Yes, I do, sorry. I mentioned that I replaced the 5v reg, well I also replaced the caps and I didn't put them back·before I took the picture. I have .1uf cap from vin to gnd and 1uf cap·from vout to gnd on the 5v reg.
Hey guys, im new to this thread and to the forums actually, so please bear with my "amatuerness." I too have the parallax GPS and have had some issues.
First off i started with the idea that the GPS module was 2 stop bits, i recently checked the PDF file and it says 1 stop bit. Maybe they came out with a new revision? To test it i hooked it up to my computer serial port via RS-232 level shifter and tried 4800 baud with 1 stop bit and 2. Both worked!? can someone please explain this to me.
Then tried the GPS board on my the PJRC 8051 dev board in smart mode. I tried the smart mode for the reasons of being easier to use. I connected VCC-5V GND - Vss /RAW - UNCONNECTED and had the same dilemma you guys previously discussed about how to connect the SIO. I tried devising schematics for connecting my dev boards seperate Tx and Rx pins to the single SIO, i saw the schematic with the 2 resisters on each line. Can someone explain 2 me the electronics behind the schematic attached. wont the Tx signal go through both the SIO and the Rx, even through theres another resister.
1) All that's required for serial I/O is one stop bit. Most serial I/O ports will accept even a partial stop bit (somewhat more than half). Since idle on a serial port is a logic high, more stop bits are really just additional idle time. The reason for sometimes requiring more than one stop bit is to allow an additional bit time of idle time for an I/O device to do some internal processing where it might not be able to watch the input for a start bit.
2) Your schematic will only work reliably if "open mode" is used (see the documentation for the serial I/O routines). When the Propeller's TX line is idle, it's set to logic high (about 3V). Depending on the resistor values, this may pull up the signal from the GPS to where it looks like a logic high even though it's intended to be a logic low (like a start bit or a zero data bit). You can't reduce the resistor values too much or either the Propeller's I/O pins or the GPS's I/O pin will be damaged. The answer is to change the Propeller's TX pin to an input (high impedance) when it's not being used. You can do that by modifying the serial I/O routines or by specifying "open mode". Since the GPS receiver is designed to connect directly to a Stamp I/O pin set for "open mode" serial I/O, it presumably has a pullup resistor (to 5V) already.
Sometimes transmitting 2 stop bits is a good thing - particularly if you've got your protocol set up to receive only 1 stop bit. I used this recently in an application that sends continuous comms. The messages are short (about 5 bytes) but are transmitted without any breaks. The problem with this is that it can take a receiver a long time to sync onto the message - reading 0 bits in the middle of bytes as new start bits. My solution was to transmit an $ff character once per cycle (of 5 bytes). With the extra stop bit this means that an entire serial byte (10 bits) of idle-state is sent, and that the next start bit stands out as far as any receivers are concerned.
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It's not all that hard to count the number of grains of sand on the beach. The hardest part is making a start - after that it just takes time.·· Mirror - 15 May 2007
Hi Chris. sorry, It's been a while since I looked at this thread.
You were great in helping me dig into this.·In my book, you're right up there with Mr. Mike Green for having an action·figure created·in your·likeness. I never got it to respond in smart mode and gave up. I do have a new propstick and fresh bread board. Mabey I will try again and have better luck this time! I will let you know·if I get it working.
thx a bunch. fish
Chris Savage (Parallax) said...
Fish, anything new on this?
·
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
Still nothing.
It's·curious that my BS2 can talk to the GPS mod in smart mode, but my propstick can't.
I don't have a prop clip yet to try it out with my prop demo board.
Using Chris's suggested setup and code, I have tried 3 different propsticks and no go.
The GPS module must be fine since my BS2 can talk to it in smart mode.
I realize that using a prop demo board·shouldn't be any different than using a propstick, but for my own warm fuzzy, has anyone anywhere successfully used a PropstickUSB to communicate with the GPS module in smart mode?
thx
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
I don’t remember if I asked if you were sure what resistor size you were using…For a temporary test try using a 470 ohm resistor (yellow, purple, brown, gold) and see if that works. Typically 1K (brown, black, red, gold) works fine. But you could try something a little smaller to see if that is an issue. Take care.
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Chris, at long last, it's finally working! I thank·you, and·everyone who helped.
