GPS module - advice needed

[flotulopex]

Hi there,

I want to make a "cruise control" for a friend's carting.

I had a look in the internet and found several GPS modules like those ones:
http://www.futurlec.com/GPS.shtml
http://www.parallax.com/Store/Sensors/CompassGPS/tabid/173/ProductID/396/List/0/Default.aspx?SortField=ProductName,ProductName

I have never used such kind module before so I don't really know what are the important caracteristics I need to take care of.

Any advice?

[ScaleRobotics]

The gps modules you mention look to be very similar. Basically, the more channels, the better, and the quicker the warm and cold boot up the better. The two you mention have a 1 hertz update rate. In my mind, this may be on the verge of being a little slow for cruise control updates.

SparkFun.com has a good selection of gps's. If you wanted to go to 5 hertz updates, these two gps's can do it. I have the EB-85a, which is like the second link, but unfortunately mine does not have a battery back up. You will want one of those, but all the gps's mentioned in here, and in your links have battery back up.

http://www.sparkfun.com/commerce/product_info.php?products_id=8975
http://www.sparkfun.com/commerce/product_info.php?products_id=8266

The other thing to look at is the serial baud rate, to make sure they are able to adjust to what you want.

[mackrackit]

Not sure if I would use a GPS for cruise control. It is too easy to loose the signal. Been there done that...
A Hal-Effect reading the drive shaft or wheel hub will work better.

[flotulopex]

Your right mackrackit,

But this cart is only used outside.

BTW, the cart has already an "electonic" speed indicator (looks like a cheap gadget).

The sensor's output must be an open-collector type contact (I might be wrong).

I tried to capture the signal in parallel with the sensor but I must do wrong an the only result I get is to make the signal crash completely (no speed is indicated anymore). I use an OpAmp for this but there is surely a better way...

[mackrackit]

What kind of cart is it? Maybe someone here has some info on it.

Outside yes. But outside there are things like power lines, buildings, mountains...Lots of things to get in the way of the signal.

[flotulopex]

...The two you mention have a 1 hertz update rate. In my mind, this may be on the verge of being a little slow for cruise control updates.


This is interresting for me; where do you see this information (1Hz update) in this datasheet please?
http://www.sparkfun.com/datasheets/GPS/EM-406A_User_Manual.PDF

[ScaleRobotics]

Well, they don't spell it out too well in the data sheet. I think that it what they are referring to in "C/A Rate 1.023 hertz", but I guess I have read a lot on different forums about the em406a. Most receivers do the 1 hertz rate. So if it doesn't mention 5 or 10 hertz, you can assume it does 1 hertz.

Here is a little gps tutorial from Sparkfun. They also mention the em406a being 1 hertz. There is some good information here: http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=127

Oooh! There is also a nice one here that does 10 hertz, but you need to get an external antenna. Might be good if you have a metal "cart". Then you can mount the antenna on top. http://www.sparkfun.com/commerce/product_info.php?products_id=9133

[flotulopex]

Nice links ;)

Thanks a lot.

Gonna have some work for the next weeks now :)