GPS not producing sat data (again)

This isn’t a new issue, but gee, I really want to understand what goes wrong.

I got a new Neo module this week form Core E.
( )

I’ve only got a fix from it twice. Now it produces no sat data at all. And I got the fixes not using the supplied active patch antenna, but with a 10cm antenna wire that had broken off another patch antenna.

I now have four modules identical or similar to this one and none produce sat data. The older ones used to work well but no more. I’ve been working them for more than 2 years.

This is not an issue of having a clear skyview – that is the easiest factor to get right and be certain you’ve got right.

For power supply, I use USB from laptop, power bank (my favourite) or phone via OTG cable.

I carefully monitor the NMEA sentences with either u-center or a custom app on an Android phone.

From other forums it’s apparent many others have the experience of never getting sat data from this type of board. The usual advice is to ensure a clear view of the sky but that isn’t always the solution.

One thing I recently realised is that it is easy to inadvertently short the antenna socket when connecting the tiny ipex connector. If the board has a power LED it will go out with the short. If it doesn’t have a power LED you have no indication a short has occurred.

The rule has to be: never connect or disconnect the antenna with power on. I’m confident I have not caused such a short with this new module. Would a short damage the RF circuit of the Neo?

Anyone with similar experience with their Neo modules?


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Hi John.
If your antenna is an active type as you say it is it will be supplied power via the coaxial connector and cable, similar to a TV mast head amplifier. A short on this could do anything. Only someone with experience with the inner workings of the device could tell you.

Don’t agree with a power bank being used as a power supply. Two different applications. Some shut down after a short time if the load is too small. After all it is designed to be a back up charger for phones etc and if the load is too small it thinks the connected battery is charged and stops. Also the 5V can be quite “dirty” which is of no consequence when charging a battery but could cause some bother when used to power other electronic devices.

In other words in this instance you are using your power bank for something it is not designed to do. The old saying “horses for courses”.

I would suggest you do all your testing and/or trouble shooting with a power source that is meant to be that and will be a clean 5V or you could find yourself going in circles and getting erroneous information. This does not only apply to your situation but anywhere a power BANK is used as a power SUPPLY.
Cheers Bob


Hi Bob.
Thanks for replying. As I see it, I’m the common factor with these failed boards so I’m ready to accept it’s something I’m doing.

I’m happy to stick to one “approved” power supply type for the sake of eliminating one variable. That said, it is a fact that that I have used one particular board for more than 12 months almost on a daily basis powered by power banks.

What’s your view on power from a laptop USB?

The u-blox specs state a voltage tolerance of 10%. I used a scope on a few mains powered chargers and they varied by 10%, but a wall wart has worked for me.

What do you think of using a phone’s power over an OTG cable?



Hi John

That is a good idea. You may have had some success with power “banks”. I am pointing out that used as a power “supply” they could have some crap all over the 5V that could be of concern and they were never designed or intended for that use. If you are prepared to lose a bit due to efficiency there would be nothing wrong with using a power bank to keep another 18650 battery charged while said battery is driving a step up converter designed to be a power supply. There are little boards around that allow simultaneous charging and using in this manner. Keep in mind you will lose a few Watt/hrs in the conversion process. I personally use a 18650 battery and one of these little power supplies for a small power source and just charge the battery occasionally and find it quite useful as an experimental source.

USB??? That is designed to supply power to other equipment and is quite OK as long as the current limits are not exceeded. Nice clean 5V.

Don’t know. Have never done this. Have enough trouble keeping the phone charged without hanging something else off it.

My main point I was getting at is to use a known good system of powering your device until you sort out all problems then get to where you want to go one bit at a time or as I said you will finish going in circles getting nowhere fast.

Good. Not all hobbyists have one or even have access to one. I have one myself and have maintained for the last 50 years or more it is one of the most useful test items you can have on the bench. Have a look at your power bank at different loads. I have a reputable brand (Cygnet) and until I get to a reasonable load (1A+) the 5V is quite dirty with switching artefacts etc. It shuts down at about 100mA.
Cheers Bob


Thanks, Bob. I like your systematic approach.

I’ll set out to make a battery power supply. Still puzzled why my devices have worked well for months and now don’t work at all. And why the new one doesn’t work.

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The OTG cable to phone is a neat solution for feeding the GPS output into a phone app. It needs a TTL/USB converter b/w the GPS and phone. The phone powers both the converter and GPS. I’ve wondered if the GPS ought to be provided with another power source to supplement the phone supply.


Hi John
I really don’t know. I have never dabbled in that sort of thing. Probably couldn’t hurt if that can be done. It would remove the chance of the phone going flat when i the middle of something. an 18650 battery and little converter power supply would be ideal for that. As a matter of interest how much current does your GPS set up require. It may be too much for what I suggested but if your phone runs it can’t be that heavy.

