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Crimpdeq

Meet Crimpdeq, a portable digital force sensor for climbers, coaches, and therapists who want to measure and train finger strength, pulling power, and endurance. It is inspired by the Tindeq Progressor and is compatible with both the Tindeq and Frez apps.

Specs

  • Rechargeable battery with USB-C charging
  • Communicates via Bluetooth Low Energy (BLE)
  • Open-source firmware written in Rust
  • Open-source PCB design
  • Open-source 3D-printable case design
  • Automatic sleep when inactive
  • Compatible with the Tindeq Progressor app (Android | iOS)
  • Compatible with the Frez app (formerly ClimbHarder) (Android | iOS)
  • Sampling rate: 80 Hz
  • Full-scale design load: 1500 N (~150 kg)
  • Precision:
    • 0.05 kg between 0 and 99 kg
    • 0.1 kg between 100 and 150 kg
  • Operating temperature: 0 to 40 C
  • Dimensions: 80 x 90 x 35 mm
  • Uses the Tindeq Progressor API

⚠️ Warning: Some values depend on the load cell used in this project. If you use a different load cell, those values may change.

Book Contents

This book is a practical guide to understanding Crimpdeq and building your own. It covers assembly, calibration, firmware internals, and the PCB and 3D-printable case design.

⚠️ Note: If you want to reproduce this project, feel free to reach out by email ([email protected]), X (formerly Twitter), or Bluesky.

Build Your Crimpdeq

This chapter presents the two Crimpdeq models you can build.

Choose the one that matches your tools, budget, and how much assembly work you want to do.

Crimpdeq V1

Crimpdeq V1

This model uses a custom PCB and a custom 3D-printed case.

It is the cleanest and easiest version to assemble, and the final result is more compact and polished. See the PCB details and 3D case details for design details.

Follow the Crimpdeq V1 Assembly guide to build this model.

Prototype

Prototype

This model reuses a crane scale case and combines off-the-shelf modules (ESP32-C3 Rust Board + HX711).

It requires more soldering and manual assembly, but it can be cheaper because it does not require manufacturing a custom PCB or 3D-printed case.

Follow the Prototype Assembly guide to build this model.

Crimpdeq V1 Assembly

This chapter shows how to assemble your own Crimpdeq V1 using the custom PCB and 3D-printed case.

Crimpdeq V1

1. Required Materials

2. Soldering

  1. Connect the load cell to the PCB:

    • Solder the four load cell wires to the PCB:
    PCB PinLoad Cell PinDescription
    E+ (15)E+ (Red)Excitation positive (to load cell)
    E- (14)E- (Black)Excitation negative (to load cell)
    S+ (12)S+ (Green)Signal positive (from load cell)
    S- (13)S- (White)Signal negative (from load cell)

    ⚠️ Note: This assumes the typical load cell wire colors (red = E+, black = E-, green = S+, white = S-). Verify your load cell wiring before soldering, because some compatible load cells use a different color order.

    PCB Pinout

    Reference photo of the load cell wires after soldering them to the PCB:

    Load cell wires soldered to the PCB

  2. Install the load cell and battery in the case:

    1. Place the load cell in its position in the 3D-printed case.
    2. Route the load cell wires so they are not pinched by the PCB or the lid.
    3. Place the battery in the battery compartment.

    Load cell and battery placed on the case

  3. Wire the battery and switch to the PCB:

    1. Solder the battery negative wire (black) to B- (16) on the PCB.
    2. Cut the battery positive wire (red) into two sections.
    3. Before soldering the switch, pass both positive wire sections through the switch opening in the case.
      • If you solder the wires to the switch first, you will not be able to insert the switch into the case afterward.
    4. Solder one positive wire section from the battery to one terminal of the KCD11 switch.
    5. Solder the other positive wire section from the second switch terminal to B+ (17) on the PCB.

    ⚠️ Note: The switch must be wired in series with the battery positive line, and its OFF position must open the circuit. For safety, the battery should be disconnected from the PCB when the switch is off.

Assembled case

4. Place the PCB and switch: 1. Position the PCB in the case. 2. Tuck the wires neatly around it so nothing sits under the board. 3. Insert the KCD11 switch into the switch opening.

Assembled case

  1. Verify all connections with a multimeter.

3. Close the Case

  1. Place the lid on the main enclosure.
  2. Fasten it with the 4 M2.5 screws.

4. Next Steps

  1. Flash the firmware (see Firmware).
  2. Calibrate the device (see Calibration).

PCB Design

Revision 1

The PCB design is maintained in the crimpdeq-pcb repository and was created with KiCad.

It is a two-layer board derived from the ESP32-C3-DevKit-RUST-1. This version removes unused sensors from the original design and keeps only what this project needs.

