Tracker

On Mon, 12 Oct 2015 10:20:05 +0100, Alan Adams declaimed the following:

I suspect the radios needed for GPS receive and SMS transmit will be the real power drain (especially the transmit -- though keeping a GPS module running can be a problem; if you don't keep it running you're going to have start-up time every 30 minutes as the module re-fixes on the satellites*). SMS implies using the cell-phone network, and those also take a few minutes to fully negotiate a connection from a warm start.

But I'd be tempted to agree that something like the R-PI is less likely to be useful. The key feature I'd be looking for is a processor with a hibernate mode with fast wake up, and auxiliary timing module that can wake it up on some known period (every few seconds, perhaps -- long enough to update a counter until the 30 minutes has gone buy, then run code to wake up the GPS, capture a "stable" position, format/send via cell-phone system, then shut down the radios and repeat). A $13 TIVA TM4C123 Launchpad** perhaps (the Byonics units appear to use PIC chips). I don't recall if Arduino has the hibernate capability. The TIVA 123 demo program includes hibernation mode.

• First time start-up can take up to 12 minutes to capture the satellite ephemeris data [especially on the older 8-channel sequential receivers,

-- possibly useful given the smaller Launchpad has 256kB, and the larger

I just weighed my Pi, a 512MB model B mounted in a minimal 'case' (two Pi- sized 3mm perspex plates with 4 metal pillars acting as spacers). This weighs 107.3g. What does your GPS receiver weigh? If it was me, I'd be looking at the USB-connected 'hockey puck' type, but have no idea of its weight or power consumption.

Subtracting the weights of these from 500g will at least give you a ballpark weight for a battery which you can use to check out both 2 cell model aircraft Li-poly packs and/or the so-called 'portable mobile chargers', ie a case containing a Li-poly pack, v.reg and case with USB connector.

Have you talked to any of the HAB (high altitude balloon) enthusiasts? They know a lot about lightweight tracking systems and regularly fly RaspberryPi model As.

When you sat 'tracker', is this just a recorder, or does it also include a transmitter?

If it is just a recorder, I suggest you take a look at the position recorders used by glider pilots such as the EW Model D (these are now obsolete, so should be cheap on eBay), EW Microrecorder or LXnav's Nano. These weigh well under 100g and typically run for 12-24 hours on internal batteries. All (except the model D) accept external power for longer operating time and all have recording capacities of well over 5 days.

What do you want to track? What are your weatherproofing and temperature insulation requirements?

Would something built round a PICAXE chip do the job? That would certainly be a lot lighter and (probably) use quite a bit less power.

I've seen some discussion here about that topic.

It needs to transmit the position, as a mobile phone text message. It can be pure GPS coordinated, as there's an i-Phone app to convert those to UK Ordnance Survey grid refs.

There are commercially available pet trackers which come close, but most seem to be US based and I'm not sure whether those would work with the UK phone network. The one UK model I've found has a lot too many features, two-way voice call for instance, and puts the cost over

I'm looking at this for locating Duke of Edinburgh's award expedition groups. They need to carry it, hence the weight limit, and the Gold expedition runs for 4 days, hence the battery life limit. (It would be possible to exchange batteries each night if that proves essential.) The rate of travel is around 3 to 4 km per hour, so a position every

The whole thing needs to be fairly rugged, and moderately waterproof. It can be in a sealed plastic bag, and doesn't need to be accessed during the expedition.

Extra features which shouldn't add much to the complexity or power use could be a panic button, which sends an immediate update together with the word "emergency" for instance, and the ability to send to a list of maybe 3 phones. That would both allow for increased chance of receiving the message if the phones were on different networks or in different locations, and allow multiple supervisors to track all the groups.

So it would not need to run continuously for five 24 hour days - that cuts your battery requirement about in half. I'd also suggest looking at a small solar panel (which could be attached outside someone's backpack) to either power directly or to recharge one of two battery sets while the other is in use.

