[Noisebridge-discuss] I need some help with radio design

[Tomm]

Hi Martin,

I'm saying "looking for" because at low quantities (less than
thousands), you'll likely be best off buying radio modules rather than
design your own radio from scratch.

There are ~$3 each, will probably fulfill the desired function but not
in the way you're currently envisioning:
http://www.sparkfun.com/commerce/product_info.php?products_id=8945

Basically, you'd have to roam around with a mobile receiver to get into
range of the transmitter, and take multiple samples to home in on the
actual location.  Install a couple of receivers near the front gate
chokepoint, and you'll know if an errant bicycle is leaving the playa.

On the plus side, you'll actually be able to find things.  RF range and
RF triangulation location accuracy are inversely related, ie, high power
radio = small change in RSSI over distance = low accuracy.  If you had
high-power transmitters to get your desired ~1 mile range with 6-8
receivers around the outer ring, my guess is that you'd be able to get
to within 30-50 meters, but then things would get wonky: you'd get a
high RSSI off a bounce of the side of a big truck and be 100m away, and
when you're right next to the transmitter, you might get a low RSSI.  RF
is funky that way.  Go for 500', and you'll be able to get within 5-10m
of so, enough to be sure enough that the bike is hidden  inside _that_
rental truck.  You probably don't want a fixed receiver anyway because
you'll have rf null issues, and to overcome it you have to start
frequency hopping, then you get into sync issues and lots more
complexity than you likely want to deal with.

    Tom
ps: this assumes that the sparkfun receiver module will output RSSI.  I
didn't look to see, but if not, it could be hacked in if no suitable
replacement is found.  Still much easier than designing from scratch.

On 3/2/2010 2:29 PM, Martin Bogomolni wrote:
> Looking for?  I'm planning on making between 100-500 units, especially
> if I can keep them inexpensive  (say, no more than $10 each in parts
> if I can help it.)
>
> -Martin
>
> On Tue, Mar 2, 2010 at 4:10 PM, Tomm <tomm.fire at gmail.com> wrote:
>   
>> Hi Martin,
>>
>> How many devices are you looking for, and what price is "cheap"?
>>
>>     Tom
>>     
>