7\-RD
- Part Type: TVS
- LCSC Part Number: C2990428
- Role Details: VBUS TVS at connector: pin1 = cathode \-\> VBUS\_CONN, pin2 = anode \-\> GND \(verified from library symbol \+ footprint\)
- Functional Group: IO J2 USB\-C

**Pins:**
- 1 [pin 1]
- 2 [pin 2]

### D5 — [BAV199LT1G](https://flux.ai/lcsc/bav199lt1g~4rlm.md)

- JLCPCB Part Class: Extended Part
- Role: Clamping
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2410010303\_onsemi\-BAV199LT1G\_C145516\.pdf
- Role Details: RLD\_MID low\-leakage clamp to 3V3A/GND between R27 and R28
- Part Type: Diodes \- General Purpose
- Manufacturer Name: onsemi\(安森美\)
- Functional Group: ANALOG U3 RLD Driven Reference
- LCSC Part Number: C145516
- Package or Case Code: SOT\-23\_L2\.9\-W1\.3\-P1\.90\-LS2\.4\-BR
- Design Note: BAV199LT1G: pin1 A\-\>GND, pin3 C/A\-\>RLD\_MID, pin2 C\-\>3V3A\. Clamps the midpoint so a sleeve transient through R28 \(200k\) is shunted to rails before R27 and the AD8232 RLD pin; never placed directly on RLD\_JACK\. Leakage, capacitance and powered\-off behavior to be measured\.
- Product Info Url: https://lcsc\.com/product\-detail/Diodes\-General\-Purpose\_ON\_BAV199LT1G\_BAV199LT1G\_C145516\.html
- Manufacturer Part Number: BAV199LT1G

**Pins:**
- A [pin 1]
- C [pin 2]
- C/A [pin 3]

### F1 — [0805L020YR](https://flux.ai/lcsc/0805l020yr~pnxu.md)

- Package or Case Code: F0805
- Functional Group: IO J2 USB\-C
- Product Info Url: https://lcsc\.com/product\-detail/Surface\-Mount\-Fuses\_Littelfuse\_0805L020YR\_9V\_C126816\.html
- Role Details: Resettable PTC between connector VBUS\_CONN and protected 5V\_USB
- JLCPCB Part Class: Extended Part
- Manufacturer Part Number: 0805L020YR
- Role: Protection
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2410121755\_Littelfuse\-0805L020YR\_C126816\.pdf
- Manufacturer Name: Littelfuse\(美国力特\)
- LCSC Part Number: C126816
- Design Note: Littelfuse 0805L020YR \(LCSC C126816\): Ihold 0\.20A/Itrip 0\.50A @20C, Vmax 9Vdc, Imax 100A, R1max 3\.5ohm\. Ihold derates to 0\.10A @70C, 0\.07A @85C \- above 60mA design load to \~70C\. Drop at 60mA \<=0\.21V \-\> LDO in \>=4\.54V at 4\.75V supply\. Defined normal supply range 4\.75\-5\.25V; no extended range implied\. Does not rely solely on isolator current limit\. Package exception 0805: PTC hold/trip rating\.
- Part Type: Resettable Fuses

