NodeJS SPI Dump for MCP3008 (and Raspberry Pi)

readme.md

NodeJS SPI Dump for MCP3008

This is a simple script that reads all eight analog channels of an MCP3008 each second and outputs the result to the console.

I created this script to ease debugging of the MCP3008 ADC connected to my Raspberry Pi.

If you need to troubleshoot the SPI connection in itself you can check out my guide how to test SPI through the loopback "debug mode" https://mikaelleven.wordpress.com/2015/12/10/troubleshooting-spi-on-raspberry-pi-nodejs/.

Installation

Download this gist and run the following command

npm install rpio

Usage

sudo node spi_dump.js

spi_dump.js

// NodeJS SPI Dump for MCP3008 - Created by Mikael Levén
// Original https://gist.github.com/mikaelleven/c3db08ae7837eb3c8698
var rpio = require('rpio');

rpio.spiBegin();
//rpio.spiChipSelect(0);                  /* Use CE0 (slave 0) */
//rpio.spiSetCSPolarity(0, rpio.LOW);    /* Commonly chip enable (CE) pins are active low, and this is the default. */
//rpio.spiSetClockDivider(256);           /* MCP3008 max is ~1MHz, 256 == 0.98MHz */
//rpio.spiSetDataMode(0);

process.stdout.write('\x1b[36m');
for (var channelHeader = 0; channelHeader <= 7; channelHeader++) {
    process.stdout.write('ch' + channelHeader.toString() + (channelHeader == 7 ? '\x1b[0m\n' : '\t'));
}

setInterval(function() {
    for (var channel = 0; channel <= 7; channel++) {
        // Prepare TX buffer [trigger byte = 0x01] [channel 0 = 0x80 (128)] [placeholder = 0x01]
        var txBuffer = new Buffer([0x01, (8 + channel << 4), 0x01]);
        var rxBuffer = new Buffer(txBuffer.byteLength);

        rpio.spiTransfer(txBuffer, rxBuffer, txBuffer.length); // Send TX buffer and recieve RX buffer

        // Extract value from output buffer. Ignore first byte.
        var junk = rxBuffer[0],
            MSB = rxBuffer[1],
            LSB = rxBuffer[2];

        // Ignore first six bits of MSB, bit shift MSB 8 positions and
        // finally combine LSB and MSB to get a full 10 bit value
        var value = ((MSB & 3) << 8) + LSB;

        process.stdout.write(value.toString() + (channel == 7 ? '\n' : '\t'));
    };
}, 1000);


process.on('SIGTERM', function () {

    process.exit(0);
});

process.on('SIGINT', function () {
    process.exit(0);
});

process.on('exit', function () {
    console.log('\nShutting down, performing GPIO cleanup');
    rpio.spiEnd();
    process.exit(0);
});