PCB

The PCB was sponsored by PCBWay. Working with them was fast and easy, and the resulting boards are high quality.

PCBWay

Revision 1 has been tested and works as expected, but there is still room for improvement. See the Revision 2 issue.

You can find the schematic, layout, and production files in the repository latest GitHub release.

How to Manufacture

There are two ways to order this PCB:

  1. Using the PCBWay Project page — recommended, since it already includes the latest uploaded production files.
  2. Placing your own PCBWay order using the production files from the repository releases.

Using PCBWay Projects

  1. Open the PCBWay Project page using the button below.

    PCB from PCBWay

  2. On the right panel, select PCB+Assembly and click Add to Cart.

  3. Enter the desired quantity and click Calculate.

    ⚠️ Note: PCBWay shows two quantity fields. One is the number of PCBs to manufacture, and the other is the number of boards to assemble with components. The minimum PCB quantity is usually 5.

  4. Choose your shipping country and shipping method.

  5. Click Save to Cart to continue with checkout.

Placing Your Own Order on PCBWay

  1. Download the production files from the latest GitHub release.

  2. Use the included files when creating your PCBWay order:

    • gerber.zip: PCB fabrication files
    • bom.csv: bill of materials for assembly
    • positions.csv: component placement file for assembly

  3. Submit the order and wait for the manufacturer review.

    • The manufacturer may contact you with questions about substitutions, assembly notes, or file interpretation.

⚠️ Note: If the manufacturer contacts you with questions or suggestions and you are unsure how to answer, feel free to email me at [email protected].

3D-Printed Case

The case design is maintained in the crimpdeq-case repository and was created with OpenSCAD.

It consists of two parts (main body and lid) and includes mounting points for the load cell, battery, PCB, and switch.

Download the latest printable files from the repository releases and print both parts before assembly.

3D Case Model

Prototype Assembly

This chapter explains how to build your own Crimpdeq prototype.

1. Required Materials

2. Disassemble the Crane Scale

Disassembly

  1. Desolder the battery connections.
  2. Desolder the four load cell wires (E-, S-, S+, and E+) from the PCB. Crane connections
  3. Unscrew and remove the PCB and display.

3. Soldering

  1. Modify the HX711 module:

    1. Set the sample rate to 80 Hz. Most HX711 modules ship with RATE tied to GND, which sets 10 Hz. To switch to 80 Hz: HX711 Pinout
      1. Cut the PCB trace to the RATE pin.
        • Carefully scratch the trace with a knife.
      2. Verify with a multimeter that GND and RATE are no longer connected.
        • Take care not to damage adjacent traces.
      3. Solder the RATE pin to the DVDD pin.
      4. Verify with a multimeter.
    2. [Optional] Improve measurements at 3.3 V. Most HX711 modules are configured for 5 V operation:
      1. Solder a 20 kΩ to 27 kΩ resistor in parallel with R1 (highlighted in the image): Resistor to modify
      • For more information, see this blog post.
      • This step is optional but improves measurement quality.

  2. Connect the load cell to the HX711:

    • Solder the four wires from the crane scale to the HX711. Typical color mapping:
    HX711 PinLoad Cell PinDescription
    E+E+ (Red)Excitation positive (to load cell)
    E-E- (Black)Excitation negative (to load cell)
    S+S+ (Green)Signal positive (from load cell)
    S-S- (White)Signal negative (from load cell)

    ⚠️ Note: On some HX711 modules, S+/S- are labeled A+/A-.

  3. Connect the HX711 to the ESP32-C3-DevKit-RUST-1:

HX711 PinESP32-C3 PinDescription
VCC3.3VPower supply (3.3V)
GNDGNDGround
DT (Data)GPIO4Data output from HX711
SCK (Clock)GPIO5Clock signal for communication

ESP32-C3 Connections

  1. [Optional] Solder the voltage divider:
    1. Solder one end of the 33 kOhm resistor to B+ on the ESP32-C3-DevKit-RUST-1.
    2. Join the other end of the 33 kOhm resistor with one end of the 10 kOhm resistor, then connect that junction to GPIO1.
    3. Solder the remaining end of the 10 kOhm resistor to GND.
    • The firmware expects the battery sense on GPIO1 by default. Adjust the firmware configuration if you wire a different pin.
  2. Verify all connections with a multimeter.

4. Adapt the Scale Case

  1. Create space for the USB connector.
    • For example: mark the opening with a pen, then carefully heat a knife and melt the plastic.
  2. Install the battery holder:
    1. Glue the battery holder with silicone. Leave the original battery lid opening free so you can route the two battery wires through it.
    2. Solder the positive wire (red) from the battery holder to a switch/button for power. Then solder the other switch/button pin to B+ on the ESP32-C3-DevKit-RUST-1.
    3. Solder the negative wire (black) from the battery holder to B- on the ESP32-C3-DevKit-RUST-1.
  3. Close the case after confirming all components are secure.