**Pins:**
- 1 [pin 1]
- 2 [pin 2]

### J1 — [SJ\-3524\-SMT\-TR](https://flux.ai/adrian95/sj-3524-smt-tr~vh9.md)

- Design Note: CUI/Same Sky SJ\-3524\-SMT datasheet p2 \(pin table/schematic\): pin1 sleeve, pin2 tip, pin3 ring, pin4 tip switch\. Pin 4 is a switched contact that mates with the TIP \(EMG\+\) spring; it is NOT an isolated detect contact, and there is no ring switch\. Plug\-insertion detect is therefore NOT implemented: sensing ring/tip/pin4 would inject GPIO bias into an electrode path\. Pin 4 left NC\. Isolated detect needs a replacement jack with an electrically independent detect switch, subject to user approval\. Cable candidate: SparkFun CAB\-12970 \(24in 3\.5mm 3\-conductor to 3 surface snaps; https://media\.digikey\.com/pdf/Data%20Sheets/Sparkfun%20PDFs/CAB\-12970\_Web\.pdf, https://www\.sparkfun\.com/sensor\-cable\-electrode\-pads\-3\-connector\.html\)\. Published colour\-to\-contact map NOT available: continuity\-test every cable and label snaps EMG\+ / EMG\- / REF before use\. Surface electrodes only; no needle\-electrode compatibility claimed\. Never plug into audio equipment or plug audio sources into this jack\. Insert/remove plug only with electrodes detached from any person\. Bench prototype: test with simulator only until full isolation/leakage qualification\.
- Manufacturer Name: CUI Devices
- Role: Connector
- Manufacturer Part Number: SJ\-3524\-SMT\-TR
- Symbol Style: parametric\-v1
- Part Type: Connector
- Functional Group: IO J1 Electrode Jack
- Datasheet URL: https://www\.sameskydevices\.com/product/resource/sj\-352x\-smt\.pdf
- License: https://creativecommons\.org/licenses/by/4\.0/
- Role Details: 3\.5mm TRS electrode input: tip EMG\+, ring EMG\-, sleeve driven reference \(RLD\) \- sleeve is NOT ground

**Pins:**
- RING [pin 3]
- SLEEVE [pin 1]
- TIP [pin 2]
- TIP\_SWITCH [pin 4]

### J2 — [CX90M\-16P](https://flux.ai/lcsc/cx90m-16p~vilx.md)

- JLCPCB Part Class: Extended Part
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/C2889324\.pdf
- License: https://creativecommons\.org/licenses/by/4\.0/
- Symbol Style: parametric\-v1
- Package or Case Code: USB\-C\-SMD\_CX90M\-16P
- Role Details: USB Type\-C receptacle, USB2\.0 FS device/sink \(isolated 5V \+ data from user's external isolator\)
- Part Type: USB Connectors
- Design Note: Hirose CX90M\-16P \(LCSC C2889324\)\. Datasheet p2 contact map: A1/A12/B1/B12 GND, A4/A9/B4/B9 VBUS, A5 CC1, B5 CC2, A6/B6 D\+, A7/B7 D\-, A8/B8 SBU \(NC\)\. D\+ A6\+B6 and D\- A7\+B7 tied \(orientation mirror\)\. CC1/CC2 each own 5\.1k Rd \(R29/R30\), no PD, default USB current only \(\<100mA used\)\. Shell/mounting tabs tied to GND \- this GND is the isolated side, so no host earth enters\. ESD: D1 TPD2E2U06DRLR on USB D\+/D\-\. No onboard isolation: user's external isolator must be qualified before human connection\.
- Manufacturer Part Number: CX90M\-16P
- Functional Group: IO J2 USB\-C
- Manufacturer Name: HRS\(广濑\)
- LCSC Part Number: C2889324
- Role: Connector

**Pins:**
- CC1 [pin A5]
- CC2 [pin B5]
- DN1 [pin A7]
- DN2 [pin B7]
- DP1 [pin A6]
- DP2 [pin B6]
- GND [pin B12]
- GND [pin A1]
- GND [pin A12]
- GND [pin B1]
- MD [pin 27]
- MD [pin 28]
- SBU1 [pin A8]
- SBU2 [pin B8]
- SHELL [pin 27]
- SHELL [pin 28]
- SHELL [pin 25]
- SHELL [pin 26]
- VBUS [pin A4]
- VBUS [pin B9]
- VBUS [pin B4]
- VBUS [pin A9]

