Freescale Semiconductor
Document Number: AN4600
Rev 0, 12/2012
Application Note
Designing a Touch Panel using
the Xtrinsic MPR121 Capacitive
Touch Sensor Controller
By Kevin Jia, Applications Engineer
1
Introduction
This application note shows how to design a touch panel
around the MPR121 capacitive touch sensor controller,
using minimal hardware and software.
The function of a touch panel is something like the touch
panel on a laptop—when you move the finger on the
touch panel, the mouse cursor onscreen follows it.
With many consumer and industrial devices, a person
uses a finger on a touch panel or pad, touch wheel, or
slide bar to move the cursor on a display. This type of
intuitive “finger” interface makes products easy to use
and greatly improves the overall customer experience.
© 2012 Freescale Semiconductor, Inc. All rights reserved.
Contents
1
2
3
4
5
6
7
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Touch Panel Demo Example. . . . . . . . . . . . . . . . . . . . . .
Controller Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Touch Panel PCB Layout . . . . . . . . . . . . . . . . . . . . . . . .
Board Layout Tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
About the Demo Software . . . . . . . . . . . . . . . . . . . . . . . .
Demo Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
2
3
3
4
5
7
2
Touch Panel Demo Example
The following is an example of a demo board using
• a JM badge board
• and the MPR121 evaluation kit.
JM badge board
USB
Touch panel
(with no cover)
MPR121 EVK
(evaluation kit)
Touch panel
(with cover)
Figure 1. Touch panel demo assembly
Why choose a JM badge board as a motherboard?
• To calculate the coordinates for a touch sensor, you want a powerful processor, like the
MCF51JM128 (ColdFire v1 32-bit core).
• For convenience, you want a USB device interface with a HID mouse device driver already
implemented on it, so that you don't have to implement it yourself.
However, the JM badge board does not have the MPR121 sensor on it (the JM badge board has an
MPR08x, and eight electrodes are not enough for our application), so we run wires to the MPR121 EVK,
to use the touch sensor on it.
Actually, you could make your own PCB to skip the operation above. If desired, we can provide the whole
project code (include HID mouse device driver and touch sensor algorithm related code) for your
reference. This application note provides the core algorithm code of the touch sensor; the HID device
driver is not included here.
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
2
Freescale Semiconductor, Inc.
3
Controller Schematic
Using a 2.0 V to 3.6 V supply is recommended, as shown in Figure 2.
•
•
•
A separate 0.1 μF decoupling
ceramic capacitor on VREG to VSS
is applied as a bypass cap for internal
circuitry.
Pullup resistors, typically 4.7 kΩ, are
required on SDA, SCL, IRQ, and
REXT.
MPR121 has 12 input sensing
channels ELE0 – ELE11 (pins 8 –
19). Pins 12 – 19 are multifunction
pins.
Figure 2. MPR121 schematic using 2.0 V to 3.6 V power supply
The schematic for the sensor controller is simple—simply connect several resistors and capacitors. The
sensor uses I2C to communicate with the MCU. In this example, ELE0–ELE11 are used as touch panel
inputs.
4
Touch Panel PCB Layout
For accurate coordinates, apply a matrix PCB layout method, see Figure 3.
ELE0 – ELE6 are the vertical coordinates.
ELE0 – ELE11
are electrodes.
ELE7 – ELE11 are the
horizontal coordinates.
Figure 3. Track panel PCB layout
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
3
Freescale Semiconductor, Inc.
•
•
•
•
5
The vertical and horizontal electrodes have no junctions.
Blocks connect to each other in vertical or horizontal directions.
The size of the block is determined by the expected finger size. When you touch the panel, your
finger end should match four blocks for the sensor to achieve the best sensitivity and the data
(vertical/horizontal) required for calculating the coordinate.
If the block is too small, then the sensor will have low sensitivity, which can be worse if thick cover
materials are used.
Board Layout Tips
We recommend:
• Block size of 3.5 – 4.0 mm
• 0.5 mm gap between blocks
• 1.6 mm touch panel thickness
• To reduce any interference, place the sensor circuit as far away from other circuits as possible.
• The electrode trace (the wire between an ELEx pin and the blocks) must be short and slim:
— trace length should not exceed 7800 mil (200 mm)
— trace width is recommended to be 5 mil (0.127 mm)
• There should be no high frequency traces near the electrode traces (such as I2C, SPI, etc.). If you
do have high frequency traces near the electrode traces, then route the traces on different layers and
perpendicular to each other.
• When laying out the touch panel, route the blocks on the top layer, and route the traces on the
bottom layer.
• If the board exhibits no strong RF disturbance, then a ground plane is not necessary. A ground plane
will decrease the panel's sensitivity, but will improve the anti-interference capability. For safety,
you can fill a 40% ground plane on the sensing area (the top layer); the bottom layer does not need
a ground plane.
• If the board exhibits a strong RF disturbance, then fill a 40% ground plane on the top layer, plus a
a 60% ground plane on the bottom layer.
• We recommend using ABS plastic cover materials (thickness ≤ 0.25 mm) and 3M 467MP adhesive
(thickness ≤ 0.05 mm). The total thickness (plastic cover + adhesives) should be less than 0.3 mm.
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
4
Freescale Semiconductor, Inc.
6
About the Demo Software
Figure 4 shows the flowchart of a demo program; the source code follows in the next section (Section 7,
“Demo Code”).
Start
Sys_init
Click below to go to the code example
void Read_MPR121_ele_register(void)
Read MPR121 electrode register
void Get_ele_data(void)
Get electrode data
void Get_touch_status(void)
Get touch status
void Intp5x7(void)
Do interpolation
void Pol_mouse_dat(void)
(includes digital filtering and dividing)
Poll mouse data
in_report=hid_add_report(rpt_in, 0, 3);
Also see
Hid_report
int mouse_demo(void)
(the sensor application)
Figure 4. Program flowchart
MPR121 initialization: Before initializing the MPR121, know your application parameters:
• Touch button, slider bar, or touch panel?
• How many electrodes will be used?
• What is the required sensitivity?
• Which adhesive are you using, and what is its thickness?
This information helps to determine the sensor's configuration. For our finger tracking application (to
emulate a mouse), we need a faster frequency response than a touch button, so we will use 12 electrodes.
Thus, we configure the following registers:
• Electrode Configuration register (0x5E) = 0x0C (for 12 electrodes)
• AFE Configuration register (0x5C) = 0xC0 (take 34 samples, which is good for interference
immunity)
• AFE Configuration2 register (0x5D) = 0x00 (SFI = 4, ESI = 1 ms, so the response time is 4 ms,
which is the fastest response time)
Getting accurate coordinates using an interpolation algorithm: By using an interpolation algorithm,
we can get the finger's coordinate accurately. For the horizontal coordinates, we use seven electrodes
(ELE0 – ELE6). The formula is:
SumN = 1 × Dele(0) + 2 × Dele(1) + 3 × Dele(2) + …… + 7 × Dele(6)
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
5
SumD = Dele(0) + Dele(1) + Dele(2) + …… + Dele(6)
Dele(n) (n = 0 to 6) represents the delta value (difference) of electrode-filtered data and its corresponding
baseline value. After getting SumN and SumD, then:
Coordinate = SumN ÷ SumD
After getting the finger's horizontal coordinate, you use the same interpolation method to compute the
vertical coordinate, using the other five electrodes (ELE7 – ELE11).
Smoothing sensor outputs using a digital filter: We need to use a digital filter to smooth the sensor's
output. The first-order filter formula is:
FO(n) = A × FO(n-1) + B × SP(n)
A+B=1
• FO(n) represents current filter output value.
• FO(n-1) represents previous filter output value.
• SP(n) represents current sample value.
• A and B are scale factors, which represent the weights of FO(n-1) and SP(n) in the first order filter
FO(n).
— The value of A determines the digital filter effect: the greater the value of A, the smoother the
output (but this will sacrifice tracking performance, i.e., the system will respond more slowly),
so you have to find a balance.
— The value of B determines the digital filter response time: the greater the value of B, the faster
the response time is.
Reducing cursor jitter: To reduce the noise that can cause the cursor to jitter when you touch the touch
panel: after reading filtered 10-bit data value from the registers (0x04 – 0x1B), mask its lower two bits
with 0xFFFC before passing it for consecutive calculations.
Implementing a divider in software: Some 8-bit MCUs have no hardware divider, so you may have
implement the divider in software. See Section 7, “Demo Code”.
Data polling over USB: The polling time defines the frequency that the MCU polls data over the USB
link. If we configure the sensor's response time to be T ms, then the polling time must satisfy 0.5 T, which
is half the response time (according to Shannon Sampling Theory). This response performance will lose
no frames and get the best performance.
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
6
Freescale Semiconductor, Inc.
7
Demo Code
The following code example is for a low cost, high performance mouse tracking demo, using the MPR121
device. You can copy the code directly out of this PDF to a text file.
Table 1. Demo functions
Function (click to go there)
Description
void MPR121_init(void)
MPR121 and sensor initialization
void Read_MPR121_ele_register(void)
Read registers
void Get_ele_data(void)
Get coordinate data
void Get_touch_status(void)
Get touch status
void Intp5x7(void)
Interpolate coordinates
INT32 FilterXY(INT32 prev,INT32 spl,UINT8 m)
Digital filter
INT32 GetPosXY(INT32 fz,INT32 fm)
Data divider
void Pol_mouse_dat(void)
Poll for data over USB
int mouse_demo(void)
Mouse tracking demo
Example 1. Mouse tracking demo using MPR121 device
#define TouchThre 10//15//30//10
#define ReleaThre 8//8//25//8
void MPR121_init(void)
{
//Reset MPR121 if not reset correctly
IIC_ByteWrite(0x80,0x63); //Soft reset
IIC_ByteWrite(0x5E,0x00); //Stop mode
//touch pad baseline filter
//rising
IIC_ByteWrite(0x2B,0x01); //0xFF// MAX HALF DELTA Rising
IIC_ByteWrite(0x2C,0x01); //0xFF// NOISE HALF DELTA Rising
IIC_ByteWrite(0x2D,0x00); // //0 NOISE COUNT LIMIT Rising
IIC_ByteWrite(0x2E,0x00); // DELAY LIMIT Rising
//falling
IIC_ByteWrite(0x2F,0x01); // MAX HALF DELTA Falling
IIC_ByteWrite(0x30,0x01); // NOISE HALF DELTA Falling
IIC_ByteWrite(0x31,0xFF); // NOISE COUNT LIMIT Falling
IIC_ByteWrite(0x32,0x02); // //2//DELAY LIMIT Falling
//touched
IIC_ByteWrite(0x33,0x00); // Noise half delta touched
IIC_ByteWrite(0x34,0x00); // Noise counts touched
IIC_ByteWrite(0x35,0x00); //Filter delay touched
//Touch pad threshold
IIC_ByteWrite(0x41,TouchThre); // ELE0 TOUCH THRESHOLD
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
7
IIC_ByteWrite(0x42,ReleaThre);
IIC_ByteWrite(0x43,TouchThre);
IIC_ByteWrite(0x44,ReleaThre);
IIC_ByteWrite(0x45,TouchThre);
IIC_ByteWrite(0x46,ReleaThre);
IIC_ByteWrite(0x47,TouchThre);
IIC_ByteWrite(0x48,ReleaThre);
IIC_ByteWrite(0x49,TouchThre);
IIC_ByteWrite(0x4A,ReleaThre);
IIC_ByteWrite(0x4B,TouchThre);
IIC_ByteWrite(0x4C,ReleaThre);
IIC_ByteWrite(0x4D,TouchThre);
IIC_ByteWrite(0x4E,ReleaThre);
IIC_ByteWrite(0x4F,TouchThre);
IIC_ByteWrite(0x50,ReleaThre);
IIC_ByteWrite(0x51,TouchThre);
IIC_ByteWrite(0x52,ReleaThre);
IIC_ByteWrite(0x53,TouchThre);
IIC_ByteWrite(0x54,ReleaThre);
IIC_ByteWrite(0x55,TouchThre);
IIC_ByteWrite(0x56,ReleaThre);
IIC_ByteWrite(0x57,TouchThre);
IIC_ByteWrite(0x58,ReleaThre);
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
ELE0 RELEASE THRESHOLD
ELE1 TOUCH THRESHOLD
ELE1 RELEASE THRESHOLD
ELE2 TOUCH THRESHOLD
ELE2 RELEASE THRESHOLD
ELE3 TOUCH THRESHOLD
ELE3 RELEASE THRESHOLD
ELE4 TOUCH THRESHOLD
ELE4 RELEASE THRESHOLD
ELE5 TOUCH THRESHOLD
ELE5 RELEASE THRESHOLD
ELE6 TOUCH THRESHOLD
ELE6 RELEASE THRESHOLD
ELE7 TOUCH THRESHOLD
ELE7 RELEASE THRESHOLD
ELE8 TOUCH THRESHOLD
ELE8 RELEASE THRESHOLD
ELE9 TOUCH THRESHOLD
ELE9 RELEASE THRESHOLD
ELE10 TOUCH THRESHOLD
ELE10 RELEASE THRESHOLD
ELE11 TOUCH THRESHOLD
ELE11 RELEASE THRESHOLD
//AFE configuration
IIC_ByteWrite(0x5D,0x00);
IIC_ByteWrite(0x5C,0xC0);
//Auto configuration
IIC_ByteWrite(0x7B,0xCB);
IIC_ByteWrite(0x7D,0xE4);
IIC_ByteWrite(0x7E,0x94);
IIC_ByteWrite(0x7F,0xCD);
IIC_ByteWrite(0x5E,0x0C);
}
void Read_MPR121_ele_register(void)
{
// read the register before 0x2B
reading = u8VI2CRead(iBatAddress, (UINT8 *)(&readingArray), 0x2B);
}
void Get_ele_data(void)
{
UINT8 i;
UINT16 tmp_sig,tmp_bas;
for (i=0; i<13; i++)
{
tmp_sig=(((UINT16)readingArray[0x04+2*i])|(((UINT16)readingArray[0x04+1+2*i])<<8))&0xFFFC;
tmp_bas=((UINT16)readingArray[0x1e + i])<<2;
ele_delta[i]=abs((INT16)(tmp_sig-tmp_bas));
}
}
void Get_touch_status(void)
{
CurrTouchStatus.Reg0=readingArray[0x00];
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
8
Freescale Semiconductor, Inc.
