SSN Simple Sensor Network

1
SSN Simple Sensor Network

• R. Stelzer, K. Jafarmadar, A. Dabrowski

2
Agenda

• InnoC.at Who are we?
• Motivation for SSN
• What is SSN?
• SSN Protocol
• SSN Hardware
• How to Use SSN - Light Following Robot
• Discussion

3
InnoC.at

• Non-profit organisation
• Support motivation of comers in innovative
  computing

4
Main Projects
Simple Sensor Network MariaTheresia
Wiki http//wiki.atrox.at RobotChallenge http//w
ww.robotchallenge.at
5
Motivation

• Similar sensors use totally different interfaces
• Reimplementation and testing of interfaces wastes
  a lot of time
• Make it easier to get into robotics hardware
• Concentrate on logic algorithms instead of
  debugging hardware

6
What is SSN?

• SSN stands for Simple Sensor Network
• SSN is a protocol, which provides a uniform and
  simple "language" to communicate to a large
  number of different sensor and actuator devices.
• A few functions (getdata, setdata, ...) can be
  used to retreive values from sensors respectively
  to set values of an actuator.

7
Why SSN?

• Simple commands (GetData, SetData)
• ASCII mode for immediate use testing
• Based on standards (RS232, USB cables)
• Modular, Plug and Play
• Easy to implement
• Scaleable
• Open specification
• Cheap

8
SSN Topology

• Direct connect One sensor/actuator directly
  connected to the master (PC)
• Connected via SSN switch / Cascaded via Port 0xF
• I----I I-------------I I-------------I
• I PC I---I Switch 1 I-F-I Switch 2 I
• I----I I-------------I I-------------I
• I---I I---I I---I
• I A I I B I I C I
• I---I I---I I---I

9
SSN Reply Request Cycle

• Master sends request to SSN switch
• SSN switch extracts address
• SSN switch forwards complete packet to
  appropriate port
• SSN switch waits for reply

I----I I----------I I PC I---I Switch
I I----I I----------I
3 8 I---I
I---I I A I I B I I---I I---I
) Address 0xF indicates cascaded SSN switches
this exception is not considered in this listing.
10
SSN Request Packet

• Address halfbyte
• 0x0 .. 0xE (port number of SSN switch)
• 0xF .. cascading indicator
• Command halfbyte
• GetInfo
• GetData
• SetData
• ) 4 variations (1 byte, 2 bytes, 4 bytes,
  \0-terminated string)

• Data dependent on variation of SetData

• Cascading headers are additional header bytes (1
  per hop)
• First halfbyte 0xF .. cascading indicator
  instead of address
• Second halfbyte port, where the next SSN
  switch is connected.
• discarded, when passing on the packet

11
SSN Commands

• Get general Information about Device
• 0x0 ... getinfo short
• 0x1 ... getinfo long
• Get sensor value / actuator status
• 0x2 ... getdata string (\0-terminated)
• 0x3 ... getdata byte
• 0x4 ... getdata 2 bytes
• 0x5 ... getdata 4 bytes
• Set actuator value / change sensor settings
• 0x6 ... setdata string (\0-terminated)
• 0x7 ... setdata byte
• 0x8 ... setdata 2 bytes
• 0x9 ... setdata 4 bytes

12
SSN Request Example

• I----I I----------I
• I PC I---I Switch I
• I----I I----------I
• 3 8
• I---I I---I
• I A I I B I
• I---I I---I

We want to set the value of device B to 9

• Request PC -gt Switch -gt Device B
• 1st byte - 0x87 // sensor is attached to port 8,
  setbyte()
• 2nd byte - 0x09 // value is 9
• Reply Device B -gt Switch -gt PC
• 1st byte 0x87 // request header

13
SSN Request Example - Cascading

• I----I I----------I I----------I
• I PC I---I Switch 1 I-F-I Switch 2 I
• I----I I----------I I----------I
• 3 8 4
• I---I I---I I---I
• I A I I B I I C I
• I---I I---I I---I

We want to read the sensor value of device C

• PC -gt Switch 1
• 1st byte 0xFF // cascade via port F to next
  switch
• 2nd byte 0x43 // sensor is attached to port 4,
  getbyte()
• Switch 1 -gt Switch 2 -gt Device C
• 2nd byte 0x43 // sensor is attached to port 4,
  getbyte()

14
SSN Reply Packet

• 1st byte usually identical to header of request
  (address, command)
• Additional data bytes dependent on request data
  type
• ) Exception in case of timeout (recongnised by
  SSN switch), the 2nd halfbyte contains 0xF
  instead of the command

15
SSN Hardware

• SSN switch
• Microchip PIC16F877
• USB type A sockets
• Sensor/actuator Modules
• Microchip PIC12F675/683 if sufficient
• Communication
• RS232 9600 baud 8-N-1 (to Master)
• TTL 0/5 V (between SSN switch and Device)

16
Light Following Robot

• Modules
• Master device (notebook)
• SSN switch
• 2-channel LDR module
• 2 motor driver modules

• Topology
• Switch
• I---I-0--2-Channel-LDR
• Master I I
• I----I I I-1--Motor-Driver
• I PC I----I I
• I----I I I-2--Motor-Driver
• I I
• I---I-3--

17
Master Software

• setbyte(0,1) // activate channel 1 (left) on
  port 0
• leftgetbyte(0) // read value on port 0
• setbyte(0,2) // activate channel 2 (right) on
  port 0
• rightgetbyte(0) // read value on port 0
• if ( left lt right ) // light is left -gt go to
  left
• setbyte(1,100) // speed 100 on port 1 (left
  motor)
• setbyte(2,200) // speed 200 on port 2
  (right motor)
• else // light is right -gt go to right
• setbyte(1,200) // left motor fast
• setbyte(2,100) // right motor slow

18
Planned SSN Modules

• Sensors
• 2-channel ADC
• Distance (Infrared, Sharp)
• Angle (potentiometer)
• Brightness (LDR)
• 2-axis-accelleration (ADXL202)
• Distance (ultrasonic)
• Infrared (RC5-Signals)
• Compass (CMP03)
• Temperature (DS1820)
• GPS (NMEA-1083)
• Pushbutton/switch
• Dimmer
• ...

• Actuators
• Motorbridge (TC4424)
• Servo
• Stepper
• LCD-Display (I2C)
• Infrared (RC5-Signals)
• Switch (relais)
• ...

19
Sources Information

• SSN specification FAQ on the webwiki.atrox.at/i
  ndex.php/SSN_Protokoll
• Kits for SSN switch and modules available
  soonwww.innoc.atwiki.atrox.at/index.php/SSN_Modu
  le
• Dont hesitate to ask for help with implementing
  new SSN modulescontact_at_innoc.at

20

• Thank You for Your Attention!
• supported by
• www.distrelec.com