4 layers65 × 56 mm
2 layers
CurrentSensorUSB
vlust/interview-assignmentSubmission for an interview assignment
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 25
- Nets
- 45
- Pads
- 135
- Tracks, vias
- 4, 0
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 18 May 2025
- Updated
- 19 May 2025
Overview
CurrentSensorUSB is an open-source printed circuit board by vlust, from the vlust/interview-assignment repository on GitHub. It is a 2-layer board with 25 parts on 45 nets, routed with 4 tracks and 0 vias.
It is built around the ATSAMD21E18A-AF, ADS1113IDGS and ADUM1250AR, with the PRTR5V0U2X among its other parts. Its parts include 7 capacitors, 7 resistors, 4 ICs, 3 connectors and 1 diode. It belongs with the SAM D and SAM boards of this library.
Main components
4
ATSAMD21E18A-AF
TQFP-32(7x7)-40℃~+125℃ 1.62V~3.6V 10bit 12bit 256KB 26 32 Bit 32KB 48MHz ARM Cortex-M0+ Built-in FLASH TQFP-32(7x7) Microcontrollers (MCU/MPU/SOC) ROHSMicrochip TechnologyMicrocontrollers (MCU/MPU/SOC)
ADS1113IDGS
MSOP10Ultra-Small, Low-Power, 4 Channels 16-Bit Analog-to-Digital Converter with Internal ReferenceTexas InstrumentsUncategorised
ADUM1250AR
SOIC8Hot Swappable, Dual I2C IsolatorAnalog DevicesUncategorised
PRTR5V0U2X
SOT-143-55℃~+125℃ 0.3pF、0.8pF 100W 10V、15V 5V 6.5V 6A 80nA ESD IEC 61000-4-2、IEC 61000-4-5、IEC 61000-4-4 Three channels Unidirectional SOT-143 ESD and Surge Protection (TVS/ESD) ROHSTECH PUBLICESD And Surge Protection (TVS/ESD)
README
hardware/CurrentSensorUSB/README.mdDesign Considerations
1. Microcontroller (U1: ATSAMD21E18A‑A)
- Built‑in USB Full‑Speed interface simplifies serial‑over‑USB implementation.
- Proven ecosystem and popularity
- E‑Series package (smallest) has more than enough GPIO and ADC channels for this project.
2. Precision ADC (U3: ADS1113IDGS)
- 16‑bit resolution yields better than 10 µA resolution over the 4–20 mA span by adjusting the PGA settings.
- Single‑ended input with onboard reference minimizes external parts.
- I²C interface maps cleanly to the SAMD21 peripheral.
3. Digital Isolator (U5: ADuM1250)
- Provides 2.5 kV galvanic isolation on I2C lines.
- Ensures USB‑side ground is fully isolated from the analog front end.
4. DC–DC Converter (PS1: MEE1S0503SC)
- Generates an isolated 3.3 V rail from USB 5 V for the sensor‑side analog domain.
- 150 mW output rating covers the ADS1113 + op‑amps + isolator.
5. Shunt Resistor (R2: 100 Ω LVK12)
- Converts 4–20 mA into 0.4–2.0 V (with gain stage, maps to 0.2–1.0 V for the ADS1113).
- 0.1 % tolerance keeps measurement error < ±1 µA.
6. Voltage Regulator (U2: MCP1703A‑3302)
- 3.3 V LDO for the SAMD21 from the USB 5 V rail.
7. ESD Protection (D1: PRTR5V0U2X)
- I wanted to incoorperate an example for circuit protection but without having a clear safety bufget i decided to keep it minimal.
8. 32.768 kHz Crystal (Y1)
- Provides a precision RTC clock for timestamping the serial out.
- Matched load capacitance (6.8 pF) aligns with the SAMD21’s XOSC32K requirements.
Parts
25| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | 4.7 kΩ | Resistor_SMD:R_0603_1608Metric | R3, R4, R5, R6 |
| 2 | 1 μF Ceramic | Capacitor_SMD:C_0603_1608Metric | C1, C2 |
| 2 | 6.8pF | Capacitor_SMD:C_0603_1608Metric | C5, C6 |
| 1 | 0.1 μF | Capacitor_SMD:C_0603_1608Metric | C3 |
| 1 | 1 μF | Capacitor_SMD:C_0603_1608Metric | C7 |
| 1 | 32.768kHz, 7pF | Crystal:Crystal_SMD_0603-4Pin_6.0x3.5mm | Y1 |
| 1 | 5.1K | Resistor_SMD:R_0603_1608Metric | R1 |
| 1 | ADS1113IDGS | Package_SO:TSSOP-10_3x3mm_P0.5mm | U3 |
| 1 | ADuM1250 | Package_SO:SOIC-8_3.9x4.9mm_P1.27mm | U5 |
| 1 | ATSAMD21E18A-A | Package_QFP:TQFP-32_7x7mm_P0.8mm | U1 |
| 1 | C | Capacitor_SMD:C_0603_1608Metric | C4 |
| 1 | MCP1703Ax-330xxDB | Package_TO_SOT_SMD:SOT-223-3_TabPin2 | U2 |
| 1 | MEE1S0503SC | Converter_DCDC:Converter_DCDC_Murata_MEE1SxxxxSC_THT | PS1 |
| 1 | PRTR5V0U2X | Package_TO_SOT_SMD:SOT-143 | D1 |
| 1 | R_F 1 kΩ | Resistor_SMD:R_0603_1608Metric | R7 |
| 1 | R_Shunt 100 | Resistor_SMD:R_Shunt_Ohmite_LVK12 | R2 |
| 1 | SW_Push | Button_Switch_SMD:SW_MEC_5GSH9 | SW1 |
| 1 | Screw_Terminal_01x02 | TerminalBlock_Phoenix:TerminalBlock_Phoenix_MKDS-1,5-2_1x02_P5.00mm_Horizontal | J2 |
| 1 | TC2030 | Connector:Tag-Connect_TC2030-IDC-NL_2x03_P1.27mm_Vertical | J1 |
| 1 | USB_C_Plug_USB2.0 | Connector_USB:USB_C_Plug_Molex_105444 | P1 |
Questions
What parts does the CurrentSensorUSB use?
25 parts, built around the ATSAMD21E18A-AF, ADS1113IDGS, ADUM1250AR and PRTR5V0U2X. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the CurrentSensorUSB KiCad files?
From the vlust/interview-assignment repository on GitHub, at the commit this page was made from: the board is hardware/CurrentSensorUSB/CurrentSensorUSB.kicad_pcb and its schematic hardware/CurrentSensorUSB/CurrentSensorUSB.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the CurrentSensorUSB design in my own project?
Its repository states no licence, so its author keeps all rights: ask vlust before reusing the design.
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