Read and Write in NFC card

[jscaglia]

Hi, a question. If I want to save the word "test" on my NFC card.

I want to use the following methods (I don't know if it's okay to use these)

0x24 is my board address. 7 is the length I want to read

bus.i2cReadSync (0x24, 7, buffer?) bus.i2cWrite (0x24, 7, buffer ?, cb?)

But I don't know what buffer is and cb ... will they have any example to pass me?

Greetings and thanks

[fivdi]

But I don't know what buffer is and cb ... will they have any example to pass me?

buffer is a Node.js Buffer object. Unfortunately this isn't mentioned in the documentation but #81 was created to improve the documentation.

cb is shorthand for callback. Callbacks are mentioned in the documentation, for example, in the description for class Bus here. The documentation for i2cWrite also mentions that cb is a completion callback here.

If you're new to Node.js and not yet familiar with callbacks and asynchronous programming I'd suggest reading up on the topic, for example, here.

I'm not familiar with using I2C to read NFC cards, but below are two example programs that show how to use i2cRead/i2cWrite and i2cReadSync/i2cWriteSync.

I'd suggest using either synchronous methods or asynchronous, but not both at the same time. The synchronous methods are always named with the suffix Sync,

A synchronous program that uses Buffers, i2cReadSync and i2cWriteSync to determine the temperature with a MCP9808 I2C temperature sensor

const i2c = require('i2c-bus');

const MCP9808_ADDR = 0x18;
const TEMP_REG = 0x05;

const toCelsius = rawData => {
  let celsius = (rawData & 0x0fff) / 16;
  if (rawData & 0x1000) {
    celsius -= 256;
  }
  return celsius;
};

const i2c1 = i2c.openSync(1);

const writeBuf = Buffer.alloc(1);
writeBuf[0] = TEMP_REG;
i2c1.i2cWriteSync(MCP9808_ADDR, writeBuf.length, writeBuf);

const readBuf = Buffer.alloc(2);
i2c1.i2cReadSync(MCP9808_ADDR, readBuf.length, readBuf);

console.log(toCelsius(readBuf.readUInt16BE(0)));

i2c1.closeSync();

An asynchronous program that uses Buffers, completion callbacks, i2cRead and i2cWrite to determine the temperature with a MCP9808 I2C temperature sensor

const i2c = require('i2c-bus');

const MCP9808_ADDR = 0x18;
const TEMP_REG = 0x05;

const toCelsius = rawData => {
  let celsius = (rawData & 0x0fff) / 16;
  if (rawData & 0x1000) {
    celsius -= 256;
  }
  return celsius;
};

const i2c1 = i2c.open(1, (err) => {
  if (err) throw err;

  const writeBuf = Buffer.alloc(1);
  writeBuf[0] = TEMP_REG;
  i2c1.i2cWrite(MCP9808_ADDR, writeBuf.length, writeBuf, (err) => {
    if (err) throw err;

    const readBuf = Buffer.alloc(2);
    i2c1.i2cRead(MCP9808_ADDR, readBuf.length, readBuf, (err) => {
      if (err) throw err;

      console.log(toCelsius(readBuf.readUInt16BE(0)));

      i2c1.closeSync(err => {
        if (err) throw err;
      });
    });
  });
});

[fivdi]

@jscaglia Hopefully the above information was useful. I'll go ahead and close this issue as there doesn't appear to be a todo for i2c-bus.