SparkFun Forums

[Craig]

I got the GPS Datalogger kit a little while ago because I wanted something for long distance hikes without a good power source for days. Unfortunately the logger sucks up too much power so I was going to have to edit the firmware to only wake up and turn on the SD card when a the Lassen iQ has sent through some NMEA. I've not done that sort of thing before and I'd hate to introduce a bug that doesn't get noticed until I am out in the field (or the hills as the case maybe).

But I see that the new logomatic can be interrupt driven. Can anyone tell me if that means the SD card is shut down in between writes? It'd be a big power saver if that was the case, and along with the new Sirf Star III chipset it might be enough to make me fork out for a new bundle (in a few months, once I'm sure it won't get superseded again before my trip)

[ohararp]

Craig, what kind of battery life are you expecting?

[Craig]

As good as possible.

I'll be away in the hills for up to 6 days at a time and I don't want to carry dozen of batteries. I'd need it recording for upto 12 hours a day and I hope to power it from one or two of the solar cells that just arrived at SFE with the battery pack just helping out when it's dark/cloudy.

I may even power it with a Solio, it's a solar power iPod charger that has an internal battery, but I'd need to step it down from current out put of 12V.

[Craig]

I'm hoping that in the few weeks since I posted this question someone new has joined the forum and is able to tell me if the newer logomatic does powerdown the SD card between writes. Battery life is very important to me. I can carry a dozen memory cards to get over the 256 file limit, but I don't want to carry dozens of batteries with me.

[ohararp]

Craig in my design I have found that the SD cards sucks very little power (my design powers down) and that its the gps module (80 mA) and uPic (50 mA) combined with losses I ending up sucking about 200 mA of current.

[Craig]

Your design, is that firmware? And for which board, the new EM406 with seperate data logger, or the older Logomatic with Lassen iQ?

Since I'm building this for walking speed I might be dropping down the NMEA frequency to once every 10 seconds, or even down to once a minute. I imagine that would be a power saver too. The final step would be to get the chip to go to sleep waiting to be interrupted by the NMEA string.

[ohararp]

Basically the power management of the boards is to reduce the output rate of the gps. I haven't done this with the em406 but I think I'll be connecting up my volt meter to measure current at the reduced output rate to see how that effects power consumption.

[Craig]

So you sleep the SD card between writes, but don't sleep the processor between sentences?

I'm really squeezing every ounce of juice out the batteries with the idea of hiking 10+ hours a day for upto a week on just 4xAAs and maybe a solar panel or two.

[ohararp]

If you put everything to sleep for 1-5 minutes then recorded a point you could probably do it with a large lipo.

With the SD_FIle_system I am using I write to the card then turn it off.


Open the same file
append data to it
close it
shut it down

Repeat...

[ckuethe]

If you're playing with the SiRFstarIII, you might want to have a look at its power saving features. You can cut the processor to a 20% duty cycle and still get 1HZ updates. Read up on message 151 in the sirf protocol reference...

[ohararp]

ckuethe, do you know that by doing this in binary mode that it will carry over to the nmea output mode? Right now my firmware is similar to SFE's in that it looks purely at NMEA output.

[ckuethe]

If you put the CPU in power saving ("TricklePower") mode with the binary protocol, it should remain in power saving mode even when using NMEA. It would be nice if there was a proprietary message to do this, but alas, there is not.

As part of your setup function, you could switch to SiRF, adjust the power saving and then switch back to NMEA. The control messages to do this can all be easily precomputed.

[Craig]

Does the Trickle Power mode stay with the module after power loss? I'd have a breakout board to set things up as I want them, then disconnect the module and put it on the the board connected to the data logger. I'm not expecting the data logger to send any commands to the GPS, just listen and record what comes in.

[ckuethe]

I think that any time the receiver resets (power loss or software reset) the receiver goes back to full power mode. You may want to confirm that with SiRFdemo though. I'd do that for you, but I'm not running windows at the moment.