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Andrew,

the projected $20 was for an arduino mega shield with wireless chip. As for the cost of the AVR, for me personally an Atmega 128 would be the minimum requirement. I could perhaps make due with an Atmega 64xx, but it would severly cripple the capabilities of the node for me. In wireless sensor networks most AVR based nodes use some variant of the Atmega 128, usually the 128L. I think you can get 8MHz 128s for ~$8.50 if you order enough of them, although bulk is not really an option I suppose.

As for the Java stuff, there's a thin layer between Java and C that allows Java code to send raw packets. The rest is all done in Java. I implemented a collection tree protocol (CTP) which takes ~8k code. So once you have made the initial investment of putting a JVM on the chip the Java code is really small.
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Inopia,  

Ah, I thought that price was for mega + wireless not just the shield!

I haven't examined the register map on the 128 so I don't know if it is 100% compat.  However, as I think I mentioned in my blog, the 640 and the 1280 even 2560 are pin-compatible if the TQFP-100 package is used.  So that would give us some price flexibility.  I think I have come full circle and realized that this original choice is the best.  However I am still a bit worried about software compatibility since I think that the arduino MEGA is not entirely compatible with the 328.  But I guess that since there is no 648 we really have no choice here.


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Andrew,

I'm afraid that the 128 isn't compatible with the 328 like you said, but you might still achieve some sort of compatibility by going for an arduino mega. The arduino mega can use most of the current shield although SPI is a problem (SPI pins have been moved so that SPI based shields don't work. I had to write a software-spi lib to get my LCD working).
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Quote
It looks like all the chips have the same tricky antenna requirements.
The TI "Antenna Selection Guide" at http://focus.ti.com/lit/an/swra161a/swra161a.pdf mentions using antenna specialists :

"8.3 Antenna Suppliers and Consultants
It is difficult to design small and effective antennas and even if a chip antenna is chosen it is often necessary to perform impedance matching to obtain optimum performance. Therefore it could be wise to contact a consultant if a special antenna solution is required. Below is a list of companies that sell different antenna solutions and offer consultant services.

Company - Web page - Expertise
Fractus http://www.fractus.com/ Chip antennas IP Compact antennas
Johanson Technologies http://www.johansontechnology.com/ Chip antennas
Pulse http://www.lkproducts.com/ Chip antennas
RainSun http://www.rainsun.com/ Chip antennas
Vishay http://www.vishay.com/ Chip antennas
Yaego http://www.yageo.com/ Chip antennas
Antenova http://www.antenova.com/ Chip antennas Whip antennas
Badland http://www.badland.co.uk/ Whip antennas
Linx Technologies http://www.linxtechnologies.com/ Whip antennas
Antennasys http://www.antennasys.com Antenna consultant
LS Research http://www.lsr.com/ Antenna consultant
Pinyon http://www.pinyontech.com/ IP Directional antennas
Table 7. Antenna Suppliers and Consultants"
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3. Atmel AT86RF230
PROS:
- Single manufacturer solution, provides software and demo boards
- Zigbee

CONS:
- Specs on the antenna seem pretty scary compared to other chips;  it seems to be a lot more sensitive to interference (or maybe the spec is just being honest )
Atmel discuss the layout of a suitable board Antenna in the doc "AVR2006: Design and characterization of the Radio Controller Board's 2.4GHz PCB Antenna" at http://www.atmel.com/dyn/resources/prod_documents/doc8095.pdf

and they are even kind enough to provide its Gerber files.

It's the same antenna used in their ATAVRRZ200 Demonstration Kit which, surprise surprise, uses the AT86RF230 (2450 MHz band) Radio Transceiver.

[glow]A big +1 for Atmel[/glow]  smiley-wink
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vxir wrote:
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I have experience doing SMT and QFN parts so that is not an issue.
Excellent! - because the Atmel AT86RF230 only comes in VQFN 32 package.

