Interface 8051 with a GPS module (EM-406a) : 8051 Microcontroller Projects AVR PIC Projects Tutorials Ebooks Libraries codes

Forums

Rickey's World :: Discussion Forums :: Discuss and Learn :: 8051 Discussion Forum		<< Previous thread \| Next thread >>
Interface 8051 with a GPS module (EM-406a)


Moderators: Ajay Bhargav, Arun Kumar V, pdi33, Shailesh NAYAK, ۞ TPS ۞, shyam, sashijoseph, ExperimenterUK, DavesGarage

Author

Post

iam

Sat Jul 04 2009, 09:20AM

Registered Member #224

Joined: Wed Nov 22 2006, 12:28PM

Posts: 20
Thanked 2 times in 2 posts

Hello guys i just buy a EM-406a module and i need some help about the interface between GPS and uC.
Typical connection

uC <------------> GPS
--------------------------
Rx <-------------- Tx
Tx --------------> Rx

right right?
But :mad
from the GPS manual :
Electrical level : TTL level,Output voltage level :0-2.85V,RS-232 lvl

so this might be a problem ? since my uC works on 5V for Logical High
right right?

Ok now lets go back to my Electrical Characteristics of my uC
Vih = min:0.2Vcc+0.9 and max:Vcc +0.5. Vcc = 5v
Voh = Vcc-0.3 , Vcc-0.7,Vcc-1.5 *with my meter i get 4.97V but why?
so should i use the typical connection or i damage the module?
i think Vihmin = 1.9V is ok for Rx <---------------- Tx
what about Tx --------------> Rx, Voh=4.97V is too much for the module ... right right?

any explain to my questions or any source for study will be helpfull thanks

*also what is your opinion about my gps module ?

Inside the electric world
I want to fly with you
Eight bits wide is our love
Circuits our destiny
http://www.youtube.com/watch?v=mu98JyjOS8g

Ajay Bhargav

Mon Jul 06 2009, 02:41AM

Rickey's World Admin

Registered Member #1

Joined: Fri Feb 24 2006, 04:56AM

Posts: 7567
Thanked 1330 times in 1254 posts

use a voltage divider on tx line..

CODE:

uC TX PIN

   |

   \

   /  R1

   \

   /

   |

   |---- To module

   \

   /  R2

   \

   /

   |

   |

  GND

Vr2 = R2 . V /(R1 + R2)

Vr2 = 2.85V
V = 5V

2.85/5 = R2/(R1+R2)

1+R1/R2 = 5/2.85

1+R1/R2 = 1.75

R1/R2 = 0.75

R1 = 0.75R2

check your inventory and select R1 and R2 according to above equation.

www.rickeyworld.info
If you feel satisfied with the user's forum reply please click on the thank button.

Obey forum rules!
Respect others!

This post has been thanked 1 time

iam

iam

Mon Jul 06 2009, 05:56AM

Registered Member #224

Joined: Wed Nov 22 2006, 12:28PM

Posts: 20
Thanked 2 times in 2 posts

Nice thats the solution that i have in my mind Ajay
so R1 must be >= 0.75 * R2
my resistor invertory is so limit ..
i will use R2 = 261ohm and for R1=216 ohm with respect to above equation

but now another question arised and its about currents
i= 2,74 / 261 = 10,5 mA, should i use bigger resistors?
lets say i connect two 1K resistors in series with R1 and R2
R11=1K+R1 and R22=1K+R2 .

thanks

Inside the electric world
I want to fly with you
Eight bits wide is our love
Circuits our destiny
http://www.youtube.com/watch?v=mu98JyjOS8g

shyam

Mon Jul 06 2009, 07:21AM

Registered Member #2984

Joined: Mon Aug 06 2007, 11:33AM

Posts: 847
Thanked 136 times in 125 posts

most gps have two o/ps
TTL and rs232

Electrical level : TTL level,Output voltage level :0-2.85V,RS-232 lvl

if you have a rs232 o/p.. then use
gps->max232->uC
and
gps<-max232<-uC
this will be the safest solution.

lProgress is not made by early risers or hard workers, but by LAZY people, trying to find easier ways to do the same........

iam

Tue Jul 07 2009, 12:25AM

Registered Member #224

Joined: Wed Nov 22 2006, 12:28PM

Posts: 20
Thanked 2 times in 2 posts

OK shyam i connect it with max232 also i sent it but accident zero's i think ...

and later i connect it to my pc
for a simple test
pc-max232-gps

but whats wrong now ?? the led is not flashing ...
using SirfDemo i get those things see picture

http://img43.imageshack.us/img43/8335/wtfjnm.jpg

also it works only on 4800 baude rate ,at the other speeds i get errors like comm: ce_break
did i kill it? :-s

SOS SOS SOS HELP MEE!!!:-s

EDIT

OK IT WORKS BUT NOT INSIDE MY HOUSE !! :mad

[ Edited Tue Jul 07 2009, 03:28AM ]

Inside the electric world
I want to fly with you
Eight bits wide is our love
Circuits our destiny
http://www.youtube.com/watch?v=mu98JyjOS8g

shyam

Tue Jul 07 2009, 03:31AM

Registered Member #2984

Joined: Mon Aug 06 2007, 11:33AM

Posts: 847
Thanked 136 times in 125 posts

it would work only on 4800 bps.

the led is not flashing

is it stable... if yes then you getting actual data.. flashing leds indicate void data.

and please do not shout.

lProgress is not made by early risers or hard workers, but by LAZY people, trying to find easier ways to do the same........

Ajay Bhargav

Wed Jul 08 2009, 05:28AM

Rickey's World Admin

Registered Member #1

Joined: Fri Feb 24 2006, 04:56AM

Posts: 7567
Thanked 1330 times in 1254 posts

iam wrote ...

SOS SOS SOS HELP MEE!!!:-s

EDIT

OK IT WORKS BUT NOT INSIDE MY HOUSE !!

GPS should be placed in open sky to get satellite data. it wont work inside house or under roof or any kind of metallic shielding.

[ Edited Wed Jul 08 2009, 05:28AM ]

www.rickeyworld.info
If you feel satisfied with the user's forum reply please click on the thank button.

Obey forum rules!
Respect others!

iam

Sun Jul 12 2009, 01:08PM

Registered Member #224

Joined: Wed Nov 22 2006, 12:28PM

Posts: 20
Thanked 2 times in 2 posts

Well i try your ideas guys but they seems dont work ..

1st method using max232

i was getting the same none valid character all time
dunno why! :mad

actually when i was tryin to connect my GPS to PC the max232 was the only way to do it, and SirfDemo was able to get valid Data of GPS.

2nd method using a voltage divider with resistor ratio 0.75

none valid characters ....
dunno why too ! :mad

The only way to get valid data was the typical connection between
uC -- GPS
Rx <-------------- Tx
Tx --------------> Rx

Inside the electric world
I want to fly with you
Eight bits wide is our love
Circuits our destiny
http://www.youtube.com/watch?v=mu98JyjOS8g