help mystery daughterboard

Hi, I have a cf-28 and am desperate to fit an aftermarket gps, in my case a garmin etrex.

I have followed the threads intensely and studied them now for almost a week.

But, despite cahnding dip sw settings, bios settings etc etc, I just cannot make any inroads with my mod.

So far I have data that appears as junk.

I am using the mod, whereby I am interfacing my etrex to pins 1,2 and 3 to the edge connector of the daughter board. (not the ribbon cable mod)

However, my daughter board does not concur with ALL those mentioned in previous posts.

Mine has provision for the sim card but otherwise looks quite similar.
The 4 way dip switch is orientated at 90 degrees, but at least its there.

The stock gprs in my case was the Siemens MC-35 monuted on the same daughter board. Needless to say, I couldnt get that to work either, irrespective of it showing up in the bios.

The etrex works fine plugged up to com port 1 (external), but no joy on com port 4 (internal)

It may be of No significance, but also the "hidden"pcmcia card does not function.

So can anyone help with these dip switch settings, as thats about all that I can think of thats preventing it from working

 

If I'm reading this right and you are trying to connect a GPS designed to work with an external COM port to the internal connector:

Chip-level serial ports generally use 5V logic levels, inverted from the external COM standard; basically the inverting level translators (to/from the +/- 12V RS232 levels) are omitted.

I'm guessing the data you are feeding to the internal connector is inverted, hence the apparent garbage.

 

Hi thanks for the response, interesting.

But, if that was the case, why in 99% of the other threads relating to the same usage of this port, did no one else have to do any level translations.

The old posts relating to the mods have somewhat died a death now, since that at that time, the majority of GPS enthusiasts carried out the mods to the CF-28 relatively quicky at all at once.

But if you have 5 mins, you can pick up the remains of the thread and you will see what I mean.

Any clues though on the odd daughter board that I have?

 

I've done my own GPS mod on a CF-29, and I used (like others, I believe) a 'bare GPS' module designed for building in to equipment, rather than a commercial COM Port connectable unit.

These bare modules are logic level, either 5V or 3.3V and don't need any level translation, it's a direct logic-to-logic link.

The problem is that your device has got the RS232 conversion to allow it to work with a COM port. That needs removing or inverters adding to re-invert the signals.

Looking through the CF-28 GPS thread, a typical module used is an EM408.
That categorically has logic level I/O - it needs an RS232 interface adding to allow use on a conventional COM port, whereas it's wired directly to the toughbook internal GPS connector.

See the following discussion re. connecting one to a PC (A MAX232 is a common RS232 level converter):
SparkFun Electronics - EM408 Useful Info

 

Brilliant, now all is clear.. I think I have a max232 somewhere. You saved me so much head scratching.. Thanks.