DIY backpacking gear - Tyvek bivy bag

Tyvek bivy bag in "sleep under the stars" mode

Bivy bag in "inclement weather" mode

Every time I go backpacking, I keep thinking - "What more can I do to lighten my load?".  Because I live in Southern California and many (most?) trails don't have reliable year-round water supplies, we're forced to take large (heavy!) supplies with us, so the more we can lighten the rest of our loads, the better.

This time out, I was after lightening my 4 lb. "shelter" (tent and footprint), using a DuPont™ Tyvek® sheet made into a bivy bag.

Advantages:

• Lighter - bivy bag and groundcloth is 1.5 lb., vs. 4 lb. for my 1-man backpacking tent & footprint.
• Warmer - because it's such a tight weave and is so close to you, it traps body heat much better than a tent.  Claims of an extra 5°-10° F are probably not unrealistic.
• More compact - folds up smaller than my 1-man tent and footprint.

Parts list:

My Tyvek was shipped in Tyvek!
(good for small scraps)

• 1 9'x12' Tyvek sheet (~ $25.99 on eBay), available from various sellers on eBay - this is the one I used and can highly recommend.  If you don't need a Tyvek groundcloth, you can get a 9'x8' sheet.
  
  Also, I used the standard "house wrap", mostly because that's what I saw more recommended by others.  But some use the Tyvek 1443R "soft structure", which is lighter softer and quieter, but more expensive and more difficult to find in the necessary size.  I was a bit concerned about its water resistance, since I plan to use this bivy by itself, without a tarp.  If you make one from this fabric, please let me know in a comment how it works for you...
• 1 roll Tyvek tape ($12.50 or so from eBay)
• 2 36" robe zippers ($2.99 each at Joann Fabric and Crafts).  You can use most any 36" zipper; this was the only one I could find locally.
• 1 5' length of 1/4" PEX pipe ($1.76 at Lowes)
• 1 2" piece of double-sided Velcro ($4.99 for 25 8" strips at Joann Fabric and Crafts)

My pattern
(click to enlarge)

Assembly Instructions:

1. Make yourself a pattern.  I used this (dimensions are in inches), but you'll probably want to change the dimensions to fit your bag, height and girth.  I'm 6'5" and have a very long bag, so I made mine using the full 9' length of the Tyvek.  If you're shorter, you can trim to make it smaller and save some weight.
2. Knead and/or wash the Tyvek to soften and quiet it.  There's differing opinions on the 'net as to whether it's better to soften the Tyvek before assembly or after.  I chose to soften first (both by kneading the dry material by hand for 10 minutes or so and then putting in a washing machine (with no detergent or fabric softener, water only!) for a full cycle.  This has no impact on its water resistance.  Note that doing this will "shrink" the Tyvek by a few inches in both directions, so if you plan to wash after assembly, be sure your pattern is upsized to accommodate this.  Mine shrank from 12' to 11' 4" and from 9' to 8'5" or so.
3. Using your pattern, mark your cut points on the Tyvek, using either a pencil or fine-point permanent marker.  A yardstick can help keep the lines straight.
4. Make your cuts.
5. Attach the vertical zipper.  Set your sewing machine to use the longest distance between stitches.  You'll need to cut a 3/8" slit on both sides at the end of both zipper cuts in order to fold back 3/8" of Tyvek.  This makes an opening for the zipper and allows you to sew through two layers of Tyvek, making a stronger attachment.  Take your time, this is probably the hardest step.



Zipper detail
(click to enlarge)

6. Attach the horizontal zipper.  If you got a single-sided zipper, like me, you'll want to attach this one with the pull tab on the inside of the bag, to make it easy to open from the inside.
7. Using the Tyvek tape, seal all of seams of the bag.  You can do it in most any order, I opted to tape the long vertical seam (above and below the vertical zipper) first, followed by the top and bottom of the bag.  I opted to put about 1/4" of Tyvek overlap on all of my seams (with the overlap coming from the top of the bag, to keep any rain out that might get under the tape).
8. If you want, turn the bag inside out and put a layer of Tyvek tape on the inside of all of the seams.  This will help strengthen the bag and keep the overlapped flaps from catching on anything inside the bag.
9. Get inside of the bivy with your gear and the PEX pipe.  Figure out where you want to put the pockets for the ends of the PEX pipe and where you want the Velcro strap.  Mark the locations with your pencil or marker.
10. Make pole pocket by taking a 1/2" x 1-1/2" piece of Tyvek and placing it vertically in the middle of a 3" piece of Tyvek tape. Place it centered over the mark you made in the previous step.  Repeat for the other side.
11. Cut off a piece of Tyvek tape 1/2" x 2".  Use it to attach the velcro strap to the marked position on the inside of the hood.
12. Cut the PEX pole as needed to fit inside of your bag.  I needed to trim about 6" off of mine - you may want more or less.

