need help with GPS to BS2 connection
guitar_plr
Posts: 31
Hi all.· I am having problems connecting my Garmin GPSMAP 60C to the BS2.· I am already pretty familiar with doing this since have already conected an older magellan map 330 to it using the same method & program with no problems.· I initially tried Jon's EasyGPS program but I couldn't get that to output anything but "No GPS" so I tried this small program. Here are the details: (see attached schematic)
- Pin 3 of DB9 cable goes to BS2 I/O pin 0
- 22k resistor between I/O pin and DB9 pin
- Pin 5 of DB9 cable to ground
- Other end of cable (4-pin Garmin plug) to Garmin GPS
- Garmin set to "Text Out" 4800 Baud
·
A very simple BS2 program that should output something:
SerData VAR BYTE(25)
Again:
SERIN 0,16572,[noparse][[/noparse]STR SerData\25]
DEBUG STR SerData, CR
GOTO Again
·
I get nothing on the screen.· If I connect my GPS using the same cable to my computer and using the terminal program I get normal data showing!!·So that means that the gps and cable are·working ok.·
I also know that there is nothing wrong on the BS2 board or wiring because I can use my old GPS with a different cable and same setup and program and get correct results.· Also, I have tried a bunch of baud rates and no change.· Also, I don't know if this helps but if I switch the ground to any other pin but 5 I get 1 strange "Y" character with 2 dots aboove it at a rate of 1 per second...Connecting the ground to the "correct" pin results in no output.
Please help.· Thanks!
·
Post Edited (guitar_plr) : 4/26/2005 3:35:14 AM GMT
- Pin 3 of DB9 cable goes to BS2 I/O pin 0
- 22k resistor between I/O pin and DB9 pin
- Pin 5 of DB9 cable to ground
- Other end of cable (4-pin Garmin plug) to Garmin GPS
- Garmin set to "Text Out" 4800 Baud
·
A very simple BS2 program that should output something:
SerData VAR BYTE(25)
Again:
SERIN 0,16572,[noparse][[/noparse]STR SerData\25]
DEBUG STR SerData, CR
GOTO Again
·
I get nothing on the screen.· If I connect my GPS using the same cable to my computer and using the terminal program I get normal data showing!!·So that means that the gps and cable are·working ok.·
I also know that there is nothing wrong on the BS2 board or wiring because I can use my old GPS with a different cable and same setup and program and get correct results.· Also, I have tried a bunch of baud rates and no change.· Also, I don't know if this helps but if I switch the ground to any other pin but 5 I get 1 strange "Y" character with 2 dots aboove it at a rate of 1 per second...Connecting the ground to the "correct" pin results in no output.
Please help.· Thanks!
·
Post Edited (guitar_plr) : 4/26/2005 3:35:14 AM GMT
Comments
Are you sure that the cable you're using is indeed a DB-9 serial cable? I ask due to the 4 wires used on the Garmin end, and the comment on the Garmin web site that a USB cable is provided.
Regards,
Bruce Bates
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Truly Understand the Fundamentals and the Path will be so much easier...
I'm notorious for never remembing which pin is TxD and which is RxD on the DB9 connector....so try moving over to pin2 on your DB9 and see if that works!
it is 4800 8N1? or some other form of 4800?
It is indeed inverted...so you're using the proper baudvalue number to represent inverted 4800!
Double check your terminal program to find out what its' baud was set to....9600 is a fairly common 'start-up default' value in terminal programs....
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
perhaps the OP didn't measure the voltage levels of the rs232 signal and decided to err on caution in case he did have 12volt levels on the rs232 line!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Bruce: Yes, I have a specially made DB9 serial cable to Garmin GPS 4-pin.· It looks something like this:· http://store1.yimg.com/I/gilsson_1838_223668·. Also, I have confirmed that the cable has worked with the GPS by connecting it to my laptop and running the terminal program, it works fine.
Tom/ steve_b: Yes I'm using common ground, connected to the BS2 board Vss.· ·I've also tried switching the Tx/Rx pins around to see if there was a difference and it doesn't work.
Paul: Yes, Steve is correct, I used the Basic Stamp manual to find the value of 22k for the resistor.
