2 layers43.9 × 27.7 mm
2 layers25.5 × 70.6 mm
Caliper mod
RasmusKoit/caliper-mod2This project involves modifying inexpensive digital calipers purchased from AliExpress by replacing the internal CR44 battery with a custom PCB. The modification adds the following features:
- Size
- 25.5 × 70.6 mm
- Copper layers
- 2
- Thickness
- 0.8 mm
- Parts
- 19
- Nets
- 11
- Pads
- 45
- Tracks, vias
- 69, 22
- Pours
- 1
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 30 Dec 2025
- Updated
- 30 Dec 2025
Overview
Caliper mod is an open-source printed circuit board by RasmusKoit, from the RasmusKoit/caliper-mod repository on GitHub. It is a 2-layer board of 25.5 × 70.6 mm with 19 parts on 11 nets, routed with 69 tracks and 22 vias.
Its parts include 4 capacitors, 4 resistors, 2 ICs, 1 diode and 1 connector.
README
README.mdModded Digital Calipers with USB-C Rechargeable Battery
 |  |
|---|
This project involves modifying inexpensive digital calipers purchased from AliExpress by replacing the internal CR44 battery with a custom PCB. The modification adds the following features:
- USB-C Charging: A USB-C connector is added to charge a LiPo battery.
- LiPo Battery Integration: A LiPo battery powers the calipers, eliminating the need for disposable batteries.
- Voltage Conversion: The LiPo battery voltage is converted to 1.5V to match the calipers' power requirements.
This upgrade makes the digital calipers rechargeable and more convenient to use.
Features
- Custom PCB Design: A custom PCB was created to integrate the USB-C charging circuit and voltage regulator.
- Eco-Friendly: Reduces waste by eliminating the need for disposable CR44 batteries.
- Enhanced Usability: Rechargeable functionality ensures the calipers are always ready for use.
- Easy to modify: The design allows for straightforward installation into existing calipers or to other voltages by changing the regulator.
- Custom 3D Printed Case: A 3D printed case is designed to house the modified calipers and the custom PCB. Making it easy to add the extra wires and battery. MakerWorld link
Future Improvements
- Add battery level indicators.
- Break away tab to use in other projects to minimize the size of the PCB.
Assembly Instructions
Bill of Materials
- 4x M2x12mm screws
- 2x M2x4mm screws
- 1x Caliper-mod PCB
- 1x LiPo Battery (150mAh or similar) (max height 3mm)
- 1x Switch with 3-5mm slider (612-EG1271A)
- 1x Cheap digital calipers from AliExpress with the following case is the one I tested:
- Some glue (optional to secure the switch)
- Some double-sided tape for the battery
- 3D printed caliper case (optional but recommended)
Schematic and PCB Design
PCBs were ordered from ATAPCB.
Just upload the provided production zip file to their website for manufacturing.
The schematic and PCB for this project were designed using KiCad. Below is the Bill of Materials (BOM) for the components used:
| Reference | Value | Datasheet | Qty | Manufacturer Part Number | Mouser Part Number |
|---|---|---|---|---|---|
| C1, C2 | 4.7uF | ~ | 2 | LMK107BJ475KA-T | 963-LMK107BJ475KA-T |
| C3, C4 | 1uF | ~ | 2 | LMK107B7105KA-T | 963-LMK107B7105KA-T |
| D1 | LED | ~ | 1 | LTST-C190KRKT | 859-LTST-C190KRKT |
| J1 | USB_C_PowerOnly_6P | USB Type-C Datasheet | 1 | USB4125-GF-A-0190 | 640-USB4125-GF-A-190 |
| R1 | 56k | ~ | 1 | CRG0603F56K | 279-CRG0603F56K |
| R2 | 1.5k | ~ | 1 | CRG0603F1K5 | 279-CRG0603F1K5 |
| R3, R4 | 5.1k | ~ | 2 | CRG0603F5K1 | 279-CRG0603F5K1 |
| SW1 | SW_Push | ~ | 1 | EG1271A | 612-EG1271A |
| U1 | LDK130-15_SOT23_SOT353 | LDK130 Datasheet | 1 | STLQ015M15R | 511-STLQ015M15R |
| U2 | MCP73831-2-OT | MCP73831 Datasheet | 1 | MCP73831T-2ACI/OT | 579-MCP73831T-2ACIOT |
Notes
- Ensure all components are soldered correctly and oriented as per the schematic.
- Use a multimeter to verify connections and check for shorts after assembly.
- The LDO will not turn on until the switch pads are shorted/connected.
3D Printed Case
The 3D printed case is designed to house the modified calipers and the custom PCB. You can download the Bambu 3mf files from MakerWorld link. Print the case using PLA or PETG for durability.
