The basic element forming the interference of three:
This article refers to the address: http://www.eepw.com.cn/article/201606/292597.htm(1) the source of interference, refers to an element, device or interfering signals, mathematical language is described as follows: du / dt, di / dt is large local sources of interference. Such as: lightning, relay, thyristor, a motor, a high frequency clock so may become sources of interference.
(2) the propagation path, interference transmitted from an interference source to a medium passage or sensitive devices. A typical propagation path interference radiation and conduction through the wire space.
(3) sensitive device, refers to a subject likely to be interfered. Such as: A / D, D / A converter, a microcontroller , the IC number, weak signal amplifier.
The basic principles of the design of interference are: sources of interference suppression, interference propagation path off, improving the noise immunity sensitive devices. (Similar to infectious disease prevention)
A source of interference suppression
It is to reduce sources of interference suppression du / dt, di / dt of the possible sources of interference. This is the anti-jamming design of the highest priority and most important principle, often play a multiplier effect. Reducing interference source du / dt on mainly achieved by the interference-source capacitance of the parallel ends. Reducing interference sources di / dt of the interference source is in the circuit resistance and increased series inductance or freewheeling diode achieved.
Common sources of interference suppression measures are as follows:
(1) addition of a freewheel diode relay coil to eliminate interference generated counter electromotive force when the coil is disconnected. Off-time would only increase freewheeling diode lag relay, relay Zener diode increases after a unit time can be more number of operations.
(2) and connected across the relay contacts spark suppression circuit (typically RC series circuit resistance is generally selected from several tens K to K, is selected from 0.01uF capacitor), to reduce the spark impact.
(3) add a filter circuit to the motor, note that the capacitance, inductance of the leads to be as short as possible.
(4) each IC circuit board and connected to a high frequency capacitance 0.01μF ~ 0.1μF to reduce the influence of the power IC. Note that the wiring of the high frequency capacitance, wiring should be near the power supply terminal and stubby as possible, otherwise, increased capacitance is equal to the equivalent series resistance, will affect the filtering effect.
(5) 90 degree line wiring to avoid reducing high frequency noise emission.
(6)可控硅两端并接RC抑制电路，减小可控硅产生的噪声(这个噪声严重时可能会把可控硅击穿的)。
按干扰的传播路径可分为传导干扰和辐射干扰两类。
所谓传导干扰是指通过导线传播到敏感器件的干扰。高频干扰噪声和有用信号的频带不同，可以通过在导线上增加滤波器的方法切断高频干扰噪声的传播，有时也可加隔离光耦来解决。电源噪声的危害最大，要特别注意处理。所谓辐射干扰是指通过空间辐射传播到敏感器件的干扰。一般的解决方法是增加干扰源与敏感器件的距离，用地线把它们隔离和在敏感器件上加蔽罩。
2切断干扰传播路径的常用措施如下：
(1)充分考虑电源对单片机的影响。电源做得好，整个电路的抗干扰就解决了一大半。许多单片机对电源噪声很敏感,要给单片机电源加滤波电路或稳压器，以减小电源噪声对单片机的干扰。比如，可以利用磁珠和电容组成π形滤波电路，当然条件要求不高时也可用100Ω电阻代替磁珠。
(2)如果单片机的I/O口用来控制电机等噪声器件，在I/O口与噪声源之间应加隔离(增加π形滤波电路)。控制电机等噪声器件，在I/O口与噪声源之间应加隔离(增加π形滤波电路)。
(3)注意晶振布线。晶振与单片机引脚尽量靠近，用地线把时钟区隔离起来，晶振外壳接地并固定。此措施可解决许多疑难问题。
(4)电路板合理分区，如强、弱信号，数字、模拟信号。尽可能把干扰源(如电机，继电器)与敏感元件(如单片机)远离。
(5)用地线把数字区与模拟区隔离，数字地与模拟地要分离，最后在一点接于电源地。A/D、D/A芯片布线也以此为原则，厂家分配A/D、D/A芯片引脚排列时已考虑此要求。
(6)单片机和大功率器件的地线要单独接地，以减小相互干扰。大功率器件尽可能放在电路板边缘。
(7)在单片机I/O口，电源线，电路板连接线等关键地方使用抗干扰元件如磁珠、磁环、电源滤波器，屏蔽罩，可显著提高电路的抗干扰性能。
3提高敏感器件的抗干扰性能
提高敏感器件的抗干扰性能是指从敏感器件这边考虑尽量减少对干扰噪声的拾取，以及从不正常状态尽快恢复的方法。
提高敏感器件抗干扰性能的常用措施如下：
(1)布线时尽量减少回路环的面积，以降低感应噪声。
(2)布线时，电源线和地线要尽量粗。除减小压降外，更重要的是降低耦合噪声。
(3)对于单片机闲置的I/O口，不要悬空，要接地或接电源。其它IC的闲置端在不改变系统逻辑的情况下接地或接电源。
(4)对单片机使用电源监控及看门狗电路，如：IMP809，IMP706，IMP813，X25043，X25045等，可大幅度提高整个电路的抗干扰性能。
(5)在速度能满足要求的前提下，尽量降低单片机的晶振和选用低速数字电路。
(6)IC器件尽量直接焊在电路板上，少用IC座。
先说说在这方面的经验：
软件方面：
1、常将不用的代码空间全清成“0”，因为这等效于NOP，可在程序跑飞时归位;
2、在跳转指令前加几个NOP，目的同1;
3、在无硬件WatchDog时可采用软件模拟WatchDog，以监测程序的运行;
4、涉及处理外部器件参数调整或设置时，为防止外部器件因受干扰而出错可定时将参数重新发送一遍，这样可使外部器件尽快恢复正确;
5、通讯中的抗干扰，可加数据校验位，可采取3取2或5取3策略;
6、在有通讯线时，如I^2C、三线制等，实际中我们发现将Data线、CLK线、INH线常态置为高，其抗干扰效果要好过置为低。
硬件方面：
1、地线、电源线的部线肯定重要了!
2、线路的去偶;
3、数、模地的分开;
4、每个数字元件在地与电源之间都要104电容;
5、在有继电器的应用场合，尤其是大电流时，防继电器触点火花对电路的干扰，可在继电器线圈间并一104和二极管，在触点和常开端间接472电容，效果不错!
6、为防I/O口的串扰，可将I/O口隔离，方法有二极管隔离、门电路隔离、光偶隔离、电磁隔离等;
7、当然多层板的抗干扰肯定好过单面板，但成本却高了几倍。
8、选择一个抗干扰能力强的器件比之任何方法都有效，这点应该最重要。