4 layers16 × 16 mm
4 layers25.4 × 43.2 mm
Hum hw
tactical-snacks/hum_hwHour Utilization Monitor using accelerometer and RTC to track run time
- Size
- 25.4 × 43.2 mm
- Copper layers
- 4
- Thickness
- 1.6 mm
- Parts
- 30
- Nets
- 36
- Pads
- 128
- Tracks, vias
- 217, 74
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 10.0 (file 20260206)
- Created
- 10 Oct 2026
- Updated
- 2 Nov 2026
Overview
Hum hw is an open-source printed circuit board by tactical-snacks, from the tactical-snacks/hum_hw repository on GitHub, published under the MIT licence. It is a 4-layer board of 25.4 × 43.2 mm with 30 parts on 36 nets, routed with 217 tracks and 74 vias.
It is built around the STM32U031K8U6, 24FC512-I/ST and LIS2DTW12TR-MS, with the 1N4148W among its other parts. Its parts include 13 capacitors, 6 resistors, 3 ICs, 3 connectors and 2 diodes. It belongs with the sensors and measurement boards and the STM32 boards of this library.
Main components
4
STM32U031K8U6
UFQFPN-32-EP(5x5)-40℃~+85℃ 1.71V~3.6V 12KB 27 32 Bit 56MHz 64KB ARM Cortex-M0+ Built-in+External FLASH UFQFPN-32-EP(5x5) Microcontrollers (MCU/MPU/SOC) ROHSSTMicroelectronicsMicrocontrollers (MCU/MPU/SOC)
24FC512-I/ST
TSSOP-8-40℃~+85℃ 1,000,000 cycles 1.7V~5.5V 1MHz 200 Years 512Kbit 5ms I2C TSSOP-8 EEPROM ROHSMicrochip TechnologyEEPROM
LIS2DTW12TR-MS
LGA-12(2x2)-40℃~+85℃ 1.71V~3.6V 12bit 2uA Accelerometer SPI、I2C X,Y,Z ±16g LGA-12(2x2) Accelerometers ROHSMSKSEMIAccelerometers
1N4148W
SOD-123150mA 1A 1V@50mA 1uA@75V 400mW 4ns 75V Independent SOD-123 Switching Diodes ROHSSTMicroelectronicsSwitching Diodes
README
README.mdhum
Hour Utilization Monitor: a coin-cell data logger that timestamps machine run time using an accelerometer and RTC.
Hardware
| Function | Part |
|---|---|
| MCU | STM32U031K8U6 (Cortex-M0+, UFQFPN-32) |
| RTC clock | 32.768 kHz crystal, ABS07-120 |
| Accelerometer | LIS2DTW12 (I²C, INT1 → PA0, INT2 → PA2) |
| Storage | 24FC512, 64 KB I²C EEPROM |
| Power | CR2032 in Keystone 3034 holder |
| UI | Button (PA1), green LED (PA8) |
| Debug | SWD, ARM 10-pin header |
| Comms | UART, PA9 TX / PA10 RX |
Operation
- MCU sleeps in Stop 2 with the RTC running.
- The accelerometer detects activity on its own and wakes the MCU.
- Run start/stop events are logged to EEPROM as epoch timestamps, in a wear-levelled ring buffer.
- Clock set and log download over UART.
- Target battery life: 5+ years.
Jumpers
- J4: in series with the battery. Remove it to measure current.
- J1: 3.3 V bench input. Open J4 first. Never use 5 V.
Tools
KiCad, STM32CubeMX / STM32CubeIDE.
See power_budget.md.
Parts
30| Qty | Value | Footprint | References |
|---|---|---|---|
| 5 | 100nF 10V X7R | Capacitor_SMD:C_0603_1608Metric | C4, C6, C7, C11, C13 |
| 3 | 4.7k | Resistor_SMD:R_0805_2012Metric | R3, R4, R5 |
| 2 | 6.8pF C0G/NP0 | Capacitor_SMD:C_0603_1608Metric | C1, C2 |
| 1 | 0R | Resistor_SMD:R_0805_2012Metric | R2 |
| 1 | 10k | Resistor_SMD:R_0805_2012Metric | R1 |
| 1 | 10nF 10V X7R | Capacitor_SMD:C_0603_1608Metric | C10 |
| 1 | 10uF 10V X7R | Capacitor_SMD:C_0805_2012Metric | C5 |
| 1 | 1N4148W | Diode_SMD:D_SOD-123 | D1 |
| 1 | 1k | Resistor_SMD:R_0805_2012Metric | R6 |
| 1 | 1uF 10V X7R | Capacitor_SMD:C_0603_1608Metric | C9 |
| 1 | 24FC512-I/ST | Package_SO:TSSOP-8_4.4x3mm_P0.65mm | U1 |
| 1 | 32.768kHZ | Crystal:Crystal_SMD_3215-2Pin_3.2x1.5mm | Y1 |
| 1 | 4.7uF 10V X7R | Capacitor_SMD:C_0603_1608Metric | C12 |
| 1 | 4.7uF 10V X7R | Capacitor_SMD:C_0805_2012Metric | C8 |
| 1 | 47uF 10V X7R | Capacitor_SMD:C_1210_3225Metric | C3 |
| 1 | Battery_Cell | Battery:BatteryHolder_Keystone_3034_1x20mm | BT1 |
| 1 | Conn_01x02_Pin | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | J1 |
| 1 | Conn_01x03 | Connector_PinSocket_2.54mm:PinSocket_1x03_P2.54mm_Horizontal | J2 |
| 1 | Conn_ARM_JTAG_SWD_10 | Connector_PinHeader_1.27mm:PinHeader_2x05_P1.27mm_Vertical_SMD | J3 |
| 1 | LED | LED_SMD:LED_0805_2012Metric | D2 |
| 1 | LIS2DTW12TR | Package_LGA:LGA-12_2x2mm_P0.5mm | U3 |
| 1 | STM32U031K8U6 | Package_DFN_QFN:QFN-32-1EP_5x5mm_P0.5mm_EP3.45x3.45mm | U2 |
| 1 | SW_SPST | Button_Switch_SMD:SW_SPST_PTS645Sx43SMTR92 | SW1 |
Questions
How big is the Hum hw PCB?
It measures 25.4 × 43.2 mm and has 4 copper layers, 1.6 mm thick.
What parts does the Hum hw use?
30 parts, built around the STM32U031K8U6, 24FC512-I/ST, LIS2DTW12TR-MS and 1N4148W. 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 Hum hw KiCad files?
From the tactical-snacks/hum_hw repository on GitHub, at the commit this page was made from: the board is hum_hw.kicad_pcb and its schematic hum_hw.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Hum hw design in my own project?
Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).
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