NodeJS example using SPI communication to retrieve analog data through MCP3008 and Raspberry Pi

spi_example.js

var rpio = require('rpio');

rpio.spiBegin();
//rpio.spiChipSelect(0);				/* Chip select: use CE0 (default) */
//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);

// Prepare TX buffer [trigger byte = 0x01] [channel 0 = 0x80 (128)] [placeholder = 0x01]
var sendBuffer = new Buffer([0x01, (8 + 0 << 4), 0x01]); 

// Send TX buffer to SPI MOSI and recieve RX buffer from MISO
var recieveBuffer = rpio.spiTransfer(sendBuffer, sendBuffer.length); 

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

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

console.log('ch' + ((sendBuffer[1] >> 4) - 8), '=', value);

rpio.spiEnd();

Hi, I've been trying some node.js experiments on my RPI for the ADC3008 and came across your very interesting blog about it. The issue I have though is that I am not getting the same output with the code examples you have made. When I run 'sudo node spi_example.js' I get this back:

/home/pi/jperkin/node_modules/rpio/lib/rpio.js:446
return binding.spi_transfer(txbuf, rxbuf, len);
^

TypeError: Incorrect arguments
at TypeError (native)
at rpio.spiTransfer (/home/pi/jperkin/node_modules/rpio/lib/rpio.js:446:17)
at Object. (/home/pi/jperkin/spi_example.js:13:26)
at Module._compile (module.js:398:26)
at Object.Module._extensions..js (module.js:405:10)
at Module.load (module.js:344:32)
at Function.Module._load (module.js:301:12)
at Function.Module.runMain (module.js:430:10)
at startup (node.js:141:18)
at node.js:980:3

I don't suppose you have any ideas about this?

Thanks,

jamms

I'm getting the same error as @jamms

Any ideas?

Could you please post the code executed before the rpio.spiTransfer() call? I have not seen this error myself but could be related to the input (txbuf) or output (rxbuf) buffer.

Or if you used my example without alternation maybe you could verify which version of rpio-lib you have installed?

@mikaelleven I'm using your code unaltered, and with rpio 0.9.7 installed

got the exactly same error with this script here:

var rpio = require('rpio');

var rxBuffer = rpio.spiTransfer(new Buffer('HELLOSPI'), 8);

for (var i = 0; i <= 7; i++) { 
 process.stdout.write(String.fromCharCode(rxBuffer[i]) + (i == 7 ? '\n' : ' '));
};

looks like the signature of the spiTransfer() has changed. the rxBuffer is now an argument, not a return value
if you look in the file rpio.js , you see that it it needs 3 parameters now .
the following should work

var rpio = require('rpio');

var rxBuffer = newBuffer(8);
rpio.spiTransfer(new Buffer('HELLOSPI'), rxBuffer, 8);

for (var i = 0; i <= 7; i++) {
process.stdout.write(String.fromCharCode(rxBuffer[i]) + (i == 7 ? '\n' : ' '));
};