Using Java8 on the Raspberry Pi, coupled with an Arduino and a mobile web application.

1. Micro & Mobile
Java8 on the Raspberry Pi
22 Dec 2013, JavaDay, Pance Cavkovski

2. The Device
- Raspberry Pi + Arduino
- Basic multimeter: AC/DC
voltage, frequency spectrum,
resistance
- Results shown in a mobile web
application
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3. The hardware
- Raspberry Pi
- Arduino Mega 2560
- Custom adapter and
interface board
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4. The software
Browser app
- Arduino readings
- Java8 SE Embedded
server
- D3.js animated SVG
graphs
d3js
JSON
Java
Java8
WebSocket
lighttpd
pi4j
Serial communication
Analog read + FFT
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5. The software
Arduino read
void loop() {
val1 = analogRead(A1); //AC input
val2 = analogRead(A2); //DC input
val3 = analogRead(A3); //Resistance input
for (i = 0; i < 128; i++) {
val1 = analogRead(A1);
data[i] = val1/2 - 256;
im[0] = 0;
}
//Fast Forward Fourier Transformation
fix_fft(data, im, 7, 0);
for (i = 0; i < 64; i++) {
data[i]= sqrt(data[i]*data[i]+im[i]*im[i]);
lastpass[i] = ylim – data[i];
}
Serial1.print(“ S “);
Serial1.print(val1, HEX);
Serial1.print(“ “);
Serial1.print(val2, HEX);
Serial1.print(“ “);
Serial1.print(val3, HEX);
Serial1.print(“ “);
for (i = 1; i < 21; i++) {
Serial1.print(“ “);
//take the max out of 4 readings
Serial1.print(max(max(max(data[i*4],
data[i*4 + 1]), data[i*4 + 2]),
data[i*4 + 3]),HEX);
}
Serial1.flush();
}
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6. The software
Java server
final Serial serial = SerialFactory.
createInstance();
Serial.addListener(new SerialDataListener() {
private ReadValues readValue =
new ReadValues();
@Override
public void dataReceived(
SerialDataEvent event) {
String received = event.getData();
String[] parts = received.split(“s+”);
//parse the output here.
//reset on each „S‟ received
}
}
serial.open(Serial.DEFAULT_COM_PORT, 115200);
while (true) {
Thread.sleep(10);
if (currentData != null) {
//ReadValues has overriden toString method
//which renders JSON object
String toSend = currentData.toString();
webSocket.send(toSend);
}
}
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7. The software
D3 graphs
//Define the scale and axis
x = d3.scale.linear().range([0, width]);
y = d3.scale.linear().range([0, height]);
yAxis = d3.svg.axis().scale(y).orient("left");
...
//init the svg
svg = d3.select("body").append("svg")...
...
//define d3 enter sequence
selector = svg.selectAll(".bar").data(data);
selector.enter().append("rect")
.attr("class", "bar")
.attr("x", function(d) { return d.x; })
.attr("width", width/50 - 1);
...
//Define d3 update sequence on 100ms interval
selector
.attr("x", function(d) { return d.x; })
.attr("height", function(d) {
return height - y(d.y);
})
.attr("y", function(d) { return y(d.y);})
...
//Start the WebSocket
var socket = new WebSocket("ws://" +
document.domain + ":8887/");
socket.onmessage = function(a) {
lastReceivedValue = a.data;
}
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8. The homepage
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9. The graphs
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10. The demo – DC Voltage
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11. The demo – AC waveline
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12. The demo - Spectrum
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13. The demo - Resistance
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14. The mobile reason
- Mobile is not just responsive
- Mobile browsers are getting lot faster
- JavaScript applications can run smoothly
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15. The micro reason
- Micro devices are catching on and improving
- Raspberry Pi B 2: 700MHz ARM, 512MB SDRAM
Rumored Model C: Dual Core, 1GB RAM?
- Arduino TRE: Intel 1GHz ARM, 512GB DDR3l RAM
- Lots of sensors and shields available
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16. The Java reason
- Java8 improves the embedded editions
- Java8 SE Embedded:
mid-high range, Full OS, general functions, limited I/O integration
- Java8 ME Embedded (v.3.3):
low-mid range, Full/min OS, I/O integrated, optimized, available tools
- Developer versions available
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17. - Source code at https://github.com/hsilomedus/pi4jmultimeter
- Blog post / instructions at http://hsilomedus.me/index.php/pi4jmultimete/
- Questions?
- https://twitter.com/hsilomedus, http://hsilomedus.me/
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