CyBENCH :: Robotics - Electronics Resources
Home Projects Cybot ScrapBots Part Salvage Site Map Links
  CYBOT PAGES
Motor Board
Light IO
Processor 1
Sonar Processor
Line Follow
Sonar IO
IR comms PCBs
Cybot Display
Handset
FAULT FINDING
  SITE INFO
Contact Info
Disclaimer

The CYBOT Light INPUT/OUTPUT Board

HOW IT WORKSPROBLEMSDOWNLOAD


HOW IT WORKS

SOUNDER

The sounder outputs are driven using a complementary drive method.
This allows for a greater peak-peak signal.


The top waveform represents a single output, giving a peak to peak output of 5v

The lower waveforms represent a complementary drive system.
Outputs 1 and 2 represent the output from the microcontroller to the sounder.

When the combined output is observed, say with respect to output 2.
Firstly Output 1 is at +5v with respect to Output 2.
Next, Output 1 is at -5v with respect to Output 2.
This gives an overall peak to peak waveform of 10v.

This frequency has approx 1.4ms period ( t=700uS ), giving a frequency of around 714 Hz
Piezo sounder Application Guide

Again, in the off-state, as with the ultrasonic transducers, the +ve line is left at +5v,
the other connection is at 0v. There is a DC potential of 5v placed across the piezo element.

If you have a look in the piezo application guide above, page 2 of the PDF, it clearly
recommends that this is not done.


LINE FOLLOW DETECTION


Due to the way that Cybot has been designed, it only has one input signal for line following.
This input is the output of a comparator, LM311, this compares both line sensor inputs.

The following table shows what cybot see's with various line conditions:

Left SensorRight SensorLM311 Output
WhiteWhiteLow
WhiteDarkLow
DarkWhiteHigh
DarkDarkHigh

Cybot would be able to perform faster and smarter line following if it see both inputs.

For example:
Continue on in a straight line if it detected DARK-DARK.
Move in an ever increasing circle or other search pattern for WHITE-WHITE.
Move left or right in the other states.
Possibly finding the left edge, then the right ede, then steering to approx center, then straight.

As this is not the case, cybot has to wiggle to find the left hand edge of a line.

Below is a logic analyser capture of the motor drive during line follow:



The top trace is Left Forward, Left reverse and the bottom is Right Forward.
Right reverse is kept low.

This was observed while cybot was on a black surface.

The same is observed on a white surface, but exchanging left and right channel labels.

Therefore, these two sequences alternate as the sensor moves between the above states.

I have observed this in both line follow modes, there is no difference.

Return to TOP of the page




PROBLEMS

There a few potential problems:

  • Ignoring Light Dependant Resistors
  • Spinning in circles
  • One motor not spinning at all

Please refer to the Fault Finding Guide.

Return to TOP of the page




DOWNLOAD AREA

Light IO Board Schematic
gif
pdf
zipped pdf


Datasheet
LM311 Comparator
Piezo sounder Application Guide

Analyser Capture
Line Follower Capture (PDF)

Return to TOP of the page