How high the thing being tracked will fly and where in the world it will do its flying, there may be a problem with cell-phone coverage. For instance, in the flatter parts of the UK the phone base stations have distinctly pancake-like coverage patterns. I've sat over the centre of Huntingdon at 3000ft, going slowly up in a nice thermal, and was unable to get any phone signal at all.

The HAB crowd all use lightweight, narrow-band kit in ham bands for telemetry and tracking.

Have you looked at any of the satellite-linked tracking systems? I know nothing about what is made and/or sold in the UK, but the Americans seem to like the SPOT2 and and the Delorme inReach systems. Both have a 'Red Button' help capability and the inReach offers 2-way text messaging, and those flying gliders in the US west tend to carry them because they can get a text message or position out when a satellite is in view.

This link gives the inReach's capabilities, battery life, weight etc. as well as UK sources for it.

Both are fairly rugged and weight somewhere in the 100 -150g range, so comfortable under your 500g limit, even with a few sets of spare batteries.

I think the above devices both fit these requirements.

There may well be other similar devices, but I haven't seen them discussed on rec.aviation.soaring, which is where I heard about these.

When you buy one of these, you set up login on their website, pay for a satellite subscription (typically 12months) and register one (or more?) phones. I gather that they ring the phone(s) in an emergency, i.e. if the red button is pressed. You can use the website login to see where the device is on a map, follow progress, etc.

The snag with that is that the person doing the tracking may well be in a poor signal area and unable to access the internet. Typical areas would be the New Forest, where there's only a data connection in the immediate vicinity of Lyndhurst and Brockenhurst, and Dartmoor where away from Princetown you are isolated. The Lake District too is very sparsely covered.

how will it send its position?

Arduino?

That lack of good coverage is exactly why I suggested using a system with a satellite link: if mobile coverage is so poor that the tracker, who is presumably in a campsite or motel near some town or village, is getting poor signal, then I wouldn't hold out much hope for the party being tracked being able to send any sort of message, even a text, especially as their phone will go through battery quite fast: if a phone can't contact a tower, it will set its transmit power to max and leave it there until it either gets a response or flattens its battery.

The support group / tracker's connection is surely quite easy to solve: set up base where there is good phone coverage and a working internet connection. I don't know the New Forest, but in the Lake District I'd have thought somewhere like Penrith would have both mobile coverage and an internet connection - and maybe wifi as well.

Apart from that all I can suggest is to make friends with a local radio ham and see what their relay networks have to offer and how heavy and/or expensive their transceivers are. Ask them about the 2-meter (144-146MHz) band, which has 5W hand-held transceivers that would fit your size/weight/ ruggedness criteria. I've used this kit over flat land up to 3-4km without problems, however, I have a feeling it may not have the range you seem to need in more rugged terrian: without using repeaters the person- to-person range is suitable for use within a smaller town but would certainly be limited to a similar extent within a forest or among hills.

I don't see the system using a phone, but a phone dongle. The whole system would be powered down between 30-minute activations.

The trackers aren't in a fixed location, but driving round visiting checkpoints. Occasionally they are able to drive to a high spot to pick up any awaiting text messages. As long as the message contains its send time, it's not critical if delivery is delayed.

For some of these expeditions groups can be up to 20km apart, with staff similarly scattered.

We ran a complex Gold expedition on Dartmoor this year, and communication was almost entirely by text message. The beauty of text is that it does get through in difficult conditions - if the send fails, the message is re-presented and the sender can try again until it gets to the centrsl system. Then the central system retries until it gets to the end user.

Since a text only needs one network packet, instead of around 400 per second for voice, it's much less demanding.

This is why you can now register your phone with the emergency services, then in emergency communicate by text to 999. That's even better since it will use any reachable network.

Trying to get an internet connection so that a web based service could be used requires better signal even than voice.

SPOT systems don't work too well at UK latitudes, certainly in Scotland. There can be noticeable delays before they can uplink due to the low inclination of the satellites used.

