Line Following Sensor

This page describes the connection of the i2c line following sensor to the Boe-Bot robot.

• I2C Line Following Sensor by the Robotics Connection Inc.

This sensor uses an i2c bus for connection with the processor. To understand more about the communication, read following two articles:

• Jon Williams: I2C Fun For Everyone
• Jon Williams: I2C Again – And the Case for Continuos Improvement

The connection diagram:

The photo of the connection:

The demonstration software:

'   {$STAMP BS2}
'   {$PBASIC 2.5}

' -----[ I/O Definitions ]-------------------------------------------------
SDA             PIN     0                       ' I2C serial data line
SCL             PIN     1                       ' I2C serial clock line

' -----[ Constants ]-------------------------------------------------------
Ack             CON     0                       ' acknowledge bit
Nak             CON     1                       ' no ack bit

' -----[ Variables ]-------------------------------------------------------
slvAddr         VAR     Byte                    ' slave address
devNum          VAR     Nib                     ' device number (0 - 7)
addrLen         VAR     Nib                     ' 0, 1 or 2
devAddr         VAR     Word                    ' address in device

i2cData         VAR     Byte                    ' data to/from device
i2cWork         VAR     Byte                    ' work byte for TX routine
i2cAck          VAR     Bit                     ' Ack bit from device

' -----[ Initialization ]--------------------------------------------------

  devNum = 0                                    ' device address %000
  slvAddr = $50
  addrLen = 0                                   ' no internal addresses

  DEBUG CLS,
        "Line Sensor Demo"                         ' setup output screen

' -----[ Program Code ]----------------------------------------------------

  DO
      GOSUB Read_Byte                           ' read switches
                                                ' report
      DEBUG CRSRXY, 0, 2, "In.... ", BIN5 i2cData
      PAUSE 100
  LOOP

END




' -----[ Subroutines - Don't change nothing here!!! ]----------------------


' -----[ High Level I2C Subroutines]---------------------------------------

' Random location read
' -- pass device slave address in "slvAddr"
' -- pass address bytes (0, 1 or 2) in "addrLen"
' -- register address passed in "devAddr"
' -- data byte read is returned in "i2cData"

Read_Byte:
  GOSUB I2C_Start                               ' send Start
  i2cWork = slvAddr | %00000001                 ' send slave ID (read)
  GOSUB I2C_TX_Byte
  GOSUB I2C_RX_Byte_Nak
  GOSUB I2C_Stop
  i2cData = i2cWork
  RETURN


' -----[ Low Level I2C Subroutines]----------------------------------------

' *** Start Sequence ***

I2C_Start:                                      ' I2C start bit sequence
  INPUT SDA
  INPUT SCL
  LOW SDA

Clock_Hold:
  DO : LOOP UNTIL (SCL = 1)                     ' wait for clock release
  RETURN


' *** Transmit Byte ***

I2C_TX_Byte:
  SHIFTOUT SDA, SCL, MSBFIRST, [i2cWork\8]      ' send byte to device
  SHIFTIN SDA, SCL, MSBPRE, [i2cAck\1]          ' get acknowledge bit
  RETURN


' *** Receive Byte ***

I2C_RX_Byte_Nak:
  i2cAck = Nak                                  ' no Ack = high
  GOTO I2C_RX

I2C_RX_Byte:
  i2cAck = Ack                                  ' Ack = low

I2C_RX:
  SHIFTIN SDA, SCL, MSBPRE, [i2cWork\8]         ' get byte from device
  SHIFTOUT SDA, SCL, LSBFIRST, [i2cAck\1]       ' send ack or nak
  RETURN


' *** Stop Sequence ***

I2C_Stop:                                       ' I2C stop bit sequence
  LOW SDA
  INPUT SCL
  INPUT SDA
  RETURN

Results: