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关于MPR121，论坛可用的资料太少，大量的都是要花C币下载的资源。作为菜鸟，搞来搞去主要就是初始化配置棘手，主要就是可配置的寄存器实在太多了。根据官方MPR技术文档及网页搜索一些信息得出以下初始化函数，实测采用3mm亚克力板稳定可用。
说明：芯片为STM32F103C8T6，采用硬件IIC，管脚定义：
PB6=SCL
PB7=SDA
PB8=IRQ，中断输出。
我在IIC总线上还接了一个OLED屏。需要特别注意的是，OLED屏和MPR121对硬件IIC都有速度要求，实测必须在240K~290K之间才能正常运行，太快OLED屏会死机，太慢MPR121会死机。
MPR初始化函数如下：
void MPR121_Init(void)
{
//复位 MPR121
MPR121Write(0x80, 0x63); //软复位，官方指定写入0x63值。
MPR121Write(0x5E, 0x00); //停止模式
// Section A // 该组控制过滤。 data is > baseline.
MPR121Write(MHD_R, 0x01);
MPR121Write(NHD_R, 0x01);
MPR121Write(NCL_R, 0x00);
MPR121Write(FDL_R, 0x00);
// Section B // 该组控制过滤。data is < baseline.
MPR121Write(MHD_F, 0x01);
MPR121Write(NHD_F, 0x01);
MPR121Write(NCL_F, 0xFF);
MPR121Write(FDL_F, 0x00);
//基线过滤控制寄存器
MPR121Write(0x33, 0x00); //noise half delta touched
MPR121Write(0x34, 0x00); //noise counts touched
MPR121Write(0x35, 0x00); //filter delay touched
MPR121Write(0x36, 0x0F);
MPR121Write(0x37, 0x0F);
MPR121Write(0x38, 0x00);
MPR121Write(0x39, 0x00);
MPR121Write(0x3A, 0x01);
MPR121Write(0x3B, 0x01);
MPR121Write(0x3C, 0xFF);
MPR121Write(0x3D, 0xFF);
MPR121Write(0x3E, 0x00);
MPR121Write(0x3F, 0x00);
MPR121Write(0x40, 0x00);
// Section C // 该组为每个电极设置触摸和释放阈值
MPR121Write(ELE0_T, TOU_THRESH);
MPR121Write(ELE0_R, REL_THRESH);
MPR121Write(ELE1_T, TOU_THRESH);
MPR121Write(ELE1_R, REL_THRESH);
MPR121Write(ELE2_T, TOU_THRESH);
MPR121Write(ELE2_R, REL_THRESH);
MPR121Write(ELE3_T, TOU_THRESH);
MPR121Write(ELE3_R, REL_THRESH);
MPR121Write(ELE4_T, TOU_THRESH);
MPR121Write(ELE4_R, REL_THRESH);
MPR121Write(ELE5_T, TOU_THRESH);
MPR121Write(ELE5_R, REL_THRESH);
MPR121Write(ELE6_T, TOU_THRESH);
MPR121Write(ELE6_R, REL_THRESH);
MPR121Write(ELE7_T, TOU_THRESH);
MPR121Write(ELE7_R, REL_THRESH);
MPR121Write(ELE8_T, TOU_THRESH);
MPR121Write(ELE8_R, REL_THRESH);
MPR121Write(ELE9_T, TOU_THRESH);
MPR121Write(ELE9_R, REL_THRESH);
MPR121Write(ELE10_T, TOU_THRESH);
MPR121Write(ELE10_R, REL_THRESH);
MPR121Write(ELE11_T, TOU_THRESH);
MPR121Write(ELE11_R, REL_THRESH);
MPR121Write(0x59, 0x02);
MPR121Write(0x5A, 0x01);
MPR121Write(0x5B, 0x00);
MPR121Write(0x5C, 0x10);
MPR121Write(0x5D, 0x24);
// 启用自动配置和自动重新配置
MPR121Write(0x7B, 0x0B);
MPR121Write(0x7D, 0xC8);
MPR121Write(0x7E, 0x82);
MPR121Write(0x7F, 0xB4);
//电极配置（重要）
MPR121Write(0x5E, 0xBC);//1011,1100。启用基线跟踪，启用接近检测，启用所有12个电极
}
MPR121.H文件主内容：
#define MPR121_ADD 0xB4 //（相当于0x5A<<1）将ADDR引脚连接到VSS、VDD、SDA或SCL线，得到的I2C地址分别为0x5A、0x5B、0x5C和0x5D//本例 ADDR引脚接地，故地址是0x5A
// MPR121 寄存器定义
#define MHD_R 0x2B
#define NHD_R 0x2C
#define NCL_R 0x2D
#define FDL_R 0x2E
#define MHD_F 0x2F
#define NHD_F 0x30
#define NCL_F 0x31
#define FDL_F 0x32
#define ELE0_T 0x41
#define ELE0_R 0x42
#define ELE1_T 0x43
#define ELE1_R 0x44
#define ELE2_T 0x45
#define ELE2_R 0x46
#define ELE3_T 0x47
#define ELE3_R 0x48
#define ELE4_T 0x49
#define ELE4_R 0x4A
#define ELE5_T 0x4B
#define ELE5_R 0x4C
#define ELE6_T 0x4D
#define ELE6_R 0x4E
#define ELE7_T 0x4F
#define ELE7_R 0x50
#define ELE8_T 0x51
#define ELE8_R 0x52
#define ELE9_T 0x53
#define ELE9_R 0x54
#define ELE10_T 0x55
#define ELE10_R 0x56
#define ELE11_T 0x57
#define ELE11_R 0x58
#define FIL_CFG 0x5D
#define ELE_CFG 0x5E
#define GPIO_CTRL0 0x73
#define GPIO_CTRL1 0x74
#define GPIO_DATA 0x75
#define GPIO_DIR 0x76
#define GPIO_EN 0x77
#define GPIO_SET 0x78
#define GPIO_CLEAR 0x79
#define GPIO_TOGGLE 0x7A
#define ATO_CFG0 0x7B
#define ATO_CFGU 0x7D
#define ATO_CFGL 0x7E
#define ATO_CFGT 0x7F
// 全局常数（实测“3/2”参数适用3mm有机玻璃板）
#define TOU_THRESH 3 //触摸阈值 0x0F 10//15//30//10//3
#define REL_THRESH 2 //释放阈值 0x0A 08//08//25//08//2