Greetings,
I am trying to use ADS7828 which is an 8-channel I2C ADC from TI. I am
using javascript to accomplish this task. I am using the latest version of
bonescript.
I have added this line: echo BB-I2C1 > /sys/devices/bone_capemgr.9/slots
to /etc/profile.d/node.sh to execute upon power up or reset.
Executing ls -l /sys/bus/i2c/devices/i2c-*, gives the following results:
lrwxrwxrwx 1 root root 0 May 15 04:39 /sys/bus/i2c/devices/i2c-0 ->
../../../devices/ocp.3/44e0b000.i2c/i2c-0
lrwxrwxrwx 1 root root 0 May 15 04:39 /sys/bus/i2c/devices/i2c-1 ->
../../../devices/ocp.3/4819c000.i2c/i2c-1
lrwxrwxrwx 1 root root 0 Nov 4 16:27 /sys/bus/i2c/devices/i2c-2 ->
../../../devices/ocp.3/4802a000.i2c/i2c-2
Here is my code:
var b = require("bonescript")
var port = '/dev/i2c-2';
b.i2cOpen(port, 0x49, {});
testADC();
function testADC()
{
// Internal Voltage Reference 2.5V
// Single-ended conversion
// channel number address is kind of weird on this chip
var channelNumber = [0x00, 0x04, 0x01, 0x05, 0x02, 0x06, 0x03, 0x07];
var channelOutput = [0, 0, 0, 0, 0, 0, 0, 0];
var n;
// b.i2cOpen(port, 0x49);
for (n = 0; n < 8; n++)
{
channelOutput[n] = readADCchannel(channelNumber[n]);
}
}
function readADCchannel (adcChannelNumber)
{
var command;
var singleEnded = 0x80;
var voltageReference = 0x0C;
var buffer = [];
command = singleEnded + (adcChannelNumber << 4) + voltageReference;
// send command to start conversion
*b.i2cWriteByte(port, command);*
// Conversion should start immediately
console.log(command);
// serves as a time delay
for (var x = 0; x < 300000; x++)
{
}
// read the conversion result
*buffer = b.i2cReadBytes(port, {} , 2);*
console.log("Buffer0 = " + buffer[0]);
console.log("Buffer1 = " + buffer[1]);
var voltage = ((buffer[1] + (buffer[0] * 256)) * 2500) / 4096;
var s = "Output Voltage of Channel: " + adcChannelNumber + " = " +
voltage + "mv";
console.log(s);
return voltage;
}
I am using Cloud9 to debug this. I put two break points where I am writing
to and reading from the chip. I am using a Gabotronics Xmega Xminilab to
read the I2C exchange between the BBB and the ADC converter.
http://www.gabotronics.com/development-boards/xmega-xminilab.htm
After executing the b.i2cWriteByte((port, command); I correctly see the
following bytes on the Xminilab display 49> 8C+ the > indicates a write
cycle to address 0x49 which is the ADC address and the + sign indicates an
ack from the ADC. If I execute the b.i2cReadBytes(port, {} , 2); command
I see the following: 49> 00+ 49< 00+ 00- . The 49> 00+ indicates another
write cycle with 00 command , the < indicates a read cycle from address
0x49 followed by the two bytes that I am interested in, basically the ADC
reading, the - sign indicates no ack..
The question is where is the second write cycle coming from? It basically
screws up the ADC reading and all I get is a zero reading from the ADC.
So, what am I doing wrong here? I can't use i2cReadByte because the ADC
outputs 2 bytes as a result of read request.
This is driving me crazy.
Thanks in advance,
Mostafa
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