### J3 — [PZ254V\-11\-05P](https://flux.ai/lcsc/pz254v-11-05p~00c1.md)

- Connector Gender: Male
- Package or Case Code: HDR\-TH\_5P\-P2\.54\-V\-M
- Functional Group: IO J3 SWD Debug Bench Only
- Manufacturer Name: XFCN\(兴飞\)
- Operating Temperature: \-40\~\+105℃
- Product Info Url: https://lcsc\.com/product\-detail/New\-Arrivals\_XFCN\-PZ254V\-11\-05P\_C492404\.html
- Manufacturer Part Number: PZ254V\-11\-05P
- Role: Connector
- Connector Rows: 1
- Connector Positions: 5
- Part Type: Pin Headers
- Design Note: BENCH ONLY\. A debugger bonds board GND to the debugger host earth and bypasses the external USB isolator: never connect a debugger while electrodes are attached to a person\. Pin 1 is 3V3 reference sense for the probe, not a supply input\.
- LCSC Part Number: C492404
- JLCPCB Part Class: Extended Part
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2409302300\_XFCN\-PZ254V\-11\-05P\_C492404\.pdf
- Connector Pitch: 2\.54mm
- Role Details: SWD debug header BENCH ONLY: 1 3V3, 2 SWCLK, 3 GND, 4 SWDIO, 5 NRST

**Pins:**
- 1 [pin 1]
- 2 [pin 2]
- 3 [pin 3]
- 4 [pin 4]
- 5 [pin 5]

### J4 — [22284020](https://flux.ai/lcsc/22284020~toxy.md)

- Manufacturer Name: MOLEX
- Product Info Url: https://lcsc\.com/product\-detail/Others\_MOLEX\_22\-28\-4020\_MOLEX\-22\-28\-4020\_C234182\.html
- Design Note: Shunt ties GAIN\_SEL \(R19\) to VMID: AD8232 postamp 1\+R17/R19=5\.02 \(total 502 nominal\); open = unity postamp \(total 100\)\. Firmware cannot read it; record gain setting manually\. Change only with electrodes disconnected\.
- JLCPCB Part Class: Extended Part
- Package or Case Code: HDR\-TH\_2P\-P2\.54\-V\-M\-1
- Functional Group: ANALOG U3 Postgain and Midrail
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2408121843\_MOLEX\-22284020\_C234182\.pdf
- LCSC Part Number: C234182
- Role: Switching
- Manufacturer Part Number: 22284020
- Part Type: Pin Headers
- Role Details: Gain select jumper: open = total \~100, shunt fitted = \~502

**Pins:**
- 1 [pin 1]
- 2 [pin 2]

### U1 — [STM32F401CEU6](https://flux.ai/lcsc/stm32f401ceu6~plbz.md)

- JLCPCB Part Class: Extended Part
- Part Type: ST Microelectronics
- Package or Case Code: UFQFPN\-48\_L7\.0\-W7\.0\-P0\.50\-BL\-EP
- Role Details: STM32F401CEU6 recorder: ADC1\_IN0 \(PA0\) timer\-triggered 8kS/s DMA, USB OTG FS device \(PA11/PA12\), SWD \(PA13/PA14\)
- Manufacturer Part Number: STM32F401CEU6
- Functional Group: MCU U1 STM32F401 Recorder
- Manufacturer Name: ST\(意法半导体\)
- Design Note: Clock: HSE 12MHz \-\> PLLM=6 \(2MHz VCO in\), PLLN=168 \(336MHz\), PLLP=4 \-\> SYSCLK 84MHz, PLLQ=7 \-\> 48\.000MHz USB \(ST DS: OTG FS needs 48MHz PLL from HSE; HSE 4\-26MHz\)\. ADC: 12\-bit, ADCCLK 21MHz \(PCLK2 84/4\), sample time 480 cycles \(22\.9us\) \>\> RC settling with 100ohm/1nF drive; TIM2/TIM3 TRGO at 8kHz \-\> ADC1 regular conversion \-\> DMA circular double buffer \-\> USB CDC/vendor bulk with sequence numbers and gain\-jumper metadata \(firmware not built\)\. VDDA=3V3A \(ratiometric with VMID\)\. Supplies: VDD x3 \+ 100nF each \+ 4\.7uF, VDDA 1uF\+100nF, VCAP1 4\.7uF ESR\<1ohm, VBAT\-\>3V3\+100nF, VSS/VSSA/EP\-\>GND\. BOOT0 10k pulldown \(flash boot\)\. NRST 100nF \+ internal pull\-up\. Unused GPIO marked NC: configure as analog input in firmware \(lowest leakage/noise\)\. PB3 \(SWO\) NC\.
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2304140030\_STMicroelectronics\-STM32F401CEU6\_C161736\.pdf
- Role: Processing
- Product Info Url: https://lcsc\.com/product\-detail/ST\-Microelectronics\_STMicroelectronics\_STM32F401CEU6\_STM32F401CEU6\_C161736\.html
- LCSC Part Number: C161736

