When I first built my GPS receiver over a year ago I was fairly pleased with its performance. After using it more, however, it became obvious that I needed to make some improvements. The following were my biggest problems with the device.
- Battery life. The 9V battery and 5VDC regulator combination that powered the receiver wasted a lot of energy in the process of reducing the 9V input to the 5V needed to power the receiver. I wanted to find an alternative power source that could use rechargeable batteries with more capacity.
- Build quality of the receiver’s enclosure. I found that the enclosure I had been using was too large to conveniently fit in a backpack with other gear. I also wanted to rewire the device to better utilize wire management techniques inside the enclosure.
- Power & Backlight Controls. In my first attempt I used slide switches which, while functional, looked terrible. In my revised build I used push-on-push-off switches. This was an improvement, but they were still poorly placed and could turn on accidentally when pressed against other objects in a pack.
The solution I found for this problem is actually a project that I’ve built before called the MintyBoost. This ingenious device takes a 2-3V input from 2 AA batteries and boosts it to 5V. While originally intended to charge USB devices such as cell phones or mp3 players, the MintyBoost works perfectly with my GPS receiver and offers a big improvement in convenience and performance. I can now use rechargeable NiMH AA batteries which provide 2000mAh of power, constituting over 300% more capacity than a typical alkaline 9V battery. This should translate into over 12 hours of battery life.
While I would normally build a simple circuit like this from scratch, I decided to get MintyBoost kit for this build. Aside from the obvious convenience factor, it also packs the circuit into a much smaller package than I could accomplish on a proto-board. The only changes I made to the kit were that I did not install the female USB connector and its associated pull-up/down resistors since I connected my power wires directly to the board itself.
I looked around for a new enclosure with a AA battery compartment, but I couldn’t find one that was the right size, so I decided to use a generic 6x4x2 project box from Radioshack and modify it for my purposes. While somewhat thicker, it is otherwise much smaller and fits better in the hand than my previous enclosure.
Because I need to access the inside of the case every time the batteries have to be changed, I wanted to be able to take the cover off without having to use tools. As with all Radioshack project boxes the cover is normally held on with 4 countersunk Phillips head screws. To allow for hand access, I drilled and tapped the screw holes in the body of the box to accept 6-32 cap screws. These machine screws have a knurled head instead of a screwdriver slot, allowing you to grip the head of the screw with your fingers. This makes removing the cover by hand a breeze.
In addition to modifying the case I also rewired all of the connections from the LCD and GPS module to the main board. This means I now have only 4 wires going from the main board to the lid, allowing me to bundle the wires and secure them with wire ties to the lid and body. Another change I made was mounting the two circuit boards and battery holder to the enclosure with double sided foam tape instead of stand-offs and bolts.
Power & Backlight Controls
To resolve my complaints about the receiver’s controls I decided to change both the placement and type of the switches I used. Instead of the face of the receiver, I moved the controls to the top of the unit. The main idea behind this is that it streamlines the profile of the receiver so that there are no protrusions when it is placed vertically in a backpack, making it less likely that the unit will be turned on accidentally. For the power switch I used a large rocker switch with a fairly stiff action. This switch is both functionally and aesthetically superior to my previous choice. For the backlight control I stuck with a pushbutton, but this time I went with a small momentary version. This was done because I rarely use the backlight and by requiring the user to hold down the button they are more likely to use it sparingly, thereby conserving the battery.
I am very pleased with this latest revision of my GPS receiver. It has always been a fun project and now it is even more capable and robust. Check out the video below for a walk-through and a demonstration of the unit.