The Atmel AT86RF230  Description states:

The AT86RF230 is a low-power 2.4 GHz transceiver specially designed for low cost ZigBee/IEEE802.15.4 applications. The AT86RF230 is a true SPI-to-antenna solution. All RF-critical components except the antenna, crystal and de-coupling capacitors are integrated on-chip.

Antenna - discussed in previous post.
Crystal - to be done.
De-coupling capacitors - to be done.
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Inopia and vxir,
you guys were discussing minimum microcontrollers ...

Atmel do sell microcontroller and AT86RF230 radio bundles.  These may assist with costs.
See http://www.atmel.com/dyn/products/devices.asp?family_id=676
« Last Edit: October 10, 2009, 04:46:18 am by novice » Logged

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Another thing ...  smiley-wink

Are you guys aware of Atmel's ZigBit™ 2.4 GHz Wireless Module with Dual Chip Antenna (Atmel Ordering code: ATZB-24-A2)?.

Description:
ZigBit Module with Dual Chip Antenna is a low-power, best-in-class sensitivity 802.15.4/ ZigBee module. In just over half a square inch of space comes an impressive set of features you will be hard pressed to find anywhere else. Based on a solid combination of the popular ATmega1281V MCU and the latest Atmel AT86RF230 radio transceiver, this ZigBit version offers superior radio performance with exceptional ease of integration.

ZigBit Module with Dual Chip Antenna eliminates the need for costly and time-consuming RF development and shortens time to market, while embedded 802.15.4/ZigBee software ensures standards-based wireless connectivity for a wide range of applications.


See http://www.atmel.com/dyn/products/tools_card.asp?tool_id=4539

Sounds like a quick way of achieving what has been discussed ...

It looks like Digikey charge US$17.49/unit

PS: I've listed the information above in 5 separate posts to separate the issues.   8-)
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@inopia:  That's too bad about the 128.  Yes I had heard that the 1280 isn't fully compatible either.  However, it is not so bad since the MEGA is out there so people are working on new libraries, etc.  
Actually, I can try to put the QFN-32 328 footprint inside the TQFP-100 footprint so that either chip can be chosen when the board is populated.

@novice:  Yes they sell bundles but they are not really any cheaper (and not stocked).  Also, all of the major RF chips have example implementations with PCB designs to make it easier to deal with the RF side of things.  By copying the exact design and being careful about RF on the digital side we shouldn't have to use an antenna specialist.  You also ask if we are aware of the modules.  Yes, we are.  This issue is that you can buy the RF chip for $2.36 but the module costs $17.  If you look at the XBee solution for Arduino the breakdown is like this: Arduino: $30, Xbee module $20, Xbee shield $20.  So the total cost is $70.  That is a LOT especially when you consider that the point is communications, so you need to buy at least 2 but 10 would be really cool.  So what does the difference between $2 and $17 pay for?  I'm guessing a lot is just "engineering/lab" markup... but I am sure that there will be some extra costs that we will discover as time goes on. :-)



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I'm using a mega and you're dead right about libraries and people working on them, they will all work with a little care and attention to ifdefs I think, at the moment I've hard coded my philips nokia LCD library so that a 6100 shield will work on the mega.  

When I learn how to ifdef/else I'll post about how to do it, works for any SPI based device I've seen so far, I'm in the process of sorting out the mmc lib for the mega too using standard mega SPI CLK,MISO, MOSI pins and any digital pin you like for for the Slave Select pin.  

I've also developed a little 'wing' style breakout board to breakout the pins on a 'standard arduino shield that doesn't break all the pins out so they're accessible' (like the nuelectronics.com nokia lcd keypad shield) and another small wing board that breaksout the SPI pins on a arduino shield to the mega (well, it provides a header for me to connect to the megas SPI pins smiley ).  