CurrTouchStatus.Reg1=readingArray[0x01];
if (((CurrTouchStatus.Reg0 & 0xff) != 0) || ((CurrTouchStatus.Reg1 & 0x1f)!= 0) )
{
CurrTouchStatus.Touched=1;
}else
{
CurrTouchStatus.Touched=0;
}
}
void Intp5x7(void)
{
UINT8 i;
SampSumX=0;
SampSX=0;
SampSumY=0;
SampSY=0;
for(i=0;i<12;i++)
{
if(i<7)
{
SampSumX+=(i+1)*ele_delta[i];
SampSX+=ele_delta[i];
}
else
{
SampSumY+=(i-6)*ele_delta[i];
SampSY+=ele_delta[i];
}
}
}
INT32 FilterXY(INT32 prev,INT32 spl,UINT8 m)
{
//X=6/8*X'+2/8*X''
if(m==1)
return prev-(prev>>2)+(spl>>2);
// 4/8
4/8
else if(m==2) return (prev>>1)+(spl>>1);
// 5/8
3/8
else if(m==3) return prev-(prev>>1)+(prev>>3)+(spl>>2)+(spl>>3);
// 7/8
1/8
else if(m==4) return prev-(prev>>3)+(spl>>3);
}
// divider
INT32 GetPosXY(INT32 fz,INT32 fm)
{
UINT8 i;
UINT32 w=0;
UINT16 q=0,b=0;
UINT8 s=0,g=0;
if(fz==0||fm==0) return 0;
for(i=0;i<5;i++)
{
if(fz<fm)
{
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
9
if(i==0)
if(i==1)
if(i==2)
if(i==3)
if(i==4)
w=0;
q=0;
b=0;
s=0;
g=0;
fz=(fz<<3)+(fz<<1);
continue;
}
while(1)
{
fz-=fm;
if(i==0)
if(i==1)
if(i==2)
if(i==3)
if(i==4)
++w;
++q;
++b;
++s;
++g;
if(fz<fm)
{
fz=(fz<<3)+(fz<<1);
break;
}
}
}
// y.yyyy*10000
w=(w<<13)+(w<<10)+(w<<9)+(w<<8)+(w<<4);
q=(q<<9)+(q<<8)+(q<<7)+(q<<6)+(q<<5)+(q<<3);
b=(b<<6)+(b<<5)+(b<<2);
s=(s<<3)+(s<<1);
return w+q+b+s+g;
}
void Pol_mouse_dat(void)
{
if(CurrTouchStatus.Touched==1)
// pressed
{
// get CurSumX,CurSumY,SX,SY
CurSumX = FilterXY(PrevSumX,SampSumX,1);
CurSX
= FilterXY(PrevSX,SampSX,1);
CurSumY = FilterXY(PrevSumY,SampSumY,1);
CurSY
= FilterXY(PrevSY,SampSY,1);
CurPosX = GetPosXY(CurSumX,CurSX);
CurPosY = GetPosXY(CurSumY,CurSY);
// G Filter
#if FILTER==G
CurPosX = FilterXY(PrevPosX,CurPosX,2);
CurPosY = FilterXY(PrevPosY,CurPosY,2);
CurDX = CurPosX-PrevPosX;
CurDY = CurPosY-PrevPosY;
#endif
// D Filter
#if FILTER==D
SamDX = CurPosX-PrevPosX;
SamDY = CurPosY-PrevPosY;
CurDX = FilterXY(PrevDX,SamDX,1);
CurDY = FilterXY(PrevDY,SamDY,1);
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
10
Freescale Semiconductor, Inc.
#endif
// A Filter
#if FILTER==A
CurPosX = FilterXY(PrevPosX,CurPosX,3);
CurPosY = FilterXY(PrevPosY,CurPosY,3);
SamDX = CurPosX-PrevPosX;
SamDY = CurPosY-PrevPosY;
CurDX = FilterXY(PrevDX,SamDX,3);
CurDY = FilterXY(PrevDY,SamDY,3);
#endif
if(PreTouchStatus.Touched==0) // fast track when finger just pressed
{
#if FILTER==D||FILTER==A
SndFlg=1;
#endif
PrevSumX=SampSumX;
PrevSX=SampSX;
PrevSumY=SampSumY;
PrevSY=SampSY;
PrevPosX=GetPosXY(PrevSumX,PrevSX);
PrevPosY=GetPosXY(PrevSumY,PrevSY);
}
else
// when finger pressed for some time
{
if(FstFlg++>=3) // ingored first three samples for avoid cursor's tremble
{
FstFlg=3;
// for debug
/*
if((CurSumX!=PrevSumX)||(CurSX!=PrevSX)||(CurSumY!=PrevSumY)||(CurSY!=PrevSY))
{
SendChar((char)(CurSumX>>8));
SendChar((char)(CurSumX&0x00ff));
SendChar((char)(CurSX>>8));
SendChar((char)(CurSX&0x00ff));
SendChar((char)(CurSumY>>8));
SendChar((char)(CurSumY&0x00ff));
SendChar((char)(CurSY>>8));
