Based on 51 single automatic washing machine control system of a circuit diagram of an analog
clock circuit: passive contact 12MHZ crystal, which two pins have to take two 30pf capacitors and grounded. With the clock circuit, the microcontroller, program code executed sequentially.
Reset circuit: microcontroller 51 is reset only then a high level for 2us can be achieved in the ninth pin (RST). As long as the capacitor charge and discharge time is greater than 2us, the reset can be realized, so that the capacitance value of the circuit can be changed. System reset button is pressed, a short circuit in the capacitor, the release voltage of all the electric energy caused by an increase in resistance of two.
Display circuit: The circuit uses two common anode LED. Two common cathode LED pins are 1.2 second LED is respectively connected to a common terminal P0.6, P0.7. If you want the first LED does not light the second light output low P0.7 to P0.6 high, particularly by the high and low level digital control pin P2.0-P2.7.
Exclusion: RESPACK-8 is exclusion, i.e., resistor networks, is the exclusion of several parameters identical resistors then assembled together. Their pins are connected together as a common pin, the rest of the normal lead pin. If the exclusion of n resistors, then it has n + 1 th pin. General public foot on the left, there is little red mark above exclusion. P0 port connected to the microcontroller 51, because the internal port P0 does not pull, can not output high, so to pull-up resistors.
Pull-up resistor: a signal is uncertain, the power supply is connected to the VCC via a resistor, is fixed at the high level. Action: pullup current is injected into the device; sink; IO port when connected with a pull-up resistor is provided as an input state, its normal high level.
Pull-down resistor: a signal is uncertain, connected to GND via a resistor, fixed at low level. Action: is a pull-down current from the output device; sourcing current. When the IO port connected with a pull-down resistor is provided as an input state, its normal low level. Common effect of both the pull-up resistors and pull-down resistors are: avoiding voltage "floating" circuit instability.
Buzzer drive circuit: due to the operating current buzzer generally larger, so that the microcontroller IO port can not be driven directly. So use the amplifier circuit is driven using a transistor to amplify a current on it. 
Transistor: 1. The role of the amplifying circuit (transistor operate in the work area) used to form the transistor amplifier circuit has a current amplification, in essence, to the base current of the transistor can be a slight change in the control amount of variation in the collector current larger the amount. If you encounter a more powerful devices, or other AC power transistor can be driven by a relay, then the relay control apparatus or a high-current AC power source, forming a secondary drive. 2. Electronic switching function (work off the triode region and a saturation region).
