Revised pressure sensor lab went very well

Today I ran a revised version of the pressure sensor lab (see
Pressure-sensor lab went well, Class-D lab revision didn’t work, Blood pressure monitor, Blood pressure lab, and Blood pressure lab part 2 for descriptions of the old labs).

The revised lab included both blood pressure cuffs and breath pressure using the simplified breath pressure apparatus of Simplified breath pressure apparatus:

The ½” elbow is small enough that I can put my lips around the opening, which would have been a bit difficult with the 1″ tee.

To make the apparatus, the students had to drill 2mm holes in PVC elbows, so I packed up my drill press last night and hauled up the hill in my bike trailer this morning.  For those unfamiliar with Santa Cruz, that is a 3-mile ride with a fairly steady 4% slope, resulting in a climb of about 715′ (218m).  Needless to say, I went slower than usual uphill!  There is a drill press only about 150′ from the lab the students were working in, but the bureaucracy for getting the students access to the drill press is incredible (I tried, and failed, to get a dozen students access last quarter). So it was easier for me to haul my own drill press up the hill on my bike than to deal with the dysfunctional bureaucracy at UCSC to use the drill press supposedly there for student use.

I explained to each pair of students how to use a drill press, including basic safety precautions, and had them drill a 2mm diameter hole in their PVC elbows.  There were no problems with this, and I plan to do the same for the lab in future.

Each pair of students designed an instrumentation amplifier with an INA126P chip as a first stage and an op-amp as a second stage, wired it up on breadboards, checked the calibration, and recorded both breath pressure and blood cuff pressure.  A few students used extra time to play around with some toys I brought in: a hand vacuum pump, a Lego pneumatics pump, and an aquarium air pump.  One group even tried using the pressure sensor as a microphone, using a loudspeaker with a 300Hz sine wave for input (the pressure sensor could detect the 300Hz input without problems, though I suspect that it was not registering the full pressure fluctuation, as I think that the sensor has about a 200Hz bandwidth).

Most groups were done with this week’s lab in the 3 hours of today’s lab, so Thursday’s lab will consist mostly of students doing make-up work to redo old labs, with a few finishing up this week’s lab.  I expect to spend most of Thursday’s lab time grading design reports (I’m about 2 days behind—I got the design reports that were turned in a week ago done and returned yesterday, and I got the prelabs turned in yesterday done and returned today, but I haven’t started yet on the reports turned in last Friday, nor the stack of redone work turned in last week).

The instrumentation-amp lab went surprisingly well this year, despite adding the drill press.  I think that the big advantages over previous years are that they did not have to solder the inst amps this year and that they had already done a multi-stage amplifier for the microphone amp.

I think that I should rewrite the book to introduce multi-stage amplifiers as the default design (since every amplifier they do in the course is now multi-stage), and talk about how to choose the gain for each stage in general, before getting into individual labs.

One minor problem in lab today—students didn’t have the short pieces of tubing to connect up their breath-pressure apparatus.  This turned out to be my fault—I hadn’t included them on the parts list for this year!  Luckily the BELS staff had some pieces leftover from last year, and I had about 20 feet of my own tubing in the box of stuff I’d packed for the lab, so we had enough for everyone to get 6″.

 

Tread Lightly with Terra Nova!

A friend of mine, Ken Foster, has just started an Indiegogo fund-raising campaign, Tread Lightly with Terra Nova!, to raise money to restart the bicycle landscaping service that he ran for over 20 years:

Terra Nova’s Tread Lightly Service

Bicycle Powered Landscaping

In 1991 I started a service I dubbed Tread Lightly. This was a bicycle-powered landscape service that served our Santa Cruz area clients. For over twenty years the community hailed the ‘Tread Lightly’ service as an authentic, profoundly ecological approach to landscape care and as a symbol of innovation and hope. One of the principles of permaculture is “Use Small and Slow Solutions.” Tread Lightly was definitely that! Pedal-Powered Permaculture!