Velcro strap
holding PEX pole
(click to enlarge)

PEX pipe inserted
into pole pocket
(click to enlarge)

OpenSprinkler Pi - smart sprinkler timer review

Due to the ongoing California drought, I decided to upgrade my old Toro sprinkler timer.  Some of the things that I wanted out of a new unit included:

• Weather "smarts" - ie. the ability to lengthen watering during the hot months, shorten it during the winter and turn it off completely when it's raining (or will rain in the next day or two).
• Logging capability - I want to see how much water I'm using on my lawn (our department of water & power bills sewer charges based on how much water is consumed - which isn't ideal if 75% of your water usage goes into your landscaping and not down the drain.
• Remote control - the ability to view and control the system from afar, preferably using a web- or smartphone-based system.

 With these requirements, run-of-the-mill sprinkler timers from your local hardware store are out of the question.  The only commercial offerings are "smart" units, aka Weather-based Irrigation controllers.  The good thing is that many qualify for rebates.  The bad thing is that all that I could find are ridiculously expensive - starting at well over $200 and going up from there.  And most didn't satisfy one or more of my other requirements above.

The OpenSprinkler Pi controller

What to do?  I'm a tinkerer and a Linux aficionado, so I starting thinking - is there a way to make a Linux-based sprinkler contoller?  After some Googling, I came across the OpenSprinkler project.  A great idea, but Arduino-based.  I have no experience or expertise in Arduino systems.  But wait - the same guy now has OpenSprinkler Pi - a Raspberry Pi-based version.  Perfect!  He even has users who had written a number of programs to control the system in various ways - using your SmartPhone, using Google Calendar, using the web, and more.

So I ordered the parts:  The OpenSprinkler Pi 1.4 kit, a Raspberry Pi model A and a tiny USB WiFi dongle.  Total cost was around $150.00 Everything showed up within a couple of weeks and I set about assembling the unit.

Assembly: 

Quite quick.  Everything necessary is included - no soldering required.  Just mount the Raspberry Pi on the OpenSprinkler board with the included screws.  Then attach the WiFi dongle to the USB port.  I reused the power supply from my old Toro controller, which saved a few dollars.

A pleasant surprise when I received the OpenSprinkler Pi kit was that Ray had thoughtfully included a MicroSD-to-SD card adapter that allowed a MicroSD card to be used without having to cut the OpenSprinkler Pi case.

That said, I personally am not a fan of his new "one-size-fits-all" case.  Basically, he custom-designed a case for his original OpenSprinkler (Arduino-based) system.  It's great for that, but then he decided to shoehorn the Pi-based version to that case.  In order to make everything fit, he redesigned the PC board so that the Pi mounted at an odd angle.  But all of the connections were in different places, so few of the holes in the case are used for their original purposes. And because there's no display on the Pi-based system, the prominent display slot used on the Arduino-based system is covered with a piece of adhesive-based white paper.  It works fine, it just doesn't feel professional, and isn't something I'm proud to show to others who might be interested.

Testing:

Ray recommends testing the power output on the OpenSprinkler Pi board before attaching the Raspberry Pi to it.  I did so using a Volt/Ohmmeter (VOM) of mine and it tested fine with the Toro power supply.

I downloaded the software image from Ray's website and put it onto an 8 GB MicroSD card that I had laying around.  I decided to use Rich Zimmerman's excellent sprinklers_pi program, which seemed to be the most feature-complete and also provided a way to use the information from my personal weather station on Weather Underground to adjust watering times.  Cool!

