There was just toooo much on that first bottle story page - getting longer every day as the story unfolds. So here is some of the older stuff, with lots of nitty gritty detail for those very few of you who might be interested.
Robin's priority task over
the coming days is converting our prototype design into five reliable GPS bottles
that have a chance of survival for long periods at sea and bumping into
coastlines. We hope the finder of a GPS bottle will return it into the sea
to continue its journey: if not immediately, then soon after. It is the 45 smaller
bottles that will carry a special message and things for the finder to do.
We now have all the components including STEPP units, solar panels, timers,
batteries and the important 2 litre Frascati bottles. The design is based on that
proven by Snoopy in the sea trial, but changes include reducing the length of antenna
wires, changing the shape of the battery pack, removing parts of the solar panel
that were not required, and adding 1/2 lb of lead ballast at the back to bring
the top of the bottle clear of the water.
The metal cap will soon corrode in salt water and so this will need to be replaced
or augmented with plastic stopper, screw cap and sealing tape. GPS bottle 2 on the
left has a label on the antenna giving information to be agreed with Layla to supplement
that carried by the main label along the lower half of the bottle which can be A3 size.
The details of this big label will be provided by Layla and will be slightly different
from the label on the smaller bottles carrying the paper messages for the finder.
e.g. it will ask the finder NOT to open the GPS bottle and may suggest the finder look
for one of those other smaller bottles which carry a special message.
Our DRIFT model, described below, is also alerting us to the importance of launching
the bottles so that they spread out rather than stay together and all do exactly the same thing.
There are several good reasons for this including wanting to increase the chances
that at least some have a fighting chance to make it towards the Chatham Islands, and to make the tracks
more interesting.
Layla has explained that there will be 50 bottles in total: 45 small bottles holding the notes for the bottle finders, and 5 "tracked bottles" to help the software calculate where all the bottles are now and predict where they might go next.
This choice of bottle launch pattern will be determined by very practical issues such as over what period of time can we launch the bottles due to constraints such as how many boat trips can the project afford (only one planned), how long children will want to stay at sea before they get sick (2 hours ?), and how fast our little fishing boat can sail. These things are critically effected by the weather, of course. No doubt we will seek to make good use of the tide. e.g. in the DRIFT model run below, and picture on the left, the launch pattern was a diamond shape. The boat started south east (white bottles), then north east (blue), and back north west (green) then south west (yellow then purple), dropping bottles all the way. By the time it returned to where it dropped the first (white) bottle, the tide has carried these bottles far south. On the right you can see the dramatic effect delay of launch by a day or two can have. This is not surprising since the wind has the most long term effect and the wind can change a lot within a day or two, if not hours.
Final choice of launch pattern should be chosen to make best use of wind and tide.
Very early in the project it seemed a good idea to model, however crudely, the
drift of each bottle due to the tidal currents and the wind (and waves).
The fact that we will be tracking several bottles very accurately, hour by hour,
means that it should be possible to adjust the "fiddle factors" in our model,
included with the GPS Software, to make the model accurate and track ALL the bottles
- if we record the exact time and position of each bottle launching.
On the right is an animated GIF file produced using the excellent "GIF Construction set" software from www.mindworkshop.com and 190 BMP images from one of the latest experimental versions of our DRIFT model, which is intended to provide "artistic tools" for Laylas' exclusive use. You can look at the larger size version here. In this particular run, the bottles hit the French coast. They hung around on the beach until the wind shifted before resuming their journey more widely seperated.
The drift/wind factor is one of the
most important of these "fiddle factors". It is the speed and direction of bottle drift due to the wind
and resulting waves.
We are using 3% (0.03) and in the same direction of the wind - but this will
depend on things like how low the bottle is in the water. This is where we have started to
do some real tests, on large inland patches of water on a windy days, measuring
exactly how far (and therefore how fast) bottles move in a given wind speed.
"Bottle Dog" on the left, and his radio controlled boat, have been recruited
for the deployment and recovery of GPS bottles at places like local reservoirs.
Tests on Robins pond showed he can happily tow a bottle tied on with string,
so we now have a suitable matching wire hoop and hook "docking system".
Strange as it may seem, the experts at places like the Met Office - to whom Robin has spoken, and is very grateful - say that the drift may be at an angle to the wind due to the Coreolis effect. The more tests we do now the better: a realistic model could be used now to make continguency plans for where the bottles are launched, according to the weather.
For those interested in the DRIFT model detail, here on the right is the PC screen
of version 1b of the model simulating five bottles. The big white arrow
over the red trails is the wind direction, controlled by the values near it.
