51 single chip microcomputer (STC89C52RC) small comprehensive experiment

　　This experiment includes the following contents:

1. 51 MCU Minimum System

2. MCU external relay

3. Use of rectifier bridge

4. Use of LM393 voltage comparator

　　First, let’s look at the experimental results:

 The two relays in front, the smallest system in the middle, and the rectifier and LM393 voltage comparator at the bottom.

Well, let's talk about the experience in making this board:

　　First, the voltage output by the rectifier bridge is input into the voltage comparator. This involves the concept of zero drift of the voltage comparator, that is, when the input is zero, the output is not zero. The main reason is the influence of temperature on electronic components. Electronic components are generally not purebred. Second, the output of the regulated DC voltage. Here, a system of regulated power supply is used. If the requirements are not high, it is generally linear voltage regulation: AC voltage->rectifier->RC circuit filter->LR filter (optional)->voltage regulation (three-terminal voltage regulator)->voltage regulator. Third, the 51 single-chip microcomputer is downloaded. After the serial port line is connected, it is found that the voltage light of the single-chip microcomputer is on, indicating that there is current. The main reason is that there is a voltage difference between RXD and TXD and GND. The voltage does not only enter from the vcc IO port, Other IO ports can also be used for input, and they are not insulated from VCC. This current will affect ISP downloading and cause failure. The specific solution has not been verified yet. After switching to the 5V voltage output by the USB standard, the download is normal. Note that it must be 5V with a fluctuation of 0.01. Fourth, pay attention to the layout. Usually, a pin hole should be reserved and one side should be connected to the external circuit. Fifth, try to add a working indicator light to the main working component of concern, so that you can intuitively understand the working status of the component. Avoid unnecessary measurements. Sometimes when it is necessary to measure at the same time, the conditions cannot be met. Sixth, the power supply part of the component should be separated and powered by a separate power supply. If conditions permit, leave an extra power supply port for the same component.