SendChar((char)(CurSY&0x00ff));
SendChar('\r');
SendChar('\n');
}
*/
if((CurPosX!=PrevPosX)||(CurPosY!=PrevPosY))
{
// for debug
/*
SendChar((char)(CurPosX>>24));
SendChar((char)((CurPosX&0x00ff0000)>>16));
SendChar((char)((CurPosX&0x0000ff00)>>8));
SendChar((char)(CurPosX&0x000000ff));
SendChar((char)(CurPosY>>24));
SendChar((char)((CurPosY&0x00ff0000)>>16));
SendChar((char)((CurPosY&0x0000ff00)>>8));
SendChar((char)(CurPosY&0x000000ff));
SendChar('\r');
SendChar('\n');
*/
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
11
// delta counts < threshold?ingored
if(((CurDX<S_X)&&(CurDX>=0))||((CurDX>-S_X)&&(CurDX<=0)))
{
// send 0
DX=0;
}
else
{
// every 50 delta counts corresponds to 1 amplify factor
// amplify factors could be adjusted by cursor's move performance
if(CurDX>0)
{
if(CurDX>=S_X&&CurDX<S_X+50)
DX=2;
// 2
else if(CurDX>=S_X+50&&CurDX<S_X+100)
DX=2;
// 2
else if(CurDX>=S_X+100&&CurDX<S_X+150)
DX=2;
// 2
else if(CurDX>=S_X+150&&CurDX<S_X+200)
DX=2;
// 2
else if(CurDX>=S_X+200&&CurDX<S_X+250)
DX=3;
// 3
else if(CurDX>=S_X+250&&CurDX<S_X+300)
DX=3;
// 3
else if(CurDX>=S_X+300&&CurDX<S_X+350)
DX=3;
// 3
else if(CurDX>=S_X+350&&CurDX<S_X+400)
DX=3;
// 3
else if(CurDX>=S_X+400&&CurDX<S_X+450)
DX=4;
// 4
else if(CurDX>=S_X+450&&CurDX<S_X+500)
DX=4;
// 4
else if(CurDX>=S_X+500&&CurDX<S_X+550)
DX=4;
// 4
else if(CurDX>=S_X+550&&CurDX<S_X+600)
DX=4;
// 5
else if(CurDX>=S_X+600&&CurDX<S_X+650)
DX=5;
// 5
else if(CurDX>=S_X+650&&CurDX<S_X+700)
DX=5;
// 5
else if(CurDX>=S_X+700&&CurDX<S_X+750)
DX=5;
// 6
else if(CurDX>=S_X+750&&CurDX<S_X+800)
DX=5;
// 6
else if(CurDX>=S_X+800&&CurDX<S_X+850)
DX=6;
// 6
else if(CurDX>=S_X+850&&CurDX<S_X+900)
DX=6;
// 7
else if(CurDX>=S_X+900&&CurDX<S_X+950)
DX=6;
// 7
else if(CurDX>=S_X+950&&CurDX<S_X+1000)
DX=6;
// 8
else if(CurDX>=S_X+1000&&CurDX<S_X+1050)
DX=7;
// 8
else if(CurDX>=S_X+1050&&CurDX<S_X+1100)
DX=7;
// 9
else if(CurDX>=S_X+1100&&CurDX<S_X+1150)
DX=7;
// 10
else if(CurDX>=S_X+1150&&CurDX<S_X+1200)
DX=8;
// 11
else if(CurDX>=S_X+1200&&CurDX<S_X+1250)
DX=8;
// 12
else if(CurDX>=S_X+1250&&CurDX<S_X+1300)
DX=9;
// 13
else if(CurDX>=S_X+1300&&CurDX<S_X+1350)
DX=9;
// 14
else if(CurDX>=S_X+1350&&CurDX<S_X+1400)
DX=10;
// 15
else if(CurDX>=S_X+1400&&CurDX<S_X+1450)
DX=10;
// 16
else if(CurDX>=S_X+1450&&CurDX<S_X+1500)
DX=11;
// 17
else if(CurDX>=S_X+1500&&CurDX<S_X+1550)
DX=11;
// 18
else if(CurDX>=S_X+1550&&CurDX<S_X+1600)
DX=12;
// 19
else if(CurDX>=S_X+1600&&CurDX<S_X+1650)
DX=13;
// 20
else if(CurDX>=S_X+1650&&CurDX<S_X+1700)
DX=14;
// 21
else if(CurDX>=S_X+1700&&CurDX<S_X+1750)
DX=15;
// 22
else
DX=18;
// 25
}
else
{
if(CurDX+S_X<=0&&CurDX+S_X+50>0)
DX=-2;
// -2
else if(CurDX+S_X+50<=0&&CurDX+S_X+100>0)
DX=-2;
// -2
else if(CurDX+S_X+100<=0&&CurDX+S_X+150>0)
DX=-2;
// -2
else if(CurDX+S_X+150<=0&&CurDX+S_X+200>0)
DX=-2;
// -3
else if(CurDX+S_X+200<=0&&CurDX+S_X+250>0)
DX=-3;
// -3
2
2
2
3
3
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
12
Freescale Semiconductor, Inc.
