This is a significant cost of the whole system. You can definatly get by with a screen that costs less. There are a couple of things to look for in a screen:
- Brightness; It should be at least 200 cd/m² (also known as nitts) so that it does not wash out daylight conditions.
- Contrast; Supposedly the higher the contrast the easiser it will be to read text on the screen
- Viewing Angle; Will everyone in the car be able to see the picture or will the colors look inverted to them
- Refresh Rate; If you are planning on watching movies or playing games on it, it must refresh at 30 fps or more
- Touch Screen; For me, this part was essential
Xenarc makes some great screens. The one listed in the partsl list has a brightness of 300 cd/m². This is easily visible in the daytime although it still washes out when the sun is directly on it. It has all the connections I needed (VGA for computer and 2 RCA video inputs) and has a built in USB touchscreen. Its native resolution is a funky 16x9 format of 800x480 pixels. You can buy video cards that output at this resolution. It supports up to 1600x1200 but I have found that anything higher than 800x600 is too difficult to use the touchscreen. On a side note, 640x480 really looks great. The text is very sharp and readable but my operating system does not do well at this resolution.
It is possible to get far less expensive screens and add a touch screen layer to it for about $120. This would include a USB touch controller. So why spend so much more for this screen? Because it is really made with the car environment in mind. It will autodetect a video signal and turn itself on. Likewise if there is no video signal it will automatically turn off. It will autodetect the resolution and refresh rate (very nice). It looks and performs great! Finally, its worth it just to have everything in one package. The touchscreen is built in and so is the video controller card and the electronics for the power. Did I mention it looks great?
Just get whatever will fit in your car and whatever you can power (read the power supply section for more on this). The asus board I listed is a micro ATX board. As it turns out this was more difficult to fit in my car than another full size board I just had laying around. The fullsize board was longer but less wide which was perfect for my glovebox. I opted to get a regular PC rather than something like a Epia or Lillyput (get more info) because I wanted to easily be able to expand later. After looking at some of those Micro ITX computers though, they look pretty good for the price, plus they dont use much power.
I have learned lots about GPS recently. Here is what to look for:
- NMEA Output; If it does not output data in this format, than you are severly limiting your software options. I had a Sony GPS that I love to death but it only outputs data in a proprietary format that only works with their now out of date software
- Serial Connection; Yes I said serial, not USB. Several reasons, if you plan to put your PC into hibernate mode, some, if not all USB GPS will not work upon resuming. This is definatly the case with the Delorme Earthmate. Also, my USB GPS only gets power when it is being used. A serial GPS will get power from the moment you boot up your PC. By the time you get your computer fully resumed, a serial GPS may have already locked on to your position. Finally, get a serial because it is easier to get them working with 3rd party software. Not everyone supports USB yet.
Well, it seemed like lots before I started typing it out. The Delorme Earthmate I bought came with a USB cable. It is possible to download a serial port emulator from their site that allows 3rd party software to access the GPS as if it was plugged in via a serial port (available here). This is very handy but you still get the resume from hibernate issue. In the end, I bought a serial cable to replace the USB cable (available here) . This provides a serial connection to the PC and a cigarette adapter to power the GPS. The adapter can easily be cut off and run to your PC power supply. Make sure you only supply it 5 volts though. More on this later.
I started out using a standard AC computer power supply with a DC to AC power inverter. It took about 10 minutes for me to get tired of having to turn on my power inverter to use the computer. I did a little research and found out that DC computer power supplies are significantly more expensive than AC, even though PCs only use DC voltage.
The only trick is to determine how much power your PC will be drawing and on which lines. In a computer power supply, there is a 12v, 5v, and 3.3v that provides almost all the power to all the different parts of a PC. A power supply should list how many amps it can support on each voltage line. Most PC components will list how many amps they can use off each line. For some things like the processor, the manufacturer will only state the wattage consumed. This can be converted to the current draw (amps) by dividing by the voltage. If my AMD processor uses a max of 62 watts, then it could use 62 watts / 12 volts = 5.17 amps off the 12 volt line. If it were to be powered off the 5 volt line it could reqire up to 12.4 amps. This section is getting to in-depth for how tired I am tonight. More to come later!