One small issue I ran into:  Rich designed his software to designate Zone 1 as a pump controller (for those on wells).  So if you're not using a pump controller, you should leave Zone 1 unused.  If you have 8 zones to control, there's a workaround.

Operation:

Sprinklers_pi graph example

It works, and works well.  I'm able to see graphs showing how much time each zone is turned on, I can control the system via a web interface from home or away, I can choose to use Internet-supplied weather information to adjust my watering schedules (or not), and I can parse the sprinklers_pi log
files to keep track of how much time each zone is being watered.  Now I just have to figure out how many Gallons Per Minute (GPM) each zone uses, and I should be able to determine how much water is going into my lawn each month.


All in all, I'm satisfied with my new smart system, even if it didn't qualify for a rebate...   ;-)  I just hope he decides to redesign his case into a true all-in-one solution for all of his OpenSprinkler options (Arduino, Pi and BeagleBoard).

Make a smartphone tripod mount for less than $10.00

Smartphones today have amazing capabilities, both as handheld computers and as digital still and video devices.  However, one thing that's difficult to do is to hold a smartphone steady when taking pictures.  A tripod helps immensely, but it's difficult to find a cellphone (or a cellphone case) that has a tripod socket.

A tripod is also very useful for taking panoramas or time lapses (or even combining the two!).

This is my DIY solution.  I think it has a number of advantages over other DIY designs, including:

• Inexpensive - it can be made for less than $10.00, even if you have to buy everything - but you shouldn't need to.
• Compact & portable - disassembles into  a very small space (about 4"x1"x1") and is lightweight (this is important if you're backpacking to your photo-op!)
• Panorama-capable - can be made to position the lens directly over the tripod pivot - necessary for panorama photography
• Adjustable - will work with most feature-phones and smartphones.

Parts list:

• 3 3"x5/8" mending brace ($2.97 for a pack of 4)Note:  Measure the width of your cellphone and make sure that the length of the brace is at least 1/2" longer.  For larger phones, you may need to use a 4" or even 5" brace.
• 1 3/4"x1/2" corner brace ($1.97 for a pack of 4)
• 3 1/4-20 x 1/2" round head bolt & 4 1/4-20 nut ($1.18 for a pack of 5 bolts & 5 nuts)
• Electrical tape or heat-shrink tubing ($0.71)
• 1 or 2 Large rubber bands

Assembly:

Wrap one corner brace with electrical tape, covering all but about 1/2" of one end.

Take the corner brace and attach it to the taped mending brace with a bolt and nut.  Make sure that the bolt head is on the inside of the brace.

Take one 1/4-20 nut and use it to attach the mount to your tripod's mounting screw.

Optional:  Panorama mount

If you plan to use your phone to take panorama shots, you'll need to ensure that your camera's lens is directly above the tripod's screw (on the axis of rotation of the tripod mount). For this we need to add a couple of extra parts.

Panorama mount assembly:

In place of step 3 above, take a second mending brace and attach it to the other side of the corner brace, again ensuring that the bolt head is on the inside of the corner.

Take a third corner brace and attach it to the second one.  Use the third hole (counting from the corner brace side) on the second mending brace and the end hole on the third brace.

Take one 1/4-20 nut and use it to attach the third corner brace to the tripod head, using the hole on the opposite end of the brace.

Mounting your phone:

Put the rubber band over the upright, taped corner brace.  Place the back of your phone against the back side of the brace and draw the band around the screen and looping it over the top of the taped corner brace.  It should be a tight fit.  If it's not, get a smaller rubber band (or loop the band over the bottom of the brace a few times to take up some  of the slack).

The photo above shows the completed simple mount on an Ikea Stam timer for doing timelapse panoramas.  See this page to build one for yourself.

If you're using the panorama mount, you'll need to adjust the angle between brace #2 & #3 (and possibly the angle of the corner brace relative to brace #2) to get the lens directly over the tripod screw.  Make sure you re-tighten the screws once the alignment is correct.

From the front, you can see how the phone's camera lens is positioned directly over the tripod's screw.  This yields the best panoramas.

Collapsed and ready for transport (LG Optimus S shown for size comparison)

---

Update 10/01/12:

Here's an even simpler, lighter design.  It's not as adjustable as the one above, but it should get you "close enough" for panorama shots.