**Pins:**
- BOOT0 [pin 44]
- EP [pin 49]
- NRST [pin 7]
- PA0 [pin 10]
- PA1 [pin 11]
- PA10 [pin 31]
- PA11 [pin 32]
- PA12 [pin 33]
- PA13 [pin 34]
- PA14 [pin 37]
- PA15 [pin 38]
- PA2 [pin 12]
- PA3 [pin 13]
- PA4 [pin 14]
- PA5 [pin 15]
- PA6 [pin 16]
- PA7 [pin 17]
- PA8 [pin 29]
- PA9 [pin 30]
- PB0 [pin 18]
- PB1 [pin 19]
- PB10 [pin 21]
- PB12 [pin 25]
- PB13 [pin 26]
- PB14 [pin 27]
- PB15 [pin 28]
- PB2 [pin 20]
- PB3 [pin 39]
- PB4 [pin 40]
- PB5 [pin 41]
- PB6 [pin 42]
- PB7 [pin 43]
- PB8 [pin 45]
- PB9 [pin 46]
- PC13 [pin 2]
- PC14\-OSC32\_IN [pin 3]
- PC15\-OSC32\_OUT [pin 4]
- PH0\-OSC\_IN [pin 5]
- PH1\-OSC\_OUT [pin 6]
- VBAT [pin 1]
- VCAP1 [pin 22]
- VDD [pin 36]
- VDD [pin 24]
- VDD [pin 48]
- VDDAVREF\+ [pin 9]
- VSS [pin 35]
- VSS [pin 47]
- VSS [pin 23]
- VSSAVREF\- [pin 8]

### U2 — [TPS7A2033PDBVR](https://flux.ai/lcsc/tps7a2033pdbvr~89ay.md)

- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/C2862740\.pdf
- Manufacturer Name: TI\(德州仪器\)
- License: https://creativecommons\.org/licenses/by/4\.0/
- Package or Case Code: SOT\-23\-5\_L2\.9\-W1\.6\-P0\.95\-LS2\.8\-BR
- Role: Power Regulation
- Role Details: Isolated USB 5V \-\> 3V3 LDO \(EN tied to IN\)
- Manufacturer Part Number: TPS7A2033PDBVR
- LCSC Part Number: C2862740
- Functional Group: POWER U2 3V3 LDO
- Design Note: TPS7A2033PDBVR: Vin max 6\.0V rec \(6\.5V abs\), 300mA, dropout 145mV max @300mA, 7uVrms\. Load budget: MCU \~25mA typ at 84MHz\+USB \(ST DS run current, verify\), analog ICs \(AD8232 \+ MCP6002\) \~0\.4mA typ, misc \<2mA \-\> \~28mA typ, 60mA design max retained\. Pdiss=\(5\.25\-3\.3\)\*0\.06=0\.12W\. EN tied to IN \(EN floating = disabled\)\. NC pin 4 left unconnected per datasheet\.
- JLCPCB Part Class: Extended Part
- Symbol Style: parametric\-v1
- Part Type: Power Management