We can put these wind
directions and speeds in for the next 7 days after visiting
Weather Online for Dover but right now we are simply trying all sorts of
wind directions and speeds, to get a feel of what we might expect.
Below the wind controls are those used to set up the times and locations
where the bottles are launched.
The smaller blue arrows show the tidal current, which oscillates back and forth
with the tide, on a 12 hour 24.5 minute cycle. We are using a SIN function, with
parameters of maximum speed and direction, interpolated from several points
taken from Tidal Stream Atlases.
Robin could use your help: he needs the simple equation ("A" level maths, "linear
interpolation" ???) which
provides an "averaged" value (of direction or speed) based on a list of values
in X,Y (lat/lon) space, which might perform better than the equation he
is using now. If you can help Robin - please contact
him
via the contact page.
The other area where Robin would like practical help is in tests to
measure bottle drift due to wind.
The predicted tracks of five bottles launched
from near Ramsgate can be seen. The tracks are green where we are reasonably confident
we will receive messages from the bottle, because they are within 5 miles of those
mobile 'phone masts (green squares) along the coast. After 5 miles the trails go
yellow, and then red outside 10 miles, since we are pretty sure they will be
out of range. But we can easily adjust these numbers if we have better information
- but do not forget that we are not talking about a mobile 'phone being used stood
on the deck of a ferry, tens of feet above the waves - our bottle system is only just
an inch or two above the waterline ! Small circles can be added along the trail to show where
the bottles might report position every hour.
We hope to make the model sufficiently accurate that it will be a useful tool
in planning details of bottle launch details, and then, as we adjust it from
incoming GPS bottle reports, it will tell us reliably where ALL the bottles are.
Also, fed with the 7 days wind forecast, we might have a good idea where the
bottles might be in the next few days, including where they might wash up on a beach.
But remember, it will only be a model, and no substitute for "real life" - which
always holds surprises up its sleeve :-)
The sea trials gave excellent results using O2, Orange and T-Mobile, and we are
now talking to the mobile 'phone network providers, hoping some will sponsor
air time for one or more bottles.
We must now decide what SIM cards to put in bottles since this will have a major
impact on the running cost of this project - particularly if these bottles continue
their journey for many months or years, reporting their position every hour.
At 10p per report this ammounts to over £2 per day per bottle, perhaps more
off some countries. We do not expect any cost when far from land, of course.
We intend to use SIM cards that also have a data line, which we can use to
"dial into" the STEPP unit and "pull out" the recorded GPS history for bottles
that drift out of GSM coverage, such as into the North Sea or Atlantic Ocean:
maybe even the Pacific - see the
Press Release
from Turner Contemporary below.
Note from Robin on Tuesday 31st March: I just spoke by 'phone with Mark Sullivan, Sales Manager
of Timeguard Ltd in London on
www.timeguard.com and they have kindly
offered to sponsor our project with the free supply of the ST77 product.
on Friday 9th April: Robin is very grateful to David De la Haye, who has designed
and built a digital timer in the same few days that we discovered and exploited the ST77
product. The reliability of these timers are critical to the bottle system, and so
we are testing Davids' prototype, seen here drawing just 0.1 mA, and sat on Daves' excellent documentation.
We will do these tests in parallel with our
other tests and use of the ST77. This will be our "plan B" if we run into problems,
or wish to add some "bells and whistles" in the future.
On the right you can see the components we are now experimenting with
to increase the duration from a few days to what we hope may be months
or maybe even more. The idea is to introduce an electronic timer that
switches the STEPP on for the required few minutes, every hour or few
hours, to make its position report. The timer only takes about 1mA from
the battery, compared with between 50 and 100mA when the STEPP is on.
The result is a much lower average current drain on whatever battery is used.
This approach may even permit use of one or more solar panels - if we are
lucky they might keep the battery topped up forever ! We are using the
standard Maplin VT27E timer kit (£5 ?), but with the addition of two 10,000 uF
capacitors to increase the adjustable time delay to one or two hours,
and the switch on period to a few minutes. We are also using a reed relay
able to operate on 6v or 9v since that in the kit requires 12v.
The flasher unit is used so we can see when the timer switches on.
We have not yet settled on the optimum battery pack, but we are using
the "silly little" 9v PP3 seen here so that we can see how well the
approach works.
We have started "duration tests" such as leaving a complete bottle system running outside the
house, including on frosty nights (started 1800 on 2nd March).
At first we thought this showed that a single 6v lantern battery may not suitable.
However, later in the day we found this particular STEPP had been put into
a power saving mode, and this is probably the cause of the problem.