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
if(CurDX+S_X+250<=0&&CurDX+S_X+300>0)
if(CurDX+S_X+300<=0&&CurDX+S_X+350>0)
if(CurDX+S_X+350<=0&&CurDX+S_X+400>0)
if(CurDX+S_X+400<=0&&CurDX+S_X+450>0)
if(CurDX+S_X+450<=0&&CurDX+S_X+500>0)
if(CurDX+S_X+500<=0&&CurDX+S_X+550>0)
if(CurDX+S_X+550<=0&&CurDX+S_X+600>0)
if(CurDX+S_X+600<=0&&CurDX+S_X+650>0)
if(CurDX+S_X+650<=0&&CurDX+S_X+700>0)
if(CurDX+S_X+700<=0&&CurDX+S_X+750>0)
if(CurDX+S_X+750<=0&&CurDX+S_X+800>0)
if(CurDX+S_X+800<=0&&CurDX+S_X+850>0)
if(CurDX+S_X+850<=0&&CurDX+S_X+900>0)
if(CurDX+S_X+900<=0&&CurDX+S_X+950>0)
if(CurDX+S_X+950<=0&&CurDX+S_X+1000>0)
if(CurDX+S_X+1000<=0&&CurDX+S_X+1050>0)
if(CurDX+S_X+1050<=0&&CurDX+S_X+1100>0)
if(CurDX+S_X+1100<=0&&CurDX+S_X+1150>0)
if(CurDX+S_X+1150<=0&&CurDX+S_X+1200>0)
if(CurDX+S_X+1200<=0&&CurDX+S_X+1250>0)
if(CurDX+S_X+1250<=0&&CurDX+S_X+1300>0)
if(CurDX+S_X+1300<=0&&CurDX+S_X+1350>0)
if(CurDX+S_X+1350<=0&&CurDX+S_X+1400>0)
if(CurDX+S_X+1400<=0&&CurDX+S_X+1450>0)
if(CurDX+S_X+1450<=0&&CurDX+S_X+1500>0)
if(CurDX+S_X+1500<=0&&CurDX+S_X+1550>0)
if(CurDX+S_X+1550<=0&&CurDX+S_X+1600>0)
if(CurDX+S_X+1600<=0&&CurDX+S_X+1650>0)
if(CurDX+S_X+1650<=0&&CurDX+S_X+1700>0)
if(CurDX+S_X+1700<=0&&CurDX+S_X+1750>0)
DX=-3;
DX=-3;
DX=-3;
DX=-4;
DX=-4;
DX=-4;
DX=-4;
DX=-5;
DX=-5;
DX=-5;
DX=-5;
DX=-6;
DX=-6;
DX=-6;
DX=-6;
DX=-7;
DX=-7;
DX=-7;
DX=-8;
DX=-8;
DX=-9;
DX=-9;
DX=-10;
DX=-10;
DX=-11;
DX=-11;
DX=-12;
DX=-13;
DX=-14;
DX=-15;
DX=-18;
}
}
if(((CurDY<S_Y)&&(CurDY>=0))||((CurDY>-S_Y)&&(CurDY<=0)))
{
// send 0
DY=0;
}
else
{
if(CurDY>0)
{
if(CurDY>=S_Y&&CurDY<S_Y+50)
DY=2;
else if(CurDY>=S_Y+50&&CurDY<S_Y+100)
DY=2;
else if(CurDY>=S_Y+100&&CurDY<S_Y+150)
DY=2;
else if(CurDY>=S_Y+150&&CurDY<S_Y+200)
DY=2;
else if(CurDY>=S_Y+200&&CurDY<S_Y+250)
DY=3;
else if(CurDY>=S_Y+250&&CurDY<S_Y+300)
DY=3;
else if(CurDY>=S_Y+300&&CurDY<S_Y+350)
DY=3;
else if(CurDY>=S_Y+350&&CurDY<S_Y+400)
DY=3;
else if(CurDY>=S_Y+400&&CurDY<S_Y+450)
DY=4;
else if(CurDY>=S_Y+450&&CurDY<S_Y+500)
DY=4;
else if(CurDY>=S_Y+500&&CurDY<S_Y+550)
DY=4;
else if(CurDY>=S_Y+550&&CurDY<S_Y+600)
DY=4;
else if(CurDY>=S_Y+600&&CurDY<S_Y+650)
DY=5;
else if(CurDY>=S_Y+650&&CurDY<S_Y+700)
DY=5;
else if(CurDY>=S_Y+700&&CurDY<S_Y+750)
DY=5;
// -3
// -3
// -3
// -4
// -4
// -4
// -5
// -5
// -5
// -6
// -6
// -6
// -7
// -7
// -8
// -8
// -9
// -10
// -11
// -12
// -13
// -14
// -15
// -16
// -17
// -18
// -19
// -20
// -21
// -22
// -25
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
3
3
4
4
4
4
2
2
2
2
3
3
3
3
4
4
4
5
5
5
6
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
13
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
else
if(CurDY>=S_Y+750&&CurDY<S_Y+800)
if(CurDY>=S_Y+800&&CurDY<S_Y+850)
if(CurDY>=S_Y+850&&CurDY<S_Y+900)
if(CurDY>=S_Y+900&&CurDY<S_Y+950)
if(CurDY>=S_Y+950&&CurDY<S_Y+1000)
