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#52660 netduino plus 2 compatible gps/gsm module

Posted by Arbiter on 09 September 2013 - 06:01 AM in Netduino Plus 2 (and Netduino Plus 1)

You'll have to write your own drivers.

 

Most carriers charge outrageously for GSM, making it a very expensive way to do tracking comms. I had a look at the SIM908 chipset and it doesn't appear to support anything newer than GSM. Nor does it surface a connector for an external GPS antenna, which means you will need an IP66 enclosure because you'll have to roof mount it to get a lock in weak signal conditions.

 

To improve reliability and mitigate operational costs I recommend a store and forward architecture, for which this shield is not an ideal choice.

 

So far as I can determine, the SIM908 does not support altitude. If altitude matters to you then you need a shield that supports a uBlox 5, 6 or later such as this http://www.dfrobot.c...81#.Ui1kDdV-8dU.

 

I haven't personally used that one but I do intend to test one at some point.




#52654 Help with PWM

Posted by Arbiter on 09 September 2013 - 04:21 AM in Netduino Plus 2 (and Netduino Plus 1)

Frequency is Hz. Your value of 10000 means that a pulse will be generated every tenth of a millisecond. Duration is in microseconds. Your duration of zero will produce either nothing at all or a brief twitch because the rising and falling edges aren't truly vertical.

 

To produce a 50% duty cycle you need the duration to be half the interval. Specifying a frequency of 100Hz ie an interval of 10ms, you will need a period of 5000µs (5ms) to get 50%, so values of 1000, 2000, 3000, 4000, 5000 will produce duty cycles of 10%, 20%, 30%, 40% and 50%.

static PWM ledR = new PWM(PWMChannels.PWM_PIN_D11, 100, 4000, false); //40%

You could also run a short interval (higher frequency) with narrower pulses.

static PWM ledR = new PWM(PWMChannels.PWM_PIN_D11, 10000, 30, false); //30%

This will produce a smoother steadier glow.

 

I haven't played with an RGB LED but I imagine that it's essentially three LEDs in one package, probably with three signal leads one for each of R, G and B, and a shared earth lead. Presumably you will use three separate PWMs to control the intensities of R G B to mix your own colour; if you skip the PWMs and pull all three control leads high I imagine you would get bright white.

 

There is another constructor that allows duration to be specified in nanoseconds. Be aware that the inductance of thick conductors may become significant at higher frequencies. You won't notice in the kilohertz range that you seem to want to use.

 

Servomotors expect a frequency of 50Hz (an interval of 20ms) and the pulse width is what controls the servomotor. A pulse width of 1000µs turns the servo as far counter-clockwise as it will turn, and a pulse width of 2000µs turns it as far clockwise as it will go. A pulse width of 1500µs turns the servo to the centre of its range which is generally regarded as the zero position.

static PWM servo = new PWM(PWMChannels.PWM_PIN_D11, 50, 1500, false); //centre position

Other frequencies and durations may work because the servo is actually controlled by the voltage produced in an RLC circuit inside it which is a function of the duty cycle. But the specification calls for the interval and range of duration I have specified above, and there are quite enough surprises in the world without going looking for them. On the other hand if you don't mind damaging a few servos, out of range values can produce some quite fascinating behaviour.




#52653 SD extension & SIM extension

Posted by Arbiter on 09 September 2013 - 02:33 AM in Netduino Plus 2 (and Netduino Plus 1)

Probably there is no simple answer to this, but I'll ask anyway.

 

Why is it so hard to support SDHC?

 

KodeDaemon and others have been looking at this problem for years now. I imagine there is something horrible about SDHC or they would have shipped something a long time ago.




#44015 Quad.Net Quadrocopter for .NETMF

Posted by Arbiter on 23 January 2013 - 01:31 PM in Project Showcase

I cannot help but wonder whether required thrust can be expressed as a function of inputs using an FPGA. Possibly one per motor. I would expect inputs to include 

  • required vector
  • accelerometers
  • gyros
  • velocity
  • current vector
  • last-interation thrust values for all engines

and of course it would be necessary to clip the magnitude of the requested vector to what is actually possible with available thrust.

 

Using an FPGA would make it possible to make very frequent microadjustments; the Netduino would fulfil a role more like an autopilot. Such an arrangement would be excellent for building a drone.




#42908 Netduino Plus, DIS(Direct Ignition System) and transistor help

Posted by Arbiter on 07 January 2013 - 02:14 PM in Netduino Plus 2 (and Netduino Plus 1)

While it's great that you learnt to DIY, you can save yourself a lot of messing about with one of these relay shields.