So...To double check I used a meter to check the connections between both sides of the cable:
Garmin Pin 3 (Tx) = DB9 pin 2 (Rx)
Garmin Pin 2 (Gnd) = DB9 pin 5
Those were my inital connections which should be correct.· What is strange is that the cable works perfectly with the GPS and a terminal program on my laptop.· Is it possible that I may have to make connections with the DB9 pins (connecting pins 1,4 & 6 and 7 & 8) to elimiate hardware handshaking like the manual says, although I doubt that is the issue.
Thanks guys for the replies, I will·continue to test... Anyone have any other ideas?
·EDIT: Just a thought...Could the ac adapter in the cable be a problem?· When I tested the connections using a meter, the Garmin pin 1 (power input) showed a reading when connected to the DB9 pin 5 (ground).· I thought that was kinda strange.· By the way the reading was not 0, like I was expecting it was 13 or something.· Maybe I should just get a regular cable to simplify things.
Post Edited (guitar_plr) : 4/26/2005 5:30:44 PM GMT
And the 4pins on the garmin is just Gnd/TxD/Rxd/pwr? So handshaking doesn't matter at the garmin end!
if you want to try something quick....run a single wire from Vss to the GND connection on your gps and one from your input pin (P0 in your program) to the TxD pin of the garmin!
You should be able to get away with just holding them with your fingers!
Also, have you tried sitting outside with the gps! I wonder if yours doesn't output anything if it doesn't see anything!
I had one a while back (think it was an Etrex..don't know) that, after sitting in doors for a while, would tell me it can't see anything and would ask me as much...and I think it would give me the option to go in to DEMO mode (don't know if this outputs serial data).
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
As I said before, I got the GPS, cable and a laptop running a terminal program·working perfectly.· The settings on the Terminal was 2400 8-N-1 (8 data bits, no parity, stop bits = 1).· This equals 16780 for the BaudMode setting which is what I am using.· See attached diagram for what I am talking about.·
* Why would there be any difference between:
1.· connecting to the terminal program through my laptop and
2.· connecting to the BS2 using 2 pins (Rx & Gnd) and accepting serial data using the same parameters??
Any ideas?· Thanks!
Post Edited (guitar_plr) : 4/27/2005 2:15:41 AM GMT
in your initial post, you said that it was 4800
"SerData VAR BYTE(25)
Again:
SERIN 0,16572,[noparse][[/noparse]STR SerData\25]
DEBUG STR SerData, CR
GOTO Again
"
this is what you said....you should try using the 16780 that you noted in your last post!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
And post your entire code!
I'm assuming you have a breadboard that you are working with....you can still use a resistor inline if you want....but your cable might be funky!
Is the cable supposed to power the gps? I notice it has a fuse inline (on the power wire)
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Your earlier post, a few entries back, was never specifically addressed, so I repeat it here with some possible answers:
quote
* Why would there be any difference between:
1. connecting to the terminal program through my laptop and
2. connecting to the BS2 using 2 pins (Rx & Gnd) and accepting serial data using the same parameters??
end quote
In answer to the first, it is often the case that the RS-232 voltage levels as found on a laptop may be lower than those found on a PC. This happens more often than not if the laptop is being used on battery power rather than hooked to its charging station (line powered). Part of this may be due to power conservation measures. Another area to consider, although it's generally seen as a problem during Stamp programming rather than during RS-232 communication, the FIFO buffers may cause a synchronization problem. This can be avoided by shutting them down, using the advanced section of the comm port setting section of device manager. Lastly there may or may not be issues with the specific terminal program you are using. I don't remember you stating which terminal program you're using.
In answer to the second, other than the noted voltage level differences between "real" RS-232 and microcontroller RS-232 (+12 VDC and -12 VDC vs. 5 VDC and 0 VDC), and whether the signal is inverted or not, there really shouldn't be any significant difference other than the possible issue of execution speed. Both of these issues can be avoided by using a line driver (MAX-232 or equivalent) between the GPS and the Stamp. In general, the Stamp will be slower to respond than most laptops in fetching the serial data and it may have more turn-around time from SERIN to SERIN, in a loop situation as you have in your test program.
If your terminal program was successful at 2400 baud, I'd use the appropriate 16780 (inverted) or 396 (true) baudmode, and stop testing with 4800 baud values, if you are SURE that's what worked when you used your terminal program. Many of the GPS units we've seen on this forum seem to operate at 4800 baud as a default, but newer units can be strapped or set to other baud rates prior to use. Some require a configuration program to do so.
