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#187199 - 09/28/14 02:55 AM Something the same, but just a bit different...
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3889
Loc: Ozark Mountains in SW Missouri
I've been playing with some inexpensive sensors that you can hook up to a Raspberry Pi computer this past week. I have a "Triple Axis Accelerometer/Magnetometer (Compass)" sensor and a "Barometer/Temp/Altimeter" sensor. You can also get a GPS sensor but I haven't ponied up for that yet.

These little "breakout boards" are really pretty amazing, both of them are about the size of a postage stamp and only a bit thicker than cardboard. The Raspberry Pi computer can almost fit inside an Altoids tin, and there'd be a lot of airspace inside it, so all this is pretty small and light.

I've also been working on a "graphic user interface" or "GUI" so you can visualize all this data, so what I'm pretty close to making at this point is pretty much a home made GPS.

Here's what I want to do that's a bit different, so I'm going to run it by all of you because I think I may be on to something useful.

The RPi (Raspberry Pi) computer is about as powerful as your standard smart phone or high en GPS, and we all know the pros and cons of both those. Two of the most prominent are the phone has a sucky battery life and GPS has a sucky screen, and on the plus side the GPS has a pretty good battery life and the Phone has a pretty good screen.

The RPi has pros and cons too. It doesn't have a built-in screen at all, or a GPS, but you can hook up a really big screen to it, and you can add on a really good GPS sensor.

I think what I can do with a RPi is make a GPS with all the other important bells and whistles that will last a really long time on a couple AA batteries, but it won't have a screen at all. Instead, you'll use Bluetooth to access the data on it with your smart phone. When you're not looking at it you turn your phone off, but the RPi will stay on and continue to collect data and create a track while you're hiking.

One of the really cool advantages to this set up is that everyone hiking with you can use their phone to access the data too. You can all look at the same map, same waypoints, same compass, altimeter, etc. at the same time on your own phones.

If someone else is also carrying one of these RPis you can all look at theirs too. You do this by using the web browser on your smart phone, so no one has to install any apps or anything at all. They just have to connect to the Bluetooth on the RPi and type in a short URL in their web browser and they've got a full blown GPS app up and running.

Once you are connected you can all upload photos to the RPi and you can all view and share them with each other, and download and save them and your GPS track and other data onto your own phone. Same with videos, you just need to be within 10-30 meters of the RPi to connect to it with your phone and share stuff.

Even if your hiking solo, and never turn on your phone, this device could be attached to your pack and collect data for you. You could even attach it on top and outside of your pack where it will get the best reception and not worry about it because there's no screen to bust up and you can get cases that are tough as can be.

When you get home you can all transfer the GPS data from either your phone or the RPi to your favorite Desktop computer mapping app just like you would from the GPS you use now.

Finally, using these two devices, the phone and Rpi-GPS, together like this should help extend the battery life of both devices. The Bluetooth connection is the lowest power connection you can use on your phone. You don't need cell service or wifi even turned on in your phone to use it with the RPi, and it won't really use any more power on the RPi if more people are connected to it.

What do you think?
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#187200 - 09/28/14 08:58 AM Re: Something the same, but just a bit different... [Re: billstephenson]
Dryer Offline
Moderator

Registered: 12/05/02
Posts: 3571
Loc: Texas
Sounds like an inertial nav system for hikers. Am I understanding you right that the accelerometer sensor module doesn't rely on GPS sats? This sounds like ham radio stuff we're always doing. Like APRS (automatic position reporting system).
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#187201 - 09/28/14 02:03 PM Re: Something the same, but just a bit different... [Re: Dryer]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3889
Loc: Ozark Mountains in SW Missouri
You're correct, the accelerometer doesn't rely on GPS. It's pretty much the same thing used in those Wii game controllers you use to play bowling and golf games with. Here's the unit I'm using:

http://www.adafruit.com/product/1120

And here's how you use it:

https://learn.adafruit.com/lsm303-accelerometer-slash-compass-breakout/coding

I've taken this and coded an interface to animate a graphical compass. I grab data from the sensor and push it to a demo of a HTML5 animated compass I found here:

https://github.com/rheh/HTML5-canvas-projects/tree/master/compass

When you turn that sensor the compass needle moves just like a regular compass. It's pretty much the same thing you can download as an app for your smart phone if it has a similar sensor built into it and most do now.

www.adafruit.com also has GPS modules you can purchase and use to write your own software for.

So, as you can see, all I'm doing is hacking together some existing stuff here, but it works really good and you can create your own compass rose using computer graphics software like Photoshop. You could even use a photo of an old compass if you wanted.

I'm not going to try and create a fully featured GPS app, but I can create a fairly simple way to use the free government quad maps and draw tracks, routes, waypoints, and your current location on them.

I'm sure it's possible to use the digital map files like a real GPS app does, but that will have to wait because it's been years since I've messed with that stuff.

I think I can build one of these for around $150, but like I said, you still need a phone to view the data. I paid around $200 for my last Garmin GPS. It's a "Oregon 200" which is pretty nice, but it has a pretty small screen and my old eyes have trouble with it.

I have an older Motorola Droid Razr M phone and it's got a comparably sweet display on it. I think you can pick a used one of those up for around $50 now.

