Open Hardware for
Open Fitness

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DEVELOPMENTGitHub →

Digital Weight

Motorized resistance in a portable package

A compact, motorized resistance device that replaces an entire rack of dumbbells. The current V5 build packs a brushless DC motor with closed-loop force control into a 12 lb package, delivering precise, programmable resistance up to 150 lbs — or up to 300 lbs with the pulley accessory — across concentric, eccentric, and isometric modes.

  • •Replace a full dumbbell rack with one 12 lb device
  • •Lifts 150 lbs — up to 300 lbs with the pulley accessory
  • •Real-time force feedback over WiFi + BLE
  • •Open source firmware + hardware designs
  • •Compatible with standard tool batteries
Specs
Max Force::150 lbs (300 lbs with pulley accessory)
Weight::12 lbs
Connectivity::WiFi + BLE
Modes::Concentric, Eccentric, Isometric
Motor::Brushless DC, 48V
Control Loop::1kHz PID
Battery::16S LiPO4 with BMS (+ tool battery compatible)
Enclosure::3D printed + aluminum frame
Version History
v3prototype
v4prototype
v5prototype
v6concept
firmware/src/ble_force.cppView on GitHub →
#define FORCE_PIN A0
#define CALIBRATION_FACTOR 0.489f

float readForce() {
  int raw = analogRead(FORCE_PIN);
  float voltage = raw * (3.3f / 4095.0f);
  float lbs = voltage * CALIBRATION_FACTOR * 250.0f;
  return lbs;
}

void onBleForceRequest(BLECharacteristic& c) {
  float force = readForce();
  c.writeValue(force);
}
>_ View Schematics>_ Build Guide
CONCEPTGitHub →

Balance Brick (Compact Scale)

Open source smart ultra compact scale disguised as a fun balance brick

A single-foot precision body weight that doubles as a balance pose challege device. Daily balance challenges. Streams readings over wifi to the Open Workout System app for automatic logging and trend tracking.

  • •Sub-0.1 lb accuracy with proper calibration
  • •Auto-sync weight to your training log
  • •No cloud account required — your data stays local
Specs
Max Weight::400 lbs / 180 kg
Resolution::0.05 lb / 0.02 kg
Sensors::4x strain gauge load cells
Connectivity::WiFi
Power::LiFePO4 + USB-C charging
Platform::Composite wood (TBD), 3" x 6"
Version History
v1concept
tools/calibrate_scale.pyView on GitHub →
import serial
import numpy as np

def calibrate(port="/dev/ttyUSB0", known_weight=25.0):
    """Two-point calibration: zero + known weight."""
    ser = serial.Serial(port, 115200)

    input("Remove all weight. Press Enter...")
    zero = np.mean([int(ser.readline()) for _ in range(50)])

    input(f"Place {known_weight} lb weight. Press Enter...")
    loaded = np.mean([int(ser.readline()) for _ in range(50)])

    factor = known_weight / (loaded - zero)
    print(f"Zero offset: {zero:.1f}")
    print(f"Cal factor:  {factor:.6f}")
    return zero, factor
>_ View Schematics>_ Build Guide