Timer Circuit Using LED Dynamic Display Screen

The circuit is shown in the figure above. C1 and R1 are power on reset circuits, and K is start / pause switch. AT89C2051 is used for IC. Its P1. O and P1.1 ports are also the input of internal comparator. In order to ensure the normal operation of the program, an external pull-up resistor is required. R4-r11 is led current limiting resistor, which can not be used if the brightness is not enough. Dn74000190a is adopted for LED dynamic display screen. The following figure is its schematic diagram. In order to simplify the circuit, only the last two digits of LED dynamic display screen are used. The circuit is very simple, and its main work is software design. The key of software design lies in the compilation and arrangement of digital display forms. Because the pins of the dynamic display screen are time-sharing multiplexed, it is more complicated to compile its digital display table than to use Seven Segment LED digital. You can draw a form on the draft paper first, and fill in O for the bright field and 1 for the off field according to the number of o-9. Convert the binary code into hexadecimal code to get the required coding table. When the program is running, first call the code with pin 1.29 as timing one digit, temporarily store it in R7, and then adjust the code of ten digits to perform logic and operation with R7. The result is sent to port P1 to display half of two digits. Then, the 2.26 pin is encoded in the ten bit digit encoding R6, and then the bit number encoding and R6 are used to carry out logic and operation. The result is sent to port P1 to display the remaining half of the two digits to synthesize a complete digital display.

Timer Circuit Using LED Dynamic Display Screen 1

The program is designed for 0 99 seconds to check whether the program and coding table are correct. A timer of 0 99 minutes and o-99 hours can be formed by appropriately changing the software. Used in life and work. Such as car washing machine used in car beauty shop. According to the manufacturer's operating instructions, the engine oil must be changed every 100 hours, but due to the different starting time every day. It is difficult to change the oil on time. This problem is solved after the timer is installed on the machine. This paper is simplified by such a circuit.

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