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631  Topics / Product Design / Re: Licenses and copyrights on: January 22, 2012, 11:58:45 pm
It may just come down to pricing. As long as the product is offered at a nominal cost (whatever that may be) folk will be more inclined to buy your version rather than roll their own unless there are some very compelling reasons. For example, I own a Chronodot and yet my current boards incorporate the same chip that it's based on (space constraints prevent the use of the Chronodot...). 

Similarly, I remember 20 years ago how a local gallery was selling those plasma gas spheres that feature lots of different colors based on the gas mixture inside. Thousands of bucks a pop... that is until the Chinese started to mass produce them, and suddenly something that you could buy a car with became as precious as a couple of DVDs...
632  Topics / Science and Measurement / Re: 200-500mV Sensor? on: January 22, 2012, 06:56:17 pm
Unfortunately the latter device has ground plane too close to the current-sense traces to be safe at 500V - elementary error in PCB layout!  It might flash-over at that high a potential despite the actual chip being rated for 2.1kV...

I'm impressed that they were able to get that much of a measurement range into such a tiny chip.... passing 25A through a SO8 is a truly impressive feat. But then I took a look at the heat sink requirements to do something like this on a continuous basis  and then I started to wonder just how much of my PCB I would have to set aside to prevent this chip from blowing up. So I went with a Tamura S22P instead - 3x the money, much bigger package but no heat and the same 2.5V centered output signal.

What's also nice about the S22P is that you can adjust the sensitivity of the unit on the basis of how you configure the current flow through the three conductors that pass through the center of it. So, a nominal 0-18A sensor can become a 0-6A sensor, for example. I also sleep a lot better with three comparatively fat lugs on either side of the hall effect sensor carrying a 18A load vs. two legs of a SO8. Not saying that it doesn't work, it obviously does, but the Allegro solution likely needs more finesse to remain robust at continuous high currents, a condition I cannot discount in my design.

For example, it wasn't unusual to find a high-powered residential microwave pulling over 1800W on startup. While the power draw decreases somewhat over time, it's still close to 16A the whole time it's running. Makes me wonder if the 712 shouldn't be brazed to the PCB instead of being soldered.  smiley-lol
633  Using Arduino / General Electronics / Re: I2C and voltages on: January 22, 2012, 06:44:43 pm
Allow me to take a slightly different position on this. I prefer using a bi-directional voltage translator instead. Something like a PCA9306. For relatively little money (i.e. less than $1 in single unit quantities at Digikey) you get a chip custom-made for these sorts of applications. Seems like a more reliable solution. I take the same approach on the SPI bus.

Lastly, I'd check digikey and other sites for similar gyros that can run on 5V logic levels to avoid the translation need in the first place. Or, run the Arduino at a lower speed and turn the system voltage down to 3.3V...
634  Using Arduino / Microcontrollers / Re: Looking for a bootloader for the 1284p at 16mhz, anyone know of one? on: January 22, 2012, 06:33:15 pm
Skyjumper, nice to hear from you. Keep in mind that you'll likely forget more about these chips, etc. in a day than I'll ever know.

What made the Brewtroller suite a compelling sell for me was the seamless integration of all the required modifications to make a 1284P work with the Arduino IDE. I did have to learn some of the pin assignments but that's not a big deal. They have a complete IDE to download on their web-site, where all the Sanguino files are in the right places, all the core files have been modified to suit the 1284P, etc. It's the package to download, IMO.

So, I'm still using the 022 IDE for now, never upgraded to 023 because everything 'just works' as is. At some point in the future, the Brewtroller folk may upgrade their software releases to version 1.0 of the IDE. Similarly, Maniacbug appears to have cracked the bootloader nut also. As for me, even though I successfully burned a Brewtroller bootloader, the pain involved in switching to and fro in terms of programmers (ISP) made me decide to use my AVR ISP exclusively as a uploader. So I don't know if the bootloader works - but presume it does since it uploaded OK.
635  Using Arduino / Microcontrollers / Re: Looking for a bootloader for the 1284p at 16mhz, anyone know of one? on: January 22, 2012, 03:14:59 pm
I have several custom boards with 1284Ps. The bootloader combination that worked best for me was the brewtroller software suite. Last time I checked, it wasn't yet up to Arduino 1.0 but you can download a customized version of the 0023 IDE that contains all the files to make these chips work.