It seemed
the type of battery we tested gives substantially more than the nominal 6v in its first
few hours of use (Robin just measured over 8v on a new one). After an overnight
test (outside in low temperatures) the STEPP began to "misbehave" (e.g. failing
to reply, or reply without an updated GPS fix). Closer examination showed this
battery still delivering 6.3v into the STEPP (Note the official lowest operating
supply for the STEPP is 10v, so we should not be too surprised). Bringing the unit
inside into the warm seems to fix the problem. i.e. it starts working again.
We have added a single 1.5v A sized cell to
the 6v lantern battery, bringing supply to 8.1v (at 1030 on 3rd). Unit was
put in the 'fridge for a few minutes before taking outside.
Duration tests
continue with a second STEPP on the same single 6v lantern battery (restarted 0830 Thursday)
and the first STEPP will be used for power saving mode experiments.
Tests continue to see if this is the low temperatures making the
supply voltage more critical, and reviewing what batteries should be used.
But now to details of construction for those "Blue Peter" types among you:
I've used a 2 litre plastic lemonade (or Coke) bottle, and another identical one
to make things like the seal explained on the right here. Use a sharp craft knife
to cut the bottle above what will be the waterline, but below where it starts to
taper. Cut a piece from a spare (2nd) bottle, just above where it starts to taper
and an inch or two below - to give a good overlap between the two halves of
bottle #1. Apply gentle heat (a hair dryer?), some inches way from the cut top
of bottle #1 lower part, to make it shrink just a fraction. This should enable
you to push the cylinder from bottle #2 OVER it. You should also be able
to push the TOP of bottle #1 OVER this seal made from bottle #2. After checking
you've not made mistakes, glue the seal to the lower part of bottle #1 using
sandpaper to roughen mating surfaces then "LOCTITE soft plastic adhesive" glue.
Note that we've had "mixed results" with this and other glues on various plastic
bottles. Any seals will probable need a "belts and braces" approach, such as
addition sealing inside and out with water proof adhesive tape. e.g. parcel tape.
The first prototype above has the components such as battery, STEPP unit, ballast, etc.,
mounted within an inner bottle, which is itself expected to float. This was constructed
from a split cylinder from another bottle, removing top and bottom. The side and bottom was
sealed roughly with parcel tape, before pressing in ballast and strengthening using
"polymorph" low melting point plastic purchased from Maplins. The intention is to
produce a complete inner bottle, holding all the bits, capable of being easily
fitted within the outer standard 2 litre plastic bottle. Suitable artwork would
be placed between the two bottle surfaces with things like instructions for the
finder in several languages including English, French, Dutch and Danish (emails
have been sent to a few overseas friends for this). This special artwork for the bottle
labels is where any logos of sponsors, such as soft drink makers, would appear.
I'll put up more details here as work on the prototype bottle proceeds.
These will include any extra ballast needed to keep the bottle upright, but not sink.
This will obviously depend on what we put inside the bottle. We want it to ride as
high as possible out of the water, but to remain upright in all but the roughest conditions.
For a stable bottle it looks like we need it to displace about 3 lbs or 1.7 kg of water.
However, later tests may reveal that it is better to have less weight and let
the bottle ride further out of the water, at an angle.
Note from Robin on 11 March: construction of later 2 litre size bottles showed we
need not use a seal from a second bottle as illustrated above. Heating the rim of the lower half
carefully to make it shrink, provides a tight push fit of the top half over the
lower half. However, note also that a horizontal bottle puts the joint below
the waterline and makes the waterproofing much
more critical - lots of waterproof stickytape ? :-)
Now some numbers to do with weight: the battery will be the most signficant
choice in our getting weeks rather than hours of bottle tracking. This, other than ballast, is by
far the biggest and heaviest item and will be limited not so much by cost, as the size
of bottle we use. So here are some rough weights:
Note that our first prototype weighs 1700 gm, including one 6v lantern
battery and over 500 gm of ballast
to keep the bottle upright.
We have been testing the STEPP running at 6v and it seems OK - more tests needed.
We had been thinking of rechargeable 12v 7000mAH packs at £70 from overlander.co.uk
but now see we could use common lantern batteries to give more capacity
at lower cost. A 6v 11000mAH lantern battery supplying a STEPP drawing 55mA should
last about 11000/55 = 200 hours, or over 8 days. Two batteries connected in parallel
(+ to +, - to -) would give 22000mAH or 16 days (yes I chose 55mAH to make the
calculation easier :-). Maybe we can extend this further by some combination
of solar cells (see below) and/or timer circuit to switch the system on an off
(it only need be on for a few minutes each hour, when it reports its position).
So right now we are assuming a 2 litre plastic lemonade bottle carrying
the Falcom STEPP, a 6v 11000mAH lantern battery, and ballast.
