303 MMF and fix time

Torpedo · Occasional Visitor Joined: Dec 21, 2003 Posts: 2

I have noticed that when I do not use my 303 MMF for a couple of days the time to fix goes beyond 4-5 minutes. In Winfast Navigator signal level screen, all satallites appear in red colour and, that is the weird thing, when comparing side by side with my etrex vista I see that the 303 MMF is looking for satellites that are no even in view or at different locations. Finally the 303 MMF performs a cold restart an gets the correct position in less than a minute.
I believe that the internal battery is OK as the GPS don't loose the nmea settings that I use.
Any ideas ?

DavidW · Posted: Sun Feb 08, 2004 6:57 am Post subject:

What you describe sounds entirely normal for a HI-303MMF.

The internal battery seems to have two stages of going flat. In the first, the real time clock goes wrong - which gives the effect you describe. The GPS believes that it still has valid data as to the time and its rough location so it starts looking for incorrect satellites overhead. Only once it has been through various permutations and discovers that it can't see any of those satellites does it throw away the wrong information and effectively cold start itself.

In this state, any settings you've configured are not lost.

Leave it a couple of days more and the internal battery will have gone completely flat. The GPS will factory reset when you power it up again - so it will configure itself to NMEA 4800 with SBAS off (not an entirely correct description of what is set, but it'll do).

Seeing as you have Winfast Navigator installed, look at the clock on the Navigation screen when you're in the degraded state you describe - it'll almost certainly be running but several hours wrong. The easy way to snap the GPS out of its delusion and get it to fix again quickly is to tell it to cold start using Winfast Navigator. A better option if you're using TomTom Navigator is to tap near to your current location on the map and choose the "Reset GPS for this location" option on the menu.

David

AlunS · Posted: Sun Feb 08, 2004 11:53 am Post subject:

I'm not entirely sure, but I'm beginning to get the impresion that the battery in the 303-MMF only charges when the red LED is on (either steady or flashing), i.e. when whatever program is running on the PPC is active and connected (not necessarily with a fix).

When I first got my 303-MMF, I followed the instructions (very unusual for me!) and left the unit in my PDA for 6 hours to charge the battery. I still had all sorts of problems similar to what has been described here with cold starts only a few hours after having used the unit for half an hour or so.

Having left the unit in my PDA overnight in the cradle with WinFast Navigator running and connected, seems, and I stress seems, to have helped somewhat.

DavidW · Posted: Sun Feb 08, 2004 12:00 pm Post subject:

I can understand the potential need to have a connection open to the GPS for the battery to charge, but the LED is a red herring, as the battery charges in SiRF mode (at least on my unit, the LED doesn't light in SiRF mode).

Like Alun, if I want to charge my HI-303MMF's battery, I put my Pocket PC in its cradle, put the GPS into the Pocket PC, start up Winfast Navigator, switch off the Pocket PC's backlight (long press on the power button) and walk away.

David

AlunS · Posted: Sun Feb 08, 2004 12:50 pm Post subject:

I wasn't suggesting that the LED itself indicated anything re: charging, merely that it was on if a connection was open, and that the unit appeared to charge when this was the case.

On my 303-MMF the light comes on whether in SiRF or NMEA mode.

Torpedo · Occasional Visitor Joined: Dec 21, 2003 Posts: 2

Thank you very much for your replies.
You are absolutely right: What happens when I leave my 303MMF unplugged for a couple of days is that the real time clock goes wrong, looking for incorrect satellites overhead. If I leave it for 3 days the internal battery goes completely flat, loosing all its settings and performing a factory reset.
I also charged the internal battery by leaving the GPS plugged in my cradled pda for more than 6 hours with Winfast Navigator on. The result is the same: the internal battery goes completely flat in about 3 days.
The question is: How log is the 303MMF's internal battery supposed to last ? I see that AlunS's unit has the same behaviour as mine. How long does your battery last, David ?
Btw, thank you for the Tomtom Navigator tip David.

AlunS · Posted: Sun Feb 08, 2004 6:00 pm Post subject:

I've done a bit of digging and can reveal that the GPS module in the HI-303MMF is actually made by Globalsat. I had my suspicions anyway, because I came across the string Globalsat when I was attempting to debug the little test program that came with it.

