Garmin serial to USB 2.0 adapter using FT232R
Did you know that you can buy a ready made cable with the FTDI chip built in. There are several with different UART interfaces (eg 3.3V, 5V etc).
Use Find in RS website looking for 'FTDI cable' and you can see what there is.
Not as much fun as building your own but more convenient.
Posted by diablero at
For the first question (pin names followed by a hash) the answer is simple: the pins are all active low (the others, not followed by a hash are active high). For the second question, I worked with FTDI232H one year ago and I used only a 5V regulator on mmy board. As I remember, you can obtain a 3V3 voltage form one pin of the chip (if necessary for you). Let me find my scheme and I hope I'll answer all your questions. I'll see your schematic to see what you have done.
Posted by Neil Rush at
Thanks for the answers everyone!
Diablero: Thanks for the explanation on the hash marks, that's what I thought. I want to use the 3V3 output to power the GPS (the GPS uses 3V, but I have been informed that 3V3 won't 'hurt' it) and I dont want to put too much strain on the 3V3 output of the FT232H, although, I was thinking, perhaps it would be better to just power the GPS using it's batteries, I'd be quite happy too, and I suppose that it would work, If I just left the power supply input to the GPS disconnected.
Michael: Thanks for the tip, I'll have a look and see what there is. The place I got information on the Garmin connector also sold cables that go from the garmin plug to bare wires, perhaps I could connect one to the cable you mentioned.
My main objective is to design and build a cable to connect the serial port on a Garmin eTrex GPS receiver to the USB port on a computer, but I'm not too good (well, ok, I'm VERY BAD) at soldering, so perhaps I could settle on just joining the FT232H cable to the Garmin cable. The reason for wanting to design this is that Garmin charge WAY too much for their cable (over US$30), and then, if, like me, you're using a new computer that doesn't have serial ports, you have to purchase a serial-USB adapter, which Garmin sell (again, at around US$30), or from another manufacturer (as low as US$10). All in all, you're looking at easily over US$40, so I thought It would be useful to design a single-cable solution with a bridge chip, that would cost less to make than the Garmin cables cost to buy.
Posted by banjohat at
Wow, lot of questions there :)
I will try to answer some of them as well:
Posted by Neil Rush at
Thanks for the tip about the FT232RL. I'll definatly use that instead. Still grateful to all those who gave advice on the FT232H.
The FT232R is way easier to understand and I've almost finished the circuit, aside from a little confusion about the level converter, as you can see in my edited question above.
Posted by Neil Rush at
I've updated this question to reflect the current status of my project. Some answers may not seem to make sense, and this is why.
I'm currently working on a design for a project to connect the RS232 port on a Garmin eTrex GPS receiver to the USB port on a computer. I've settled on using the FTDI FT232R as the bridge between the RS232 and USB ports. I've currently got pinouts for the Garmin RS232 port (as it uses a proprietary plug, not a DB-9) and a USB port, and I've also located a datasheet for the FT232R. The FT232R datasheet has application examples which told me basically all the wiring that I need to do, but when it comes to connecting the RS232 pins, I became confused:
According to the datasheet, the RS232 pins on the FT232R should be connected to a RS232 level converter. After researching what this was, I discovered that it is an IC used to convert the voltages provided by an IC (0 - +5) to those used for RS232 communication (-14 - +14), however, the GPS in question only uses 3V, so do I still use this converter, or do I use one with differant voltages (-3 - +3v?)?
I've attached my circuit diagram so far in GIF. It shows the circuit based on the application example from FTDI with the level converter.
The CBUS pins have the following assignments:
I've also attached the datasheet for the FT232R in PDF.
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