We will need to review these
weights if we choose a stronger glass bottle or change the bits used.
Now some rough costs of "the bits" - remember that these do not include the
time, travel expenses or profit of anyone putting each package together. But
they should help to indicate how many bottles we might afford to track accurately,
and where the major costs lie:
i.e. maybe close to £300 per bottle + £80 air time. Air time could be a significant cost. Each text from the bottle includes lat/lon
position, speed, course, altitude (tells us when the bottle is thrown off the boat into the sea ?),
time (GMT) and date. It is in the same standard NMEA format as the data from a GPS.
That's the good news: the bad news is that each report may cost 10p, or maybe
nearer 5p if the receiving phone is on the same network. Any phone asking for
a report will also be charged a similar ammount for each request. However, the
STEPP unit permits us to send a command telling the bottle to automatically report every
so many seconds. e.g. 900 is every 15 minutes. If we use this figure, of 4 reports
per hour, and we hope for 2 weeks of operation, then the air time cost might be
4x350x5p=£70 - this is where we need and expect to reduce cost. But remember:
we will need to send quite a few messages while we are testing, both at home/office
and during those sea trials. It is just possible that a solar panel might give useful
power in daylight hours, even if within the bottle and not getting direct sunlight.
Another "flasher" for those who can use a soldering iron is a little kit
from Maplin called "DUAL WHITE LED STROBOSCOPE" ( MK147 ) at about £7 and
taking perhaps 1/2 hour to put together. It runs for a few hours off a small 9v PP3,
but could last much longer running off a bigger battery, or only switched on occasionally. Right now we are experimenting with a Seiko
electronic clock mechanism switching on the flasher(s) for a minute every 1/4 hour.
Each bottle might have its clock a few minutes slow - so we might identify it by
flash pattern and when it appears. The most practical aspect of the clock is being
able to predict when a particular bottle with begin flashing, so we might locate
it ourselves, without attracting too much attention from others at sea.
So how can we use this information ? Well, if that cycle flasher above is pulling an
average of 20mA, and we connect it to a 2000mAH battery, it should run for 2000/20
= 100 hours, or nearly 5 days. If we switch it on for a few minutes when we need it,
it will last for years.
Unfortunately the sizes of bottle we are considering will not support a 12v car battery,
and so we will have to make do with smaller, less powerful batteries :-)
You need not bother about these details if the tracking is being done
automatically on a PC running GPSS, the GPS Software. However, the fact
that we only need any mobile 'phone to do it means that real trials,
including at sea, can be done very simply.
Asking the STEPP to give you a GPS report: send it the text "&REQ POS"
What reply does the STEPP return ? You should soon get a text message
back (if the STEPP is switched on, and in a suitable position for its GPS
and 'phone to work) holding two NMEA messages, $GPGGA then $GPRMC.
You may recognize things like lat/lon above, but this may help:
this was the reply I got at 09:46 and 41 seconds, on 18 Freb 2004,
from the STEPP here. The Lat/Lon was 51 degrees 23.8117 minutes North,
0 degrees 39.6179 minutes West. Lat/Lon is in WGS84, not the OSGB
you will see printed around the edge of Ordnance Survey maps.
So any mobile phone, and knowledge of the bottle 'phone number,
enables you to find out the position of the bottle in lat/lon
which you could then look up on a suitable map. However, if you
also have a handheld GPS such as the Garmin etrex,
you could type this lat/lon into the GPS then ask it to guide
you to the position. The GPS will then display the updated distance
and direction to the position, to within a few yards. This could
be invaluable for testing on land or at sea. But for sea I also
reccomend having the bottle tethered on a long piece of string ;-)
The lat/lon can be abbreviated for typing into GPSS running on a PC
which does not have a GPS or GSM modem as:
For a PC equipped
with a GSM modem (or 'phone that includes a modem), a program
called
SMSH is used to poll the bottles and take
their incoming positions and put them on the displayed map.
The picture below shows SMSH (which is normally hidden, and only
displayed when testing) taking the incoming position report from
the STEPP unit. The unit was on my front lawn, marked by the
square icon, and the reported position, marked by the circular icon,
was 15 metres in error - which rapidly changed to only 3 metres when
I realised I'd put the STEPP antenna upside down on the grass - it
was amazing that it had worked at all :-)
glass or plastic bottles ? clear 2 litre wine bottles ?
I understand that Layla has now chosen the type of bottle to be used for the
majority (maybe 40?) that are not fitted with GPS tracking - the smaller glass 0.75 litre
Lorina lemonade bottle seen on the left.
