Frez Dyno

The Frez Dyno streams signed raw ADC values at 250 Hz. Grip Connect follows the official Frez protocol v1: it fetches the device coefficient, subscribes before Start, establishes tare from the first 100 unloaded samples, and reconstructs the sample timeline from the device elapsed time.

Developer Portal and access key

Frez provides API access through the Frez Dyno Developer Program. The standard Developer Program key is for a personal, non-commercial application.

Personal use only

The standard agreement does not permit commercial development or use, including paid apps, subscriptions, advertising, work for a company, gym, coach, team, clinic, client, or a product intended for commercial release. Read the current Frez Developer Agreement. Contact support@frez.app before developing or testing a commercial integration.

Get a personal, non-commercial key

Follow the instructions in the Frez Developer Portal to enroll and issue a personal, non-commercial key. Manage the key and Personal API devices on the Access key page, and manage Web Bluetooth device names on the Allowlist page. Keep the key secret and out of distributed client bundles.

Use the key in a Grip Connect project

1. Install the package for your platform

# Web
npm install @hangtime/grip-connect

# Capacitor
npm install @hangtime/grip-connect-capacitor

# React Native or Expo
npm install @hangtime/grip-connect-react-native

Capacitor and React Native require native Bluetooth configuration and a physical device. Expo requires a development build; Expo Go cannot load the native BLE module.

2. Add the key to your local environment

Create a local environment file in your project root:

FREZ_ACCESS_KEY=your-access-key

Add the file to .gitignore. Grip Connect reads FREZ_ACCESS_KEY or EXPO_PUBLIC_FREZ_ACCESS_KEY automatically when your project loads the environment file into process.env.

3. Create the Frez Dyno

Import FrezDyno from the package installed in step 1. This example uses the web package; change only the package name for Capacitor or React Native:

import { FrezDyno } from "@hangtime/grip-connect"

const dyno = new FrezDyno()

Grip Connect reads the device serial on Capacitor and React Native, or its allowlisted Bluetooth name on web, and then uses the key to load the correct coefficient automatically when stream() starts.

Keep the key private

This direct setup is for personal, non-distributed development. Do not publish a web or mobile build containing the key. For a distributed application, keep the key on an authenticated server and provide a custom coefficientLookup to FrezDyno.

Connection and measurement

Create the configured device, subscribe, and connect. Keep the Dyno unloaded while the first 100 samples establish tare:

dyno.notify((measurement) => {
  console.log(measurement.current, measurement.unit, measurement.timestamp)
})

await dyno.connect()

try {
  await dyno.stream()
  // Keep the device unloaded until measurements begin arriving.
} finally {
  await dyno.stop()
  await dyno.disconnect()
}

Native transports read 0x2A25 and request the coefficient by serial. Web Bluetooth cannot expose that characteristic, so web clients use the allowlisted Bluetooth name. The official coefficient API accepts exactly one of these identifiers.

The simple client-side conversion is:

tare_adc = average(first 100 unloaded samples)
weight_kg = a × (raw_adc - tare_adc)
force_N = weight_kg × 9.80665

Call tare() during an active measurement to discard the current tare and collect another 100 unloaded samples.

Protocol v1

Service	Characteristic	Usage
da8a6c41-154b-4b9a-9b00-2f84dfcebfe9	da8a6c42-154b-4b9a-9b00-2f84dfcebfe9	74-byte notifications
da8a6c41-154b-4b9a-9b00-2f84dfcebfe9	da8a6c43-154b-4b9a-9b00-2f84dfcebfe9	Acknowledged command writes
0000180a-0000-1000-8000-00805f9b34fb	00002a25-0000-1000-8000-00805f9b34fb	Serial number
0000180a-0000-1000-8000-00805f9b34fb	00002a28-0000-1000-8000-00805f9b34fb	Firmware/API version
0000180f-0000-1000-8000-00805f9b34fb	00002a19-0000-1000-8000-00805f9b34fb	Battery percentage

Command frames contain an opcode followed by a reserved zero byte:

• Start: 01 00
• Stop: 02 00
• Power off: FF 00

Each notification is exactly:

[0x01] [0x00] + 9 × [int32LE raw_adc] [uint32LE elapsed_ms]

Capacitor and React Native request MTU 85 when the platform supports it. Grip Connect rejects truncated packets, non-zero reserved bytes, unexpected response codes, and duplicate or decreasing device timestamps instead of guessing.