**Pins:**
- EN [pin 3]
- GND [pin 2]
- IN [pin 1]
- NC [pin 4]
- OUT [pin 5]

### U3 — [AD8232ACPZ\-RL](https://flux.ai/lcsc/ad8232acpz-rl~oh06.md)

- LCSC Part Number: C652575
- Functional Group: SENSE U3 AD8232 EMG Front End
- Package or Case Code: LFCSP\-20\_L4\.0\-W4\.0\-P0\.50\-TL\-EP2\.7
- Role: Amplification
- Manufacturer Part Number: AD8232ACPZ\-RL
- Product Info Url: https://lcsc\.com/product\-detail/Pre\-ordered\-Products\_Analog\-Devices\_AD8232ACPZ\-RL\_Analog\-Devices\-ADI\-LINEAR\-AD8232ACPZ\-RL\_C652575\.html
- Role Details: AD8232 EMG front end: fixed G100 INA, servo high\-pass, REFOUT midrail buffer, RLD driver, postamp x1/x5\.02
- Manufacturer Name: ADI\(亚德诺\)
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2008191809\_Analog\-Devices\-AD8232ACPZ\-RL\_C652575\.pdf
- Part Type: Analog To Digital Converters \(ADCs\)
- JLCPCB Part Class: Extended Part
- Design Note: AD8232ACPZ\-RL \(LCSC C652575\), LFCSP\-20 \+ EP\. Pin map per ADI datasheet p6: 1 HPDRIVE\-\>HPDRIVE \(C23\), 2 \+IN\-\>INA\_INP, 3 \-IN\-\>INA\_INN, 4 RLDFB\-\>RLDFB \(C30\), 5 RLD\-\>RLD\_OUT, 6 SW\-\>VMID \(reviewed disabled\-switch tie, never GND\), 7 OPAMP\+\-\>INA\_OUT, 8 REFOUT\-\>VMID, 9 OPAMP\- \-\>GAIN\_FB, 10 OUT\-\>GAIN\_OUT, 11/12 LOD\-/LOD\+ NC \(no GPIO\), 13 SDN\-\>3V3A \(enabled\), 14 AC/DC\-\>GND, 15 FR\-\>GND \(fast restore disabled\), 16 GND, 17 \+VS\-\>3V3A \(C21\), 18 REFIN\-\>VMID\_DIV \(R14/R15/C22\), 19 IAOUT\-\>INA\_OUT, 20 HPSENSE\-\>HPSENSE, 21 EP\-\>GND\. Fixed INA gain 100\. Servo fc=100/\(2pi\*R16\*C23\)=19\.75Hz nominal \(18\.6\-21\.0Hz at R 1%/C 5% endpoints\)\. Postamp R17 402k / R19 100k via J4: x1 open, x5\.02 closed; total 100/502 nominal, \~96\.7/485 V/V ideal peak including input loading\. RLD integrator: internal 150k with C30 10nF\. The \+/\-300mV feature is settled electrode\-offset handling, not instantaneous artifact headroom; sudden offsets can saturate the G100 stage\. EP land 2\.15mm vs datasheet EP 2\.35\-2\.65mm judged acceptable \(0\.30mm clearance to signal pads\); pad/paste audit before PCB release\. No vendor nonlinear model executed; bench and whole\-system isolation qualification required before human connection\.

**Pins:**
- \-IN [pin 3]
- \+IN [pin 2]
- \+VS [pin 17]
- \~\{SDN\} [pin 13]
- AC/\~\{DC\} [pin 14]
- EP [pin 21]
- FR [pin 15]
- GND [pin 16]
- HPDRIVE [pin 1]
- HPSENSE [pin 20]
- IAOUT [pin 19]
- LOD\- [pin 11]
- LOD\+ [pin 12]
- OPAMP\- [pin 9]
- OPAMP\+ [pin 7]
- OUT [pin 10]
- REFIN [pin 18]
- REFOUT [pin 8]
- RLD [pin 5]
- RLDFB [pin 4]
- SW [pin 6]

