I just saw that you had to solder all sorts of things

Not all sorts of things, just pins 2, 3, and 5 of a serial cable.

And if it were a regular GPS unit with a regular serial port, I wouldn't even have had to do that. The only reason I had to solder was because my GPS didn't come with a serial port, it came with a Palm3 connector. So I had to solder onto the three pins on its PCB that corresponded with the three pins of the serial data on the Palm3 connector.

It's possible that a straight-through serial cable would just work for you. But if you run into trouble, just open the hood of the serial cable and pull all pins except 2/3/5 and try swaps of 2/3 until it works. (2/3=rx/tx, 5=gnd).

Sled serial is DCE, but also has 12V (Remote Amp) on pin4, and a couple of the handshake lines are actually Dimmer and Mute, but I forget which.

I would bet that most GPS receivers are also DCE, so you would need to cross TxD and RxD in the cable.

Basically, you need (assuming GPS is standard DCE)

Sled<->GPS
2 <--> 3
3 <--> 2
5 <--> 5 (Ground)
4 <--> GPS 12V in. (Assuming your GPS accepts 12V in - otherwise a power regulator will be req'd)

but also has 12V (Remote Amp) on pin4

DAMN, I'd forgotten that. I went to a lot of trouble to wire up to the remote amp line on the main wiring harness. I could have saved myself some work if I'd just thought about it.

Any good affordable GPS's accept 12V in on pin 4? I'd like the easiest (plug-and-play) solution available...

Probably NONE, pin 4 is DTR. So you're going to have to at least pull some pins.

Easiest solution is probably a garmin etrex venture ($150-200?) which comes packaged with a pc interface cable (db9 serial) and a gender changer ($2-5?) to connect it to the sled's serial cable. It eats a pair of AA's in about 10-20 hours though. But then again, as it doesn't rely on the car for a power supply, you can use it for geocaching without needing a 4x4. Nothing will expect 12V on pin 4, that's an empeg specific feature.

Ah.

Hm...

I don't like the idea of relying on batteries. I wouldn't care much about geocaching.

The ideal GPS receiver for me would *support* battery power, but also have some easy way for me to give it power from the Empeg's serial connector. I don't mind cutting some wire and soldering a little bit to do it, but I don't want to have to open a brand new GPS receiver up to do it.

but I don't want to have to open a brand new GPS receiver up to do it.

For me, it was the $9.50 price tag and the fact that all of the Palm software sucked that gave me the confidence to do it.

Garmin sells these combination 12v cigarette adapter/serial cables on their website. They are pretty expensive. Some people are building their own and are often selling them on ebay.

But it all depends on what you want to do. Expensive gps's have builtin maps and as such can be really usable by themselves. But there are also things like the Earthmate, and gps-mouses, and things like the SV6 or Oncore receivers, that have no display and completely rely on a laptop, pda, or empeg , to handle the user interface, and in some cases need a custom built 12V->5V power supply or RS232 line level convertor. Tony got lucky there, nothing to solder but 3 wires.

Yeah, I don't necessarily need it to have its own screen, as I mainly want it as an in-car thing that works with the Empeg. I'd rather take advantage of the Emeg's VFD... Even if it is limited in what it can display clearly, it's good enough for my purposes.

I'll look up those SV6 and Oncore ones you mentioned... I assume they both speak NMEA and would be happy talking to your GPSApp? I'll probably pick the one that will be easiest to hack to work off the 12V power on the Empeg's DB-9 cable. Not sure which that'd be, though.

Edit: Okay it seems the Oncore is just a board that I'd have to solder a DB-9 to... Probably not ideal for me. Couldn't find anything concrete on the Trimble SV6.

I did find this "GPS mouse." But it expects power from a PS/2 connection. Would I need something special to connect that to the 12V on pin 4 of the Empeg's DB-9? It says it supports the following NMEA messages: NMEA-0183 ver2.01 or Rockwell Binary, PRWIBIT, PRWILOG, PRWINIT, PRWIPRO, xxGPQ, GGA, GSA, GSV, RMC, VTG PRWIRID, PRWIBIT, PRWIZCH sentences. Is that good enough?

Low Power Consumption- 55mA/12V
On-board Power Supply- 4.5 to 16V
Looks perfect, you can hook it's power line (whatever goes to the ps2 port) directly to pin4.
Currenly I'm using GGA, GSA, GSV and from the other sentences it looks like it is the rockwell Zodiac chipset that dbrashear sent me the documentation for. It is probably identical to the chipset in the Palm III streetfindere, maybe even the same thing in different packaging.

Damn, 'cept they want $250 for that sucker. There's a cheap knockoff on EBay, but they don't say what kind of juice it needs. I'm guessing converting 12V to 5V isn't elementary.

It is with a $10 PT5101

        PT5101

         | | |

12V o----+ | +----+-------o 5V

           |      |

           |     === 100 uF capacitor

           |      |

GND o------+------+-------o GND

Here is a source for GPS at "fair" prices.

http://www.navtechgps.com/supply/equipment.asp?Line=smartant

The Garmin GPS 16 will do what you want and is somewhat less than $250.

You can also find antennas here but their stuff is new.

I have no connection but I delt with them in a previous life and I think they are legit.

Lynn

Hmm, I think this might be the animal I'm looking for...

If you get the one with the unterminated power/data cable, you could wire that to your own serial plug with pin4 as power and you'd literally have a single-plug solution. Nifty.

If the GPSapp software proves useful to me in the long run, I might have to save up for something like this just to get the fast aquisition times.

They don't seem to clarify the difference between the high voltage and low voltage models, though.

Of course, something like this is cheaper. Dunno if it uses a serial port or what, though.