if(CurDY>=S_Y+1000&&CurDY<S_Y+1050)
if(CurDY>=S_Y+1050&&CurDY<S_Y+1100)
if(CurDY>=S_Y+1100&&CurDY<S_Y+1150)
if(CurDY>=S_Y+1150&&CurDY<S_Y+1200)
if(CurDY>=S_Y+1200&&CurDY<S_Y+1250)
if(CurDY>=S_Y+1250&&CurDY<S_Y+1300)
if(CurDY>=S_Y+1300&&CurDY<S_Y+1350)
if(CurDY>=S_Y+1350&&CurDY<S_Y+1400)
if(CurDY>=S_Y+1400&&CurDY<S_Y+1450)
if(CurDY>=S_Y+1450&&CurDY<S_Y+1500)
if(CurDY>=S_Y+1500&&CurDY<S_Y+1550)
if(CurDY>=S_Y+1550&&CurDY<S_Y+1600)
if(CurDY>=S_Y+1600&&CurDY<S_Y+1650)
if(CurDY>=S_Y+1650&&CurDY<S_Y+1700)
if(CurDY>=S_Y+1700&&CurDY<S_Y+1750)
DY=5;
DY=6;
DY=6;
DY=6;
DY=6;
DY=7;
DY=7;
DY=7;
DY=8;
DY=8;
DY=9;
DY=9;
DY=10;
DY=10;
DY=11;
DY=11;
DY=12;
DY=13;
DY=14;
DY=15;
DY=18;
}
else
{
if(CurDY+S_Y<=0&&CurDY+S_Y+50>0)
else if(CurDY+S_Y+50<=0&&CurDY+S_Y+100>0)
else if(CurDY+S_Y+100<=0&&CurDY+S_Y+150>0)
else if(CurDY+S_Y+150<=0&&CurDY+S_Y+200>0)
else if(CurDY+S_Y+200<=0&&CurDY+S_Y+250>0)
else if(CurDY+S_Y+250<=0&&CurDY+S_Y+300>0)
else if(CurDY+S_Y+300<=0&&CurDY+S_Y+350>0)
else if(CurDY+S_Y+350<=0&&CurDY+S_Y+400>0)
else if(CurDY+S_Y+400<=0&&CurDY+S_Y+450>0)
else if(CurDY+S_Y+450<=0&&CurDY+S_Y+500>0)
else if(CurDY+S_Y+500<=0&&CurDY+S_Y+550>0)
else if(CurDY+S_Y+550<=0&&CurDY+S_Y+600>0)
else if(CurDY+S_Y+600<=0&&CurDY+S_Y+650>0)
else if(CurDY+S_Y+650<=0&&CurDY+S_Y+700>0)
else if(CurDY+S_Y+700<=0&&CurDY+S_Y+750>0)
else if(CurDY+S_Y+750<=0&&CurDY+S_Y+800>0)
else if(CurDY+S_Y+800<=0&&CurDY+S_Y+850>0)
else if(CurDY+S_Y+850<=0&&CurDY+S_Y+900>0)
else if(CurDY+S_Y+900<=0&&CurDY+S_Y+950>0)
else if(CurDY+S_Y+950<=0&&CurDY+S_Y+1000>0)
else if(CurDY+S_Y+1000<=0&&CurDY+S_Y+1050>0)
else if(CurDY+S_Y+1050<=0&&CurDY+S_Y+1100>0)
else if(CurDY+S_Y+1100<=0&&CurDY+S_Y+1150>0)
else if(CurDY+S_Y+1150<=0&&CurDY+S_Y+1200>0)
else if(CurDY+S_Y+1200<=0&&CurDY+S_Y+1250>0)
else if(CurDY+S_Y+1250<=0&&CurDY+S_Y+1300>0)
else if(CurDY+S_Y+1300<=0&&CurDY+S_Y+1350>0)
else if(CurDY+S_Y+1350<=0&&CurDY+S_Y+1400>0)
else if(CurDY+S_Y+1400<=0&&CurDY+S_Y+1450>0)
else if(CurDY+S_Y+1450<=0&&CurDY+S_Y+1500>0)
else if(CurDY+S_Y+1500<=0&&CurDY+S_Y+1550>0)
else if(CurDY+S_Y+1550<=0&&CurDY+S_Y+1600>0)
else if(CurDY+S_Y+1600<=0&&CurDY+S_Y+1650>0)
// 6
// 6
// 7
// 7
// 8
// 8
// 9
// 10
// 11
// 12
// 13
// 14
// 15
// 16
// 17
// 18
// 19
// 20
// 21
// 22
// 25
DY=-2;
DY=-2;
DY=-2;
DY=-2;
DY=-3;
DY=-3;
DY=-3;
DY=-3;
DY=-4;
DY=-4;
DY=-4;
DY=-4;
DY=-5;
DY=-5;
DY=-5;
DY=-5;
DY=-6;
DY=-6;
DY=-6;
DY=-6;
DY=-7;
DY=-7;
DY=-7;
DY=-8;
DY=-8;
DY=-9;
DY=-9;
DY=-10;
DY=-10;
DY=-11;
DY=-11;
DY=-12;
DY=-13;
// -2
// -2
// -2
// -2
// -3
// -3
// -3
// -3
// -4
// -4
// -4
// -5
// -5
// -5
// -6
// -6
// -6
// -7
// -7
// -8
// -8
// -9
// -10
// -11
// -12
// -13
// -14
// -15
// -16
// -17
// -18
// -19
// -20
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
14
Freescale Semiconductor, Inc.
