Showing posts with label raspberry pi. Show all posts
Showing posts with label raspberry pi. Show all posts

Friday, March 17, 2017

Gumstix Pi Compute Boards are CM3-Ready


If you follow me on twitter (@gstixguru), you might know that I recently ordered an RPi CM3.  Lots of people have been contacting us to find out how well our Pi Compute boards support the new, faster module, so I found a bit of time to play around with it.  I'd worked with the original CM on our dev board for my GPS and RTK project a year ago with great success, and was looking forward to getting back to the Pi Compute boards.

First Steps

As always, my first step was to flash a brand new image onto the CM's eMMC.  I downloaded the latest Raspbian Jessie Lite ISO and mounted my CM on a Gumstix Pi FastFlash.  Next, I ran rpiboot, plugged the board into my USB hub and CROSSED MY FINGERS!

RPi CM3 on a FastFlash getting flashed. Pardon the clutter.
So what happened next?  Exactly what should:  the eMMC was mounted to my file system like any unpartitioned flash drive would be.  So I dd'ed the image, moved the module over to the Gumstix Pi Compute Dev Board and got ready to Pi.

First Boot

At first, all I wanted was proof of life.  That and I was sure the default wpa supplicant and network interfaces config would not get me on the WiFi network.  So I screen'ed in and powered up the board.  And yes, the console came to life, spewing forth those familiar Linux startup messages.  No kernel panic, no errors, no problem.  So far so good. Raspbian Lite was up and running.  Oh, all the things I should test: GPIOs, I2C, SPI....  BORING!

Let's start with USB (Oh, and get the WiFi up and running while we're at it; screen is not my friend and SSH makes me smile:).  The WiFi dongle goes into the port and lsusb shows a list of devices.  And there it is.


Bus 001 Device 002: ID 148f:5370 Ralink Technology, Corp. RT5370 Wireless Adapter

Beautiful.  I fix up /etc/network/interfaces and add the office WiFi network to wpa_supplicant.config and shut it down.  Time to set this asside and get back to my other tasks.

Day 2

Before ditching the USB console connection, I have to go into raspi-config and enable the SSH host, and reconfigure the daemon:


sudo rm /etc/ssh/ssh_host_*
sudo dpkg-reconfigure openssh_server
After a restart, ssh works fine.


Let's got straight up the food chain to the camera!  That's what I want to see!  I want to get that Sony IMX219 taking stills and recording videos.  I want to see those LVDS signals in action.  The CSI-2 camera connector is by far my favorite feature of the dev board.  So while I was in raspi-config, I made sure to enable the camera as well.

Here's my Frankenberry Pi camera rig, ready to go, I hope.
So I hooked it up, fired up the module and... nothing.  Did I forget something?  Of course I did! I needed the device tree overlay blob for the camera.  Oops.  OK, so I grab the binary, -- I get the one for both camera and display, just because I can -- copy it to the boot partition and restart.

And did it work?  See for yourself:
Me and my clipboard.
Edit: Here's me trying to pretend I'm not being recorded by the Pi Camera:


Also

I also took a few minutes and got the USB-Ethernet board fired up, and yes, everything works great.
I am very happy.  Stay tuned!  I have a Raspberry Pi DSI display around here somewhere and I want to get that up and running too.

Friday, May 20, 2016

RTK Rover Project Chapter 1: RTK and RTKLIB

Not long ago I posted about getting the Pre-GO PPP GPS modules up and running on BeagleBone Black with our Gumstix BBB Rover cape.  Now that I have them working on both this and the Gumstix Pi Compute Dev Board, it's time to take the GPS fun to the next level.  So what can we do with two incredibly accurate GPS modules running on tiny devices?  How about Real-Time Kinematics?