From http://www.garmin.com/products/gps35/

GPS35-LVS Attached 10 foot power/data cable with bare wire ends. Accepts power from
unregulated low voltage power supplies between 3.6 and 6 VDC. Asynchronous serial data interfaces
via 2 serial ports with true RS-232 voltage level outputs.*

GPS35-HVS Attached 5 meter power/data cable with bare wire ends. Accepts power from
unregulated high voltage power supplies between 6 and 40 VDC. Asynchronous serial data interfaces
via 2 serial ports with true RS-232 voltage level outputs.*

GPS35PC Attached 10 foot power/data cable with female DB-9 serial connection, ready to attach to
your PC. Additional 8 foot power cable extension from the DB-9 connector terminates in a cigarette
lighter plug for easy application of power supply voltage between 6 and 40 VDC. Asynchronous serial
data interface via a single serial port with true RS-232 voltage level output.* **

*All serial inputs on all versions are compatible with either true RS-232 or TTL/CMOS voltage levels.
Port 1 uses NMEA 0183 data format. Port 2 transmits binary position and raw measurement data and
receives RTCM SC-104 differential corrections data, message types 1, 2, 3, and 9.



So the "low voltage" and "high voltage" numbers are clarified there, and the 35PC version just has the car adaptor plug instead of an unterminated wire. And just one serial port outputting NMEA, instead of one with NMEA and a 2nd one outputting binary data. Who cares?!?

So I guess the one I want is the high voltage one without the car adaptor. Since the 12V coming from the Empeg is within the 6V-40V range, it sounds like it's a no brainer.

Based on this page it is RS-232 but it wants 5V power from a laptop's keyboard port. It mentions a cigarette lighter adaptor, but I'm not sure if a software/hardware bundle from 2000 is going to have widely available accessories...

>can someone recommend a good GPS receiver then?

Avoid the Garmin eTrex series -- their dinky antennas render them near useless under tree cover, rainy skies, and even in my living room.

I got a Magellin "Meridian Platinum" (same as "Gold", plus compass, barometer, and temperature sensor.. only the compass is useful, though), which has a proper internal antenna that is mostly unaffected by trees, rain, single story dwellings, etc.. Other models from other brands also have good antennas.

Cheers

It is with a $10 PT5101

How much heat does it dissipate? I'm dissatisfied with the 7805 solution I have now, though truthfully I shouldn't worry since I bought some DC-DC converters salvaged from (I don't remember what, I think telco equipment) to put in both vehicles... useful since at least one is getting an access point as soon as I have a minute.

Next to nothing, it is a switching regulator probably has about 80% efficiency. As the gps draws about 1.2W (240ma at 5V), it is probably in the order of 0.3W. I mounted it inside the same aluminum box as the receiver, and the box gets warmer on the gps side than on the max233/pt5101 side.
It doesn't need an additional heatsink even when you draw a full amp at 5V.

Ok. Well, I guess if I build any more of these other than for vehicles which will get DC-DC converters the 7805s go out the window.

Only trouble is the PT5101 is £15 in the UK - little bit more than < £1 for a 7805. I bought a bag of 2A ones (in the oval cases) from a car boot sale for a couple of quid a few years back, so I'm going to use them otherwise fitting two cars with antennas and power circuits will cost more than the encore GPS units!

In fact, I have just paid $50 for two active antennas off ebay (inc shipping) - they qre quite nice and come with 16ft cables so I am pretty pleased. A fair amount of searching found £30 each was the cheapest I could find in the UK. I could have done better but at $50 I gave up wasting my time!

Gareth

I bought an Sv6 from bgmicro for $25, purely for the antenna to use with my Oncore. Then I found that antenna had a 6" cable, and no extension cable. With different connectors to the Oncore. Then I found out that the minimum quantitiy of RG174 that I could easily buy was 30ft which cost me about $30.

So $50 with shipping for 2 active antennas with 16ft cables doesn't sound too bad at all.


If anyone in the USA/Canada needs some RG174, but doesn't want to fork out for 30ft, I'm willing to sell some at $1.10 per foot (inc shipping). You'd have to deal with the connectors yourself - it'd just be a coil of wire.

anybody know if the empeg has a 5V line we can tap? Of course doing so would probably void your warranty immediately, but hooking up a home-built circuit shaddily soldered (in my case because my soldering skills are bad) to the serial port might too...

Two reasons for sticking with the 7805 approach. The first is that the 7805 is virtually free compared to any of the intergrated switchers and much easier to find as well. It isn't nearly as elegant or satisfying technically but who is going to see it? An extra watt in a car is easily provided and easily dissapated. I don't think any part of my 7805/SV6 is over 45 degrees C.

The other reason is that you are dealing with a radio receiver designed to recover a signal that is nominally -130 dbm at the antenna. We are talking about something that is well below the ambient noise level. GPS only works because of the spread spectrum, synchronous detection architecture. It doesn't take much noise to start to degrade the sensitivity of your preamp and switchers are clearly much noisier than three terminal series pass regulators.

If you do go the switcher route be careful with grounds and shielding. If you keep the radiated noise of the switcher and its external components (particularly the inductors and any schottky diodes) bottled up you can certainly make it work.

Lynn

Hmm, I have the switcher in the same aluminum box as the receiver's PCB. So although it probably is shielded well enough to avoid the antenna picking up any interference, it might still influence the receiver? At least now I see why I had a hard time getting a lock when everything was still a bunch of wired up parts on my desk.

Most of the receiver's RF stage is already shielded on the pcb - the only part that isn't is the (very short) pcb trace from the antenna connector to the RF circuitry within the shield. The antenna cable is also shielded. I would imagine that unless you got unlucky, the signal from an active antenna would swamp any noise that the trace could pick up from a PT5101.

yea, what he said.....