http://www.posdsm.com/uploads/images/53/DSC_2394%20(Medium).JPG

http://www.posdsm.com/uploads/images/53/DSC_2395%20(Medium).JPG

You have made a great job on the build and enclosure. I have never tried soldering SMDs and think I will stick to through hole components for the time being and hope to be able to squeeze it into a small Hammond enclosure (Prob the same one that Al Chin is using). I was planning to use this ‘upside down’ i.e. the hotshoe screwed to the lid and keeping the screws out of sight (and out of the way of the GPS antenna).

I echo Ian’s comments - thanks to Rick for the design.

John

I was wondering the same in regards to battery drain. I guess just keep it simple. : )
I will see how my box work. Thanks.

Al.

The box I used is a transit box for antistatic electronic devices, used in my workplace. Nothing special really other than just the right size, and they are scrap after first use.

As regards using a zener diode, sure it fixes the level at 3.2V ok. It will cause a heavier discharge on the camera battery. A fully charged battery kicks out over 8 volts, that means you have 4.8+V across the 470ohm resistor, thats 10 ma being wasted, using resistors only dumps less than 1ma. As far as I can see it just holds the Rx pin on the GPS to logic 1, the two resistors does that fine.

Ian

Great job on the project. Like the small foot print.
I have a Hammond box but they have two screws holding both sides together. Your box does not have any screws; may I ask where did you get that box.
In the EM-406A spec sheet they mention a 470 ohm resistor with a 3.2 V Zener for the voltage divider; seem like it would be more accurate than two resistors. Thanks.

This circuit is a common base configuration, which is an impedance translator as well as voltage gain, low impedance in and high impedance out. Its a very stable config and commonly used in hi frequency applications to prevent unwanted oscillations. (important when dealing with the NMEA data). It certainly works well with the EM-406A.
You can see my finished receiver here http://www.flickr.com/photos/sandozer/tags/gps/

Thanks again to Rick, for the concept.

I still don’t understand the circuit that is proposed here. I see how Rx is kept high by the voltage divider as specified in the 406 module datasheet. As several previous authors have made clear, this should actually be Pin 3 and both Pin 3 and 4 should be swapped.

The diagram that I am working from seems to have the base of the transistor connected to Vcc and the (supposed) Tx pin connected to the emitter. I would have thought that this would have meant that the transistor was simply open circuit and therefore doesn’t really doing anything. It would seem that the Tx pin is thus connected to Vcc via the 10k and 4k7 resistors in parallel (i.e. a resistance of about 3k2), shifting the resting voltage towards Vcc. I have seen something similar advocated when using the old Macintosh RS422 interface which similarly sometimes needed an extra voltage boost by simply soldering a battery between the rails to boost the baseline voltage. I am by no means an electronics expert and am prepared to believe that people have used this design but I fail to see how it works!

John

I have just finished my one now and got it in a box one inch and a half square by .5inch deep. Used surface mount components and a small power switch. Suppose I could post pics on Flickr if anyone needs it, just let me know here.

Many thanks to you Rick for showing how it was done, and giving us all hope that it could be done.

Thanks again, Ian