Inmarsat for non polar regions and Iridium for all over the earth are the best solutions. However, worldwide connectivity with minimum latency comes at a price.

DeLorme units also use Iridium for the satellite transport. There are some issues with there SMS provision. You don't get a dedicated phone number with DeLorme, instead your SMS is sent from a pool of numbers you have little control over which is confusing for some recipients expect a message from a certain number.

Running an SMS gateway, with several hundred users sending SMS from remote rural locations, coverage by the UK networks is often surprisingy good from remote locations. Better from higher ground especially if it overlooks A roads or Motorways even if these are some miles distant. But you can't guarantee coverage for all 4 networks from the same rural location will be good. It depends on the network and the phone, especially the phone band in use.

My own satellite comms system is not used as a tracker but a method of guaranteeing SMS type connectivity when a mobile phone might not work. It also works worldwide without worrying about roaming charges etc. It consists of an rPi, an Iridium modem and a Wifi dongle. The modem is about the same size as an rPI board. The modem is powered from the USB connection on the rPi and understands Hayes modem AT type commands. The Pi runs up Linux and starts a Wifi AP plus some scripts in Python. You use your mobile phone to connect to the AP on the Pi and browse to a webpage generated by the scripts, fill in the fields with the message to send and away it goes. It normally takes about 20secs from hitting send for the message to arrive as an email on my server.

The modem is powered from the USB connection but only draws 95mA. It has a charger which uses 5V from the USB to charge up a 3F (farad) AeroGel capacitor. From cold it takes about 3mins to charge up ready for use. The power drawn during uplink is such that you get to send about 1 message every 30secs max.

The Pi was the perfect solution for my needs. I was able to develop all the software in Python on a normal x86 Linux box. When working it was merely a case of making the necessary changes to put the Wifi on the Pi into AP mode and move the Python scripts. By using Linux + Python + the Pi's USB I was able to put the system together for the minimum of effort. Originally I was going to use a Bluetooth serial module available for a few pounds connected directly to the serial port of the modem. I'd have then needed to write an Android app to send the commands via Bluetooth to the module and hence modem. I'm very time poor but moderately cash rich, so spending 30ukp on a Pi saved me a huge effort in writing software (and learning about Android internals).

YMMV

On Mon, 12 Oct 2015 13:50:47 +0100, Alan Adams declaimed the following:

Given the nature of GSM, I suspect if a voice connection wouldn't get through, neither would an SMS message -- since voice data is digitized for GSM, no analog, it is just another data stream.

However... Arduino world:

And the other half of the equation:

I'll have to confess I didn't check to see if the pin-outs conflict between the two items.

Different networks for the receiving phones wouldn't be a factor -- once the SMS message is accepted by the ONE network the sender is using, it is up to the network to route it -- SMS is a store&forward type protocol; the message can be delivered whenever the recipient phone becomes available.

It really sounds like what you want are APRS (amateur radio) units. There are a number made these days with both APRS protocol and GPS built in. (Yaesu VX-8DR/-8GR; Kenwood TH-D72) Of course, you'd need a licensed amateur with each radio.

However -- battery life won't satisfy you... maybe 7 hours depending on transmit power level, and beacon interval (some models have a "smart beacon" mode which will send beacons based upon travel speed [and preset mode: pedestrian, bicycle, motorized] and turns (since they send current location, bearing, and velocity, they assume one will be on straight line for some period of time before doing an update).

AIUI, each GSM base station supports one control channel and one or more data channels. The control channel is used to signal the mobiles when to transmit, while the data channels carry voice. SMS is carried in spare capacity within the control channel.

The control channel is engineered to be more robust than the data channels, to avoid a 'runaway' mobile transmitting when it shouldn't. Hence the observation that text messages get through when voice fails.

I think a simple microcontroller, like ATMega168 (like in arduino) with a GPS and GSM module can do a better work for less cost.

Franssoa