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Author Topic: GPS accuracy on Android HU  (Read 361 times)
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pascal06
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« on: April 30, 2023, 03:06:02 15:06 »

Hello everybody,
I've got an Android head unit in my car, a "Chinese" one bought on eBay.
It was delivered with a generic indoor GPS antenna, and I fixed it on the car's wind-shield.
The problem is that whatever the app I use (Google map, Waze, etc...) positioning accuracy is very poor. I tried many other positions for fixing the antenna on the wind-shield, and even outside the car, the problem is identical. So, I tried another indoor antenna, this time a known brand (Tomtom) and the problem is identical. I learned after my purchase that theses HU are often crap...
I measured voltage on GPS antenna output, and it's 3.24V (antenna works in 3 to 5V range).
Have you any ideas of other factor that can influence GPS accuracy ?
Thanks a lot in advance.

Pascal
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h0nk
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« Reply #1 on: April 30, 2023, 07:28:30 19:28 »

Hello pascal06,

G.P.S.-receivers are very susceptible to all sorts of electromagnetic noise (E.M.I.).

I had used a Nokia phone, were the internal backlight made enough
interference to reduce the sensitivity of the G.P.S. to loose the lock.

What You should try:

Power the module with 3 AA-Cells. If the module works better with this,
the source of noise is the power supply.
If the module uses a direct serial connection, filter this through a so
called Pi-filter. Another solution would use optocouplers to isolate
the module from the head unit.

Edit:
You should also try with a known good working G.P.S.-receiver (mobile phone)
that may be Your car makes the interference itself.
With modern phones i had never any problem with the reception of
their internal G.P.S in a Car.
They even worked through the small windows of an airplane.


Best Regards

« Last Edit: April 30, 2023, 07:41:13 19:41 by h0nk » Logged
bigtoy
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« Reply #2 on: April 30, 2023, 10:42:37 22:42 »

Try a different GPS program on the HU? I have a cheap Chinese Android HU (brand is Pumpkin) and I tried a few different "GPS Test" type programs. From what I understand, the GPS modules are all pretty much the same - they transmit position etc information over a serial port. The HU just takes that data and reports it. So the data should be accurate, unless you're located in an area with lots of tall buildings around you (multipath reflections).

After some experimenting, I put my GPS module on the dashboard, tucked close to the passenger side corner of the windshield.
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pascal06
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« Reply #3 on: May 02, 2023, 08:29:11 08:29 »

Hello @h0nk and @bigtoy
thanks a lot for your suggestions.
Trying to supply the antenna module with 3 cells is a good idea. So I guess I must wire this additional batteries in parallel to the HU's GPS output port by a mean or another (it's a SMA connector) ?
Moreover, I think I'll try to power the HU with an standalone small battery but as the car's ground will be always connected I don't know if it'll filter EMI enough...
I compared with a my phone's GPS at the same time, with the same app, and positioning is a lot more precise and smooth.
Have a nice day,

Pascal
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h0nk
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« Reply #4 on: May 02, 2023, 09:56:16 09:56 »

Hello pascal06,

You will need a DC-injector/blocker.
A small capacity (some pF) couples the HF and blocks the DC
from the G.P.S.
And an inductor (10 uH) blocks the HF and powers the G.P.S.
This must be built with very short wires and SMA-connectors.


It might be easier to open the antennar circuit and look for the
power path and open it. There will be similar circuit to the above.

> I compared with a my phone's GPS at the same time, with the same > app, and positioning is a lot more precise and smooth.

So it seems that there is no interference from the cat and
the receiver is a little numb.

Goot Luck, and

Best Regards





Posted on: May 03, 2023, 04:03:01 04:03 - Automerged


Hello pascal06,

just another idea:
Instead of the internal G.P.S.-receiver You may use a
G.P.S.-mouse and connect it via Bluetooth.
For Nokia phones with internal G.P.S. and Symbian S60V3/V5,
i have also a small java application, which "exports" the G.P.S.-data
to a serial bluetooth port. Let me know i You need it.


Best Regards
« Last Edit: May 02, 2023, 09:59:21 09:59 by h0nk » Logged
Sideshow Bob
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« Reply #5 on: May 02, 2023, 10:36:11 10:36 »

You have this aplication.
https://play.google.com/store/apps/details?id=com.pierwiastek.gpsdata&hl=en
Check how many satellites and the signal strength. Poor satellite tracking . will give an inaccurate or non-existent map position. You have tried an antenna swap. So could the problem be someplace inside the HU? like a bad antenna connection or soldering.
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