From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from snark.thyrsus.com (static-71-162-243-5.phlapa.fios.verizon.net [71.162.243.5]) by huchra.bufferbloat.net (Postfix) with ESMTP id 85BC72012AC for ; Wed, 9 May 2012 14:15:04 -0700 (PDT) Received: by snark.thyrsus.com (Postfix, from userid 1000) id 0351D40478; Wed, 9 May 2012 17:14:27 -0400 (EDT) Date: Wed, 9 May 2012 17:14:27 -0400 From: "Eric S. Raymond" To: "Ron Frazier (NTP)" Message-ID: <20120509211427.GA4099@thyrsus.com> References: <02af01cd2daf$05b24bb0$1116e310$@navisys.com.tw> <20120509164726.GA2102@thyrsus.com> <4FAAAE4F.80409@techstarship.com> <4FAAD66F.3090405@techstarship.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FAAD66F.3090405@techstarship.com> Organization: Eric Conspiracy Secret Labs X-Eric-Conspiracy: There is no conspiracy User-Agent: Mutt/1.5.21 (2010-09-15) Cc: thumbgps-devel@lists.bufferbloat.net Subject: Re: [Thumbgps-devel] Article -- Macx-1: GPS receiver with standard USB connector and PPS support X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list Reply-To: esr@thyrsus.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 May 2012 21:15:04 -0000 Ron Frazier (NTP) : > * Hi sensitivity internal antenna / chipset that can be used indoors > in a residential type structure. The Macx-1 already has this. It's sitting on my desk 5 feet from a window blocked by large trees and hasn't lost lock once since it got here. Gary says it's working just as well in his basement. Truly, this is the most indoor-friendly GPS I've ever seen. Puts the general run of SiRF mice to shame, and raises my opinion of uBlox a *lot*. > * External antenna port in case you're in a steel building or > basement or something with no signal. Use commonly available, > generic, possibly powered, antennas. Doesn't have it. Doesn't seem to need it! > * GPS status led. (My BU-353 slowly flashes when it has a fix, > shows steady with power but no fix.) The led should be synchronized > to the pps. Has it. > * Supercap preferably, or battery which is easily user replaceable > and a common part number, such as CR2032 for example. That battery > may be too big, but you want something readily available. Doesn't have it. But the unit price is low enough that I don't care; the widget is disposable. > * If a battery is involved, a small flashing led to indicate a weak > battery alert, kind of like what is on a smoke alarm. Doesn't have it. > * My BU-353 has a magnetic base. Something like that might be > useful for positioning the antenna. Has it. > * May or may not be relevant, but, would 5 - 10 Hz position sensing > improve accuracy and stability for your purposes? No, not for a timing GPS. And modules with multiHz sampling are tres expensive. > * You may wish to expose the pps signal on a screw terminal or > connector in case you want to attach other instrumentation to that > signal. You may wish it. I don't. I *like* the sealed case, the low parts count, and the rock-bottom cost. For the kind of deployment we're doing, this design is optimal. > Here's a possible alternative to providing an external antenna port, > and all the hassles of piping RF around. With my BU-353, the "puck" > device contains both the electronics and the antenna. The only cord > coming from it is the USB cable. So, it might be preferable to have > a sealed weather proof unit, and just use extension cords for USB > rather than extending the RF section. I know you can easily extend > USB 10 feet or so. I think you can go much further with powered > hubs and such. Just a thought. Way ahead of you. This is why I *didn't* spec an antenna. One cable is simpler (therefore better) than two. > Here's a wild idea, maybe not practical, but, you could attach a > solar cell to the external antenna and / or the thumb-gps case. > This could feed power back to the GPS board and prolong the life of > the battery or slow the drain of the supercap while powering the > antenna if the antenna is in the sun. You could even draw some > energy from ambient indoor lighting. I have a solar powered > "atomic" watch from Casio that does this. It never needs a battery, > never needs charging, and never needs setting. Very handy. I also > have two "atomic" wall clocks that do the same thing. I think they > use a rechargeable battery instead of a supercap. > > Here's another idea, which may or may not have already been > discussed. Do you want to have an on board RTC, which can keep > outputting valid time for a while, if the satellites are not > available due to weather, jamming, interference, etc.? Custom hardware. Expensive. Not suitable for bufferbloat deployment. -- Eric S. Raymond