Has anyone got a 'common GPS hardware HOWTO' someplace?

I just picked up one of the Motorola Oncore GT modules from B&G Micro, but seem to have lost my link to the post somewhere here that pointed to specs, etc...

Thanks!

--pj
Austin, TX

For the Oncore's that bgmicro was selling, the techdocs are still on their website
http://www.bgmicro.com/pdf/acs1397.pdf

Woo, thanks!

--pj

PS: They're still selling them, and still for $15 ea.

...and they work great.

You might want to remember that you need an active antenna from somewhere. (5V, not 3.3)

How are you guys getting power to this? And where are you getting the antenna?

Sean

Since the Oncore I bought from bgmicro uses 5V, and also needed RS232 level conversion, I built a circuit to handle both - taking the 12V from pin4 on the sled.

I also bought an Sv6 from bgmicro for $25 that did come with an antenna, and used the antenna for the Oncore. Since I had to buy a 30ft roll of RG174 cable @ ~$30 and then crimp connectors to suit, it ended up costing more than justing getting an active antenna with cable from ebay for around $30. Oh well.

Any way you could describe the circuit you built, and what parts are needed to make it? Is it the same as the one in the PDF linked from above?

If you want a *real* simple circuit for the RS232 level translation, I can outline the 1 chip circuit I did for my SVee6 using a Dallas Semiconductor (now MAXIM-IC) DS275 8 pin "level shifter chip".

I made mine on a small piece of Perf Board (aka Veroboard), small enough to slip inside a "DB9 serial port adaptor" (the sort with a RJ45 connector on one end).

You still need the +5 volts conversion - the simplest way to do this is to obtain the PT1501 for about $10 and use that.

You could build the voltage convertor and level shifter using 1 PT1501, 1 capacitor and 1 DS275 chip - you can probably order those from Digikey or similar and maybe Radio Shack - if you're real lucky. You might get all those for under $20.

Make sure that the PT1501 is mountedn well away from the antenna of the GPS - otherwise the GPs may not lock on to the signal well or at all.
[you could probably put the PT1501 inside the metal case of the GPS to shield its RF from the antenna - but make sure its properly mounted and can't short out.

If you want a photo of what I built - post here, and I'll put one up later today (about 5 hours from now) when I get home.

Hey genixia,
what crimp connectors did you use for the Svee6 Antenna to make it oncore compatible, and how wherre did you source them from?

I have the same problem with my units and I wondered if the Svee6 antenna was usable with the Oncore units - so it appears it is?

Feel like making some antenna extension cables from your 30ft roll of RG174 to help offset your costs?

I'd buy 3 of them for say $10 to $15 each plus p+p [airmailed to me].

if you could outline that I would very much appreciate it. If it is VERY simple, with detailed pictures, and or simple instructions, I should be able to build it.

I used SMA connectors from a local source - but digikey carry them....they weren't exactly cheap either (about $5 per from my source). It would probably be more economical to go with 50ohm BNC as you can get BNC connectors suitable for RG174.

The Svee6 antenna has an SMB connector on it, but since SMB jacks only appear to come as pcb- or bulkhead- mount (ie not as cable ends), I just hacked it off and put on an SMA jack.

I *really* don't want to sell complete cables - unfortunately I don't own a nice set of expensive crimping tools (well I have a tool for the inner crimp, but not the correct locator plug for it, or the tool for the outer crimp.), so my crimps are.....somewhat less than optimal. Good enough for my use - I can replace a connector if my overzealousness gets the better of a 'crimp' - but I certainly wouldn't be comfortable selling cables in that condition.
Add in the fact that it'd cost me a minimum of $8.20 + ($1.10 per foot) for a male-male SMA cable assuming that I don't screw up any crimps, before I even factor in any consideration for my time and effort, and you should be able to see that you'd soon be looking at $30 for a single 6ft cable of 'dodgy' workmanship..... and then you'd still have to deal with the connector on the antenna yourself.

If I had the tools to do a good job, it'd be a different matter - but I think that without them I'd just be doing both of us a disservice..

I'm perfectly willing to sell you some RG174 at $1.10 per foot though

BTW,

if you want to remove that plastic mount from the antenna, then leave on your dashboard in full sun for an hour or so - this will allow it to become flexible enough to carefully bend away from the antenna itself, and soften up the glue - allowing you to carefully separate it with a razor blade. ( I fortuitously discovered this by accident). I'm sure that the defrosting vents would have the same effect if the weather isn't playing nice.