It seems to me that every improvement to the longevity of a phone battery is negated by putting more stuff into the phone. I am afraid I am a bit old school. I use my phone as a phone. When I want to take a picture I use a camera, when I need some numbers crunched I use a calculator (used to be a slide rule) etc. So it goes on.
Cheers Bob


The Neo 6M data sheet indicates that typical current useage is around 40mA. The active antenna might need to be added to that.I have no idea what the TTL/USB converter draws.

I’m now supplementing the power with 4x AA dry cells and keeping away from the power banks.

The measured voltages are 4.7v at the board’s VCC and 3.3v at the Neo VCC pin (pin 23).

The data sheet specifies for the VCC pin: Min 2.0, Typ 3.0, Max 3.6.

Still not producing sat data.


Hi John,

While I have seen these units fail, generally, if you’re getting NMEA over serial just fine, then your module is likely OK.

When testing them here at Core, I used the included square antenna, and waited a good number of minutes for it to get a fix. Subsequent fixes were faster.

If you’ve waited a good while in conditions like that, then you might have a bad unit, and can investigate it further with us via email.

Great tips on power supply Robert! (And happy cake day :slight_smile: )

Keen to see your project back on track!


Hi John
If you are measuring only 4.7V from a 6V supply (4XAA) you are somehow drawing too much current. More than the batteries can stand. If the data sheet says max 3.6V why are you even applying 5V. a 3.2V 1860 lithium should be OK directly connected. If the max is indeed 3.6V it may be you have done some damage with over voltage. I am not familiar with this type of thing so cannot be sure.
Cheers Bob
I wonder if this is why it worked for a while then stopped???


It’s ok applying 5v to this board. It has a regulator that delivers 3v to the Neo GPS component. There’s a picture of the board in the link in my very first post. U-blox make the Neo GPS component and that’s what the data sheet refers to. Someone else assembles it onto the breakout board.

I think the 4.7v from the 4x AAs is cos one is an undercharged rechargeable battery. Will attend to that.


Hi John

You didn’t say that. Sometimes getting the whole picture is like pulling teeth.
I have had no reason to look at the Core blurb on this module. I have just done that and I see the reference to this regulator This should have cleaned up any “dirt” on the power bank 5V but going to battery for initial trouble shooting is a good move as it eliminates one variable.
Something I did notice however is
“Do not connect the RX pin to 5V signals - it will damage the module”.
Are you in fact using 3.3V signals to communicate or did you miss this.

Batteries. It is pretty basic to use a series string of batteries with all the same type and age. Anything else is only as good as the weakest link and very bad practise. Your rechargeable is as you say not only discharged but even in a good state will be 1.2V instead of the 1.5V for alkaline. I am assuming a non lithium AA here. A lithium AA will be about 3.7V.
Cheers Bob

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Sorry about that, Bob. I’m used to discussing GPS with other GPS tinkerers and they are familiar with this type of board. A link shows others the exact board you are using as they do vary in design detail.

But you make a really good point. A GPS setup involves many elements, all of which have to work. A verbal description lacks much detail. Theory doesn’t always correspond to practice, does it?

When I get access to a scope again (after lockdown) I want to examine the voltage from a power bank. I’m curious to see how dirty it is. I didn’t know the regulator would clean it up. Will examine that too. Ta.

I know the limit for the RX pin is 3.3V. I do not use that pin – it’s only needed to send configuration commands to the GPS and I don’t need to do that. So in each setup I make where I connect the GPS board to some computer device I have nothing wired to the GPS RX pin. That said, I cannot swear 5V has never contacted that pin. I do think it’s something I’ve done that has caused my boards to fail, so that is the kind of thing I’m looking for.

You’ve given me something to think about there. I’ve got some questions to throw James’ way.

You are helping me understand power supply much better than I used to.


Hi James.

I need to understand why my modules have gone from working well to not producing sat data at all (they all produce NMEA sentences, but unpopulated). I’ve been working with these type of boards for over two years. They are great when they work, frustrating when they don’t.

I think it’s something I’m doing that causes them to fail. I’ve had a couple of boards that never worked from the get-go (one had a component that got extremely hot). The boards I’m concerned about now have given good service and now do not.

The new board I got from Core this week achieved a fix on two occasions and now does not produce any sat data. I need to understand what has happened.

Can you tell me, please:

What physical setup do you have when you test one? I mean, what software & hardware do you use to monitor the NMEA sentences?

What is your wiring setup? Everything soldered? Jumper wires & breadboard? Power supply? How do you physically assemble everything? (there’s a lot of manual handling involved and I wonder if that can cause damage)

Do you do your test at the workbench? Do you take it “on the road”?


