As you may have heard, UCSB is suspending in-person classes effective tomorrow morning. I was told I cannot allow the use of the lab tomorrow, Thursday, or Friday.
Your TAs have graciously agreed to staff the lab this evening until 11:00 PM for those of you who would like to try to complete this week's assignment. If you are unable to do so, I will provide you with an alternative. More details to follow.
Unfortunately we must also cancel tomorrow night's social event.
Here is how grading will work for the course:
The student shop is now closed for the quarter, and I will therefore not be able to use the shop project as part of your grade.
Attendance will be graded up through last week's lab sections.
Problem 1 of Homework #9 will be graded as usual, and no other part of this assignment will be required. You may simulate temperature readings to test the plotting part.
Extra credit will be offered for completion of all or part of problems 2 and/or 3 in lab through tonight.
Extra credit will be offered for completion of all or part of problems 2 and/or 3 using code you have written to simulate the aluminum block. If you want to do this, you should for each one-second interval simulate a cooling rate based on temperature, and a heating rate based on PWM duty cycle. You should also build in a delay for conduction from the heater to the thermistor. You should be able to estimate these physical parameters from your work over the past couple of weeks.
The ninth and final homework assignment has been posted here.
The eighth homework assignment has been posted here.
The seventh homework assignment has been posted here.
You may have noticed a discrepancy between the comments in pwmset.py and pwmdemo.py and the PWM frequencies you are measuring with the oscilloscope. Here is the explanation.
The comments are correct for the Raspberry Pi 3B+ and earlier versions. In the RPi 4, the clock base frequency has been increased from 19.2 MHz to 54.0 MHz. In order to ensure that old code continues to work (roughly) as expected, the author of the wiringpi library modified the pwmSetClock() function as follows. First, the function checks to see if it is running on an RPi 4. If not, it operates as described in my comments. If so, the PWM_DIVISOR we pass to the function is multiplied by 540/192, and the integer part of the result is used as the actual divisor for the 54.0 MHz clock frequency.
So, for example, say we choose PWM_DIVISOR = 2 and PWM_RANGE = 300. With an old RPi, this would give us an effective clock frequency of 19.2/2 = 9.6 MHz, and with 300 clock ticks per cycle, we would get a 32 kHz signal. With the RPi 4, the divisor (2) is multiplied by 540/192 to give 5.625, and this is truncated to 5. The effective clock frequency is then 54/5 = 10.8 MHz, and with 300 ticks per cycle we get a PWM signal frequency of 10.8 MHz/300 = 36.0 kHz (12.5% higher). With PWM_DIVISOR = 2 and PWM_RANGE = 4000, our signal will be at 2.7 kHz.
I had to read the wiringpi library source code to understand what my oscilloscope was showing me, which is unfortunately sometimes necessary.
The sixth homework assignment has been posted here.
The fifth homework assignment has been posted here.
The fourth homework assignment has been posted here.
The third homework assignment has been posted here.
The machine shop training schedule has been posted
here.
The student shop is on the ground floor of Physical Sciences
South. Use the main shop entrance half way down the
hall on the north side.
The second homework assignment has been posted here.
The first homework assignment has been posted here, and the Homework Guidelines handout has been posted here. The assignment is due either Thursday or Friday of next week, depending on which lab section you are in, at 11:55 PM.
The Course Information handout has been posted
here.
On all parts of this web site, “Physics 13” should be taken to mean “Physics 13 / Physics CS 15.”
Class will meet for the first time on Tuesday, January 7, at 12:30 PM in Broida 5223.
Information about enrollment can be found here.
For information about the required course materials, see here.