You will, however, need the proper hardware to burn the bootloader. The Adafruit unit I have won't do the trick, the AVR MSKPII I bought later does.
636  Using Arduino / General Electronics / Re: Isolation on: January 22, 2012, 03:10:28 pm
You could go a slightly different route, as others have before.

Use a three-pin header with a shunt jumper. The pin in the middle is the 5VDC source for the board. The two other jumpers are either fed by USB or a different voltage source (on board or external, your choice). Then switch the shunt back and forth as needed. Not automatic as the current revision of the Arduino board but also dirt simple to implement.

Based on comments by others, I am not the greatest fan of the automatic switchover on the 2009 board I own (and that may have been rectified by now int he UNO design) since certain voltage levels on the input side (source: barrel jack) can lead to uncertain states in the switching circuit (i.e. between 5-7VDC). By comparison, a simple jumper is pretty hard to screw up. But I can see why a project that is designed to bring microcontrollers to the masses would try and eliminate as many common failure points for first-time users as possible.

FWIW, I use the shunt approach. It allows me to use a external 5VDC power supply that hence does not add even more heat to the enclosure. Even if you decide to regulate the voltage on-board, dropping from 6VDC to 5VDC with a LDO linear regulator will result in less heat being dumped into the enclosure than if you start at 7 or 9VDC.
637  Using Arduino / General Electronics / Re: Data cable issues - problem goes away when touching cable with my hand! on: January 22, 2012, 02:57:18 pm
Great news and I'm sure the above advice regarding proper SPI bus termination and so on will help others also.
638  Using Arduino / Sensors / Re: Detecting Possums on: January 22, 2012, 08:30:42 am
We have bunnies (another creature like the cane toad that Australians love to hate) and squirrels that are also quite destructive once the traditional food supplies dry up. Going forward, I am putting an electric fence around our bed of tulips to at least allow the flowers to break the surface before being eaten.

You could go the ultra-sonic route, there are integrated motion detector / ultrasonic blare horn combinations for sale over here. Though I am not sure that possum ears are sensitive in the ultrasonic frequency range - they do work for non-deaf dogs, cats, squirrels, etc. The best part is, put the thing on a timer and you won't accidentally blast yourself either (for whatever reason, I can hear the things faintly but they give me a nice headache).

Along similar lines, we have 'scarecrow' systems here that use motion detectors to turn on sprayers to dissuade naughty deer and like animals from entering yards. If the possum is simply seeking shelter on your porch, this will be a good reason to leave. Naturally, it might also be a nice surprise for any other visitors or homeowners stepping into the covered zone at the 'right time'.

But the electric fence could work also, depending on how the possum is getting onto your porch. For example, if the primary means of getting in are the steps, uou could try using strips of Cu or Stainless backed with a thick double-sided tape (to insulate and hold in place) to make getting up the steps more interesting - if one tape is on the tread edge, the other below, no human will ever likely make the contact. Similarly, you could run parallel strips on the eaves and other roof sections that the possum might be using.

They key thing here is to figure out how they get onto your porch and why they have taken an interest in it. As others have mentioned, removing food sources is a big plus. Once you know the preferred path, make it less appealing.
639  Using Arduino / Sensors / Re: Detecting Possums on: January 21, 2012, 05:42:58 pm
How about setting up an electric fence with a timer. Only energize them at night.
640  Topics / Home Automation and Networked Objects / Re: Where to start? on: January 21, 2012, 12:42:24 pm
May I suggest a simpler implementation:

Drop the ethernet. Use RF modules instead to do the POE interruption - there are car garage fob / receiver modules you can buy that feature rolling code security, etc. If it's good enough for a car... Cheap and simple too.

Or use a timer (RTC) to do this at a regular interval (in the middle of the night, for example).

There are relay modules /shields out there that can interface directly with the Arduino. Use a separate switch-mode power supply to supply power via the relay(s) to the POE injector(s). That way you can do a rolling reset, i.e. turn off the base stations sequentially, allow them to reboot before turning off the next one, etc. so you might be able to maintain a wireless network coverage continuously (though degraded temporarily in spots).

