Chaos Circuit

1
Chaos Circuit

• Tim Klein
• Senior Seminar
• 12/11/01

2
The Circuit
3
Our Goal

• Use the circuit to produce experimental data
• Convert this data into some usable form
• For us this is using the PIC to take data,
  transfering it to the PC and then making a
  bifurcation plot
• Compare this data to the theoretical data from
  the Differential Equations

4
Basic Rundown of Getting Data

• Control the circuit by using a potentiometer.
• Scale both x and x-dot to between 0V and 5V
• Convert x and x-dot from analog to digital
• Store the data to a serial EEPROM
• Dump the data to a file on the PC via a serial
  port

5
The Way Things Were
PC
PIC

• Waits for a signal from the PIC (anything) and
  then starts taking data
• If it gets a BADTYPE, It dumps the data file and
  starts over again
• The Resistance values are hard coded in the file

• Once it started, it collected the data using a
  hard-coded resistance value
• It stores the Data and then Pings the PC with
  0x55
• It dumps the data to the PC

6
Problems with this way

• The resistance value is hard coded in and there
  is no handshaking between the PIC PC
• The PC starts wanting to take data when it gets
  anything from the PIC
• The PC would dump the data file whenever there
  was an error
• There was no handshaking between the number of
  data sets

7
Changes, Changes

• In order to solve many problems (and create a few
  more) I totally revamped the handshaking between
  the PC and the PIC
• Now, the PIC always initiates every transfer with
  a ping of a certain type
• However the PC is the master and the PIC does
  nothing without the PC saying so

8
Problems Solved

• There are now two initiate commands 0x55 and 0xFE
• 0x55 is still for starting the data transfer but
  0xFE is for transferring the R-value
• All the PIC does now is wait for an R-value, take
  data, send the data, and then wait for another
  R-value.

9
Problems solved II

• If there is an error somewhere in the
  transmissionthe PC simply ignore that data set
  and resends the same R-value to retake the data
• In order to ignore the data that was taken with
  an error, the PC first writes to a temp file and
  then transfers that over to the master file.

10
Error Checking

• There are 4 error checking places built into the
  System
• 1. 2.) The PC sends the hi and lo R bytes and
  the PIC returns them
• 3.) The PIC sends the number of data bytes and
  the PC returns them
• 4.) The PC counts the number of bytes received
• If any of these are different than expected, the
  PC resends the same R-Value to retake the data

11
The Digital Pot Problem

• The Digital pot that we had was not working
  effectively
• The wiper could only be set right after power-up
• Only the resistance between R-hi and WPR worked
• Solution, putting the R-values in reverse order
  on the PC side
• Put a wait command on the PC side to reset the
  Pot and then manually reset the Pot after every
  data set

12
The Second Data Point is Bad

• Whenever we received the data on the computer,
  the second pair of data is usually bad
• I think that this is due to the retrieving the
  data from the EEPROM
• One possible solution would be to store the
  Second Point in the PICs memory
• However, the easy way out is to just ignore the
  first couple of data points on the PC side
• This also has the effect of cutting down on
  Transient effects

13
The Circuit was Noisy

• When we finally did end up getting data, it had
  all kinds of noise associated with it
• This made the Bifurcation Plot almost unreadable
• We finally solved this by putting the A-D
  converter on its own isolated power supply to cut
  out some of the noise

14
Finally, the Part we are all waiting for The
Data
15
X Vs. Time
16
Phase Space
17
Transient Motion
18
Noisy Data X vs. Time
19
Noisy Data Phase Space
20
After Noise Reduction -X vs. T
21
Noise Reduction Phase Space
22
Where Do We Go From Here?

• 1.) Fix Digital Pot and take a long sampling
  period to obtain the bifurcation plot
• 2.) Program into the handshaking a method to tell
  the PIC how much data to take
• 3.) Speed up the circuit
• 4.) Solve the 0xFE data problem
• - Perhaps send a combination of signals to mean
  BADTYPE

23
The Rundown of Friends and Not So Much Friends
Friends
Not Friends

• The Digital Logic Analyzer
• The Debugging code for the PIC
• The Fluke
• Dr. Kiers Dr. Holmes
• My Trusty Laptop

• That digital pot!!
• That one capacitor that held me up for an entire
  week
• The person who decided to make the digital pot a
  surface mount.