 Basically, you just eliminate the 3rd mending brace in the design above
and rotate the angle bracket by 90°, then use the third hole out to mount
it to the tripod.  Rotate the angle bracket a bit more or less to center
the lens over the pivot point of your tripod.

The photo above shows the completed simple mount on an Ikea Ordning timer for doing timelapse panoramas.  See this page for inspiration.  To build it:

1. Epoxy a 1/4-20 x 1/2" bolt onto center of the top of the timer.
2. Epoxy a 1/4-20 nut to the center bottom of the bottom of the timer.
3. Glue a piece of foam, rubber or other cushioning material onto the bottom of the timer.  It should be about 1/8" thicker than the height of the nut, so that if you mount the timer on a flat surface, the nut doesn't hit.
4. Screw a 1/4-20 nut onto the top bolt, then put on the mount and finally a 1/4-20 bolt (or wing nut, as shown above) and tighten until the unit is secure.

If your camera is heavy and you want to use a modified timer like the Ordning for timelapse panoramas, you might need to use a counterweight to level the top of the timer.  You can use a third mending brace attached to the timer bolt, sticking out in the opposite direction.  Attach a bolt with a nut or two on it as a counterweight (or tape coins, lead weights, etc.).

A simple but elegant barn door tracker

Completed barn door tracker

If you've ever tried to take a photograph of the night sky you know that it's not easy.  Even with a good tripod, any exposure longer than a few second will start to result in the stars turning into streaks - commonly called "star trails".  Don't get me wrong - star trail photos can be absolutely beautiful, but if you want to see dim objects, you've got to move the camera in sync with the earth's rotation.

Enter the "barn door tracker".  You can read all about the theory on the Wikipedia page.  I'm here to tell you about my version, which can be made from easy-to-purchase materials and will cost less than $30.00. It's not a fancy motor-driven version - in fact, it's the simplest kind, good for exposures of no more than 5-10 minutes, but if you take multiple 5-minute exposures and "stack" them in software with a program such as StarStaX, you can get some truly inspiring results.

About tracking error

This (simplest) type of barn door mount will start to show errors (in the form of star trails) due to tangent errors.  The maximum exposure time will vary with the focal length of your lens.  Here's a rough guide:

• Wide-angle lens (35mm or less) - about 15 minutes
• Normal (50-60mm lens) - about 10 minutes
• Telephoto lens (70mm or longer) - about 5 minutes

Materials list

(links may be out of date - most hardware is available at Lowes or Home Depot):

1 ball head ($13-20)
1 8" strap hinge ($6.00)
1 1-1/2" 10-32 round-head bolt  ($1.20 for 5 - includes 5 nuts) - this will give a maximum of about 20 minutes of exposure time.  If you want longer, use a longer bolt (2" or even 3"), but be aware that this type of tracker isn't designed for exposures of more than about 10 minutes, due to tangent error.
1 1/4"x3/4" flat weasher ($0.07 in the store) - that's a 3/4" diameter washer with a 1/4" diameter hole
1 1/2" 1/4-20 flat head machine bolt ($1.20 for 4, includes nuts) - needed only if ball head doesn't come with an attachment bolt
1 1/4-20 wing nut ($1.20 for 2)
1 2-part epoxy ($4.00)
1 plastic straw (free - go to McDonalds and order a drink!)
1 wooden popsicle stick (free with a nice, cold popsicle - and don't you want one right now?)
1 small piece of flat, smooth plastic (I cut one from a strawberry container, but most anything that's thin and slick should do - an old CD case lid, perhaps?)

Construction details

When making barn-door trackers, there's one critical dimension - the radius of curvature.  This is the distance between the lifting screw and the center of the hinge.  This depends on two factors - the speed  (in Revolutions Per Minute, or RPM) with which you'll be turning the screw and the number of threads per inch (TPI) of the screw - in other words, how far the camera platform rises with each turn of the screw.  Here's the formula (shamelessly stolen from this barn door website, which has an elegant motor-driven tracker that's worth a look):

Radius (in inches) = RPM / (0.004375 x TPI)

We're going to assume 1 RPM (because it's easy to do with a watch handy) and we're using a 10-32 bolt (a #10 size with 32 TPI), so the calculation becomes:

Radius = 1 / (0.004375 x 32) = 7.142 inches (or 181.5 mm)

We're in luck, because the 8" strap hinge just happens to have a hole centered about 182 mm away from the center of the hinge!