Assembly

Firmware & Flashing

The Crimpdeq firmware is written in async Rust (no_std) using esp-hal and a small set of supporting crates.

This section explains how to flash the firmware to your device and, optionally, how the code is organized.

Choose a Flashing Method

There are two supported ways to flash the firmware:

1. Web Tools

  • No local setup required
  • Fastest way to install the latest release
  • Best if you do not plan to modify the firmware

See Flashing with Web Tools

2. Local Setup

  • Requires installing Rust and probe-rs
  • Lets you build from source and modify the code
  • Better for development and debugging

See Flashing with Local Setup

Firmware Internals

If you want to understand or modify the firmware, see the Firmware Details chapter.

If you only want a working device, you can flash the firmware and continue to Calibration.

Flash with Web Tools

This chapter covers how to flash your device with a pre-built binary.

  1. Connect the device with a USB-C cable.

  2. Download a .bin from the latest GitHub release:

    • If this is the first time you are flashing Crimpdeq firmware to your device, download crimpdeq-merged.bin.
    • If you are updating firmware on a device that is already flashed, download crimpdeq.bin.

  3. Choose a web flasher. Use either:

  4. Click Connect and select the serial port for your ESP board.

    • In Adafruit ESPTool, the port often appears as USB/JTAG serial debug unit....

  5. Click Erase only if this is the first time you are flashing this device.

    ⚠️ Note: Erasing the device also erases stored calibration values. Skip this if the device was already programmed and calibrated.

  6. Upload your .bin:

    • If you are using crimpdeq-merged.bin -> address 0x0
    • If you are using crimpdeq.bin -> address 0x10000

  7. Click Program.

Flashing with ESPTool

Flash with Local Setup

This chapter covers how to compile and flash the Crimpdeq firmware to your device.

Prerequisites

To build and upload the firmware, install:

  • Rust
  • The stable toolchain with the ESP32-C3 target: 
    rustup toolchain install stable --component rust-src --target riscv32imc-unknown-none-elf
  • probe-rs, see installation instructions

    ⚠️ Note: Depending on your OS, you may need extra setup steps:

    • Linux: set up udev rules for your debug probe or USB-serial device (see the probe-rs udev guide).
    • Windows/macOS: ensure the correct USB drivers are installed and select the appropriate serial port in your tooling.

How to Build the Firmware

To build the firmware, run:

cargo build --release

This compiles the firmware only. To build and flash the device, see Build and Flash your Device.

How to Flash Your Crimpdeq

Erase Device Memory

If this board was previously used for other projects, erase its flash once:

probe-rs erase

⚠️ Note: Erasing is only needed once. Avoid erasing routinely, or you will lose your calibration values.

Build and Flash Your Device

With a custom runner configured in .cargo/config.toml, you can build, flash, and open a serial monitor with:

cargo run --release

This opens a serial monitor, allowing you to view log messages in real time.

To modify the log level, update the DEFMT_LOG value in .cargo/config.toml or set it when running the command:

DEFMT_LOG=debug cargo run --release

⚠️ Note: If your DevKit does not include USB-Serial-JTAG, flash over UART by updating the custom runner in .cargo/config.toml to use espflash instead of probe-rs.

Configuring Environment Variables

If you need to change DEVICE_ID, DEVICE_NAME, or DEVICE_VERSION_NUMBER, update their values in .cargo/config.toml.

After making changes, rebuild and flash the device for the new values to take effect.

Firmware Internals

Code Structure

hx711

This module implements load cell support. It is an async version of the loadcell crate with project-specific changes.

ble

This module implements the Bluetooth Low Energy (BLE) functionality:

  • Defines the GATT server and services
  • Handles advertising and connections
  • Defines the Progressor service with data point and control point characteristics

progressor

The progressor module implements the Tindeq API used for BLE communication between the ESP32-C3 and a smartphone.

Main Tasks

The main.rs file defines several asynchronous tasks that run concurrently:

  • measurement_task:
    • Initializes the load cell.
    • Handles taring and reads measurements from the sensor.
  • ble_task:
    • Long-running background task required alongside other BLE tasks.
  • gatt_events_task:
    • Processes GATT events such as control-point writes.
  • data_processing_task:
    • Handles sending notifications with data points.
  • battery_voltage_task:
    • Periodically reads the battery voltage.
  • deep_sleep_task:
    • Monitors inactivity; after a timeout, the device enters deep sleep.