They're not designed very well, just made on copper track vero board, but they are dead cheap and simple to make if you have a soldering iron, I'm sure there are other useful configurations that could be made, I also made standard sets for the diecimila that gives me extra pin headers on all pins which is useful for breadboarding different sensors in quickly to clock/miso/mosi lines.  I'd like to make one that swaps the 8 and 9 pins so I can pwm the backlight smiley-grin
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vxir,
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This issue is that you can buy the RF chip for $2.36 but the module costs $17
There's a microcontroller on the module too. Also 2 chip antennas, and the board itself.  There could be other bits too, but I have not looked yet.

digikey have 128 in stock of the ATmega128RZBV which is a "bundle of ATmega1280 AVR and AT86RF230 radio" for US$11.03

If one of these modules was used, I anticipate that the only extras required would be a board and some headers - though this would depend on your desired functionality. This would be much cheaper than the $70 alternative you mentioned.

vxir: don't think I am excluding engineering it all yourself.  I am just tossing ideas around to 'air' it.  You're already au fait with all the material I've posted, so you are knowedgable.
« Last Edit: October 10, 2009, 05:46:48 pm by novice » Logged

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@novice, vxir: I think the ATMega128RZBV that vxir suggested is ideal. It's a cheap, arduino mega compatible chip with a 2.4GHz packet radio. As for platform support it's really close to the AVR Raven boards, so Contiki should also work pretty much out of the box. (Contiki is sponsored heavily by Atmel btw) The antenna could be simply a connector for a standard 2.4GHz whip, with a board trace antenna to fall back on.

@reggi: I have a mega and a Nokia LCD, but I solved the problem in software using software SPI. Might not be as fast, but works fine for practical purposes.
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Also, those modules are $30 @ DigiKey, the unit price of $17 is for min. 200 units. The modules are pretty cool, a breakout board with headers for the various pins such as ADC, UART, SPI, I2C etc would be a nice platform. You could even make it somewhat compatible with Arduino shields I suppose, although there are only three ADC pins brought out from the ATmega.
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Hi Inopia, sounds interesting but I'd like to keep the speed up, I had thought about going the pure software route, but ideally I'd like to be able to use the hardware SPI with many different slave types, mmc, nokia lcd, rtc , eeprom etc. and implementing a seperate SS pin for each would be the best way forward I feel, it's the only thing that doesn't rely on anything other than a simple pin state change.  I really could do with a better understanding of how to address different slave types on the same SPI bus.

page 201 of the 1280 datasheet:

21.1.2 Master Mode
When the SPI is configured as a Master (MSTR in SPCR is set), the user can determine the
direction of the SS pin.

If SS is configured as an output, the pin is a general output pin which does not affect the SPI
system. Typically, the pin will be driving the SS pin of the SPI Slave.

so quite feasible and reasonable to hook up any slave spi device to the spi ports clk,miso and mosi lines and then hook its SS pin to any digital pin that you like smiley  Looking at the clock speeds as well for the most part I guess you want the the hardware spi in master mode otherwise the spi speed clocks back from 1/2 the master clock speed to 1/4 smiley-sad

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@Inopia:
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Also, those modules are $30 @ DigiKey, the unit price of $17 is for min. 200 units. The modules are pretty cool, a breakout board with headers for the various pins such as ADC, UART, SPI, I2C etc would be a nice platform. You could even make it somewhat compatible with Arduino shields I suppose, although there are only three ADC pins brought out from the ATmega.
The datasheet for those ATZB-24-A2/B0 modules states:

Wide range of interfaces (both analog and digital):
– 9 spare GPIO, 2 spare IRQ lines
– 4 ADC lines + 1 line for supply voltage control (up to 9 lines with JTAG disabled)
– UART with CTS/RTS control
– USART
– I2C
– SPI
– 1-Wire
– Up to 30 lines configurable as GPIO
– Capability to write own MAC address into the EEPROM
– Optional antenna reference designs
– IEEE 802.15.4 compliant transceiver
– 2.4 GHz ISM band
– BitCloud embedded software, including serial bootloader and AT command set


Thanks for clarifying the 200+ units price.  200 is not a large number really, I mean if you guys come up w/ a cheaper alternative to the previously mentioned 'expensive' Zigbee units then they'll sell themselves.
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