Hi John

Understood. I have been using these things for many years. At first in Indonesia with the original Magellan devices. In those days there were not enough satellites visible to determine altitude and you had to know this and enter it into the Magellan to get a reasonable position fix. But we were usually more preoccupied with the task in hand to worry about how all this worked and unfortunately I for one never did. Marine GPS devices were the early common ones as these were easier By the very nature of the device everything is at sea level and altitude does not play a part. I think it is more in later years as these devices became more common that the hobbyist has started to tinker and explore the messaging system to recover all the other bits if info available. The availability of the receivers themselves at reasonable pricing has helped too.

With my ignorance of the subject details in mind my main aim has been to respond along the lines of logical trouble shooting. Like getting rid of any variables and unknown potential problems. Starting with the power source. Start with everything you can to be known as OK. That way you can avoid other little peripheral problems masking the one you are trying to fix.

Extremely useful instrument. I have been using one since mid 60’s and for the last 20 odd years had one of my own. I regard this thing as indispensable going from analog (even had a Tektronix) to an inexpensive Digital (Atten) which I currently use.

Reading the rest of your post cleared up a lot of queries. It would appear you do have a serious problem. I don’t believe that several units have failed in a similar fashion (without there being a design problem which I doubt). The fact that they start out working OK then fail after a short period certainly appears you are doing something wrong or something wrong with your set up. But what ??? You could be on the right track by replicating James’ or another set up. It would be a good place to start. Unfortunately that probably means another new unit or you would already be starting with one unknown. The only way to really find that out would be to insert your (faulty ???) board into a known good set up but that may not be possible.

I am sorry I can’t be of more help but my ignorance of the details of these systems hinders me a bit.
Cheers Bob

Hi John
ADD ON to my last reply.
Just had a look at the data sheet for this device. I note that the manufacturer emphasises in bold type antistatic problems and states it is a static sensitive device.
I don’t suppose by any chance you have a high static charge problem ??? This could be worth considering. Static damage is cumulative, that is damage may not show up at the time but such damage accumulates until it gets to a breakdown point. If I have need to handle such devices I have an “Antistatic mat” fitted with a wrist band to keep your body and mat at the same potential

A practical example. One of the last projects I worked on had transparent windows in the cabinet rack doors. We had to use glass instead of perspex or similar material as this was capable of having up to 30kV charge on the surface. Kind of damaging. The whole room was carpeted with anti static carpet also. Some carpet materials are unbelievable. If you rub it with something the fibres leap out at you from everywhere, Bad for electronics.
Cheers and just something else to think about. Bob

If you are seeing empty NMEA sentences then that indicates a problem at the RF end - the aerial and the RF receiver. The MCU is obviously running, so power can’t be a problem. It is obviously communicating, so the connections to your monitoring device must be OK. I’m not sure how much that helps, because the devices are pretty much sealed as far as diagnostics on the radio receiver is concerned. u-center is going to be your best source for any information about the internal operation of the device: Have you stepped through all the views (packet, binary, text message, data) to see if there is an data at all? Are any satellites listed in sky view? Is there any oddity in the device information that is displayed? Have you tried a hot/cold/warm restart?

Note that other references to problems with these devices are almost always due to failing to put it into NMEA mode at the correct baud rate, and not understanding how to use the default protocol.

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A snapshot of the u-blox display.

Hi Jeff.
Thank you for the thoughtful response.

My previous shows a typical behaviour that I’m getting. I grabbed the screen when it is reporting reception of a sat. It’s SV 26 at an apparent signal strength of 24dB. See the sentence at time 06.661. You can see it’s only momentary. Mostly there are no sats reported.

The overall behaviour is like this: Most GSV sentences are unpopulated. Then it will report on one sat with a dB of twenty-something. Then back to nothing for maybe 20 seconds. Then it reports on another sat at twenty-something dB. And so on. The sats reported are 1,2,3,4…up to 32 then back to 1. Not always every sat but most from 1 to 32 in sequence (there are 32 sats in the American GPS constellation).

Occasionally it holds on to one sat but the dB value quickly decreases to nothing. Occasionally it reports on two sats in the same sentence, but not for long.

I don’t think it is reporting genuine reception of these sats. It can’t see all 32 sats from one point on the globe. I think it’s doing a scan. There is never any elevation or azimuth reported.

Early on I got a fix on two separate occasions with this module. It picked up about 12 sats with elevation and azimuth and 5 or 6 useable (green, not blue). Can’t expect better performance than that. But for a week now – bugger all. Just like the other modules that used to work well, but no more.


These pics shows a Neo GPS board connected to the TTL/USB converter which connects to the OTG cable and then the phone. The apps are displaying the sentences.

The converter can be plugged into a USB port on a PC/laptop and feed u-center or the Arduino IDE.

Different GPS board in each pic. The top one I’ve been using reliably for over 12 months & it is producing some sat data in this pic. The bottom one is my recent purchase. Neither produce sat data nowadays.

GPS to phone by OTG