2 layers101.5 × 83 mm
2 layers14.6 × 13.6 mm
Chip and transistor
gidim/e61-gauge8An analog temperature gauge for E61 espresso machines. A custom PCB drives a VID6606 stepper motor gauge needle, reading temperature from an NTC thermistor.
- Size
- 14.6 × 13.6 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 15
- Nets
- 40
- Pads
- 87
- Tracks, vias
- 134, 11
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 3 May 2026
- Updated
- 4 May 2026
Overview
Chip and transistor is an open-source printed circuit board by gidim, from the gidim/e61-gauge repository on GitHub. It is a 2-layer board of 14.6 × 13.6 mm with 15 parts on 40 nets, routed with 134 tracks and 11 vias.
It is built around the 2N2222A. Its parts include 3 capacitors, 3 resistors, 2 ICs, 1 transistor and 1 connector. It belongs with the nRF52 and nRF5x boards of this library.
Main components
1README
README.mdE61 Gauge
An analog temperature gauge for E61 espresso machines. A custom PCB drives a VID6606 stepper motor gauge needle, reading temperature from an NTC thermistor. The gauge connects via BLE to a web app for calibration and real-time monitoring.
The dial has a non-linear scale (0–150°C) with an expanded green zone at 92–97°C for precision in the critical temperature range.
Hardware
Built around a Seeed Studio XIAO nRF52840. Key components:
- VID6606 stepper driver (SOIC-28) driving the gauge needle
- 100kΩ NTC thermistor for temperature sensing
- 2N2222A transistor switching a 5V boost converter
- Momentary button for power management (deep sleep after 10 min idle)
- JST connector for the stepper motor coils
The PCB was custom manufactured and assembled. The dial face is a custom design with a non-linear scale — the green zone (92–97°C) is expanded for precision while the cold and hot extremes are compressed. The SVG is in hardware/dial_face.svg. KiCad source files, schematic, and BOM are in hardware/.
Enclosure
The enclosure was SLM (selective laser melting) 3D printed in metal and hand-sanded to achieve the chrome-like finish. Fusion 360 source (enclosure/gauge_enclosure.f3z), STEP, and STL files are in enclosure/.
KiCad libraries
The schematic uses two non-standard libraries included in libraries/:
XIAO_nRF52840.pretty/— footprint for the XIAO nRF52840 moduleSeeed_Studio_XIAO_Series/— schematic symbol
Add both to your KiCad library paths before opening the project.
Firmware
Arduino sketch in firmware/gauge/. Uses the Adafruit nRF52 BSP.
Dependencies (install via Arduino Library Manager):
Adafruit TinyUSBAdafruit nRF52BSP (includesbluefruit,Adafruit_LittleFS,InternalFileSystem)AccelStepper
The gauge supports BLE serial commands for calibration, homing, sweep tests, and configuration. See firmware/gauge/commands.h for the full command set.
Web App
A Web Bluetooth app in webapp/ — open index.html in Chrome (Android, macOS, or Windows). iOS Safari does not support Web Bluetooth.
Connect to the gauge over BLE to monitor temperature, set calibration points, and control the needle.
Tools
Python utilities in tools/ for serial-based development and testing.
pip install -r tools/requirements.txt
python tools/serial_terminal.pyvid6606
vid6606/ contains a standalone sweep demo sketch and a copy of the SwitecX25 stepper library used for the VID6606 driver.
test_ntc_sketch
A minimal Arduino sketch for validating NTC thermistor readings independently of the main firmware.
Parts
15| Qty | Value | Footprint | References |
|---|---|---|---|
| 2 | 0.1uF | Capacitor_SMD:C_0805_2012Metric | C2, C3 |
| 2 | 10k | Resistor_SMD:R_0805_2012Metric | R2, R3 |
| 1 | 10uF | Capacitor_Tantalum_SMD:CP_EIA-1608-08_AVX-J | C1 |
| 1 | 1k | Resistor_SMD:R_0805_2012Metric | R1 |
| 1 | 2N2222A | Package_TO_SOT_SMD:SOT-23 | Q1 |
| 1 | 5v Boost | Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical | J1 |
| 1 | BTN | TestPoint:THT_2PAD_SOLDER_P5.08MM_GIDEON | SW1 |
| 1 | Battery | TestPoint:THT_2PAD_SOLDER_P5.08MM_GIDEON | Battery1 |
| 1 | NTC | TestPoint:THT_2PAD_SOLDER_P5.08MM_GIDEON | NTC1 |
| 1 | Stepper_Motor_bipolar | Connector_JST:JST_SM04B-SRSS-TB_LF__SN_ | M1 |
| 1 | VID6606 | Package_SO:SOIC-28W_7.5x17.9mm_P1.27mm | U2 |
| 1 | XIAO-nRF52840-DIP | XIAO_nRF52840:XIAO-nRF52840-DIP | U3 |
The 14 most common of 15 parts.
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Questions
How big is the Chip and transistor PCB?
It measures 14.6 × 13.6 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Chip and transistor use?
15 parts, built around the 2N2222A. 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 Chip and transistor KiCad files?
From the gidim/e61-gauge repository on GitHub, at the commit this page was made from: the board is hardware/chip_and_transistor.kicad_pcb and its schematic hardware/chip_and_transistor.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Chip and transistor design in my own project?
Its repository states no licence, so its author keeps all rights: ask gidim before reusing the design.