 

http://littlebirdele...ts/relay-shield




#42502 Diodes and SN754410

Posted by Arbiter on 31 December 2012 - 03:01 PM in Netduino Plus 2 (and Netduino Plus 1)

Schottky dodes are fast switching with a low forward bias. They're fast switching because they have a zero recovery time - there is nothing to recover from because they don't use a charge carrier depletion region at the junction (which is how a PN diode works).

 

Over-engineering is always better than under-engineering in a prototype or a one-off. If you don't fit them you'll probably get away with it. If you do fit them you can be certain there won't be backlash, assuming they're big enough. Your next step is to fret about how big is big enough. Are you going to add input protection? An over voltage zener shunt? A current-limiting thermistor? Where do you stop? You might think, "Not in the prototype, I'll get it right and then add all that bunk." but in fact you are more likely to blow up your prototype than a finished product.




#37273 Running out of memory

Posted by Arbiter on 16 October 2012 - 10:20 AM in Netduino Plus 2 (and Netduino Plus 1)

Declare the socket outside the loop and just open and close the connection in the loop. Don't create stuff dynamically. In embedded systems you need resource usage to be very predictable if you want long term stability. You could also leave out most of that post header, it's unnecessary. You only need host, content-type and content-length. If you put content-length at the end you can make up a single string constant and greatly reduce the amount of gratuitous object creation.



#35411 Introducing Netduino Go

Posted by Arbiter on 17 September 2012 - 11:54 AM in Netduino Go

I was joking, Fred. I know about the limitations. Nes is right about the chipsets, except that anyone can buy them if you don't mind paying a premium with minimum quantities of 10,000. Of course, if you did that you would attract what might be described as scrutiny from people whose sense of humour has been surgically removed.

Domestic GPS chipsets use some assumptions about altitude to speed things up. If you invalidate those assumptions they will mostly work, but "mostly working" is not a phrase that pilots find reassuring.



#35394 Netduino Plus Firmware v4.2.0

Posted by Arbiter on 17 September 2012 - 02:39 AM in Netduino Plus 2 (and Netduino Plus 1)

Nak, the patent issue relates to compatibility between SDHC readers and SDXC cards.

SDXC cards shipped with Microsoft exFAT which is proprietary, patented and mostly undocumented.

SDXC host devices accept all previous families of SD memory cards.[26] Conversely, SDHC host devices will accept SDXC cards that follow Version 3.0, since the interface is identical,[3] but the following issues may affect usability:

  • SDXC cards are pre-formatted with Microsoft's proprietary and patented exFAT file system, which the host device might not support. Since Microsoft does not publish the specifications of exFAT and its use requires a non-free license, many alternative or older operating systems do not support exFAT for technical or legal reasons. The use of exFAT on some SDXC cards may render SDXC unsuitable as a universal exchange medium, as an SDXC card that uses exFAT would not be usable in all host devices. Since the FAT32 file system supports volumes up to the SDXC's maximum theoretical capacity of 2 TB as well, a user could reformat an SDXC card to use FAT32 for greater portability between computers (see below). FAT32-formatted SDXC cards can be used in a host device built for SDHC if the host device can handle 64 GB and larger volumes.
  • SDHC host devices will not test the new capability bits defined for SDXC 4.0 cards. It will therefore not be able to use the new features of SDXC, such as transfer speeds above UHS104 (104 MB/s).


The difference between SDSC and SDHC is mostly redefinition of the Card-Specific Data register (CSD), plus SDHC cards ship with FAT32. SDHC is "limited" to 32G. I think this is probably enough for an embedded logger even with video. Any more than this and you may as well build something with an underclocked ITX mobo and an SSD drive.Although I notice in the Wikipedia text that you can dodge the patent by reformatting with FAT32.



#35392 Introducing Netduino Go

Posted by Arbiter on 16 September 2012 - 10:14 PM in Netduino Go

And you should also be able to do the Kalman filtering in hardware on the module too...



And it needs its own GPS module to provide absolute frame of reference so it doesn't get confused by a coordinated turn.

If you can get it to work at 200 degrees and 50G accelerations we can build our own space probe. There may also be interest from small countries with hard to spell names run by alarming people.



#35148 Netduino Plus Firmware v4.2.0

Posted by Arbiter on 14 September 2012 - 01:59 AM in Netduino Plus 2 (and Netduino Plus 1)

but until then, you are stuck with <=2GB cards (which are still widely available and cheap btw!)


Uncommon and getting rarer where I live. Alas, before I could even think about fixing it myself I would have to
  • Learn to build the framework.
  • Learn to deploy the framework.
  • Learn how SDHC works.
  • Learn how the <2G driver works.
  • Figure out what is needed for larger cards.
I wish I'd known it would take so long, I would have started this learning process immediately.




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