On Wed, Jul 25, 2012 at 8:34 AM, Greg Peek <gpe...
> Both are 802.15.4 radios at heart. The only significant difference I could
> see is the 915 MHz has a much lower receive current. If you are leaving
> the radio on, that will be important for battery life. I assume you are
> putting the sensor's radio to sleep between readings, so it won't be a real
> If I were doing it, I'd probably go with the 915 MHz to avoid all the 2.4
> GHz interference, plus the somewhat better propagation.
> These are the least expensive 802.15.4 radio modules I've seen that have
> certification. I might buy a few myself. I wonder if they actually don't
> have RF shields as pictured.
> On Wed, Jul 25, 2012 at 7:56 AM, Doug Ausmus <daus...@gmail.com> wrote:
>> I agree with Jared on the 900 or 400 MHz bands- generally a better
>> choice when wall penetration and such is needed, especially for short
>> intermittent packet type of needs. Just be sure (as with all open
>> bands that are crowded with hardware) that you implement some kind of
>> protocol that guards for occasional stomping from other devices and/or
>> hack attacks.
>> On Tue, Jul 24, 2012 at 6:13 PM, Jared Boone <jbo...@earfeast.com> wrote:
>> > On Jul 24, 2012, at 5:50 PM, Aaron Eiche wrote:
>> > The project I have in mind is an air vent automation system. Range
>> needs to
>> > cover the house, so about 150 feet, through some walls. The receiving
>> > will need to be battery powered and the speed is not a big deal. Data
>> > transfer does need to be reliable as I'd like to potentially report
>> > information back - how much air is going through (this is gonna be
>> tough to
>> > measure), if the vent is closed, etc. Finally, it does need to be
>> > powered, and a only-on-when-needed type deal.
>> > Ideally, I'd go with a 915 or 433/315 MHz device. Range should be
>> better for
>> > a given power consumption level, since lower frequencies propagate
>> > Being in a quieter frequency band will also help, as there will be less
>> > noise to overcome (like you said -- 2.4G has Wi-Fi, Bluetooth, baby
>> > monitors, and microwaves). I'd also go with a device that has the lowest
>> > acceptable bit rate. It seems like 9,600 baud would do just fine for
>> > you're doing. The higher the bit rate of the device, the less tolerant
>> > be of noise (usually). Some devices are configurable, so you can make a
>> > trade-off between the bit rate and the noise susceptibility. Of course,
>> > low a bit rate means the device takes longer to transmit or receive
>> > which means it's burning more power. So for battery operation, you have
>> > consider a module's transmission/reception time and current consumption
>> > together.
>> > On the other hand, you can't really beat 2.4GHz devices for price vs.
>> > ease-of-use. Some of the disadvantages of 2.4GHz operation can be
>> > compensated for with smarter protocol design. ZigBee, for instance,
>> does a
>> > lot of work to make a more reliable wireless network from unreliable
>> > spectrum. Some tricks are: transmitting a packet multiple times,
>> (hoping at
>> > least one gets through), scheduling receivers to listen at a specific
>> > interval (so they can sleep in between and save power), frequency
>> > (so a congested frequency band is avoided most of the time).
>> > I've used the 915MHz Digi modules, and they'd work great for your
>> > application, but they're considerably more expensive (about $40 a piece)
>> > than the devices you mentioned earlier. Perhaps with application of
>> some of
>> > the tricks I mentioned above, the Microchip modules can be reliable
>> > to work well for you.
>> > I'm not sure I've answered your question very well, but hopefully you
>> > more of a feel for the tradeoffs involved.
>> > - Jared
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