### U4 — [MCP6002\-E/SN](https://flux.ai/jecstronic/mcp6002-esn~qzl.md)

- Datasheet URL: https://ww1\.microchip\.com/downloads/en/DeviceDoc/MCP6001\-1R\-1U\-2\-4\-1\-MHz\-Low\-Power\-Op\-Amp\-DS20001733L\.pdf
- Role Details: Dual unity\-gain Sallen\-Key low\-pass \(A: Q0\.548, B: Q1\.306\) and ADC driver
- License: https://creativecommons\.org/licenses/by/4\.0/
- Functional Group: ANALOG U4 Dual Sallen\-Key LP
- Role: Filtering
- Manufacturer Name: Microchip Technology
- Manufacturer Part Number: MCP6002\-E/SN
- Part Type: Operational Amplifier \(OP\-AMP\)
- Design Note: MCP6002\-E/SN SOIC\-8, pins per Microchip datasheet p11: 1 VOUTA \+ 2 VINA\- \-\>LP1\_OUT, 3 VINA\+ \-\>LP1\_B, 4 VSS\-\>GND, 5 VINB\+ \-\>LP2\_B, 6 VINB\- \+ 7 VOUTB \-\>LP2\_OUT, 8 VDD\-\>3V3A \(C29\)\. Lower Q first\. LP1: R20/R21 287k, C24 1\.2nF feedback, C25 1nF shunt: f0 506\.2Hz, Q 0\.548\. LP2: R22/R23 549k, C26 1\.5nF feedback, C27 220pF shunt: f0 504\.7Hz, Q 1\.306\. Typical GBW 1MHz, Iq 100uA/amp typ, noise 28nV/rtHz typ\. Vos \+/\-4\.5mV max at 25C, VCM=VSS: offsets pass DC to the ADC \(\~9mV screening sum\)\. Drives R24 100ohm / C28 1nF ADC reservoir, which exceeds the 60pF headline phase\-margin condition; switched\-load stability and settling are bench test gates\. Library footprint pads 1\.95mm long vs Microchip 1\.55mm land, outer edges match; usable\.

**Pins:**
- VDD [pin 8]
- VINA\- [pin 2]
- VINA\+ [pin 3]
- VINB\- [pin 6]
- VINB\+ [pin 5]
- VOUTA [pin 1]
- VOUTB [pin 7]
- VSS [pin 4]

### Y1 — [12MHz Crystal Oscillator](https://flux.ai/collinsemasi/12mhz-crystal-oscillator~wc.md)

- Manufacturer Name: YXC
- Datasheet URL: https://datasheet\.lcsc\.com/lcsc/2304140030\_YXC\-X322512MSB4SI\_C9002\.pdf
- Design Note: YXC X322512MSB4SI 12MHz, 3225: pins 1/3 crystal, 2/4 GND; ESR\<=80ohm, C0\<=3pF, 10ppm \(family table\)\. Load capacitance: family offers CL 10/12/20pF etc\.; exact CL of this MPN NOT confirmed from datasheet \- C16/C17 18pF assume CL\~12pF with \~3pF stray; adjust C16/C17 once CL confirmed\. gm startup calc \(see C16\) retained; frequency accuracy not verified\. Replaced NDK 8MHz \(ESR 500ohm failed STM32 gm\)\.
- Functional Group: MCU U1 STM32F401 Recorder
- Role: Clock Source
- Role Details: 12MHz HSE crystal for 84MHz SYSCLK and 48MHz USB
- Manufacturer Part Number: X322512MSB4SI
- Part Type: Resonator

**Pins:**
- 1 [pin 1]
- 2 [pin 2]
- 3 [pin 3]
- 4 [pin 4]

*The full schematic, PCB layout, bill of materials, and interactive design are available at [https://flux\.ai/dantheman/stm32\-surface\-emg\~c9](https://flux.ai/dantheman/stm32-surface-emg~c9).*

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*Generated from [https://flux\.ai/dantheman/stm32\-surface\-emg\~c9](https://flux.ai/dantheman/stm32-surface-emg~c9)*