The idea behind this project was born when a friend asked me too take a look at he’s broken GPS unit (MyGuide 3000) to see if I can fix anything. I started checking various parts like voltage regulators, but found nothing wrong. The gps unit was still not powering up so I checked the cpu, an ARM9 from Samsung and found it broken. Of course I couldn’t do anything about that, because of the BGA package and the bootloader needed after replacing it so the gps unit became a source for parts. The most useful and interesting parts from the GPS were the LCD display and the GPS module.

The GPS module is a RoyalTek RGM-3550LP which has an integrated antenna and is powered by SiRF Star III technology. I immediately connected the gps module to my computer’s serial port(using a max232) to test if it was still working. To my surprise the gps module was working and sending NMEA compliant sentences. Then I had this idea of using the gps module as a navigation system together with a notebook computer, but notebooks don’t have a serial port so I had to use a UART to USB bridge.

RoyalTek rgm-3550lp-gps-module

The most common used UART-USB bridge is the FT232 manufactured by FTDI which is about $4 which is a fair price because you don’t need any external parts for this chip except some bypass capacitors and that saves you time and money. I never used the chip before but it was really easy to get it working. It even has this custom utility that let’s you program some features saved in the internal EEPROM like the maximum bus power and the product and manufacturer descriptor strings. Anyway these are the only two settings that I tinkered with, but the utility let’s you change some more stuff.


The next thing I had to worry was where to get the power for the GPS unit, because it needs 3.3V and the acquisition current is 50 mA. The FT232 has an internal voltage regulator which provides 3.3 V and 50 mA but I decided not to use that in order to extend it’s life so I ended up using the TPS2148 which is a 3.3V LDO from Texas Instruments. It’s specifically designed for USB peripheral power management, and it’s tiny package(MSOP-8) made it ideally for my application. The TPS2148 handles the current limitation so I didn’t had to worry about that either.


After figuring out the parts I was going to use and the schematic, I had to chose an enclosure for this project. The main target was to get it as small as possible but the limit was the gps module size, I couldn’t of got it smaller then the module :). So I went and searched for a plastic enclosure, and I found one just perfect for what I needed, the PP85D from Supertronic. The gps module fits just nicely between the screw channels.

Then after I got the enclosure, I made the pcb using the photo etching technique.. I assembled and tested it, and to my surprise everything worked just fine from the first try. I’m usually not that lucky when I make stuff using new IC’s that I haven’t used before. Sometimes I don’t pay enough attention to the datasheet and I get some small stuff left behind and that messes my entire circuit. Anyway, happy as I was that everything worked from the first try, I put everything inside the enclosure and snapped some pictures of it. As a final note, this was a great project which I enjoyed making, and I really recommend you do something like this if you have a gps unit laying around.

more pictures:

parts-for-the-usb-gps-project gps-module-and-pcb ft232rl-board

board-inside-the-enclosure pcb-with-gps-module-inside-the-enclosure new-hardware-found

parts list:

  • RGM-3550LP gps module x1
  • FT232RL x1
  • TPS2148 x1
  • capacitor 10uF x3
  • capacitor 100nF x3
  • led x1

schematics and board files were designed in Eagle and can be downloaded here.

March 22nd, 2009

Asus Eee PC car charger

Since I often find myself on the road with my battery drained out and because I intend to use my Eee Pc together with a GPS module as a navigation system I thought it would be a good idea to make myself a car charger. The charger would have to output 9,5 V 2.5A, and it would have to be able to maintain the output voltage constant over variations of the input voltage. Of-course there are lots of voltage regulators these days that would fit my circuit, but I chose to use the LM2576 because such a charger has already been build and tested here (also featured on Youritronics here).

Here is the schematic of the charger:

Eee Pc charger schematic

After ordering the needed parts I noticed that the  inductor is slightly bigger than I expected it to be, so fitting the board into a small box became a bit of a problem. But I managed to designed the board so that it fits into the chosen box. I also fitted a medium sized TO-220 radiator so the circuit would dissipate the heat even in continuous use of the charger. The pcb was made using the photo etching technique and I tried spraying it with a mix of colophonium and alcohol that would act as a soldermask. The result is not pretty but I hope it will protect my board from corrosion.

EeePc charger pcb

After the soldermask dried it was only a matter of minutes until I assembled and tested it. The charger works great, the output voltage remains constant over continuous variations of the input voltage. Now all I have to do is close the box, solder a cigar lighter connector and pack it into my arm rest compartment.

Asus eee pc car charger

July 26th, 2008

ASUS Eee Pc Car Charger

ASUS Eee Pc Car Charger

You’ve probably seen the article about the Asus Eee PC and what can be integrated inside it’s case. But after you’ve done some modding and added different devices your battery probably doesn’t last as it was intended to last, so if you need to charge it in the car you either buy a commercial adapter or you make it.

This projects shows details on how to build an Eee Pc car charger. There are actually a small number of parts so the whole cost should be small.

ASUS Eee Pc Car Charger: [Link]

July 20th, 2008

Eee PC Internal Upgrades

Eee PC Internal Upgrades

We’re talking about everything, every device that you can think off hass been integrated into the Eee PC by these guys. All the info is nicely presented with pictures, so anyone with some electronic skills should be able to make hi’s Asus Eee PC trully custom. These are some of the devices that were integrated into the Eee PC:

  • USB hub
  • GPS with antenna
  • Bluetooth
  • Card reader
  • Flash drive
  • Power switch
  • Wifi
  • FM transmitter
  • Modem
  • System memory
  • Touch screen
  • Temperature sensor
  • Heatsink

Eee PC Internal Upgrades: [Link]

Read my Asus Eee PC Review

New Asus Eee PC with 9 inch display

If you hadn’t guessed from the headline, and as rumored just an hour ago, there’s 9-inches of LCD on this thing. Actually, 8.9, but who’s counting? We found out that and a few other little tidbits about this Eee PC “New Generation” at the ASUS booth just now, but for the most part the 9-inch Eee PC is quite similar to its 7-inch forebearer. Anything past that ASUS is saving for tomorrow’s press event when this laptop will become officially official, but whatever they end up calling it (Eee PC 900 is rumored), it’s certainly for real. The battery impact of the new display is said to be “negligible,” with 2.5 to 3 hours of battery quoted. ASUS wouldn’t let us turn it on since it’s all so very secret at the moment, but they did confirm some release details. The 9-inch Eee will hit in the “middle” of 2008, with that €399 pricetag for the 12GB version, but other capacities available (we saw an 8GB on display). No word yet on US pricing, but we’re trying to pry it out of them.

source: Engadget

New Asus Eee PC with 9 inch display: [Via]

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