Display Technology 4 Wire Operational Life Standard Size Linearity Resistive Value Note
Figure 3: 5-wire resistive touchscreens use four corner electrodes on the bottom plate to produce voltage gradients in the X and Y directions and two pairs of edge electrodes on the top plate to sense voltage. (Image source: NKK Switches)
They are typically capable of millions or even tens of millions of operations without failure. Resistive touchscreens can also be manufactured with protection against water and chemical splashes.
The difference between 4 and 5-wire touchscreen configurations A 4-wire touchscreen employs two electrodes on the bottom plate and two on the top plate. On the bottom plate, the electrodes run along the Y axis, enabling resistance to be measured along the X axis. Similarly, the top plate has edge electrodes that run along the X axis, enabling the resistance to be measured along the Y axis (Figure 2). At the point of finger contact, the bottom
layer effectively divides the top layer into two resistors in series. The bottom layer is similarly divided at the point of contact with the top layer. With appropriate biasing, each plate can function as a divider where the output voltage represents the point of contact coordinates. In a 5-wire system, the top plate has four edge electrodes and functions as the voltage sensing node. The four corners of the bottom plate form electrodes that produce voltage gradients in the X and Y directions. Different bias configurations are used to obtain the X and Y direction measurements (Figure 3). In the 5-wire construction, only the bottom plate is active. That means the top plate can sustain damage, yet the touchscreen can still operate. In contrast, both plates of the 4-wire
1 million 5.7" to 19.0" +1.5% Max
250 ~ 850Ω 120 ~ 1500Ω (wide type)
Cost effective, Various standard sizes
Touch Activation Force Flexible Printed Circuit 1.4N
5.7, 6.5, 8.4, 10.4, 10.6 (Wide), 12.1, 12.1 (Wide), 15, 15.6 (Wide), 19
Table 1: A comparison of 4 and 5-wire resistive touchscreens shows the 5-wire version offers longer operational life, measured in tapping operations. (Image source: NKK Switches)
touchscreen are active; damage to the top plate can cause the touchscreen to fail. The 5-wire touchscreen tends to be more durable, but the trade-off is increased design complexity and expense.
Commercial resistive touchscreen solutions
To minimize complexity and accelerate time to market, NKK has proven commercial solutions for both the touchscreen and the
matching controller. The designer still has the option to source a touchscreen from NKK and match it up with a controller from a different supplier, or one of their own.
The FT series from NKK is an excellent example of resistive touchscreens. Available in a variety of screen sizes ranging from 5.7 to 15.6 inches (in.) (diagonal), the series is offered in both 4 and 5-wire configurations with a touch activation force of 1.4 N (Table 1). continues on page 48
5 Wire 10 million 10.4", 12.1" and 15.0" +2.0% Max (After 9 points calibration) 20 - 80Ω
Do not measure voltage from the upper layer so it's more durable.
1.4N
Figure 4: The FTCSU548 controller IC (IC1) is mounted on the FTCU04B (4-wire USB) controller board. CN1 (left) is the connector for the touchscreen’s 4-wire flexible circuit tail. (Image source: NKK Switches)
www.cieonline.co.uk Components in Electronics September 2024 47
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
