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External GPS RS232 receiver
#1
Hello,

I want to connect a external GPS receiver, it has RS232 connection: https://es.aliexpress.com/item/32848905490.html

[Image: HTB18r89B4uTBuNkHFNRq6A9qpXa3.jpg]

How could I connect the 5 wires to the Raspberry PI? Need I an adapter? Or could I conect to the GPIO pins?

Anyone has experience with this devices?

Kind regards.
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#2
I've got one, and while I haven't hooked it up permanently, I have done research and testing on what would be needed.
The two black wires are ground, one is the shield and the other signal/power ground.
The red wire is power. Some of these are 5V, it looks like the one you got is 12V. You power the unit by putting 12V between the red and the black.
Green is TXD (the one you'll get NMEA Strings on)
Yellow is RXD (If you need to communicate with the unit)
You receive or transmit data by using the black as a reference and going to TXD or RXD.

You'll need a signal level converter to make this work, either to USB or to GPIO. When I originally tested mine, I used an RS232-USB cable. The small issue was that I had to break out the red and black wires to power the unit externally. Unfortunately, you won't be able to connect this directly to GPIO, but RS232 to TTL (3.3v) converters are available if you want to do some circuit wiring.

If you decide to use GPIO, you are going to need to either connect to one of the UART pins or use something like SoftSerial.
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#3
Thanks for the reply.

Could you recomend a signal level converter? I prefer a USB one.

Kind regards.
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#4
(2021-06-21, 09:32 AM)zorrua Wrote: Thanks for the reply.

Could you recomend a signal level converter?  I prefer a USB one.

Kind regards.

I have used these in the past in similar circumstances, search for USB-RS232-WE-1800-BT_0.0 for instance here.

This is the 1.8m version but there is a 5m one. The 0.0 at the end specifies a 0V power requirement which is right as you don't need to provide power, just the data connections. The datasheet is available on that webpage.

You'd need to use a ground and the 12V wires on your GPS to power it of course but for data connection, the Yellow on your device (RxD) goes to the Orange in the convertor (Txd), The Green in your device (Txd) goes to the Yellow in the convertor (Rxd). A ground is also required so black to black.

It is possible to buy a version of this cable which doesn't have the transmit/receive LEDs in the clear plastic USB housing but I like to see that stuff is happening.

There are of course cheaper options and equivalents but I have found that genuine FTDI chips are excellent and reliable.
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#5
Thanks!

I just buy a similar one, hope it will work, I will post later.

Regards.
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#6
Hello,

I buy this device: https://es.aliexpress.com/item/400102738...Title=true

The GPS is working great wheh connecting to VHF radio. But when I connect to the USB converter, I have no data in OpenPlotter.

I do a "tail -f /dev/ttyXXX" and there are some not-readable data. it look like is not well formated.

I try different baud rates, but nothing. Need I by other device?

Someone could help with this?

Best regards.
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#7
(2021-08-06, 10:16 PM)zorrua Wrote: Hello,

I buy this device: https://es.aliexpress.com/item/400102738...Title=true

The GPS is working great wheh connecting to VHF radio. But when I connect to the USB converter, I have no data in OpenPlotter.

I do a "tail -f /dev/ttyXXX" and there are some not-readable data. it look like is not well formated.

I try different baud rates, but nothing. Need I by other device?

Someone could help with this?

Best regards.
That device looks like it's TTL rather than "true" RS232. I have a feeling that's your issue.

Apart from having different operating voltage levels, the 0 and 1 are different between TTL (lower voltage =0) and RS232 (higher voltage =0).

You can buy RS232<>TTL level shifters but it's just another link in the chain. A USB to true RS232 cable like the one I use should work fine.
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#8
Thanks!

I buy a serial/USB converter and it works great now.

Thanks for your help.

Kind regards.
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