The PCB layout is an important part of system design. The first thing to consider are some of the basic features of the devices offered by ST. The devices listed here differ mainly in the number of channels. The STMPE1208 is a twelve-channel device while the STMPE1218 is another twelve-channel device with additional features. Then there are the STMPE921/821/521 and 321 with nine, eight, five and three channels respectively. Also, there are slight differences in what is called the dynamic range, which is the range within which the device can actually make a reading. The effective range of measurement is given by the sum of three different elements. All of these devices can have an external capacitor that can be set up to 33pF. This capacitor has to be physically added to the board, which is important to note as will be shown later. Then there is the internal reference capacitance, which can have a maximum value of 7.8pF, 6.4pF, or 5.1pF, depending on the device. Additionally, the dynamic range, ranging from 7.8 to 5.1pF in 128 steps, needs to be accounted for. Factoring in all of these capacitance contributions results in an effective range of about 50pF maximum.