We now have a simple, proven electronic design for the five tracked bottles, capable of reliable operation within
a moderately sized clear bottle, and now we must now build the actual tracked bottles
to be launched in mid May. These must be constructed to look good and survive
over what may be many months or years at sea. Plastic was convenient to work with
for the early prototypes,
but glass might better survive the occasional brush with a rocky coastline, or
a few weeks erosion by sand on a deserted beach.
Glass also seems a more
"artistic" choice of material. We've discovered how to break the bottle
where we need to from a search on the net for "bottle cutting" and finding the
craft-ideas.co.uk page.
in short: 1) scratch with a glass cutter. 2) heat with a candle flame. 3) pour on
cold water 4) repeat 2 and 3 until it breaks. I've been looking for a suitable clear
glass bottle (1.5, 1.7 or 2 litre ?) to see if this is our preferred solution.
On April 3rd I found what I thought might be a suitable bottle: Budgeons "SOAVE DRY 2003",
1.5 litre clear glass bottle at only £4.99 - and you do not need to throw away the
contents :-) This bottle has
a metal screw top with soft plastic inner seal, and it seems probable this bottle
is used for other drinks. On Monday much of the work was done of squeezing the
electronics into the bottle - and it WAS a squeeze. It looks as if we need a bottle
of similar shape but slightly larger. However, shaving the odd millimetre off the
sides of the solar cell, and lower corners of the timer, just about gets it in. The final versions cannot afford
to be a tight fit, or different expansion rates might cause the bottle to break.
If this bottle is used, then the label inside needs to be no larger than 21 cm x 17 cm.
The timer at the front can be reached by a suitably bent stick. Right now the 20
available on/off programs are set to every hour, other than the small hours
of the morning. i.e. 2300, midnight, 0200, 0500, 0700 then every hour again.
I now understand that the final bottles will not include flashing lights or mascots,
but our new glass prototype has Bart Simpson sat in the back with his hand held GPS :-)
Note from Robin on 18 April: the 1.5 litre sized glass prototype seen above sits a little too low
in the water (almost exactly 50% below - including the top) compared with our plastic one which sits
a little higher (no weight of glass).
Latest view is that either we must find
a larger suitable 1.7 or 2 litre clear glass bottle, or revert to our original
plastic bottle design. This is no big problem since our electronic package is
the same, fitting in any of these bottles. We are also doing drift/wind tests on
a range of bottles carrying the same 950 gm of electronics worth of ballast.
Here on the left is the only large clear bottle I've found:
the 2 litre scrumpy bottle just purchased from Waitrose. It was not too difficult
to cut off one side, above the waterline - as seen here, testing in the rain.
Note that the handle has weight, so must hang down. I would prefer a more elegant
wine bottle: any ideas ?
Note added on 25 April: maybe we've found it: the 2 litre Frascati bottle seen earlier
and here on the upper right with a bunch of friends :-)
Robin would like to say thankyou to the "Mezza Luna", his local Italian restaurant,
who kindly donated three boxes of empty 2 litre bottles. They were green, and therefore
not suitable to take the solar panel, but they have been invaluable for our tests on Bray Lake
which need to continue. I've now tested our solar package in this 2 litre bottle - that's
Snoopy sailing it around our pond - and I've now started some temperature testing.
That "greenhouse effect" inside the bottle raises the temperature from 21c outside
to over 40c inside the bottle - electronics can only stand so much ! Hopefully
this will not be a problem: the water around the bottle should help keep it as cool as Snoopy :-)
choice of SIM card and GSM service provider
prototypes used in sea trials - Tweetypie and Snoopy ! :-)
On the left you see Tweetypie, our mascot in the bottle prepared by Robin, holding
12v of two 6v lantern batteries and Laylas' STEPP #1. This bottle is a "stretched" lemonade
bottle, 48 cm high instead of the usual 35cm, made from two plastic bottles, one cut high
and the other low. The bottom holds 750 gm of ballast to keep the bottle upright and the
combined GPS/GSM antenna about 5cm above the waterline. On the right you can see the
bottle being tested in Robins' garden pond.
The two bottle halves overlap about 3 cm, are smeared with Geocel flexible aquarium
sealant, then bound by two types of outdoor sellotape - we hope it don't leak !
The ON/OFF switch can be accessed by a stiff wire from the top of the bottle.
Layla may also have time to
make a bottle, similar to our first prototype, holding a single 6v lantern battery
- it will be interesting to see if it performs as well as the 12v version.
We expect any sea trial this week to be based on the first prototype already tested
over several days of continuous running: i.e. one or two 6v lantern batteries switched
permanently on, and not using the electronic timers. This will ensure that we are
in continuous GSM contact with the bottle, so that we can be sure that any problems
are due to the location at sea rather than components, such as electronic timers, that are still being tested.