I took my unit apart (very easy ... just 3 small torx screws) and can confirm it's a Globalsat EM401 (see http://www.globalsat.com.tw/english/products_detail.php?main_id=5&p_id=13)

The specs don't say very much about the battery backup, but in contradiction to what it says in the 303MMF "manual" it's apparently a supercap, not a Li-ion battery. I measured 2.4V across the one in mine. Unfortuneately you can't really get to it very easily to see what markings there may be on it, or to see what the capacity of the thing might be. In any case, the discharge characteristics of supercaps I would think would be very different to a lithium battery, and I've noticed in an application note from uBlox that seems to use the same basic building blocks as the EM401 that they say one should include circuitry to tie the backup voltage pin to ground when the voltage drops below a predetermined value, presumably to prevent the slow running clock problem David mentioned.

Also, on another page I found for a manufacturer of small RTC chips, they were quoting typical times of 2-3 days for their chips if fed by a supercap instead of a battery.

All this having been said, it actually looks like a small button battery rather than a supercap, although I suppose the manufacturers of such things may be making them in the same form-factor to make it easier for system designers to use them interchangeably.

If anyone's interested, I took some photos of the innards I can upload somewhere?

flyhal · Occasional Visitor Joined: Nov 25, 2004 Posts: 5

I have a mouse BR305 gps that has been giving me problems since I got it. For the first month the few time that I used it, it worked great. Then I left it behind my seat in the truck for a couple of months, then tried to use it and it would not come up. Just the red LED forever. I played with it several days and one day it started blinking and all was fine. I could shut it down and it would come right back up. A week later it was bad again. In the last couple of months it has worked about 2-3 times with most of the time just a constant LED ON. The message traffic is just 3 messages and then some initialization stuff and then the 3 messages and repeating. Normally it should just show one initialization message stream and then just NEMA messages.

The adaptor cable that came with the GPS for my Dell PDA only has a receive wire connected. Inside the DELL serial plug is a chip on the receive line only; no other chip for a Xmit line. I tried a direct connection to both GPS Transmit and Receive line with another Dell serial plug but the logic levels go negative and the Dell does not respond other than displaying some garbage charachers. I was trying to be able to send intiailization to the GPS but need the XMIT line.

I have a Flash card globalsat BC307 GPS very similarto the BR305 that can connect directly to the Dell serial port without any logic chips. The small plugs and wire inside the flash card unit were intermittent so I cut off the flash card port and just use the GPS directly to the Serial port of the PDA. It works great. Some difference in the output levels of the Mouse GPS and the Flash card GPS.

Anyway the globalsats seem to have a quality control problem. And the provided adaptor cables are not really suitable for initialization without the XMIT line connected.

Any advice on my problems?

Thanks, Hal

DavidW · Posted: Mon Jan 03, 2005 5:10 pm Post subject:

It's very hard to deduce what's going on from your instructions; details of what software you're using would help a little - though I suspect that something is setting your GPS mouse into SiRF binary mode.

Software such as Winfast (Leadtek) Navigator will allow you to switch it back if that's the case.

My HI-303MMF has worked reliably for 18 months.

David

flyhal · Occasional Visitor Joined: Nov 25, 2004 Posts: 5

It's in the NMEA mode as I can see the 3 messages repeating with about 6 lines of GPS startup data in between the 3 NMEA messages. It is a Sirf II/LP model. Unfortunately, the cable adaptor that came with the GPS only has the RCV wire connected thru a chip. No other chip in the connector plug so can't make a SND connection. I think that the mouse is faulty inside. Not sure why it sends those startup lines all the time. When a GPS works, those only happen once.

There is supposed to be a year warranty but know one answers my emails. Email'ed Globalsat and no answer and also the Ebay seller a couple days ago. Maybe he will answer

DavidW · Posted: Tue Jan 04, 2005 7:20 pm Post subject:

Unfortunately your post acts as a reminder of one of the dangers of buying from eBay - you can find that you have no warranty to speak of as there's no way to claim.

The only suggestion I have is to leave the GPS unpowered for a week or two so that any internal battery or capacitor runs flat and the GPS chipset resets.

David

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