Design of Programmable Control Delay Switch Circuit Module for Small Single Chip Microcomputer

Single chip microcomputer STM32L151CCU6

Programmable Package SG-8018CA(SG7050C) 0.67M~170M

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Programmable control circuit design

The enhanced STC8051 microcontroller and its surrounding circuits are used to form the smallest single-chip system. The STC8051 chip used internally has the following hardware resources: The enhanced STC8051 microcontroller includes a central processing unit (CPU), 4K bytes of program memory (Flash), 128 bytes of data memory (SRAM), and two 16-bit reloadable timers. , 1K byte EEPROM, 6 general-purpose I/O ports, hardware watchdog (WDT), on-chip high-precision R/C oscillating 1T clock, internal clock from 5MHz to 35MHz optional, speed than ordinary 8051 Faster 6 to 12 times, and 8 high-reliability reset modules.

By defining the third bit of the P3 port of the MCU as the output, the serial port function receives and transmits data by the P3.0 and P3.1 ports respectively, calls the internal clock, and combines the timer to realize the delay time and output control.

Power supply design

The power supply module uses PI's step-down chip LNK623PG to support wide-band power supply 85-265VAC input, which is converted into two output DC5V power supplies and 12V power supplies required by the system. In the circuit, through the rectification, filtering, voltage regulation output DC12V, 0.25A and 5V, 0.15A power supply, the output end is connected with a 220μF and 330μF electrolytic capacitor for filtering, fully meet the minimum system power supply design.

Since the power module itself has an electrical isolation circuit integrated therein, the power supply quality of the power supply output is relatively high, and the voltage ripple is ±25 mV, which ensures the stability of the system power supply.

Drive circuit design

Each I / O port drive capacity can reach 20mA, through the optocoupler isolation output, and then through the R4 pull-up resistor and Q8 triode tube amplifier circuit, drive coil power 140mW relay TEV23079, control relay switch operation. As shown in Figure 3, and adding LED3 chip indicator light in the drive circuit to display the working state of the relay.

Communication interface circuit design

Since the C51 MCU is TTL level, the level voltage is only 0V or 5V. The PL-2303 chip output is the TTL level used on the MCU, so there is no need to connect the MAX232 chip and directly realize the RS through the computer USB interface. -232 serial communication, as shown in Figure 4.