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Are low powered radio signals ever used to share a timing pulse locally?
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cdev:

--- Quote from: Berni on November 02, 2018, 08:37:08 pm ---You can get GPS modules that support differential operation to a base station. And you don't need the subscription services to do it. Usually you just need to buy a 2nd one of these RTK capable GPS modules, stick it in a fixed position somewhere around your house and somehow get its UART data over to your lawnmower or whatever. It needs a good antenna and a clear view of the sky without trees and such to get a good enough signal but once you do you can get up to 2mm positioning accuracy in relation to your DIY base station.

--- End quote ---
Yes, I have 3 RTK-capable GPSs now and have used RTKlib successfully mostly to learn about GPS antennas. Its been a few years since I had it running, but recently, in order so that I could use it to learn more about robotics, Ive thought about setting up my base station permanently. Its not a high priority project though. What would make me want to do it a lot more would be finding a project which I could participate in. Other people doing the same thing. Also, cost is an issue, not spending a lot of money. The part that interests me the most is the navigation, more so than the shortening of the lawn. :)

--- Quote from: Berni on November 02, 2018, 08:37:08 pm ---I thought about doing a robotic lawnmower before but i never got around to it as i expect it being a lot of work before it works reliably.

--- End quote ---

Around two or three months ago I had an exchange with somebody on here who had bought a bunch of Skytraq S1315F RTK GPS modules very inexpensively. They are the unit I used and they can deliver very high accuracy. I forget how much he paid but it was under $10/unit. Its a GPS-only module but my own experience with them was quite good. The one thing that you need to do however is either let them run continuously or use the AGPS feature on them to download ephemeris data (which I never did) Otherwise when you turn on RTKlib and it starts collecting data if its from a complete cold start the accuracy at the beginning is typical for a cold start GPS and it takes some time to smooth out, but once its been running for a while its extremely accurate. I could give you the settings I used, i recently found the archive of stuff I saved then. the software has improved significantly since then also. You can also use Ublox and a bunch of other brands with RTKlib. performance is quite good with newer multi-band receivers. Skytraq is very good though. In my experience, more stable than Ublox.
David Hess:

--- Quote from: cdev on November 02, 2018, 07:09:35 pm ---Also I'd be interested in hearing your opinion on why shouldn't somebody buy a pre-packaged router box. I do think that is probably a good idea, BTW.
--- End quote ---

There are several reasons:

1. At least in my experience, they are unreliable but maybe that is only D-Link.

2. They have an appalling security record.

3. If you want real security, then you need something with VLAN support.  See below.


--- Quote ---What are your suggestions for flexible but inexpensive (Gigabit-Ethernet capable) hardware?
--- End quote ---

Repurposing x86 PC hardware allows using a BSD based router distribution like m0n0wall (1) or pfsense and if you want much better security, this allows the use of VLANs in one of two ways.  Either multiple ethernet ports can be installed or a VLAN capable external ethernet switch can be used as a port expander to turn one ethernet port into many although this limits total throughput.

The advantage of a VLAN versus using a switch for your internal LAN is that all traffic between the LAN ports can be routed.  So you get to decide what can access the internet and what can access other LAN ports.  If one of your systems is compromised, then it no longer has unrestricted access to everything on your LAN.

For instance your PCs and other systems could be granted access to a single file server while *not* having access to each other and the file server itself would not necessarily be able to create connections to the various PCs but can only respond to connections from them.  Stateful firewalls are so fun.

(1) m0n0wall is deprecated but has spawned several replacements.
Berni:
Yes almost all of these home grade routers are shit. Stay away from them.

The solution is to simply step up one price grade to more professional network gear meant for use in a small company. This sort of gear is a good sweet spot in that it has all the advanced features and proper firmware, but its not one of these big expensive rack mount routers with a ton of ports and screaming fans for cooling.

At home i use a MikroTik routerboard with 5 ports. In the many years of using it i only needed to reboot it once and that was because a firmware update requires a reboot. It never starts behaving strangely after running for a long time, changing any setting in the configuration interface never needs a reboot to apply it. The downside tho is that configuring a lot of things is a lot more complicated so you pretty much need to google everythyng.
David Hess:
My router for the past 10+ years has been a repurposed Pentium 2 workstation optimized for low power.  Its only unscheduled downtime was when the icemaker upstairs leaked water which dripped into it and I had it running again 24 hours later.  During that event, it took all of 15 minutes to transfer the ethernet cards and FreeBSD boot drive to a spare Gateway Pentium 4 that I happened to have.
madires:

--- Quote from: cdev on November 02, 2018, 07:09:35 pm ---What are your suggestions for flexible but inexpensive (Gigabit-Ethernet capable) hardware?

Also I'd be interested in hearing your opinion on why shouldn't somebody buy a pre-packaged router box. I do think that is probably a good idea, BTW.

--- End quote ---

A TP-Link supported by OpenWrt.
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