Assembly instructions

1. Using the 2-part epoxy, attach a 10-32 nut to the 3/16"x3/4" washer.  Be very careful not to get epoxy on the threads!

   

   Bolt and washer attached to strap

2. Once the washer/nut combination has dried solid, use the 2-part epoxy to attach the washer to the bottom side of the top of the strap hinge. Before it starts to set up, make sure you break out your ruler and double-check the distance between the center of the nut and the center of the hinge!   If you can, set something heavy onto the assembly to ensure a good bond and set it aside to dry overnight.
3. After the above have dried completely, cut a small piece of flat, smooth plastic to fit over the hole on the other side of the strap hinge, just below where the nut is glued when the hinge is closed.  This will ensure that the bolt head has a smooth surface to ride across.  Attach this to the hinge with glue or double-sided tape.



Drilled popsicle stick




4. Now thread the 10-32 bolt into the epoxied-on nut.  Open the hinge and thread it from the side where the nut is.  When the hinge is closed, the head of the bolt should hit the plastic piece on the other side of the strap hinge, and the threaded side should come out the top.  Thread it almost all the way in.
5. Carefully drill a 3/16" hole in the middle of the popsicle stick.  Thread 10-32 nut onto the bolt, run it down about 1/2", then put on the popsicle stick and thread another 10-32 nut on to firmly hold the popsicle stick in place.
6. Open the hinge and attach the ball mount through the middle hole in the top arm of the strap hinge using the 5/8" 1/4-20 bolt.



Sighting straw attached to strap hinge

7. Attach a 3" piece of plastic straw to use as a finder scope to the lower part of the strap hinge where it meets the hinge.  You can use tape or glue to keep it in place, but make sure it's as parallel to the hinge as possible.
8. Use a 1/4-20 wing nut to attach the strap hinge to your tripod using the center hole in the bottom arm of the strap hinge (the one directly below the ball mount).

Using your barn door tracker

To use your barn door tracker, take the completed unit to a dark sky area.  Using the finder straw, find Polaris (the north star, the star in the handle of the little dipper furthest from the bowl).  Now move the straw about 3/4 of a degree toward the top star of the bowl.  Your tracker is now pointed properly.

Now mount your camera to the tracker and screw the screw so that the two halves of the hinge are parallel to each other.  If you haven't already done so, set up your camera.  Here's some of the settings you'll want to use:

• Aperture:  open all the way
• Shutter:  the longest possible setting.  If you have one for multiple minutes, use it.  Otherwise you'll need to use the "bulb" setting and open and close it by hand.
• ISO: 800 or 1600 (you can go higher if your camera doesn't introduce too much "noise")
• Zoom:  to taste - with lower zoom settings you can shoot longer exposures before the errors inherent in the barn door tracker cause trails
• If you have a DSLR, turn off mirror lockup
• Turn off the "review" setting (showing you the image after its taken)
• If possible, set your lens to manual focus, and focus to infinity
• Turn off any image stabilization
• Remove any lens filters for maximum light transmission
• Shoot in RAW format if possible

 Once you've set up your camera, you're ready to shoot.  Point the camera to the area of sky you want to photograph and open the shutter.  Now start turning the popsicle stick at at pace to match the second hand on your watch.  If you don't want to be moving it continuously, you can  follow this guide, depending on the focal length at which you're shooting:

• With a wide-angle lens (35mm or less), you'll need to turn the stick 1/2 turn every 30 seconds
• With a normal (50-60mm lens), you'll want to turn 1/4 turn every 15 seconds
• If you use a telephoto lens (70mm or longer), you need to turn 1/12 turn every 5 seconds.

Acknowledgements

Many people have documented their builds, some have provided additional information which has been summarized above.  A shout-out is due - you can use these links to learn more information or build a mount that suits your needs better:

• Phil Harrington's "Scotch Mount"
• Gary Seronik's site.  If I build a powered mount, it'll be this one.
• Peter Kennett's build site with good supplemental details.