USB to RS232 conversion

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richlear

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Hi all,

I have a GPS device with a USB interface which I need to feed into a second device which only accepts RS232 using an NMEA0183 message. The receiver also has a fixed baud rate of 4800 N81
Although I can see lots of options to convert serial to USB there does not seem to be anything to convert USB to RS232.

Does anyone know of anything on the market?

Thanks

Rich
 
The only difference is the voltage levels, assuming the second device actually uses RS232 levels?, and doesn't just use the 'serial' 5V or 3.3V levels. Low voltage 'serial' is quite often referred to as RS232, so you first need to establish if it's actually RS232 or not.

If you do need the RS232 voltage levels, then you simply need a MAX232 (or similar) after your USB/Serial converter - this is an IC specifically designed to convert 5V logic levels to +/-12V(ish) levels for RS232.

Historically you could commonly buy such converters (USB to RS232), I don't know if you still can or not?.
 
Hi, the commonly available RS232 to USB converters (like the one linked above) is no good. My GPS has a male USB plug so I would need something similar but a F USB to M DB9.

I am not sure what signal levels the receiving device expects but it is a VHF radio (all it states in the manual is "NMEA0183 input)
 
A device intended to function as a USB "slave" to a computer cannot connect to anything else.

You need to use a computer board of some sort as a translator - eg. a Raspberry Pi - or get a GPS module that has a real serial data output.

Or, if you can open up the GPS unit, it's possible (though not guaranteed) it has other connections on the actual GPS Receiver module it uses.
 
richlear said:
Hi, the commonly available RS232 to USB converters (like the one linked above) is no good. My GPS has a male USB plug so I would need something similar but a F USB to M DB9.
Click to expand...

Then change your search to what you need...

Amazon.com: CERRXIAN 1 ft 90 Degree USB Type A 2.0 Female to RS232 DB9 Female Serial Adapter Cable Compatible with Windows 10, 8, 7, Linux and so on: Gateway

Amazon.com: CERRXIAN 1 ft 90 Degree USB Type A 2.0 Female to RS232 DB9 Female Serial Adapter Cable Compatible with Windows 10, 8, 7, Linux and so on: Gateway
www.amazon.com
 
Thanks, I did open it and have a look but there do not appear to be any pads easily accessible.
Using a Pi is just too difficult, I will look out for a GPS with a native RS232 output. Thanks for your help
 
Gophert - yes, I saw that but from what I can see that would not provide the required 5V for the USB GPS would it?
 
richlear said:
Gophert - yes, I saw that but from what I can see that would not provide the required 5V for the USB GPS would it?
Click to expand...

Well, you haven't mentioned what powers what to this point but power is usually the easiest thing to add. Drill a hole, add two wires of correct voltage. When you are trying to hack together a solution, sometimes you have to hack a little. If hacking is out of your scope, let us know and we can easily tell you which retail outlet you can buy a new, turn-key system from - which will be a hack-free solution in most cases.
 
Sorry, maybe I was not clear. The GPS is one of these (https://www.amazon.co.uk/GlobalSat-BU-353-S4-Receiver-SiRF-Black/dp/B008200LHW) which I have in hand. It is designed to be plugged into a laptop or similar which would provide 5V through the USB port. The output from the GPS is NMEA0183 data. My VHF radio needs a GPS NMEA 0183 input but expects an RS232 signal. I am happy hacking power and by-passing connectors etc but if the signal levels are incompatible that is a little outside my comfort zone.
 
Lol i dont think the picture is like what you get its just something they posted the usb to
Rs232 would have a male end on the rs232 side
 
I just seen the picture sorry thats got usb on
On one end your not going to find any thing that will work. You have to have a host to handle the usb like a computer or otg.
That thing has a usb to serial made into it
You maybe get lucky and open it up and go around that to get at the serial side.
 
It really absolutely depends on EXACTLY what is in the GPS module.

As I see it there are basically two options:

1) The module is a 'proper' USB slave, and needs a host computer running a suitable driver in order to work - in which case the OP is stuffed!.

2) The module includes a simple serial output internally, which connects to an FTDI (or similar) chip, thus providing a USB/Serial output to connect to the PC as a serial port.

Probably the best thing for the OP to do is to look in Control Panel, under devices and see what it says when you plug the module in.

I just plugged an FTDI module in, and this is what it says:



Clearly showing it's an FTDI serial port.
 
Hi Nigel,

I do not see any mention of FTDI so I guess my best bet is to find a proper serial device.

Thanks for your help
 
I am not 100% sure where to look. When I plug & unplug the device the only change I see is an additional COM port

 
The prolific does the same thing as FTDI if you open up the case you'd find that its sending a serial signal to the prolific chip


Pin 1 and 5 is the serial data from the GPS pin1 is TX and pin5 is RX
 
Ah - OK so it is a matter of locating the pins. I guess that soldering some leads on to the IC will not be easy unless there are pads accessible. I will take a look. Thanks
 
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