# Gas station without pumps

## 2011 October 25

### Home schooling weeks 5–8

Following up on Home Schooling week 4, this post describes our 2nd month of home schooling.  We had another meeting on Monday with the consultant teacher to touch bases and check on progress.

Spanish 3
Nothing particularly new here.  He still likes the instructor and still is doing well on tests.  They’re learning the subjunctive now.
He decided not to revise his essay on Brave New World—the corrections needed were fairly minor, but he didn’t see much point to fussing with an essay that he really didn’t care about.  He finished his map of Gethen for Left Hand of Darkness and has started on the essay about Newspeak for 1984. The essay on Newspeak will be as much linguistics as anything else, building on his interest in conlangs. I don’t know what book is next on his assigned reading list, but probably not another dystopia. He has, of course, been continuing about a book every 2 days of recreational reading.
We’ve decided to drop the creative writing idea for this semester.  We’ll look at it again next semester, and we’ll also consider his taking a tech writing course over the summer (either this summer or summer 2013) to catch up on the writing requirements.
History
He added a few more events to the timeline, so he is up to about 20 events that have some snippet of information with them.  He was able to demonstrate the timeline to the teacher this time, and he has agreed that he will (eventually) put it on-line to share with other students.  He’ll have to add links to further information (even if only Wikipedia pages) for each entry and make sure that all his images are released with a license that lets him use them.  (Many are Wikimedia images, which are all under Creative Commons license, but he has a few from other web sites that he’ll have to check on and either get permission for or replace.)
Theater
He  is mostly off-book now for the lead villain role in the play he is doing, and they have blocked most of the scenes.  I think that this play has the most lines of any of the plays he’s been in so far, but the character is a fairly simple melodrama villain, so there isn’t a lot of complexity to the part.  His improv class continues to be fun, but the average age of the kids is a bit lower than in the play production, so I think he is occasionally a bit frustrated with the quality of some of the improv.
Physics C
We had three meetings now of the Physics lab and have been making good progress on reading the book, doing problems, writing programs, and doing lab work.  About all that is missing is doing technical writing.  I think I’ll make the students write up the modeling they’ll be doing of springs (see Physics Lab 4: spring constants and Physics Lab 4: spring constants continued).  I also had a good conversation about the physics curriculum with my airport limo driver.
We’re on schedule for finishing Part 1: Mechanics in the Matter and Interactions text before the AP Physics C: Mechanics exam. I’ll take that exam along with the students in the spring.  Next year, my son and I will do the second half of the text, and in his senior year, he’ll do a chemistry course somewhere (probably at the community college).
Robotics
The top-of-tether box is done (other than some strain reliefs).  We have ordered waterproof strain reliefs for doing the dry box penetrations, which we hope will come in the next week.  We decided to go with those and home-made waterproof disconnects rather than IP68 connectors, since we can seal the penetrations with casting resin if needed, and the home-made connection boxes can hold some of the electronics (like the ethernet-to-USB converter).  I’m not 100% convinced that the homemade connection boxes are a good idea, but it shouldn’t cost any more than the IP68 connectors.
It took longer than planned to get the strain reliefs, because of some miscommunication between the students and me.  I was looking for a parts list to order, and they just had a list of cable measurements.  Finally my son and I sat down with the measurements and the computer and spent an hour finding and ordering strain reliefs that should meet the requirements.  (We ended up with Sealcon strain reliefs ordered from www.productsforautomation.com, because Digi-Key did not seem to have what we needed.)
The students have also started assembling the motor controller that I designed as an Arduino shield.  We have an earlier version that I designed that would work for them, but the newer design should be a little easier to work with if they decide to mix motors and servos.  (It also has some LEDs to show whether or not power is being supplied.)
We have a pressure sensor soldered to a breakout board now and it seems to work.  We tested it using Lego pneumatics.
In two or three weeks the machine will be ready to put in the water and start testing (there will need to be a fair amount of programming before they can actually control the robot).
Machine Learning (Science Fair)
He’s gotten the input parser written and abstract base classes for his classifiers.  He’s not been putting in much time on this project, so things are not looking good for him getting it done by science fair.  His teacher has asked him for a one-page lay-person’s overview of what his project involves.  He’ll need that for the science fair poster and report, and it would be good for him to write this in the next 2 weeks.
Calculus BC
The AoPS Calculus class has been going fine, though he is a little behind schedule on the homework.  He likes the class and the instructor, but it takes him much longer to write up the problem solutions than it should.  I don’t know whether the problem is with insufficient facility with the math or whether is it another symptom of his writing problem.
Physical Education
He continues the usual 4 hours of bicycling a week (plus nightly sit-ups and leg lifts).  He’s biked about 270 miles since the beginning of the school year. He gets a PE credit for every 15 hours of exercise, so he has earned 2 so far.  He has 5 from 9th grade PE last year, so he only needs to earn 3 more, which will take about 3 months of bicycling to the community college.  If he takes Spanish 4 there next semester, then he’ll have cleared his required PE this year.