And if you have somewhere under the dash itself that is mechanically safe, then you can just place the antenna in a balloon and tiewrap it to protect it from moisture.

thanks for all that.
I've contacted Navman (which as actually based) here in New Zealand - they do a "Stealth" GPS antenna with whatever connector you want plus a length of RG174 cable.
The stealth antenna is only 8mm thick and can be slid under the carpet on the rear parcel tray of your car.
One of the connector options is OSX which is what the Motorolas use right?

Lets see if they have a good price - if so, then I might be able to get a good deal deal for folks like you - airmail shipping from here for a GPS antenna won't be much and with our dollar half the $US I'm sure you'll get a good deal.

will keep you posted.

My digital camera is having trouble getting a decent photo of my design.
I can give you simple instructions for wiring it up.
In the meantime locate a datasheet for the DS275 chip from Maxim
(do a search for the part).
It has the pinouts there.

re: PT1501, this is also available - look for a post by Jan Harkes on this chip last week [do a search for it].

If you get the datasheets for the DS275 plus the PT1501 you're more than half way there!

According to the specs from bgmicro, the Oncore is indeed OSX.

Remember to check both the voltage, current and gain specs for the antenna with Navman and cross-ref them against motorola's specs. (www.motorola.com - follow the GPS links, and you will find a 'discontinued' link somewhere that has the Oncore specs available...I don't have the URL to hand - it's easy enough to find).

Oops, the PT1501 should be a PT5101

Ok, Got both data sheets..... Wow this is exciting Now the Oncore data sheet (linked above) has a "Suggested RS-232 GPS Receiver to Computer and Time Sync Interface" It has the PT5101 on there, so I'm guessing it is similar to what you did. But it uses a MAX233 on there, which I saw mentioned by someone else. Is this basically the same thing you have? I just take out the time circuit, and the 2 wires going in and out, just go together? Thanks for all your help! I love this place!

the MAX233 is a physically larger (longer) chip than the DS275, so it won't fit in small places [its a 20 pin chip from memory, so thats 2.5 times longer than a DS275].

But, the Oncore suggested design for power & MAX233 chip is perfectly simple to make as well.

You only need 4 wires from that circuit to run the GPS.

2: 1 for power and 1 for Ground and two more for Serial In & Out [called TxD and RxD usually].

The Gound on the Serial port (pin 5 on a DB9 connector) is shared with the "Ground" on the PT5101 and The ground on the MAX233 chip.

You simply wire the 4 wires from your "black box" circuit with the MAX233, PT5101 and 1 capacitor in it, to the GPS [you will need a small (not .1 inch spacing)connector block to connect these wires to your Motorola GPs - your best source is to probably visit a electronics junk shop and buy an old dot matrix or laser printer and scavenge the block connector out of a piece of junk like that (they tend to use them to link the fonrt panel to the printers main electronics) than to try and make your own from scratch. You can cut down a larger connector (with more 'pins' in it than you need, not a connector thats too large) to the 10 or so pin connector block that the Motorola wants with an Xacto or similar knife. You can usually remove the pins from these block connectors with a very small screwdriver or a small point [like a needle or pin etc] - lift the small plastic 'lock' on the side of the connector block up, and then the pin slides out of the block.
You only need to populate the connector block with the 4 actual pins that the Motorlola needs to operate.

If you want "battery backup" for the GPS, then you can add 2 more wires for the battery backup and wire that up to a small 3V or whatever cell - making sure it can't short out when its in the car! But thats not necessary - the GPS will work without it, but it will take a bit longer to get a lock from when the car is started.

Then you Route another 4 wires from the (DB9 Male) Serial connector the the
"black box". You need 2 wires for TxD and RxD signals that go to the RS232 output and input on the MAX233, 1 ground wire, and the +12V power wire that goes to the +12V the Empeg outputs (on pin 4) of the Docking sled serial connector [or elsewhere in your car - such as the accessory line, where its only powered on when the car is - otherwise you'll flatten your car battery evenutally if you leave it permanently wired into your cars battery].

Thats it, easy to build, and you'll have you Empeg hooked up to your GPS in no time.

Sounds like it'd just be easier to buy a GPS with an RS232-compatible connection.

You will (currently) *need* battery backup with the Oncore. gpsapp will not initialise NMEA mode, and the Oncore will use motorola-binary by default. With a battery you can initialise the Oncore to NMEA from a PC app, and then the battery will remember it across reboots.

I'm kinda hoping that may Jan can add in support for switching various GPSs to NMEA - which would make battery backup un-neccessary. (But still a good idea IMO). My current setup uses 2 AA cells for backup, since I couldn't locally source a suitable lithium cell holder, where-as a 2AA cell holder was 99c. Obviously lithium will be smaller, and notionally might last longer (assuming that the AA cells hit their shelf-life limit), but you can pick up a 2AA holder at RatShack.