Our latest prototype is a 2 litre plastic bottle, floating horizontally, holding
the STEPP unit, with its combined GPS/GSM antenna, a 12v 1400mAH rechargeable NiMH
battery pack, a solar panel, and two electronic timer units. The timers arrange
that 55 minutes of each hour are spent with the STEPP switched off, giving the solar
panel the opportunity (during daylight hours) to re-charge the battery. Every hour
the timer switches on the STEPP, and waits two minutes to give time for the GPS
to start tracking and registration with the GSM network to be established.
A text message is then sent to the mobile 'phone, providing identification
of the bottle, and the GPS data including latitude-longitude position, speed,
course, date and time of fix in Universal Time (GMT). A small bright flashing light
is also switched on for these few minutes each hour, to assist eventual bottle recovery,
give us confidence that the system is working, and permit investigation of options
such as optical tracking of bottles from the shore - at dusk or hours of darkness.
Switches accessable from the top of the bottle will support us switching the bottle
system from "continuous mode" (for initial sea trials) to "timer mode" (for longer
duration). Yes, that is Snoopy, navigating the way with his handheld GPS, and
stood in the space reserved for a small paper letter.
Use of digital timers
The section below on timers was written some days ago, and we experienced
difficulty in getting these modified timers to work reliably. Problems included
mechanical relays welding closed or not working at all, and timing not being
reliable after adding much larger capacitors. Recently we had what
may be a small breakthough: use of digital timers from mains products such
as these on the left. The first type we tried with success was the "7 day Digital
Timer L28AC" from Maplins at £10 - seen on the left in both pictures here.
The timer runs off its own 1.2 volt cell - which was replaced by a much bigger
one. Most of the mechanism including mains plugs and sockets and higher voltage
circuitry, was thrown away. The switched output (rising from 0v to 1.2v) is used
via suitable transistors to switch our 6v, 9.6v or 12v supply through to the STEPP
and a flasher. These timers seem to be very accurate and reliable - tests continue.
The main limitation of the L28AC is the fact that it can only be programmed
(via buttons on the front) to switch on and off up to 8 times a day.
e.g. every 3 hours, or at whatever time is required (less often at night?).
However, we found the "SURE time, 24 HR/7 DAY ELECTRONIC TIMESWITCH model ST77" was
similarly priced, had a similar internal design, and permits 20 on/off events
per day.
on Friday 2nd April: a dozen ST77 timers arrived from Timeguard today. Measured
the tiny current drawn from the 1400 mAH battery at less than 2 micro Amps - which
means over 80 years ! But I expect we will still trickle charge it from the
solar panel main supply - just to be sure :-) Many Thanks Timeguard - these will
be put to good use in the coming days.
Timer to increase life 100x ?
this is old stuff - to show you where we started...
first prototype ...
The first prototype, seen here floating on the right, is
based on a 2 litre plastic bottle (see construction details below), holding a
Falcom STEPP unit with its combined GPS/GSM antenna, and one 6v lantern battery.
Ballast, presently consisting of over 500gm of copper coins,
keeps the bottle upright and with about 30% above the waterline.
We've had "the bits" for this prototype of what might go in each bottle for
some days now,
and have tested these connected together (see "STEPP Testing Details" below).
Layla has ordered a further two STEPP units, keeping some of her tight budget
back for other alternatives as we identify and test them. We are now cofident that
her budget will permit at least six bottles to be tracked with GPS/GSM, and
this may be increased significantly if we get any further sponsorship.
Right now we expect this prototype to provide continuous tracking for 8 days,
at a rate limited only by our spend on text messages.
In the coming days we expect to add a few small but important items like
an on/off switch and a flashing light (timed to come on for a minute every 1/4 hour) to aid recovery after
the sea trial, and also to investigate
if the light can be seen from suitable viewpoints on land. It is possible we
might also squeeze a second battery into the bottle, increasing the 8 days to 16.
We will also be experimenting with power saving options, to further increase lifetime.
What you see on the left is simply the components, with coin ballast, in the bottle
being tested for balance in water. These compenents will be mounted within an
inner, waterproof container. Laminated paper artwork can be placed
inside the outer bottle, hiding the components and providing suitable information
(in English, French, Dutch, Danish and Norwegian ?) for any lucky finder.
However, we do not plan to leave this first prototype more than a few days
in the sea, and hope to recover it within a few days.
First sea trials might start within days: we need to checkout some basics:
such as how well the GPS and mobile 'phone work when inside a bottle and only just
above the waterline - and bobbing about like crazy ! :-) Lots of changes are
expected, including the bottles themselves and what bits we put inside them.