Regards,
Bruce Bates
Since the GPS worked with the laptop, he wants to know why the GPS didn't work with his stamp. This says his cable is ok.
And being that there are only 4wires going to the GPS, I doubt this is a 'handshaking' problem.
And if his laptop 'picked up' the data at 2400 then he should use the 16780 as the rs232 will be inverted.
Guitar_plr, have you measured the voltage coming off of the GPS' TX pin? Just wondering if Paul was right about the voltage levels being low and the resistor value being too high!
The 22kohm resistor is there to limit the current to the stamp. There is a voltage drop associated with this, but it doesn't drop the 12V (rs232 level) down to 5v(ttl level) so the stamps internal clamping diodes will clip the excess voltage. It might be hard to measure your voltage coming out, but you may have to reduce the value of your resistor.
OR, you have a connection problem. Maybe you didn't initially use the 22kohm (been there) and toasted your P0 pin. Maybe reassigned the stamp serin pin to a different pin!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Steve:· Could this be a voltage issue like you suggested or the 22k resistor is too much?· To measure the voltage coming out of the Tx pin on the GPS do I just touch one lead from the DMM to it and the other to ground on the BS2 board??· Also, what setting should I put the DMM on, DCV 20, 200, 2000m?· (I've only used it for continuity and resistance measurements, so far!)
Should I try a lower resistor?· What should be safe?· (By the way, Steve, thankfully I didn't toast my I/O pin, I tried it out with another GPS.)
Thanks guys!
you are right about how to place your meter leads!
One on the GPS TxD pin and the black lead on the ground of the GPS.
Even if you have an autoranging meter, set it to the 20V scale (I think the next scale down is 3V which is too low).
See if you can slow the data coming out....can you set the baud to anything lower than 2400? I say this because, unless you are using an analog meter, your digital meter won't be fast enough to pick up the readings (as it's trying to get an average voltage of a data stream (high and lows).
BUT, you should get a quick idea of what kind of voltages you might expect...AND, if data flows (of course it worked thru the same cable on your PC).
Lettuce know what kind of voltages you see with your meter and we'll take a guess at what kind of resistor to use!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
20v: -.06 to -.07
200mv: -60 to -90
2000mv: -85 to -90
Thanks for the help!
You would've been looking for peak values that would look like they're jumping. It certainly doesn't look like you have anything based on those readings.
Don't use your cable....if you can connect directly to your pins on the GPS--I know the Etrex had those contact pins that were big enough that you could actually solder a wire to them...but you could certainly make good contact with your meter).
what's the make of this GPS?
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
35-36 (2000mV) and
.03 (20v)
The reason they are not negative numbers anymore is because I swapped the meter lead positions.· The interesting thing I have found is even when I turn off the serial interface choice in the GPS menu, the numbers above stay the same...The GPS model is a new Garmin GPSMAP 60C.
I have also double checked that I connected the proper pins.
In comparison, my old GPS (magellan map 300) ouputs 3.35-3.51v on the 20v scale...
Any thoughts?
Thanks.
EDIT:· I believe that even when there is no satellite data recieved on the GPS, it continues to send serial data because I was getting consistent meter readings even·when there was no satellites in view.
Post Edited (guitar_plr) : 4/29/2005 2:13:09 AM GMT
Do you have access to the GPS pins while connected to your laptop?
I wonder if you GPS is doing a similar thing that the BS2 does...by stealing power from the laptop, to generate the rs232 voltages.
If you connect your laptop up and measure voltages as you just did....see what you get.
Have you tried supplying power to your GPS with this cable as well?
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
They obviously don't describe issues with connecting to stamps....but here's a link that might shed light!
http://www.garmin.com/support/faqs/faq.jsp?faq=417&webPage=Main%20web%20page
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
So, most likely after seing that article, it is possible that the voltage differences could be a major factor in this.· I have to find my RS-232 breakout box so that I can check the voltages of the GPS Tx pin while connected to the laptop com port.
Forrest:· I don't·have the USB·cable·connected at the same time, so it shouldn't be·an issue.· Thank you for the heads-up, though!·
The Serial Protocol is based on RS-232. The voltage characteristics are compatible with most hosts; however, the device transmits positive voltages only, whereas the RS-232 standard requires both positive and negative voltages. Also, the voltage swing between mark and space may not be large enough to meet the strict requirements of the RS-232 standard. Still, the device voltage characteristics are compatible with most hosts as long as the interface cable is wired correctly.
