With voltage monitoring in place, the system can safely be used in standby mode, as once the battery dips below safe levels the computer will automatically be shutdown until power returns to a safe level again. The M1-ATX is 6.31" wide, 1.77" deep, and under one inch in height. Startup and shutdown sequences are controlled by on on-board PIC and four jumpers (Figure 4).

Figure 4: Power Supply PIC and startup / shutdown jumpers

Using a 2.5" laptop hard drive has many advantages, most notably the fact that it makes the system less sensitive to potholes and bumps in the road. According to some users of MP3car.com community, if you were to use a standard 3.5" hard drive, it would most likely crash after only 6 to 12 months of use, due to all the wear and tear caused by driving. The other downside of using a desktop hard drive is that they are power hungry, and the M1-ATX would most likely not be able to supply the amount of power needed.

For the optical drive, we chose a Panasonic slot load DVD-ROM/CD-RW Combo, which seemed a better match for car entertainment system use.

We crammed these four items into our 7" x 10" x 2" case, which we had custom-cut at a local plastic shop. The acrylic we used for the case, plus the glues, all came to the princely total of £5. Since the acrylic was pre-cut, all that was needed to complete the case was to glue it together and drill the holes in the bottom for the cables to go though.