RTK eliminates the jitter experienced by solitary GPS receivers using differential techniques.  It requires a base station with known co-ordinates and a mobile reciever. By using the difference in signal-to-noise (SNR) ratios and phase for common satellites, RTK algorithms can cancel out atmospheric effects that can pollute geopositioning results.  I won't go into incredible detail here since Navipedia has a great wiki on the subject.
This image shows the GPS/GNSS data in pink and the RTK results in green of a rover driving around in a  6-meter circle.

So why do we care about RTK?  It's primarily used for surveying, but there are many situations when a robotic rover may want to track its path, report its exact position or navigate to a given waypoint with a high level of accuracy.  That's what I'm excited about.  I'm going to rig an automated robot with a BBB and Rover cape, use my RPCM rig as a base station and use the GPS data to control the rover.

First we have to get some RTK software up and running.  There aren't a lot of options for this in the open-source world, but the biggest name is RTKLIB.  It's not only an open source library, but it also includes a complete set of GUI and CLI apps to get you started.

Sadly, the GUI elements are written for Windows, so there's no chance of using them on the Pi Compute dev board, and I'll have to monitor operations from my laptop.  But the str2str and rtkrcv command line programs are the two most important elements of the software suite for my needs. these applications, and eventually their source code, will be the backbone of the RTK project.  The easiest way to compile these for ARM Linux is to download the source code onto your BBB and Raspberry Pi and compile them natively.  I ran into a little linking problem after I cross-compiled the applications on my PC and tried to run them on the COMs.  In the end, it was just far less hassle to go native.


Having set a precedent with the Gumstix Pi Compute Pre-GO PPP project, I felt I had to build a fancy box for my Gumstix BBB Rover.



I got the COMs equipped with their expansion boards, Pre-GO PPPs and antennas and wrapped up in a nice package.  With the RPCM being my base station, I used a Pre-GO PPP SMA so I could use a more sensitive antenna.  This will get me a more accurate fix on the rover's position.  The antenna I'm using is the Dominator AA.161 from Taoglas.  The BBB Rover has an on-board TI WiLink8 WiFi and Bluetooth modem that requires a u.FL antenna, and I'm using the Pre-GO PPP with the built-in antenna.


With the binaries and data files on the boards, I started experimenting, streaming data from the COMs to my laptop and trying to get a fix.  I tried a myriad of config files and, after some digging, I put together this file. The commands therein are transmitted to the u-blox NEO-7P on the PPP boards and instruct them to transmit tuples that are normally blocked across the UART channel.  These strings carry the phase data of the satellite signals which RTKNAVI, the GUI I use on my laptop, uses for RTK solutions.

After some trial and error, I began to see SNR data.  It looked something like this:


The top graph is the data from the BBB, and the bottom from the RPCM.  Each bar represents the SNR from a satellite.  In order to get a solution, the two computers have to be able to get a strong fix (shown as a colored bar) on several common satellites.  Unfortunately, the window in the office only provides half a constellation.  Not nearly enough for RTK... Barely enough for a single fix.
My little computers are getting their fix.  Tux is helping.

 Clearly, I need to get outside.  That'll have to wait until next week.  In the meantime, I'm all set up, apart from a battery pack for the BBB, to do some real testing.

NEXT TIME: The great outdoors, differentially.

Monday, May 16, 2016

Gumstix Pi Pre-GO PPP Project Chapter 5

I took my equipment to the tennis court yesterday and gathered some data.  When I arrived, I was saddended to discover that the two main courts were occupied so I went to the last one. Ten minutes at each of the eight corners I'd mentioned before  gave me quite a bit of data.  When I plot it on Google Earth, it looks like this:



OK so something's wrong.  First off, the orientation Google's image is clearly incorrect. Secondly, there's that tree!  It's covering the entire back-right corner!  I might be able to go again some other time, but let's make some observations first.  Looking at the inner corners, [LBS, RBS, LFS, RFS], the dimensions are reasonably correct.