The difference between using a DS275 and a MAX233 is little in the empeg world. A DS275 will probably only allow half-duplex communication where-as the MAX chips will allow full-duplex. But as gpsapp only talks briefly to the receiver during startup, and everything after that is the receiver talking to gppsapp, this shouldn't matter.

[edit] Actually the DS275 solution will probably work full-duplex with the empeg anyway. The only reason that it's supposed to work half-duplex only is because it uses the PC's (ie empeg's) RxD line when at -12V and charges a capacitor which it then uses as it's -12V source. But the empeg (or most PCs for that matter) doesn't actually need -12V as a mark - TTL level switching is enough. Case in point, I used a 1489 quad RS232 receiver in my interface (I had one lying around) in both directions with no problems. I'm sure that if I were trying to drive 100ft of serial cable then issues may start to crop up, but for under 10ft it works fine.

[edit2]
and then the battery will remember it across reboots
Obviously, what I meant here was "and then the receiver will remember...". Batterys can't remember that kind of information as they don't have a memory. (*)

*...well, not that kind of memory. Many batteries have been found to contain memory over the decades since their discovery. Sir Nicolas Cad for example, discovered that certain batteries could remember just how much energy they were usually asked to expend, and use this information to achieve their goal of laziness by refusing to store any more energy than necessary. And it is widely believed that the reason that citrus fruits have tough skins is due to the selfish gene and self-preservation, whereby the fruits have attempted to prevent the insertion of metal electrodes by the native indians. **
And as for that poor bunny....

** It has also been speculated that they migrated to Florida for the same reason.

You're right, but I don't know of too many 8 channel GPS receivers for sale with serial port and 12 volt interface for $15 each.

If you know of some, then post here.

Still, the thing with GPS, is that the serial interface and power requirements to interface your GPS to the Empeg keeps the "tyre kickers" out - those that can do this sort thing will, those that can't can find someone who can do it for them, and those who only want a "finished" solution can go to Garmin or whatever and plunk more than they probably paid for their [firesale] Empeg in the first place!

Okay, that's not a bad price at all. That's nearly as low as my $9.50 closeout StreetFinder.

In fact, if it does fast satellite acquisition even without battery backup (assuming that the discussed software support ends up in GPSapp), then I might just make one of those interfaces and switch to it. Because I have to say, the long acquisition times on my StreetFinder are a problem. I want to turn it on and have the track data there instantly.

By using the empeg clock and adding a place in config.ini to store your approximate coordinate (within a couple of hundred miles), we can probably speed up the initial startup significantly.

The receiver then doesn't have to guess which part of the sky it is looking at and as soon as it sees one satellite it receives enough information about other satellites to known which others are visible. The problem is that all of these initialization sequences are receiver specific. So fixing this for you will only help your case.

It will probably never be instantaneous because any receiver will have to wait for current satellite trajectories, although receivers with a backup battery can start 'locating' as soon as power comes up.

/me delurks after far too long.

I'd be very interested in such an antenna, probably at least two units, maybe more.

On another note, I'm considering doing a board to plug in to the Oncore (I'm still waiting for mine) that would have:

A DB9 to connect to the empeg sled.
+5V supply for the Oncore derived from Pin 4 +12V
A backup power source, either a Lithium coin cell, or perhaps a supercap.
Level shifters to interface the TTL serial to the empeg's RS232

The notion is that this would piggyback on the Oncore board.

Is anyone else interested? I don't yet have a good idea of cost, but I will let you know when I do.

-Zandr

Im interested, but that still leaves the antenna to deal with.

Good to hear from you again, sir.

By using the empeg clock and adding a place in config.ini to store your approximate coordinate (within a couple of hundred miles), we can probably speed up the initial startup significantly.

I would be very grateful for this if you could implement it.

I'm interested, but that still leaves the antenna to deal with.

It does, but the fewer things in the RF path the better.

Depending on what I find, I'll either a) solder a BNC pigtail (RG-174) to the board, b) use OSX to whatever adaptors (just scored one on eBay), or c) hope that number6 gets us a good deal on antennae with OSX connectors.

c) is obviously preferable, though I'm going to hit one of my favorite sources for weird RF stuff at lunch today.

-Z

This sounds interesting (for my Oncores; I'm not worried about the SVee6-CM3s)

Let us know.

I haven't heard back from Navman here, but in case you're interested & want to follow up with NavMan OEM in the US, heres the
address for their US operation:

Navman OEM
27121 Towne Centre Drive
Suite 220
Foothill Ranch
CA 92610-2807
U.S.A
T: +1 949 461 7150
F: +1 949 461 7860

The part you want is the:

"AA004000" (OEM) "Stealth" antenna


See what you come up with price and delivery wise.
I will try to get a price here, then see which one is the cheapest.