What I can do is create a working demo, provide a materials list, schematics, software, and step by step instructions on how to make your own, and release all the software with an open license so anyone can modify it and share their modifications if they want.

At that point, anyone of us can start making, improving, and even selling them if we want. Kind of like Super Cat Stoves. cool
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"You want to go where?"



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#187202 - 09/28/14 02:38 PM Re: Something the same, but just a bit different... [Re: billstephenson]
aimless Offline
Moderator

Registered: 02/05/03
Posts: 2859
Loc: Portland, OR
This is a very interesting idea, bill.

I am not a smartphone owner or user, but I'd be interested in an inexpensive RPi GPS unit, if I could take it with me on a hike, use it to gather data about location, distance traveled, elevation gained and lost, speed of travel etc., then download it at home and view a statistical summary of my hike and view a trace overlaid on some form of topo map that I could access for free on the web.

iow, I don't feel the need to view all that data on the trail, but I am always curious about such data when my hike is over. Up to now I've not wanted to spend any real money to satisfy that idle curiosity, but I'd be willing to pony up maybe $40 or so to gaze lovingly on my hiking accomplishments at home on my PC. I'm not sure anyone could make any profit off such a low price point as a cheapskate like me would be willing to pay, or whether I'd ever try to cobble together my own system out of free software and DIY instructions for constructing the unit, but I like your thinking here.

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#187206 - 09/28/14 08:15 PM Re: Something the same, but just a bit different... [Re: billstephenson]
Dryer Offline
Moderator

Registered: 12/05/02
Posts: 3571
Loc: Texas
I've messed with basic stamp and the like....it just keeps getting better!
A flux gate compass and inertial nav would be fun. I wonder how the reolution is compared to satellite based GPS? The early cruise missiles used inertial navigation and mapping systems before GPS happened. It worked but got the vehicle close, not dead on.
_________________________
paul, texas KD5IVP

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#187210 - 09/28/14 11:52 PM Re: Something the same, but just a bit different... [Re: aimless]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3889
Loc: Ozark Mountains in SW Missouri
This kind of stuff isn't really hard. So much of the real work for stuff like this is already done now that it's more akin to building the old Radio Shack projects when we were kids back in the olden days.

You pretty much grab stuff off a shelf and bolt it together and wire it up and play with it.

The Raspberry Pi has a "Getting Started with Python Programming" lesson that is so well done that anyone who can read and write and do basic math will understand how code works. From there you can pretty much jump right into using example code for things like this compass I'm fooling with now.

The Raspberry Pi cost about $35 + shipping, and you can get a nice GPS receiver to wire into it for about $35-$50 or more. I'm not sure what kind of software is out there that will run on the RPi though. I found one project that's making something pretty close to commercial GPS software, but my Garmin doesn't let me access the data I need to use it and I haven't tried installing on a RPi yet. I have my doubts that it will run very well on one, but it's worth trying cause it's free smile

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"You want to go where?"



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#187225 - 09/30/14 02:47 PM Re: Something the same, but just a bit different... [Re: billstephenson]
finallyME Offline
member

Registered: 09/24/07
Posts: 2710
Loc: Utah
I started going down this route when I first started looking at arduino and RPi stuff. But, it is still hard to beat an Etrex 10. Of course, all I really want my gps to do is tell me my grid coordinate. Then I can check it against my map. Storing location data is pretty cool, and I will probably try that. Last Christmas, a family member gave me their old etrex 10 that they had never used. So now, it is hard for me to justify making one. Plus, it is in a weatherproof case.

However, I think you should make one. Why not? Give it a shot and tell us. I can almost guarantee that someone out there will benefit from your prototyping and code writing. I don't write code and I benefit from a lot of those types of people that write an arduino code for something, and I am able to take that and modify it slightly for my own specific project.
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#187239 - 09/30/14 10:00 PM Re: Something the same, but just a bit different... [Re: finallyME]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3889
Loc: Ozark Mountains in SW Missouri
The eTrex is a great unit for what you're doing. I was pretty disappointed to find my Oregon won't let me grab real time data, but I wouldn't be surprised at all to learn your eTrex would. My old eMap let me do that.

I'm going to play with the concept. I like the idea of being able to share the GPS with other hikers in a group, and I know it's possible. I'm sure I could probably estimate the power consumption with the specs on the hardware I am considering using, but from what I think I know, I think it's doable. smile
_________________________
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"You want to go where?"



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#187247 - 10/01/14 12:14 PM Re: Something the same, but just a bit different... [Re: billstephenson]
4evrplan Offline
member

Registered: 01/16/13
Posts: 653
Loc: Nacogdoches, TX, USA
You should add an external switch to toggle the bluetooth radio on and off. Only turn it on when someone wants to pull an update.

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#187256 - 10/01/14 04:20 PM Re: Something the same, but just a bit different... [Re: 4evrplan]
billstephenson Offline
Moderator

Registered: 02/07/07
Posts: 3889
Loc: Ozark Mountains in SW Missouri
Originally Posted By 4evrplan
You should add an external switch to toggle the bluetooth radio on and off. Only turn it on when someone wants to pull an update.


Yep, no doubt. That is probably the biggest drain and if you only had it on when in use it would make a huge difference.

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"You want to go where?"



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