## Related articles

### HexMotor 2.3 and pressure-sensor boards

Top view of my second PC board. 3 copies of HexMotor 2.3 and 2 copies each of 3 different breakout boards for a pressure sensor.

I got the boards back from 4pcb.com about a week ago.

The HexMotor rev2.3 boards have several new features: LEDs for +5v and +6.25v, a reset button, 16-bit shift register instead of 8-bit, servo outputs connected to pins 13, 7, 2, 9, 10 (rather than to the pins used for PWM).  The new board should be able to do either 6 PWM motors or 4 PWM motors, 5 servos, and 2 non-modulated reversible motors.  I was going to have the robotics club solder the board today, but they did not have time.

[Note: as of 1March 2012, I have put the HexMotor Eagle design files on the web.]

I made some breakout boards for the MPXHZ6250A pressure sensors from Freescale Semiconductor,  which gave me my first taste of SMD soldering.  At least the design uses gull-wing pins, which can be hand soldered.  The breakout board that I think that the robotics club will end up using puts a pressure sensor on one side and headers for a piggyback ADXL335 breakout board on the back.  that way there only need to be one set of wires for connecting the analog inputs and power to the sensors.

That is the board I soldered a sensor to.

Top view of the breakout board with the sensor and headers soldered in place.

The pressure sensors are tiny! I found it fairly difficult to solder the  sensor to the boards, even holding it with clamping tweezers. I did eventually get everything to stick with no shorts between the 3 signal wires, but I did have some trouble with the unused copper pads delaminating from the board.  For future reference: all pads should have wires going to them (even the unused pads) to have enough surface area for good adherence and so that some of the pad is tucked under the solder mask.

Here are the solder connections on the side where none of the pins are used.

Here are the solder connections for the power and signal pins (and an SMD capacitor).

Despite the rather sloppy soldering, the pressure sensor does work.  It turns out that the port size is just the right size for Lego pneumatics components, so testing was pretty easy.

Sensor attached to Lego pump and gauge for testing.

Here are the results of calibration tests with the (probably not very accurate) Lego gauge, done by my son and me.

0 367
5 518
6 542
7 576
8 599
9 632
10 657
11 683
12 710
13 734
14 775
15 801
16 832
17 861
18 887
19 915
20 941
21 967
22 1000

The range is about right, since 22 psi plus one atmosphere is about 250kPa, which is supposed to be the high end of the sensor’s range. Also, 600″ (50′) of water is 21.67 psi, so the range from 367 to 1000 corresponds to about 50′, so the sensor should give the robotics team a resolution of about 1″ for measuring depth, as expected from the spec sheet.

The data are well fit by $\mbox{Arduino reading}= 28.57 \mbox{psi} + 371.$ The club members will have to recalibrate the pressure sensor in water, to get calibration as depth in cm. They’ll probably have to re-zero the sensor every day they use it, to compensate for atmospheric pressure, since it is an absolute pressure gauge.