7, good decoupling capacitors
A good high-frequency decoupling capacitor can remove high-frequency components up to 1GHZ. Ceramic chip capacitors or multilayer ceramic capacitors have high frequency characteristics. Design printed circuit board, each integrated circuit power supply, ground must be added between a decoupling capacitor. Decoupling capacitors have two effects: on the one hand is the integrated circuit of the storage capacitor, to provide and absorb the integrated circuit door open door instantaneous charge and discharge energy; on the other hand bypass the device's high-frequency noise. The typical decoupling capacitor with a decoupling capacitor of 0.1uf in the digital circuit has a 5nH distributed inductor, and its parallel resonant frequency is about 7MHz, which means that the noise below 10MHz has a better decoupling effect. For a 40MHz or more The noise is almost ineffective.

1uf, 10uf capacitor, parallel resonance frequency above 20MHz, remove the high frequency noise effect is better. It is often advantageous to place the power supply into the printed board and a 1uf or 10uf high-frequency capacitor, even in battery-powered systems.
About 10 per cent of the integrated circuit to add a charge and discharge capacitors, or called the storage capacitor, the capacitor size optional 10uf. It is best not to electrolytic capacitors, electrolytic capacitors are two layers of thin film rolled up, this roll up the structure at high frequencies when the performance of the inductor, it is best to use the gallium capacitor or polycarbonate capacitor.

Decoupling capacitor value selection is not strict, according to C = 1 / f calculation; that is 10MHz take 0.1uf, the system composed of micro-controller, take 0.1 ~ 0.01uf can be between.

Third, reduce the noise and some of the experience of electromagnetic interference

(1) can use low-speed chip without high-speed, high-speed chip used in key places.
(2) can be a string of resistance to reduce the control circuit up and down along the rate of change.
(3) as far as possible for the relay to provide some form of damping.
(4) Use the lowest frequency clock that meets the system requirements.
(5) The clock generator is as close as possible to the device using the clock. Quartz crystal oscillator housing to ground.
(6) with the ground clock to circle up, the clock line as short as possible.
(7) I / O drive circuit as far as possible * near the edge of the printing plate, let it leave the printing plate as soon as possible. The signal into the printed circuit board to filter, from the high noise zone to the signal should also add filtering, while the use of string termination resistor approach to reduce the signal reflection.
(8) MCD useless end to high, or ground, or defined as the output, the integrated circuit on the power supply to the end of the ground, do not vacant.
(9) idle Do not use the gate input do not vacant, idle unused op amp is the input terminal ground, negative input termination output. (10) Printed board Try to use 45 fold lines instead of 90 fold lines to reduce the high-frequency signal from the external launch and coupling.
(11) printed circuit board by frequency and current switching characteristics of the partition, the noise components and non-noise components to distance and then far.
(12) single-sided and double-sided single-point power supply and single-point grounding, power lines, ground as thick as possible, the economy can withstand the use of multi-layer board to reduce the power supply,
(13) clock, bus, chip select signal away from I / O lines and connectors.
(14) analog voltage input line, the reference voltage side to try to stay away from the digital circuit signal lines, especially the clock.
(15) on the A / D class devices, digital parts and analog part of the unified but also do not pay *.
(16) The clock line is perpendicular to the I / O line than the parallel I / O line interference is small and the clock component pin is far from the I / O cable.
(17) component pins as short as possible, decoupling capacitor pins as short as possible.
(18) the key line to be as thick as possible, and on both sides with protection. High-speed line to be short to straight.
(19) Noise-sensitive lines do not parallel to high-current, high-speed switching lines.
(20) Quartz crystal below and noise-sensitive devices below do not route.
(21) weak signal circuit, low frequency circuit around do not form a current loop.
(22) Do not form any signal loop, such as unavoidable, so that the loop area as small as possible.
(23) a complementary capacitor for each integrated circuit. Each electrolytic capacitor edge should add a small high frequency bypass capacitor.
(24) with a large capacity of tantalum capacitors or cool capacitors instead of electrolytic capacitors for the circuit charge and discharge energy storage capacitor. When using a tubular capacitor, the housing is grounded.