Archive for June, 2012

Snap (by Synapse)

Posted in Hardware, MESH on June 29, 2012 by asteriondaedalus



• 15 GPIO, 4 with 10-bit ADC
• 128k flash, 56k free for over-the-air uploaded user apps
• One UART port
• Low power modes: 2.3 ?A w/ internal timer running
• Spread spectrum (DSSS) technology
• Socket-able or solder-able
• Up to 2 Mbps Data Rate
• 2.4 GHz RF Frequency
• Receive Amplifier (10 dBm) standard
• Transmit amplifier (20 dBm) for best-in-class range
• Chip antenna (up to 4000 feet, LoS at 250kbps)

SNAP’s on-board Python interpreter provides for rapid application development and over-the-air programming

I was poised to buy the ZIGBEE modules for a couple of my ZIGBEE mounts when I came across the SNAP alternative.  A plus because they have ZIGBEE footprint.    A plus because they come with a cut down version of python on them and allow for RPC and a whole range of useful things, over the wireless.

Of note, they appear to allow for the raw data flow transparency under the RPC and other layers so I can still use them for MAVLINK as well as using them for other smart applications.

The most useful thing is that, plugged into the arduino boards, they can offload the raw I/O to the arduino board.  The remote programming (over the air) will allow for more malleable smarts – especially as a PC can join in and act as a node using full python.

OR, at least, they can be used simply as a ZIGBEE replacement.

I have two on order to start looking at the MAVLINK side.  Noting, of course, that MAVLINK already has python bindings.

Yeah well

Posted in Sensing, Software on June 25, 2012 by asteriondaedalus

I have looked at two AHRS for the razor.  One of then doesn’t appear to have  a means to calibrate but also appears to claim it isn’t needed.  The nuisance, the yaw setting (compass) didn’t seem to behave the way I would have expected.

It appeared that the north-south axis wasn’t 90degrees with the east-west.

Now, I found an EMI meter (so-called) for my iPhone and … well I should have known, I was trying to calibrate the compass while the sensor sat on the top of my laptop.

There was beer involved.

Mental note to oneself:  Use a longer usb cable and find a spot half a meter at least from the laptop.

Still, I am happier with the other version of the AHRS as the on screen behavior seems to equate (mostly) with the behavior of the sensor.  Still needs calibration so still a little work.

Razor up

Posted in Arduino, Sensing on June 22, 2012 by asteriondaedalus

A little soldering and then using the 3v usb to FTDI gadget and viola!  Now (as long as you have that pesky Apple plug in)

Testing Razor .

Nothing to brag about, someone else’s hardware, someone else’s code.

That’s integration.

Well the real integration will be using the SPI port to hook into the mouse sensors.  There is code a diydrones to read the mouse sensor and it looks straight forward to add odometry to the Razor the same way they used the mouse sensor for a position hold for a quadcopter.


Visual odometry – optical flow

Posted in Ground, Hardware, Sensing, Vision on June 18, 2012 by asteriondaedalus

Well.  I lost heart after buying a couple of mouse sensors to find that buying a separate lens was possible from china … but then diydrone/3drobots helped out by putting a mouse sensor and a lens together.  In fact, they matched the lens and mounted them so was cheaper all up to bin the raw mouse sensor and buy the unit (or two of them in fact – very popular).

Along with an SPI interface I can now add optical flow/visual odometry input to my IMU/AHRS for the rock crawler.   I opted for that, initially, since it will likely be prone to wheels spinning etc so encoders on the wheels would not help as they would generate errors where the wheels turned but the chassis stayed put.

Mind you, an encoder on each wheel, and one on each drive shaft (to detect wheel spin etc) might be an interesting project but alas no open source code base for it 😉

Plenty of code comes with the kit from diydrones.  The thing is working the sensor into the IMU code – just another sensor to fuse.


Yes, that is my medicine in the background – no really, I was laid up after major abdominal surgery and they prescribed Stout.

Finally, a HDMI to VGA female adapter cable

Posted in Hardware on June 10, 2012 by asteriondaedalus

I was loathing firing up the Beagleboard XM because I was either spending on a new monitor with DVI-whatzit or trying to track down an S-Video to vga cable or converter.

Turns out someone has come up with an HDMI to VGA cable so fingers crossed I can get a screen up for a mere $16.