Installation Steps
- Remove the existing CR44 battery from the calipers.
- Remove back stickers and screws to open the caliper casing.
- Gently extract the internal components.
- Print out the new caliper case, this is technically optional but recommended for a better fit. MakerWorld link
- Install the switch into the new case.
- Install units button into the new case.
- Install the reset button into the new case.
- Install the screen into the new case.
- Solder wires from the PCB to the caliper's original battery contacts (observe polarity).
- Place the caliper PCB into the case, ensuring the wires are routed out from the dedicated side gap, alternatively you can route them through the USB measurement hole/Battery compartment if not using the 3D printed case.
- Secure the original PCB to the new case.
- Add the metal scroll wheel back to the calipers.
- Place the calipers into the new case
- Add the caliper-mod PCB into the new case, ensure the holes line up.
- Secure the caliper-mod PCB and caliper with M2x12mm screws.
- Solder the battery to the + and - pads on the caliper-mod PCB, righet next to the USB-C connector.
- Solder the switch wires to the switch pads on the caliper-mod PCB.
- Solder the caliper's original battery contacts wires to the Cal+ (OUT+) and Cal- (OUT-) pads on the caliper-mod PCB.
- Technically the Cal- is just GND and the Cal+ pad is duplicated to add more soldering options.
- Close the caliper case and secure it with the M2x4mm screws.
- Install back the screen cover.
Parts
19| Qty | Value | Footprint | References |
|---|---|---|---|
| 3 | TestPoint | TestPoint:TestPoint_Pad_2.0x2.0mm | TP1, TP2, TP4 |
| 2 | 1uF | Capacitor_SMD:C_0603_1608Metric | C3, C4 |
| 2 | 4.7uF | Capacitor_SMD:C_0603_1608Metric | C1, C2 |
| 2 | 5.1k | Resistor_SMD:R_0603_1608Metric | R3, R4 |
| 2 | TestPoint | TestPoint:TestPoint_Pad_D2.0mm | TP3, TP7 |
| 1 | 1.5k | Resistor_SMD:R_0603_1608Metric | R2 |
| 1 | 56k | Resistor_SMD:R_0603_1608Metric | R1 |
| 1 | LDK130-15_SOT23_SOT353 | Package_TO_SOT_SMD:SOT-23-5 | U1 |
| 1 | LED | LED_SMD:LED_0603_1608Metric | D1 |
| 1 | MCP73831-2-OT | Package_TO_SOT_SMD:SOT-23-5 | U2 |
| 1 | TestPoint | TestPoint:TestPoint_Pad_2.5x2.5mm | TP6 |
| 1 | TestPoint | TestPoint:TestPoint_Pad_D2.5mm | TP5 |
| 1 | USB_C_Receptacle_PowerOnly_6P | Connector_USB:USB_C_Receptacle_GCT_USB4125-xx-x-0190_6P_TopMnt_Horizontal | J1 |
Questions
How big is the Caliper mod PCB?
It measures 25.5 × 70.6 mm and has 2 copper layers, 0.8 mm thick.
What parts does the Caliper mod use?
19 parts. 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 Caliper mod KiCad files?
From the RasmusKoit/caliper-mod repository on GitHub, at the commit this page was made from: the board is PCB/caliper-mod.kicad_pcb and its schematic PCB/caliper-mod.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Caliper mod design in my own project?
Its repository states no licence, so its author keeps all rights: ask RasmusKoit before reusing the design.
Similar boards
- 2 layers50 × 60 mm
Debate Device
hackclub/OnBoard
💡 Join 1,000 teenagers and make your first PCB with a $100 grant!
19 parts915 - 2 layers102.9 × 96.7 mm
ISA adapter
polpo/picogus
Emulation of ISA sound cards and CD-ROM on Raspberry Pi Pico (GUS, SB/Adlib, MPU-401, Tandy, CMS, Panasonic CD-ROM) with USB mouse/joystick support
19 parts805 - 2 layers60 × 39 mm
- 2 layers70.1 × 43.2 mm
Iaq device
nkitanov/iaq_board
IAQ Board is a DIY (Do-It-Yourself) device for measuring internal air quality
19 parts396 - 2 layers80 × 80 mm
- 2 layers25.4 × 25.4 mm
Ina169
Ardumower/ardumower
Develop an open source robotic lawn mower (HW+SW reference platform)
19 parts282 - 2 layers58.4 × 28.6 mm
New rele
zmaker/arduino_cookbook
gli sketch del nuovo progetto Arduino Cookbook e dei video di YouTube
19 parts269