Communication between tasks occurs via a Channel.

Calibration

This guide explains how to calibrate Crimpdeq for accurate measurements.

You can calibrate in two ways: with the Crimpdeq app or nRF Connect.

The Crimpdeq app is recommended because it is simpler and gives visual feedback.

⚠️ Note: The device ships with a default calibration. Test it first in the Frez or Tindeq app. If accuracy is already good enough for your load cell, you can skip this chapter.

Calibrate with Crimpdeq App

Prerequisites

  • Crimpdeq app on your platform:
    • Web version (no installation): Crimpdeq web app
    • Native builds from the latest release: crimpdeq-app/releases/latest
      • Android: crimpdeq-app-v<x.y.z>.apk
      • macOS: crimpdeq-app-v<x.y.z>-macos.zip
      • Windows: crimpdeq-app-v<x.y.z>-windows.zip
      • Linux: crimpdeq-app-v<x.y.z>-linux.zip
  • A stable mounting point so the device hangs freely and remains still
  • At least one known weight (ideally near your typical maximum load)

Calibration Steps

  1. Connect to your Crimpdeq

    1. Launch the Crimpdeq app and grant permission to access device location (required for Bluetooth).
    2. Tap Scan to pair with your device.
    3. Once connected, the app shows device info (firmware version, battery, and current calibration).

  2. Add calibration points

    1. Open the Calibration tab.
    2. For each point:
    • Hang the corresponding load on the device (or leave it empty for zero).
    • Enter the weight value in the app and tap Add Calibration Point.
    • Recommended: Add at least 2 points—zero (nothing hanging) and full scale (the maximum weight you expect to measure). The device supports up to 20 calibration points for finer accuracy.

  3. Check the result

    1. After adding at least 2 points, the app displays the current calibration curve. Confirm it matches your expectations.

    Calibration Result

Adding more calibration points (up to 20) improves measurement accuracy across the full load range.

Calibrate with nRF Connect

Prerequisites

  • nRF Connect installed on your platform:
  • A stable mounting point so the device hangs freely and remains still
  • At least one known weight (ideally near your typical maximum load)

Calibration Steps

  1. Connect to Crimpdeq with nRF Connect:
    1. Launch the app and go to the Scanner tab.
    2. Find your device (for example, Progressor_7125) and tap Connect.
    3. Once connected, the app will display the device’s services and characteristics. nRF Discovered
  2. Locate the calibration characteristic:
    1. Expand Unknown Service.
    2. Find the characteristic with UUID: 7e4e1703-1ea6-40c9-9dcc-13d34ffead57. Services
  3. Compute the hex value of your known weight:
    1. Open the Floating Point to Hex Converter.
    2. Select Single-precision (32-bit) floating point.
    3. Enter your known weight in the Float value field (in kilograms unless your device expects grams; see Important Notes).
    4. Click Convert to hex and save the resulting Hex value. Example: 75.3 kg → 0x4296999a.
  4. Zero the device (tare):
    1. Hang Crimpdeq with no weight attached.
    2. Send the command 7300000000 to the characteristic:
      • Tap the Up Arrow icon on the characteristic (7e4e1703-1ea6-40c9-9dcc-13d34ffead57).
      • Enter the command as shown. Send weight
  5. Perform the calibration:
    • Commands and values are hex strings without spaces (letter case does not matter).
    1. Attach your known weight to Crimpdeq.
    2. Build the calibration command by prefixing 73 to your hex value.
      • Example: For 75.3 kg (0x4296999a), send: 734296999a.
    3. Send this command to the same characteristic (7e4e1703-1ea6-40c9-9dcc-13d34ffead57).
    • You can add up to 20 calibration points. Repeat this step if you need higher accuracy.
  6. Verify:
    1. Remove the weight and reattach it.
    2. The reported value should be within a small tolerance of the known weight. If not, repeat steps 4-5.

⚠️ Note:

  • Units: Some devices expect the calibration value in grams instead of kilograms. If, after calibration, the measured value looks off by a factor of ~100 (e.g., 75.3 kg shows ~0.75), convert your known weight to grams and repeat step 5.
  • Use a weight close to the maximum load you expect to measure (while staying within device limits) for best accuracy.
  • Ensure the device is stable and stationary when sending commands.
  • Perform calibration in a controlled environment (avoid wind, vibration, and temperature swings).

Battery Charging

To charge the device:

  1. Connect a USB-C cable:
    • Plug the device into a power source using a USB-C cable.
    • Turn on the device.
    • The red LED turns on while charging.
  2. Wait for the charge to complete:
    • When the red LED turns off, charging is complete.
    • Unplug the device and use it normally.

Device Charging