On the right, with a plastic coke bottle, is a Falcom STEPP with its combined
GPS/GSM antenna on the left, and a rechargable 2000mAH NiCad battery pack.
You can also see the "SIM card card" I got from Tescos. This combination works,
providing tracking from any mobile 'phone (see testing section below) or GPSS PC connected
to a GSM modem - as planned for the Exhibition. Testing does not even require
a PC - just a mobile 'phone. A handheld GPS such as the Garmin etrex can be
used to guide you to within yards of the last position obtained over the 'phone
- could be useful for our sea trials - we do not want to lose the bottle ! :-)
We estimate that a 2000mAH pack could keep the system working for 40 hours,
nearly 2 days, based on the STEPP drawing 50mA. However, we hope to improve
on this by reducing the STEPP current to perhaps nearer 20mA and using a bigger
14000mAH battery. So it is possible we might get nearer 700 hours or over 4 weeks.
latest tests - horizontal bottles ?
The first bottle prototype ran for the equivalent of over 4 days continuously, which matches
the 4.5 days calculated from 100mA consumption from a 11,000 mAH 6v lantern battery.
A timer such as that above should increase this to nearer 5 or 6 weeks.
We are
now testing power saving features such as switching the STEPP
unit on for only a few minutes each hour, and the use of solar cells.
On the left you see a second prototype: a 3 litre bottle holding a solar panel and
the electronic switch to only power the STEPP and a flasher for 5 minutes in every hour;
a small 9v 170mAH battery to confirm that solar panel can charge faster than the system discharges.
All mounted on a "plant solar turntable" so that the solar panel inside the bottle gets
a typical dosage of sunlight each day.
If we are very lucky, this system will prove the feasibility
of solar panels giving a bottle unlimited operational life. The small 170mA battery would
be replaced by a much larger capacity battery to avoid temporary loss of operation
late at night or during prelonged periods of particularly gloomy weather.
On the right you see the 3 litre bottle balanced to float horizontally to get more sunlight
onto the solar cell.
We have now managed to squeeze all this into the 2 litre size bottle,
with just a 7.2v 2000mAH NiCad pack providing power and sufficient ballast for the bottle
to float, keeping the solar panel up - as here below.
We are moving towards bottles floating horizontal and with solar power a "definate maybe".
No extra ballast seems to be needed, other than ensuring the battery is correctly positioned.
Note that use of a solar panel means our label can only occupy half the bottle. i.e. A3 not A4 in size.
Use of the timer gives a massive increase in bottle life, but it does mean we may need
to make use of the STEPP "alarm" facility, to initiate the position report after power
is switched on, since we probably cannot rely simply on the GSM system delivering
a request in those few minutes the STEPP is switched on. However, there may be many
ways of getting around this problem.
The words
below were put up a few days earlier...
The Bottle
You may think this question of the bottle trivial - compared with the
more obvious technical details of what we put inside the bottle. But don't be
fooled into complacency - poor attention to this detail could result in the
bottle sinking, with all its' expensive content, within a few days at sea.
More subtle points, beyond ingress of water, will be it floating upright, with
the GPS and GSM antenna above the waterline, and it not building up a coat of
salt or moisture that may attenuate the signals - maybe we will spray the outside
with something ? Other important points will be strength, including avoiding
cracks if dropped onto the deck before launch. We may also have to worry about
unforseen events such as being pecked by hungry sea gulls ? :-)
weights and measures ...
Batteries and bottle should chosen so that the majority of the weight is at
the bottom, so the bottle floats upright - giving less problem with keeping
seals water-tight and the GPS/GSM antenna above the waterline. Unfortunately
two 6v lantern batteries, one above the other, make a plastic coke bottle top-heavy.
One lantern battery (see right) can be used with suitable lead ballast at the bottom of the bottle.
Component Costs
Flashing Lights ?
This pair of "Super bright cycle LED" cost me £15 from Halfords in Bracknell.
One is red, the other green, and each holds two pen cell batteries, giving 3v.
A button switches the light on, through a choice of flashing patterns, to off again.
This might be a low weight and cost option for all the bottles, or just for those
carrying the STEPP phone or similar device. One option is for the light to be
switched on with a 'phone call to the STEPP when we want it to flash.
e.g. for a few minutes after the hour in the evening, when observors on land
can be looking out to sea for it. It may also be of value when recovering a lost
bottle being tested in first sea trials. We have yet to see from how far we
can see these lights, but I would be surprised if it is not several miles
at dusk or night-time. Each light seems to draw an average of between 20 and 50mA,
depending on what flash pattern is selected.
Solar Power ?