What it looks like to me is that the court sits on a slope, which I hadn't considered to be a major source of error.  I had assumed that the courts would be level but, having been there for some time, they have most likely sunk in places and bubbled in others.  I may have had more luck had I acquired access to Wimbledon,  but the fact of the matter is I'm trying to measure exact distances with chunks of metal free-falling high above the earth and no fixed point of reference on a surface with random elevations.

Here is my conclusion for this project:  The Pre-GO PPP works beautifully with the Raspberry Pi Compute Module through the Gumstix Pi's UART breakout connection. It is able to measure GPS position with decimetre-level accuracy and sub-decimetre jitter.  However, measuring distances with sub-metre-level accuracy is next to impossible using GPS coordinates alone.

There are many reasons.  First off, environmental factors, such as trees and bridges will drastically increase dilution of precision.  Reason number two is explained above.  Lastly,  I can't seem to get enough court time to collect all my data points.

Clearly, a new strategy must be employed.

Up next: BBB Rover and RTK

Thursday, April 28, 2016

The Gumstix Pi Pre-GO Project Chapter 4: Tennis Anyone?

I went to find the survey marker from waymarking.com and discovered that it was directly under a bridge.  It's also in the middle of a road.  I think that the coordinates they're publishing are not as accurate as I would like.  Strangely, there does not appear to be any more markers in the near vicinity of the office.  In the absence of an accurately located marker, I'm going to try and measure the dimensions of a tennis court with GPS data.   
So far, I have been very impressed with the Pre-GO PPP's performance.  I took it out for another field trip recently and had very nice 0-8 cm diameter groupings.  HDOP has been consistently near and below 1.0.  Geodetic engineers and surveyors would be pleased as punch.
I intend  to define the outer bounds of the court and the service lines within.  If I draw a 11x24m box with an 8.2x13m box smack in the middle, the test will be a success.  These measurements are based on the regulation court dimensions outlined in the image to the right.  I'm also considering measuring the accuracy of the altitude measurement.  The net is 1.6m high and if I can get that measurement from the base of the net post to the top, that will be an interesting data point as well.
The difficulty I have faced with my setup has not been the hardware itself.  This has performed perfectly throughout my experiments.  The issue has been with logging and interpreting the data.  I have been using my cellphone as an ad-hoc network router to ssh in to my Pi and during one experiment, the connection between my laptop and my GPS rig kept dropping out.  As a patchwork solution to this issue, I have added a physical connection to the RPi's system console: Just a short USB microB-to-A I can connect to with an extender cable.  If the WiFi drops out, I can just plug in.

Added to this is the fact that, in general, GPS modules spit data out once per second.  The Pre-GO PPP is no exception which means that, for a 1-hour test, there are 3600+ records to process. I'm using Python to interpret and plot the data but it still takes time.
Up next: RESULTS!

Monday, March 7, 2016

The Gumstix Pi Pre-GO Project Chapter 3: I can't Rely on Google Maps.

There was a nice break in the weather yesterday and I managed to get outside to take some readings.  I set up on an exposed hilltop with my laptop, my Pre-GO-to-go and my smartphone.  I was hoping that I might find some kind of survey marker with exact GPS coordinates at the base of the flag pole, but no such luckI fired up my Pi, gave it a few minutes to warm up, and connected it and my laptop to my phone's WiFi hotspot.

With no guarantee of clear weather, I decided to do a quick test and grab four different data snapshots over a 15 minute window.  I'll formulate some more informative tests for when the weather is better.  For now, I just want to see how accurate it is.

The PPP in Pre-GO PPP stands for Precise Point Positioning.  PPP provides centi- to decimeter-level accuracy so, even if Google doesn't drop its pin directly on the flagpole, my data points should be very close together.  I have to assume that Google Maps co-ordinates are going to be somewhat skewed.  Without an accurate geodetic survey marker, I can't be certain.

When I got back to the office, I dropped some pins on the map and here's what I came up with:



The outlier is my initial result.  The tight grouping south west of it are the three other results I recorded.  They sit about 1.5m away from the outlier but are all within 12cm of each other.

