How should zero-based learning embedded systems hardware design

1, MCU of choice

To consider the MCU to complete the function selected MCU, the MCU price, power consumption, supply voltage, I / O port level, the number of package pins and other factors of the MCU. The MCU can be found from the electrical power consumption of the performance parameters. Supply voltage is 5V, 3.3V and 1.8V low voltage power supply mode. To rationally allocated MCU's I / O resources, when the MCU selection may draw a pin assignment table, for subsequent use design.

2, power supply

(1) Consider the power requirements of the system, such systems require several power, such as 24V, 12V, 5V or 3.3V, it is estimated how much power or maximum current (mA) each require. In calculating the total power to be considered a certain margin, according to the formula "Total power = 2 × total power device 'is calculated.

(2) needs into the power device chip and volatility. Generally allows the power fluctuations within ± 5%. The reference voltage for A / D conversion chip generally require ± 1%.

(3) consider the power supply is the use of the power supply module or use an external power supply.

2, power supply

(2) needs into the power device chip and volatility. Generally allows the power fluctuations within ± 5%. The reference voltage for A / D conversion chip generally require ± 1%.

(3) consider the power supply is the use of the power supply module or use an external power supply.

3, general I / O port

Pull (1), the pull-down resistor: consider the internal or external / pull-down resistor internal / pull-down resistance is generally about 700 [Omega], the low power mode should not be used. External / pull-down resistor required between optional 10KΩ ~ 1MΩ.

(2) Digital input: clearly must ensure low voltage. High voltage power supply is Ideally, the level of the ground is low. If the external circuit can not properly distinguish between high and low, but the level is still a large pressure difference, can be considered manner designed to handle A / D acquisition. Dividing the sampling points in the embodiment, to consider when choosing dividing resistor so that the current sampling point by not less than the minimum input port a current sampling, or can not be sampled.

(3) switch output: The basic principle is to ensure a high level close to the supply voltage output, a low level near the ground level. I / O port to absorb current is generally greater than the discharge current. For low power control components is preferably controlled by way of a low level. In general, if the load requirement is less than 10mA, the chip can be used to directly control pin; transistor current can be controlled at 10 ~ 100mA, 100mA ~ 1A when using the IC control; larger current relay for the control, is also recommended optical isolation chip.

4, A / D circuit and the D / A circuit

(1) A / D circuit: to clear the basic principle of front-end sampling, resistance, current- and voltage sensors using different acquisition circuit. If the weak signal acquisition, but also consider how to signal amplification.

(2) D / A circuit: Consider the MCU pin control circuit output by which the actual object.

5, the control circuit

Foreign control circuit redundancy pay attention to the anti-posttest design, there must be an appropriate signal isolation measures. In assessing the layout design, must lead the output of the input detecting aperture member, to facilitate troubleshooting error measurement.

6, consider the low power consumption

Not only for low-power design and power saving, more benefits due to reduced cost and power module cooling system. Since the current is also reduced to reduce the electromagnetic radiation interference and thermal noise. With decreasing temperature in the apparatus, the corresponding extension of the life of the device, to achieve low power consumption typically required to note the following:

(1) Not all bus signals to be pulled up. Pull-down resistors have power issues to consider. A pull-down resistor on the mere input signal, a current will tens of microamps or less. However, the one driven pull signal, which reach milliamps current. It is necessary to consider the influence on the pull-down resistor on the overall system power consumption.

(2) do not have an I / O port not suspended, then if suspended, by a little external interference may be repeated oscillation of the input signal, the power consumption depends on the number of MOS devices substantially inverting gate circuit.

(3) for some peripheral small chip's power consumption also needs to be considered. For less complex internal chip power consumption is difficult to determine, it is mainly determined by the current on the pin. For example, some chip pins at no load power consumption is probably less than 1 mA, but later increased load, power consumption may be significant.

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