Products like this "Variable voltage charger panel", code RR53H, at £13 from Maplin.co.uk
might be used (if Layla doesn't mind a wierd looking solar panel
on a stick over the bottle) to allow tracking of the bottles (or those
we fit this option to) for an unlimited time - maybe months or even years.
It is possible we might fit one or two INSIDE the bottle, and they might
provide enough power from the indirect sunlight received.
Described on the box as "2,6,9 and 12 volt solar panel with AA and 9 volt battery charger",
I'm using it for some quick tests to see if such a product might be of use to extend
battery life significantly. If we are lucky it might give unlimited life to the bottles,
but it is also possible we would do better spending money on a bigger battery :-)
However, a first, very simple test outside on a dull day, showed this solar panel
charging 10mA into a 12v battery, so it is well worth further consideration.
what's all this mAH stuff ?
For the less technical reader, here are some basic facts of importance when
we are choosing batteries and what bits to use in each bottle. Battery capacity,
in terms of what current it can supply for how long, is measured in ampere-hours (AH)
or milliamp-hours (mAH).
1000mAH = 1AH. Current drawn by something connected to the battery is measured in Amps (A)
or milliamps (mA).
So a big 12 volt car battery might supply 40AH (or 40,000 mAH). A 6v lantern
battery (rightmost of three on right) might give 11,000mAH and the small
AA sized pen cell batteries (leftmost) might supply only 200mAH. The biggest "A" size cells
like you might find in your torch (middle) might provide nearer 2000mAH or even more. Different battery types
will vary a lot, so these are just rough figures.
GPS 'phones such as those from Benefon and Thuraya
How about the idea of a mobile 'phone inside the bottle, regulary reporting its' position,
and available for immediate voice use by whoever finds and breaks open the bottle ?
Something similar was done by Coca Cola in Australia last year - but they simply
hid the 'phone in a specially constructed bottle - and it was switched off.
For this they used a Benefon GPS 'phone - one of the first GPS 'phones
put on the market a few years back.
If you visit the
Thuraya
page you will see me testing the Thuraya GPS 'phone made
by Ascom and Hughes Network Systems. This is more than just a GPS 'phone using the
GSM network since it also includes a Thuraya satellite tranceiver and antenna.
So if you are somewhere like the middle of the north sea, outside GSM coverage,
you can still make 'phone calls or send and receive SMS messages. Iridium,
operated by Boeing Aerospace is another example of a satellite 'phone system.
Right now we are interested in any suitable GPS 'phone products which can continue
to operate for weeks rather than days (e.g. by only switching on for a few minutes
each day as is possible with the Benefon Track One). I expect to be contacting all
the obvious mobile 'phone makers including Nokia and Ericsson.
STEPP Testing Details
Here are a few details for those like Layla who may want to start some real
tests with our prototype now. They will need to be given the 'phone number of
the SIM card inside the STEPP unit, and Robin will need to ensure the unit
is powered on when the tests are done.
(if you sent "&REQ POS 15" it would then send you a report every 15 minutes
- but this is NOT reccomended until we are using the computer for this.
Sending "&REQ POS 0" cancels any request, by anyone, for a regular report)
e.g.
GPGGA,094641.000,5123.8117,N,00039.6179,W,1,03,2.8,0.0,M,,,,0000*13
GPRMC,094641.000,A,5123.8117,N,00039.6179,W,0.00,,180204,,*0
`512381n0003961w
- followed by the Enter key then V for Visit. See
TIPS page for details.
Don't worry about the details of using this software, since Robin will probably do it for you. If you do get into GPSS use, you will need to have a Laptop PC and GPS with cable (such as the Garmin etrex) and start with step 1 followed by step 2 on the DOWNLOAD page. It is always best to take it in simple steps.
Here is a typical bottle label, for illustration only. It probably has little similarity with the labels Layla will design for the actual project. However, it does serve as a prototype to see what we might show to any "bottle finder", with important information such as assuring them that the bottle is harmless. Full contact details of whoever is taking responsability may not be such a bad idea.
An A4 sheet of paper will wrap nicely around the inner bottle and can be inside the outer bottle, protected from the sea. Further protection is provided if the paper label is laminated. The lower part might include space to acknowledge sponsorship, such as those who decide to "sponsor a bottle" and pay for the cost of the components within it. Typical sponsors might include soft drink manufacturers who already distribute their drinks in these 2 litre (or 3 litre) bottles. These include Coca Cola, Pepsi Cola, 7-Up, Sprite, Fanta, Schwepps, Dr Pepper, Virgin, R Whites, Tizer, Tango, Deeside, Buxton, Sainsbury and Tesco. Other sponsors we expect to contact include the mobile 'phone product and network players.