else if(CurDY+S_Y+1650<=0&&CurDY+S_Y+1700>0)
else if(CurDY+S_Y+1700<=0&&CurDY+S_Y+1750>0)
else
DY=-14;
DY=-15;
DY=-18;
// -21
// -22
// -25
}
}
}
else
{
// send 0
DX=0;
DY=0;
}
}
else
{
//send 0
DX=0;
DY=0;
}
PrevSumX=CurSumX;
PrevSX=CurSX;
PrevSumY=CurSumY;
PrevSY=CurSY;
PrevPosX=CurPosX;
PrevPosY=CurPosY;
#if FILTER==D||FILTER==A
if(SndFlg==1)
{
SndFlg=0;
PrevDX=SamDX;
PrevDY=SamDY;
}
else
{
PrevDX=CurDX;
PrevDY=CurDY;
}
#endif
}
PreTouchStatus.Touched=1;
}
else
// unpressed
{
FstFlg=0;
PreTouchStatus.Touched=0;
DX=0;
DY=0;
}
}
int mouse_demo(void)
{
int x=0;
int y=0;
dword xinit,yinit;
const int delta=1;
hcc_u8 in_report;
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
Freescale Semiconductor, Inc.
15
PTAD=0x01;
PTED=~(0x01);
set_mode(dm_mouse);
/* Value for accelerometer when held level */
xinit=32000;
yinit=32000;
HID_init(0, 0);
in_report=hid_add_report(rpt_in, 0, 3);
LED_GRN = OFF;
while(!device_stp)
{
LED_RED = ON;
Read_MPR121_ele_register(); // read reg 0x00 - 0x2b value to readingArray[]
LED_RED = OFF;
Get_ele_data();
// get signal, baseline, delta
Get_touch_status();
// read touch status reg 0x00, 0x01, determin touched or not
Intp5x7();
// interpolation algorithm
Pol_mouse_dat();
hid_process();
if (!hid_report_pending(in_report))
{
DIR_REP_X(hid_report) = (hcc_u8)(DX);
DIR_REP_Y(hid_report) = (hcc_u8)(DY);
hid_write_report(in_report, (hcc_u8*)hid_report);
}
busy_wait();
{
long stackSize = stack_size(0x88);
}
}
return(0);
}
Designing a Touch Panel using the Xtrinsic MPR121 Capacitive Touch Sensor Controller, Rev 0
16
Freescale Semiconductor, Inc.
How to Reach Us:
Information in this document is provided solely to enable system and software
Home Page:
freescale.com
implementers to use Freescale products. There are no express or implied copyright
Web Support:
freescale.com/support
information in this document.
licenses granted hereunder to design or fabricate any integrated circuits based on the
Freescale reserves the right to make changes without further notice to any products
herein. Freescale makes no warranty, representation, or guarantee regarding the
suitability of its products for any particular purpose, nor does Freescale assume any
liability arising out of the application or use of any product or circuit, and specifically
disclaims any and all liability, including without limitation consequential or incidental
damages. “Typical” parameters that may be provided in Freescale data sheets and/or
specifications can and do vary in different applications, and actual performance may
vary over time. All operating parameters, including “typicals,” must be validated for each
customer application by customer’s technical experts. Freescale does not convey any
license under its patent rights nor the rights of others. Freescale sells products pursuant
to standard terms and conditions of sale, which can be found at the following address:
freescale.com/salestermsandconditions.
Freescale, the Freescale logo, AltiVec, C-5, CodeTest, CodeWarrior, ColdFire, C-Ware,
Energy Efficient Solutions logo, Kinetis, mobileGT, PowerQUICC, Processor Expert,
QorIQ, Qorivva, StarCore, Symphony, and VortiQa are trademarks of Freescale
Semiconductor, Inc., Reg. U.S. Pat. & Tm. Off. Airfast, BeeKit, BeeStack, ColdFire+,
CoreNet, Flexis, MagniV, MXC, Platform in a Package, QorIQ Qonverge, QUICC
Engine, Ready Play, SafeAssure, SMARTMOS, TurboLink, Vybrid, and Xtrinsic are
trademarks of Freescale Semiconductor, Inc. All other product or service names are
the property of their respective owners.
© 2012 Freescale Semiconductor, Inc.
Document Number: AN4600
Rev 0
12/2012