Skip to content
Simple JavaScript client for the Shtrikh-M POS2 scales
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.

Project is in the early stage of development

The main goal of this project is to create simple JavaScript client to work with Shtrikh-M (Russian scales manufacturer scales which use POS2 protocol (specification is available here). This project is in the very early stage of development and tested only with Shtrikh-Slim scales. For now, the client is able to connect to scales and receive current weight channel state. Also it allows to easily send raw commands (thus allowing to send any other command that is not natively supported by this library yet), taking care of LRC calculation and other boring stuff.


yarn add jspos2

Also this module depends on serialport module, which in turn uses native bindings. It means that you may need to rebuild it with node-gyp, especially if you are going to use it with electron (it that case you may find it usefull to use electron-rebuild for that purpose). For more info on this subject you may look at the serialport docs.

Basic usage

To communicate with the scales you need to create the client first. The first way to create it requires you to provide the instance of SerialPort which should be already opened. The constructor method should be used in that case, it takes port and optional second argument with options. For example, it may look like this:

import SerialPort from 'serialport';
import { Client } from 'jspos2';

const port = new SerialPort(portName, {}, err => {
  if (err != null) { // do something }
  // Starting from here we can be sure that the port is ready and opened
  const client = new Client(port, {
    // Optional. May be omitted when scales has the default 0030 password 
    password: List([0x00, 0x00, 0x03, 0x00]),

Or, alternatively, you can find it easier to make use of the factory method. To use it you need to know your scales vendor id and product id. For example, for one of the Shtrikh-Slim scales it is 1FC9 and 80A3 accordingly (library is clever enough to determine that in linux this ID will look like '0x1fc9' and in windows '1FC9', you may specify it in either form, in either case). This factory method takes vendor id, product id, and optional third argument with options, and returns Promise.

Client.fromDeviceId('1FC9', '80A3', {
  // Optional. May be omitted when scales has the default 0030 password 
  password: List([0x00, 0x00, 0x03, 0x00]),
  // Optional. If set to false, library does not make any attempts to adjust IDs to
  // the concrete OS and seeks for the strict equality
  normalize: true
}).then(client => {
  // Do something with the client
}, err => {
  // Handle the error somehow

Also, according to the protocol, you should initialize client before it can be used (ENQ byte will be sent and NAK byte is expected as a response)

client.init().then(() => {
  // Now we can be sure that the client is initialized
}, err => {
  // Handle the initialization problem 

Now, when we have our client created and initialized, we are ready to go and to receive the current weight channel state:

client.requestScalesState().then(s => {
  // Do something with s 
}, err => {
  // Handle the error somehow

Scales state has the following shape:

type ScalesStateFields = {
  isFixed: boolean,
  autoZero: boolean,
  enabled: boolean,
  tare: boolean,
  stable: boolean,
  autoZeroError: boolean,
  overweight: boolean,
  measurementError: boolean,
  underweight: boolean,
  noAnswerFromADC: boolean,
  weight: number,
  tareWeight: number

Sending RAW requests

To utilize the scales functionality which is not yet fully supported by this library, you has the ability to send raw requests. Under the hood, both the requests and the responses are represented by the RawMessage instances. For example, here is how you can request the scales state using raw command.

import { RawMessage, Client } from 'jspos2';
import { List } from 'immutable';

const type = 0x3A;
// Pure data, without STX, length, type and LRC bytes
const data = List([0x00, 0x00, 0x03, 0x00]);

const requestMessage = new RawMessage(type, data);

// Perform it on the previously created and initialized client
client.sendRawCommand(requestMessage).then(response => {
  // Response is also the RawMessage, so you can retrieve its content from its data property.
}, error => {
  // Handle the error somehow

Closing the client

To close the client and unclaim the serial port you can use .close method on the instance of the client (it returns a Promise):

You can’t perform that action at this time.