28. March 2010 by admin.

Ok, I isolated the steering issue I was having.  The digital compass was jumping over a range of about 60 degrees.  I believe it was because the compass was not completely level which I know is an issue.  Digital compasses which compensate for tilt are out of my price range, though, so I may need to rig up some sort of tilt adjustment. But, the Sparkfun course looks pretty level, so probably not a  big issue.

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27. March 2010 by admin.

Ok, here is my car doing some basic navigation at slow speed.  Here’s what’s happening.  The car heads toward the first point.  Note that steering is extreme left or right.  I think I’ve got an algorithm issue which I need to debug.  When it hits the first point, it turns around and starts heading back toward the second point which is almost at the place I started.  On the way back, the steering is better (slight, continuous adjustment) but it has trouble getting up the hill under a 20% duty cycle.  Also, it pauses when it loses the GPS signal.  I don’t know why GPS is flakey on the way back.  It could be the napkin I’ve got the module wrapped up in. 

My to-do list now is:

• control ground speed by odometer feedback, not PWM
• fix the steering algorithm
• get object detection going

It will have to wait until April 1 when I’m taking some time to focus on this project. 

Thanks to Greg and Dave for helping me with the steering algorithm.  I’m sure they got it right and it’s me that didn’t code it correctly.  

 Now to book my plane ticket…
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20. March 2010 by admin.

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20. March 2010 by admin.

A few weeks ago I decided to rip apart my protoboard and build a schematic and PCB.  It’s always a good decision because it doesn’t take long and it gets rid of the rats nest.  It’s easy to do and design changes can be iterated incrementally instead of starting from scratch each time. 

There is some excellent open source schematic and pcb software called Kicad.  It’s a bit quirky like all pcb designers but once you get past that first bit, it’s great:

http://iut-tice.ujf-grenoble.fr/kicad/

Here’s an annotated version of my pcb:

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16. March 2010 by admin.

I forgot to mention - I’m now using an 18F4525.  Compared to the 16f877a, it’s massive.  4x the programming space, 10x RAM, 4x eeprom and way more timers. 

It’s the same chip we’re using on a related project  - a GPS guided, solar powered boat:

www.solarcrawler.com

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15. March 2010 by admin.

I made some good progress this weekend.  Work (as in my day job, completely unrelated  to electronics) has been ridiculously busy so it’s been tough to squeeze this in.  But, I know the video needs to happen before Apr 1.

 I started out by ripping apart my old project from about a year ago (pictured in my first post) and put together a proper schematic and PCB using KICAD (open source, it’s great).  It took a while to get that bug free, but now all the bits are working and I just need to tie them together with some sort of behaviour logic. The GPS navigation will be ok, but I’m most worried about obstacles.  I would hate to go all the way to Boulder (I live in Victoria, BC, Canada) and have this thing get stuck on a rock or something.

Above is the set up I’m using, which is essentially this:

* MPLAB IDE
* Hi-Tech PICC-18 compiler in free mode. 
* Microchip ICD3 debugger/programer

On my board, I’ve got rs-232 out so I can do continuous debugging while downloading firmware changes using the ICD.  That’s shortened my development cycle considerably from the days of bootloaders and regular programmers.

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