641  Using Arduino / General Electronics / Re: Data cable issues - problem goes away when touching cable with my hand! on: January 21, 2012, 09:53:23 am
Another option is to go to a driver chip with a different interface and use a communications standard like RS485 that is inherently a bit more tolerant of interference to communicate among the daisy-chain of your LED assemblies. I doubt that these chips can handle SPI speeds reliably over long distances but serial should be OK and your LEDs can't blink as fast as the SPI bus and still do something useful, right?
642  Topics / Science and Measurement / Re: High Resolution Thermocouple and Data Log on: January 20, 2012, 02:19:33 pm
Honestly, if you *really* need 1000 samples per second, the only tool that would do readily do that is an oscilloscope or a dedicated data acquisition system.  Nothing really converts and sample that fast, nor does it make sense to in an industrial control setting, which is what most of these tools are.

Allow me to disagree a bit. One approach is to find an external ADC that samples quickly, with a high enough resolution, and which interfaces easily to an Arduino. Circuit #3 on this page may fit the bill, up to 12 bits of resolution with 11ksamples/s. You may be able to boost to 13 bits of resolution through decimation on the Arduino and still enjoy a faster than 1ksample/s rate. McSarge even wrote a program to interface with the LTC1298 for you. Not sure what the maximum sampling rate is, but you could time it and see how quickly the code executes.

I think the bigger challenge is what to do with the deluge of data. The serial bus is likely too slow to transfer such a quantity without significantly reducing the sampling rate at standard transmission rates. Non-standard serial transfer rates (i.e. about 115kbaud) are possible, but not with the Arduino IDE (i.e. you'll have to use PuTTy, etc.) I've transferred at 1Mbit/s between arduinos but couldn't monitor said transfer in the Serial Monitor.
643  Topics / Device Hacking / Re: Harvesting components from devices on: January 19, 2012, 01:28:15 pm
I too love to take dead devices apart... first with the hope towards arepair, second with an interest in how it was made, third to harvest components if it's truely dead.

If you're looking for high-voltage transformers, BTW, microwave ovens are a great source for them unless it's an "inverter" model. Some folk have used multiple microwave transformers in series to do stick welding projects.smiley-eek-blue

I expect these analog devices to disappear from microwaves over time thanks to the commodity price increases combined with a steady decrease in transistor prices. Just like the classic transformer/bridge rectifier/linear VR/smoothing cap circuit we used to see in all appliances..
644  Using Arduino / General Electronics / Re: How to calculate what capacitors to use? on: January 19, 2012, 01:06:44 pm
Read the datasheets carefully. One linear voltage regulator I used was not happy when it only encountered a ceramic capacitor on its output. Not only did I blow a voltage regulator, but the downstream SD card too (4.5VDC vs. 3.5VDC max allowable will do that for you). Other voltage regulators I have used subsequently specifically stated that they are safe for use with ceramic output capacitors. But they tend to sell at a premium and you have to confirm (via datasheet or inquiries with the manufacturer) that the regulator will be stable using only a (or several) ceramic output capacitor(s).

More often than not, linear voltage regulators are specified to use a large Alumimum Electrolytic or Tantalum capacitor along with a 100nF ceramic one. Data sheets and application examples by the manufacturer are invaluable to beginners like myself, they take a lot of guesswork (and magic smoke) out of the equation.
645  Using Arduino / Sensors / Re: Current Sensing on: January 19, 2012, 12:47:58 pm
A couple of suggestions:
  • Determine the maximum voltage you may be measuring. Add a safety factor (I use 25%) and then see if you can either use the internal voltage reference (1.1VDC, 2.56VDC, etc. depending on the model of your Atmel microprocessor) or whether it makes sense to apply an external voltage reference to the AREF pin. The latter approach is preferable, IMO, especially if you use a voltage reference or a small voltage regulator because variability in the power supply voltage won't propagate into your measurements as easily. However, many people use a cheaper approach using voltage divider networks that also do the trick (but which are more prone to be influenced by other devices attached to your Arduino).
  • Keep in mind: Once you set a alternate AREF voltage (through software or hardware) do not try to sample a higher-voltage signal on a analog input channel or you will blow your ADC. Here, the software approach of setting the internal reference is more flexible, you can easily switch back and forth between reference voltages though you have to add some settling time between measurements.
  • Consider using decimation for your signal. Keep the analogread results in their original integer format, oversample, decimate, and enjoy results of up to 16 bits or so. Atmel has a nice paper on this topic, just google atmel and decimate.
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