I used the Tread Lightly service for a couple of years, then decided that I did not care enough about the lawn to hire a landscape service—not even a bicycle landscape service from a friend. The service was good when I used it, and I was wondering why I never saw his bike trailers around town any more (I still see Ken riding his recumbent around town). It turned out that the trailers, bikes, and equipment eventually wore out, and the bike service was barely making enough to pay the employees. When the recession hit, it hit the local lawn services pretty hard, and Ken had to downsize his business (still doing landscaping, but with a much smaller team and no bikes).

Now that the local economy has improved, he’d like to bring back the signature bike trailers and hand equipment, but he needs to raise some capital to do it.  Borrowing from banks (a traditional business solution) is not likely to work, as the business plan does not result in a high probability of a large profit to pay off the loans. So he is looking for crowd-funding to help him restart the bike landscaping business, train youngsters in sustainable urban landscaping, and bring back a distinctive Santa Cruz institution.

In the years since I used the Tread Lightly service, I’ve bought an electric mower to mow the front yard about every 2 months, and let the back yard get covered with weeds (thistles, grass, blackberry brambles, ivy, kiwi vines, … ).  It is now difficult even to get to the compost heap, and some of the windows on the house are not openable because of the blackberries covering them.  I’ve been thinking of hiring Ken to clear the back yard for me, though I’ve no intention of actually maintaining the yard—too much work for too little reward.  If I were ever to sell the house, it would probably need over $1000 in landscaping maintenance to look attractive to a buyer, but I’m likely to be living here for the next 25 years, so any investment I make needs to pay off in personal pleasure (or reduced maintenance effort) well before then.

I enjoyed doing some gardening as a child, and thought I would enjoy it as an adult when I bought the house, but it turns out that I never have the time or energy to do any gardening. There is always something more interesting or more urgent to do. Even the tall raised beds that I built and that I had Ken build have gotten covered with weeds. It would be nice to have an herb and vegetable garden in them again, but I know I’ll never get around to planting and weeding, much less the incessant watering that is needed to have anything less hardy than thistles survive around here.  (I put in a drip irrigation system once, but such systems need annual maintenance, which I never got around to doing, so it disintegrated years ago.)

 

More trailer loads

Last week I blogged about the light, but bulky load of boxes I took to the Museum of Art and History in my bike trailer:

There are more boxes here than it might appear, since I filled each box with smaller boxes.
The trailer was made (a long time ago) by John Welch.

Today, I had to replace our live Christmas tree, which died in the past month after being kept alive for about 4 years.  I used the heavy-duty trailer to bring the tree home from the garden center:

This Christmas tree is a little lighter than our old one (smaller pot), but still took 2 people to lift it into or out of the trailer. I believe that John Welch also made some trailers with a hinged back, for unloading heavy items (like lawnmowers) more easily.  There’s also a can of primer and a toilet plunger in the trailer—the garden center is right next to the hardware store (same company), so I combined errands.

After taking the pictures, I noticed that I had some old photos of another bulky load: a plywood dollhouse that my wife was going to fix up and decorate (we got the dollhouse in 2009, but still haven’t had time to do anything with it):

Bungee cords are important for keeping bulky loads from shifting around.

Boxes to the museum

The Museum of Art and History in Santa Cruz frequently asks its members (and anyone else who gets their newsletter) for items that they need for some family art project.  This month, they said

We’re looking for brown cardboard boxes to build a giant cardboard castle for our upcoming Winterpalooza family festival in January. They can be dropped off at the front desk during museum hours.

I checked whether they were looking for just large cardboard boxes, or whether they wanted all sizes.  They said

We’re currently taking all sizes. Thanks for your message clarifying this. Please drop them off at the front desk when you have a chance. Our hours are Tues-Sun 11-5PM. Fridays open late till 9PM, and closed Mondays.

So yesterday I cleaned out a bunch of the more useless sizes of boxes from our attic and loaded up my larger bike trailer with 50–100 of them:

There are more boxes here than it might appear, since I filled each box with smaller boxes.
The trailer was made (a long time ago) by John Welch.

A few bungee cords to keep the boxes from blowing away and I was ready to go.  At the museum, I parked my bike in front, unhitched the trailer and wheeled it into the lobby, where they had me unload the boxes.

I should remember to keep an eye on their ongoing wish list also, in case there are other things I’d be glad to get rid of that they have a use for.