Keeping GPS alive

Hi all. I am just putting the finishing touchs to a project hat uses a GPS. One ofthe things that is a but annoying is the wait for the GPS to kick in. I hve seen some kits where he GPS has a battery (a watch type battery) which I can only assume is to keep the GPS alive so to speak so that when a project used it, it doesnt need to warm up (if thats the phrase to use). So taking it that this IS the case and I want to add a battery to my GPS, what sort of things would I need to consider?

2 things come to mind. 1. It can prob run off the small battery ok, but do I need to handle the fact that it now has 5v coming to it, and switch of the battery circuit?

  1. what about recharging? I am not sure that the other circuit I have seen had a charger built is,so maybe the GPS draws a small about of current when th small battery is in use.

I am not 100% sure of the above as you can tell, and would welcome any suggestions etc.

Thanks, Jeremy

I want to add a battery to my GPS

And which GPS would that be?

Some modules have a coin-cell to back up the RAM so that re-acquisition times are much shorter (the GPS almanac doesn't have to be downloaded, that takes minutes I think).

If you can keep the whole module powered up it will keep lock, otherwise I doubt you could add a battery to an existing module - but again which module?

DUH....sorry. It was late at night when I typed my question... :)

Its a Skylab SKM53. I have the datasheet, and it talks about a 36sec. Aquisition time from cold start. maybe it just seems longer :-)

Jeremy

According to the datasheet, that device already has an internal battery. The datasheet doesn't specify what type of battery and it could simply be a supercap but it is fairly easy to determine if the battery is working. Wait for the device to get a signal lock and then remove the power for a couple of minutes. As soon as you reapply the power, look at the date reported in the first few NMEA sentences and see if the date reverted back to 1980. If it did, then your battery is not working. If the date and time are correct then your battery is working. If it's a type of supercap then it may only hold a charge for a few hours. You can experiment using different lengths of time with the power off to see just how long the battery stays charged in case you need to know that for your application.

Perhaps that's why they are $26.00 on Ebay... Free shipping too at least in the US I bought 2 (Bricked one about 2 weeks ago and replaced it) and both work/d fairly well and as I remember they do keep the data for 10 - 15 minutes which was as far as I tested mine, modifying the breadboard and it took 5 10 secs and it was solid again.

Bob

yeah the device is pretty good. Ok, its prob. not as fantastic as others, but for the price, it does want I want!

Thanks for all the feed back too !

Jeremy