Administrative issues

• attendance
• journals, send in a version, URLs preferred
• March 1st -> Feb 28th
• phidget analog sensors can be used with Arduino. Just give them 5V and Ground, and the third pin will give you a voltage that you can read with analogRead(). The resistive sensors can be used also with Stamp's RCTIME.

Serial Communication

See practical how-to for USB-serial conversion

Serial= bits traveling one by one over a line

• When does the next bit begin?

Aynchronous= no clock line,

• separate clocks at the two ends

Two parties know several communication parameters:

• data rate (baud)
• number of data bits
• parity check?
• stop bits

Then they can coordinate some communication

Voltage level

• RS232 levels: -12V=1, +12V=0
• normal logic levels: 5V=1, 0V=0
  • which is why RS232 is referred to as "inverted" from the logic-level point of view
• RS232 allows longer-wire communication
• but has large voltage swings so it consumes a lot of energy
• "line drivers" do the conversion automatically

2 lines (serial and ground) needed for 1-way communication

3 lines (RX, TX, ground) needed for 2-way communication

• RX of a device linked to TX of another

Typical serial setups

• An installation reads sensors and sends all its data to a computer
• An installation or a computer read a complex sensor (accelerometer, RFID reader)
• Two installations communicate with each other
• On computers
  • you can do serial communication in Java, Macromedia Director, Processing...
  • for environments that don't have a serial library (Flash?), you can use a converter from serial to TCP/IP (SerialServer)
  • behaves like a net server but talks to a device...

DB9 connector

• needed for communication to computers, or for monitoring with serial monitors
• pin 5 is Ground
• pin 3 is host TX (other party RX), 22 K resistor for surviving higher (12V) voltage
• pin 2 is host RX (other party TX)
• you can use your hack cable as a serial communication cable, just ignore the ATTN line. Line order:
  • Ground
  • ATTN (ignored)
  • device (controller) RX (host TX)
  • device TX, (host RX)
• you can connect it directly "near" the Stamp on the breadboard but then you lose a Stamp pin (the one near ATTN)
• if you use the same cable for both programming and communication, remember to close the connection before programming

Serial monitors

• needed to test your serial program on the controller
• you can typically both type and read in them
• on some you need to set "echo on" to see what you type
• typically let you easily select the communication parameters
• Windows Hyperterminal
• Arduino Serial monitor
  • choose the port from Tools/SerialPort, you can monitor any port, not only the Arduino USB-serial o
  • you'll have to switch it back when you program it
  • although Arduino can't be programmed through ports > COM9, it can still monitor them
• BASIC Stamp environment
  • Run/Debug/New
  • no need for a stamp to use it
• Mac Terminal
• many others

A little BASIC Stamp echo program, with communication indicator LEDs.

Serial Communication in Java

http://java.sun.com/products/javacomm/

• current version seems to be available only for Solaris and Linux, javax.comm
• old Windows version here
• rxtx.org implements the Sun API but you can use it even without importing javax.comm.* but gnu.io.* (the rest of the java text stays the same)

A how-to:

• in the minimal version of using RXTX without Sun's API
• simply put RXTXcomm.jar in the CLASSPATH or in ...jre\lib\ext (/Library/Java/Extensions/ on the Mac)
• and RXTXserial.dll (Windows) or libSerial.jnilib (Mac) in the PATH or in the current directory or in ...jre\bin (/Library/Java/Extensions/ on the Mac)
• in Eclipse
  • just drop the two files in your project dir,
  • put RXTXcomm in the Project's Java Build Path
  • right-click on the Java class file and use "run as java application"

Example

• opening a port on 9600, reading data from it
• the "input" part of a serial monitor

Arduino serial

Arduino uses its serial port for programming (during bootloader run), and communication (incl. debugging)

• That means that if you use Arduino's port for communication from another application, Arduino environment won't be able to program it

• So stop your Java (or Flash or Processing or...) program, or close the connection (hang up) in HyperTerminal

• Sometimes the Arduino environment tries to upload, but it hangs.
  • Then the port may remain busy and no application can use it to communicate with the Arduino sketch
  • in an extreme case, take out the USB cable so the port dissapears

If you need more serial ports, use SoftwareSerial (has limitations!)

The led blink counting blinks out on serial

• we look what happens if we mess up the baudrate

If using the standard 0 and 1 ports (not USB)

• you need this typically to communicate to other devices (another Arduino, a Stamp, accelerometer...)
• if USB is connected, watch the RX and TX LEDs
• since your communication may conflict with the FTDI circuit, it is preferred to power Arduino externally and disconnect the USB
• a 10 KOhm from RX to ground is also recommended, so the circuit doesn't get "noise" at startup, messing up the bootloader
• even then, you will need to arrange your protocol so that the other communciation party will not mess up the bootloader at startup.
• Arduino cannot communicate directly from its digital ports (either through Serial or SoftwareSerial) to a RS232 connector of a computer
  • regardless if the RS232 is built-in or USB-serial converted
  • this is due to differences in voltage levels
  • you can do it through a line driver
  • but you rarely have reasons to avoid the USB, even if you power the Arduino separately

BASIC Stamp serial

• powerful serial communication, including timeout, parity check
• see SERIN (manual page 393) and SEROUT
• the modes are a bit cryptical
  • 9600 baud, 8 data, No parity, 1 stop, non-inverted: 84
  • 9600 baud, 8 data, No parity, 1 stop, inverted: 16468
• the BASIC Stamp has "inverted" modes, which can talk to RS232 even if they use logic levels
• the Stamp SIN and SOUT are "truly" RS232 (have line drivers)
• the other pins
  • can normally drive RS232 pins if inverted
  • can read RS232 levels if inverted, through a 22 kOhm resistor that limits current
• reading serial data from Arduino and writing it inverted to a RS232

Other issues

Data format (binary, ascii)

Synchronization, protocol

Serial timeout / freeze, buffers

Other communication modes

Many boil down to serial.

IRda

• serial communication over infrared
• requires direct line of site, or good reflection

USB

Bluethooth

• serial, there are adapters
  • one from ELFA
  • another from Parallax, nice user manual
  • see also Arduino BT
• Java programming
  • JSR 82, lets you do much more, including programmatic set-up of Bluetooth connections
  • Bluetooth is programmed serially itself! Often JSR-82 software will need a serial adapter and driver

Ethernet-serial

WLAN-serial