Cheers, fish
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
I may have missed something here but I have connected the gps module to my prop using the simple serial object and no resistors.· You have to set rx and tx pins the same.· There is something foggy in my brain about pausing after the GPS! header.· I did not like the smart mode at all because you can only access one thing each second.·
What made it start working? You’ve got my curiosity…
Erik,
You said you used no resistor…That is definitely not a good idea. You should have a resistor in there. No pause is required after the “!GPS” header…And /RAW Mode doesn’t go any faster than Smart Mode. Each mode offers one update per second. Take care.
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Chris, this round I had all new stuff (except the gps module). New·wiring and·bread board etc.·I cleaned off my workspace; got better lighting even got·a hair cut. Oh yes... and that 470 ohm resistor per your suggestion·on the rx/tx line
thx
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
Comments
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Yes, I do, sorry. I mentioned that I replaced the 5v reg, well I also replaced the caps and I didn't put them back·before I took the picture. I have .1uf cap from vin to gnd and 1uf cap·from vout to gnd on the 5v reg.
fish
Quattro
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'Necessity is the mother of invention'
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Chris Savage
Parallax Tech Support
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Chris Savage
Parallax Tech Support
First off i started with the idea that the GPS module was 2 stop bits, i recently checked the PDF file and it says 1 stop bit. Maybe they came out with a new revision? To test it i hooked it up to my computer serial port via RS-232 level shifter and tried 4800 baud with 1 stop bit and 2. Both worked!? can someone please explain this to me.
Then tried the GPS board on my the PJRC 8051 dev board in smart mode. I tried the smart mode for the reasons of being easier to use. I connected VCC-5V GND - Vss /RAW - UNCONNECTED and had the same dilemma you guys previously discussed about how to connect the SIO. I tried devising schematics for connecting my dev boards seperate Tx and Rx pins to the single SIO, i saw the schematic with the 2 resisters on each line. Can someone explain 2 me the electronics behind the schematic attached. wont the Tx signal go through both the SIO and the Rx, even through theres another resister.
2) Your schematic will only work reliably if "open mode" is used (see the documentation for the serial I/O routines). When the Propeller's TX line is idle, it's set to logic high (about 3V). Depending on the resistor values, this may pull up the signal from the GPS to where it looks like a logic high even though it's intended to be a logic low (like a start bit or a zero data bit). You can't reduce the resistor values too much or either the Propeller's I/O pins or the GPS's I/O pin will be damaged. The answer is to change the Propeller's TX pin to an input (high impedance) when it's not being used. You can do that by modifying the serial I/O routines or by specifying "open mode". Since the GPS receiver is designed to connect directly to a Stamp I/O pin set for "open mode" serial I/O, it presumably has a pullup resistor (to 5V) already.
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It's not all that hard to count the number of grains of sand on the beach. The hardest part is making a start - after that it just takes time.·· Mirror - 15 May 2007
You were great in helping me dig into this.·In my book, you're right up there with Mr. Mike Green for having an action·figure created·in your·likeness. I never got it to respond in smart mode and gave up. I do have a new propstick and fresh bread board. Mabey I will try again and have better luck this time! I will let you know·if I get it working.
thx a bunch. fish
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
Post Edited (fish) : 5/30/2007 5:41:47 PM GMT
It's·curious that my BS2 can talk to the GPS mod in smart mode, but my propstick can't.
I don't have a prop clip yet to try it out with my prop demo board.
Using Chris's suggested setup and code, I have tried 3 different propsticks and no go.
The GPS module must be fine since my BS2 can talk to it in smart mode.
I realize that using a prop demo board·shouldn't be any different than using a propstick, but for my own warm fuzzy, has anyone anywhere successfully used a PropstickUSB to communicate with the GPS module in smart mode?
thx
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
I don’t remember if I asked if you were sure what resistor size you were using…For a temporary test try using a 470 ohm resistor (yellow, purple, brown, gold) and see if that works. Typically 1K (brown, black, red, gold) works fine. But you could try something a little smaller to see if that is an issue. Take care.
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Chris Savage
Parallax Tech Support
Cheers, fish
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
What made it start working? You’ve got my curiosity…
Erik,
You said you used no resistor…That is definitely not a good idea. You should have a resistor in there. No pause is required after the “!GPS” header…And /RAW Mode doesn’t go any faster than Smart Mode. Each mode offers one update per second. Take care.
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Chris Savage
Parallax Tech Support
thx
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Did I make a unit test for it? No... Did·I run the test·suite·before checking it in? No... But it shouldn't break anything.· ~intern·(just before we let him go).
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Chris Savage
Parallax Tech Support