Serial NCI Scale

An API to query a Serial Scale which supports the NCI protocal (SCP-12, NCI 3825, NCI 3835). Tested against the Salter Brecknell PS-USB scale. Depends on the Web Serial API.

Getting Started

Page Hosting the library must be served over HTTPS. Demo is available at https://chris-rudmin.github.io/serial-nci-scale/

Installation

npm install serial-nci-scale --save

Usage

import SerialNCIScale from 'serial-nci-scale';

const scale = new SerialNCIScale();
const { weight, units, status } = await scale.getWeight();

Constructor

• const scale = new SerialNCIScale( [config] ) - Create a new instance with optional device filter array or port config object

Config Object

• config.filters - Optional - Array of filters to use when initializing the port. Defaults to [].
• config.portConfig - Optional - Object containing serial configuration to use for initializing port. Defaults to 7E1 byte format.

Instance Methods

• scale.getWeight() - Returns a promise which resolves with scale weight data. Required to be called from user action
• scale.getStatus() - Returns a promise which resolves with scale status data. Required to be called from user action
• scale.zero() - Returns a promise which resolves when the scale is zeroed. Required to be called from user action
• scale.startPolling([pollInterval]) - Starts polling the scale for weight data. Default polling interval is 500 ms Required to be called from user action
• scale.stopPolling() - Stops polling the scale
• scale.disconnect() - Returns a promise which resolves once disconnected. Closes the read and write streams and frees the serial port

Static Attributes

• SerialNCIScale.isWebSerialSupported - true if Web Serial API exists in your browser
• SerialNCIScale.supportedScaleFilters - Array of devices which are known to be supported

Events

The serial-nci-scale instance is an EventTarget and can be listened to for custom events. Scale data is contained the in the detail property.

• weight - Dispatched for every weight read
• status - Dispatched for every status read
• settled - Dispatched when the scale is no longer in motion and if the weight is different than the last settled weight

scale.addEventListener('settled', ({ detail }) => foo(detail.status));
scale.startPolling();

Supported Browsers

Currently only Chrome 89+ and Edge 89+ support the Web Serial API. Earlier versions of Chrome and Edge can use the API if it is enabled in chrome://flags