I found this blog post that confirms my assumption about Google's geodetic accuracy.  If you compare my Maps screen shot to his, it looks like the skew is about equivalent.  I trust my results over Google's now.

So I still have not concrete baseline measure of accuracy.  I really want to know if my horizontal co-ordinates, when HDOP (horizontal dilution of precision) is less than 1, are accurate at the decimetre level.

To that end, my colleague sent me a link to waymarking.com, where I found a survey marker nearby.  GPS enthusiasts have, thankfully, taken the time to accurately measure its geographic position.  OK great, but I have been rained out.  I guess the next test is going to have to wait awhile.  While we wait, let's see if the Pre-GO works with the BeagleBone Black and the Gumstix Rover cape.

Next Time:  Pre-GO and the BeagleBone Black Rover Cape

Thursday, March 3, 2016

The Gumstix Pi Pre-GO Project Chapter 2: Pre-GO Packaged to Go

So, while we're debugging the UART header, I thought I may as well get some results from the Pi using the FTDI cable. With the help of a USB hub, a WiFi dongle and some masking tape, I set the Pre-GO up on the window.  I figured if I was going to get any kind of signal anywhere in the office, this would be it.


I SSH'ed in and ran gpsmon. This is a great tool related to GPSD that spits out human-readable GPS data in real time.  It looks something like this:



Yep, my Pi kind of knows where it is... within 10 metres, that is.  Not good enough for a Precise Point Positioning (PPP) GPS module.  I have to get it outside to get accurate geolocation.

Good news! The UART problem was resolved with a single line:

dtoverlay=uart1-overlay,txd1_pin=32,rxd1_pin=33

I appended this line to /boot/config.txt and said goodbye to the FTDI converter.  With the bulky USB cable and hub gone I decided to get my gear ready for test.

A circuit board with a delicate makeshift UART connection is not easily transported.  Not to mention the need for a power cord makes taking my rig on the road a bit of a challenge.  No problem. Tape, scissors, and a shipping package, combined with a little time gives you this:

  

 

Next Up: Where am I, Precisely?

Friday, February 26, 2016

The Gumstix Pi GPS Project Chapter 1: Break it out and get it running

As my first gadget project as Gumstix Guru, I'm going to connect a Pre-GO PPP GPS to a Raspberry Pi Compute Module by way of the Gumstix Pi Compute development board, pictured below.


Getting Started


I could just build a board in Geppetto with the GPS connector on it, but I've already got my Gumstix Pi in hand.  The Pre-GO communicates over a UART connection, a header for which the Gumstix Pi has.  The trick is that I need to manually rig the connection.  Easy enough.  Let's break out the Pre-GO's header:


I made a point of labelling each one of the wires just to make life a bit easier later on.

Of minor concern is the fact that the pitch of the Pre-GO's header is considerably smaller than that of the dev board's UART header so I had to use a finer gauged wire.  Not a big deal but they aren't a good fit for my jumper wires.  My solution?  Easy:  Fold 'em.

Next I decided to forgo the extra mess of jumper wires and go straight to the jumpers.  A nice way of keeping the rat's nest to a minimum.  Oh, and my labels fell off.


First Power-Up

At this point I'm very excited.  The board's all hooked up, the Pi module is in place and it's time to plug it all in.  Hope I didn't forget anything!
Once Raspbian is up and running, I go hunting for my GPS module to no avail.  What's wrong?  Why isn't it working?

Time to go to the test bench to make sure the module works. 
  • Board configured for 3.3V - check
  • Connectors attached correctly - check
  • Waveform resembles data output - check
So I hook it up to an FTDI-UART adapter and check its output.  Looks like GPS data to me:



The Verdict

Okay so the Pi is working and the GPS module is working, they're just not talking to each other.  So the UART header isn't configured correctly.  I'll get that sorted out later.  For now, I'll just hook it up with the FTDI adapter and get some results.

Next Up:  Raspberry Pi CM and GPSD