Converting SirfIII USB modules to RS232?

[rich smith]

Hello,

I have a large collection of SirfIII modules planned for use in autonomous flight project. Some have RS232 interface, some with USB. Does anyone know if it's possible to convert the USB ones to serial?

Photo shows the three types I have: $20 USB only, new style RS232 ($70), and old style RS232. They look identical. I've opened a couple and they are the same inside too. Big Globalsat LSI.

Some say re-flashing is the way to go but that is not reliable info and Globalsat ignores you unless you are billion dollar corp.. I've also been told there's an RS232 interface inside and you only need to bypass the Prolific chip.

Anybody know for sure about these particular modules? Any help here would be greatly appreciated.

Thanks,
-Rich

[dmgoedde]

Parallax Inc sells a Serial-to-USB converter called the "Prop Plug" which you can use for general purpose serial to USB conversion, or vice versa. Around $20.

[rich smith]

dmgoedde,

Thanks for replying but I need USB-to-serial not serial-to-USB. They mislead people on the function of that product calling it USB-to_serial. And anyway I need to find if the modules can be updated, not an adapter. I have a pile of these USB GPS units and can not afford to use adapters, particularly $15 ones ($20 w/cable).

Incidently Parallax is just a hobby reseller and charges way too much. Look at what their GPS units cost compared to Sparkfun. And even Sparkfun overcharges! These so called Prolific/FTDI adapters are around $3 from china. You can buy several of them on Dealexreme for the price of 1 from Parallax.

Regards,
-Rich



Parallax Inc sells a Serial-to-USB converter called the "Prop Plug" which you can use for general purpose serial to USB conversion, or vice versa. Around $20.

[dmgoedde]

I know that, for example, Locosystech (maker of OEM GPS modules in Taiwan) sells various GPS modules each with choice of TTL serial or USB format. I bought a bunch of the TTL version, and you can see clearly on the PCB they left off components that would enable USB connectivity.

In case of your units, I doubt there is a simple way to just convert them to USB without adding components, but I hope I am wrong.

[rich smith]

dmgoedde,

I wish to convert my USB versions to serial not convert to USB. If your experience with the others is true for the SirfIII I should be able to do this by eliminating parts, not add. I am hoping you are right.

Thanks,
-Rich



I know that, for example, Locosystech (maker of OEM GPS modules in Taiwan) sells various GPS modules each with choice of TTL serial or USB format. I bought a bunch of the TTL version, and you can see clearly on the PCB they left off components that would enable USB connectivity.

In case of your units, I doubt there is a simple way to just convert them to USB without adding components, but I hope I am wrong.

[dmgoedde]

dmgoedde,

I wish to convert my USB versions to serial not convert to USB. If your experience with the others is true for the SirfIII I should be able to do this by eliminating parts, not add. I am hoping you are right.

Thanks,
-RichI was thinking backwards! Yes, you might even be able to just solder a tiny wire somewhere to tap off the serial feed!

I have a EM-406 which is SirfStarIII somewhere around here.... If chipset pinout data is not available, I would take a probe and test all IO from the chipset, determine if data is streaming out any of them. This would be a free ($-wise) "upgrade" to be able to solder a wire and bypass USB built into the OEM GPS you have. Good luck!

[rich smith]

dmgoedde,

Good suggestion but unfortunately that's difficult with BGA. No "tiny wires" to hook onto. Even the runs are buried 5 layers deep! It looks like my hope to convert these to serial is not possible. There are no USB converter chips or hidden RS232 signals floating around inside. Just one big LSI and a memory chip. Pop the top off yours and you'll see what I mean.

I've had some interesting experiences last couple days. A guy on another (non-RC) site told me he had converted several of these very same units and it was easy. So, trusting individual that I am (gullible boob), opened one of them again. This time with Tek 220 fired up. Since the LSI chip had no external pins I probed all the passive components on the board. The only active signal is a high speed 10mhz synchronous link between GSC3e and RF chips (R62,R65). No "secret" RS232 signals. Backtracking from the USB connector I found the classic USB passive devices and even detected the processors attempts to sense line impedance prior to enumeration etc.. I recognized this from experience with the Boris AVR HID stuff. So, back to the forums for help.

Meanwhile another fellow had posted indicating he repaired these units and it was not possible to do what I wanted. His comments jived more with what I actually saw myself. At least you and I admit we are just guessing. That first guy is what I call one of the "Clueless Experts". He also misled others on the subject of geting code out of locked chips resulting in destruction of valuable devices. What gets me is the absolute conviction these guys exude. Most of those who replied were well intentioned, just unfamiliar with modern GPS technology. Living a few years in the past. Fortunately there are some very knowlegeable and helpful people around on RCG.

I now know more about SirfIII technology than I ever wanted to. Several hours wasted and I'm really behind on the autonomous flight project. Live and learn. Not total loss however, the service technician offered to buy all the USB modules from me at $21 (a 1$ profit!). I'll keep a couple for the DeLorme end of the link because they do work extremely well under "winders".

Remember "NET = Not Everything's True".

Thanks,
-Rich

P.S. That "Atto" is an amazing accomplishment. I learned a lot from your thread. What's current status? Available to public yet?






I was thinking backwards! Yes, you might even be able to just solder a tiny wire somewhere to tap off the serial feed!

I have a EM-406 which is SirfStarIII somewhere around here.... If chipset pinout data is not available, I would take a probe and test all IO from the chipset, determine if data is streaming out any of them. This would be a free ($-wise) "upgrade" to be able to solder a wire and bypass USB built into the OEM GPS you have. Good luck!