Could this be a problem?
For my money, the first part of that caveat is not nearly as important as the second part, where one may not be able to differentiate a mark from a space. If this were my project, I'd be real tempted at this juncture to insert a MAX-232 in the serial line to help in bolstering what voltage difference there is, to even higher levels. There is no guarantee that that will work, but it certainly can't hurt, the way I see it. This is not the optimal solution, but there seems to be no way to correct the problem at its source. The effort here is to make the best out of a bad situation, IMHO.
Regards,
Bruce Bates
the fact that it only sends positive voltages is no big deal really. The Stamp does the same thing!
The stamp is a ttl device so when you do a serout of one of the pins (not p16) it only sends marks and spaces as 0V and 5V.
The concern here is that the GPS isn't putting out enough to cross the stamps threshold between a 1 and 0 (I beleive this is 1.47volts or something).
Because you had put your meter on the GPS pins and didn't see anything, I'm wondering if the GPS steals power from the host device. The stamp does this when you have it connected to a PC.
This all works with your laptop! This is the painful thing eh! So what's the difference here....you still only need 2 wires (GND and TxD from the GPS). So there's no 'handshaking needed'.
Now since you're using the factory cable (or aftermarket) you are using all 4 wires....the laptops TxD pin has some voltage on it that might be giving the GPS a boost in it's RS232 comms.
I searched the garmin website and couldn't find any specs on the voltages to expect from the serial comms.
When you find your serial breakout box....connect all the wires you need. Then monitor the voltage. If you have voltages on your GPS TxD line, then remove the wire going to the GPS RxD line (this would have the voltage on it from the laptop/PC) if your voltage goes away, or drops, then your GPS is a voltage leach. Then I'd wonder if you could get away with just connecting +5Vdc to the GPS RxD pin...honestly not sure if this would work....
I'm not even sure a MAX232 would work with a port power stealer (not sur ewhat you want to call it....phantom power port? haha). But lets see what you get after you find your breakout box...even get an old cable you don't mind hacking (just be sure it's a straight-thru cable).
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I'm new hear, and it seems like you are doing something that I would like to do. I'm not quite to that point yet. I was still trying to find out if I could connect a GPS to a Stamp. I just posted a few minutes ago in the Sandbox. However, if you can speak to my post, I would appreciate it... likewise if I can ever help you, I would be more than happy to.
I see that you wrote that you are using the GPS 60. I'm going with the OEM route, with the Garmin GPS 15H. I was just getting ready to order it, and a good stamp from Parallax, but I thought I would see if it has been done before.
Best of luck on your end. If I find anything out, I will let you know.
If you go to the Parallax website and look for their Nutz & Voltz articles
here's the link to 1 article http://www.parallax.com/dl/docs/cols/nv/vol3/col/nv83.pdf
here's the other http://www.parallax.com/dl/docs/cols/nv/vol4/col/nv103.pdf
I'm sure there might be another and there's certainly enough code on this forum to get you started (as well as support).
Try a search in the Basic Stamps forum and you might get some hits!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
And there were a few posts in the last month referring to the BS2 and GPS's.
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
* Measuring the GPS Tx pin alone outputs: 0V (as expected)
* Measuring the GPS Tx pin when connected to laptop using full DB-9 cable, outputs: 10v p-p @ 500Hz
Now here is where it gets interesting:
* Measuring the GPS Tx connected to laptop Rx (DB-9 pin 2) and ground pin connected ONLY: None, and no data shows on laptop.
* Measuring the GPS Tx connected to laptop Rx (DB-9 pin 2) AND GPS Rx connected to laptop Tx (DB-9 pin 3) and ground connected: and it works!
It seems the GPS NEEDS to have its Recieve pin connected (and possibly sent signals) for some reason even though it is not using it!! The laptop Tx (DB-9 pin 3) outputs a sawtooth pattern continuously (whether the terminal program is running or not) at .22v @ 3.8khz.
Why would it seem that the GPS start transmitting only when it senses input on its receive pin? This doesn't make much sense to me...
Does this mean that I will have to try to send using PULSOUT to the GPS with a specific waveform everytime I need to get GPS data? It's pretty strange because my older Magellan worked fine...but those are the facts!
Any thougths or ideas? Thanks!