CN209858954U - A timer based on single chip microcomputer - Google Patents

Abstract

A timer based on a single-chip microcomputer is provided with a single-chip microcomputer circuit, a decoder circuit, a button circuit, a display circuit and an alarm circuit, and the single-chip computer circuit is respectively connected with the decoder circuit, the button circuit, the display circuit and the alarm circuit, and the decoder circuit It is also connected with the display circuit. The microcontroller-based timer has the advantage of having a time prompt. At the same time, the timer based on the single-chip microcomputer uses a common chip U1, and the connection of each circuit and each circuit component is simple, so the timer has the advantages of simple circuit and low cost. At the same time, the timer based on the single-chip microcomputer has the advantage of high accuracy.

Description

A timer based on single chip microcomputer

technical field

The utility model relates to the field of timers, in particular to a timer based on a single-chip microcomputer.

Background technique

Timers are widely used in any electronic equipment and have become an indispensable item in people's daily life. For example, various alarm clocks, time program automatic control, timing broadcast, timing switch oven and on-off equipment, etc., all equipment with time reminder function should be based on timer. However, the circuit cost of the existing timer is relatively high and the circuit is complicated.

Therefore, aiming at the deficiencies of the prior art, it is very necessary to provide a timer based on a single-chip microcomputer to overcome the deficiencies of the prior art.

Utility model content

The purpose of the utility model is to avoid the deficiencies in the prior art and provide a timer based on a single-chip microcomputer. The timer based on a single-chip microcomputer has the advantages of high accuracy, simple circuit and low cost.

The above-mentioned purpose of the utility model is achieved through the following technical means.

A timer based on a single-chip microcomputer is provided, which is provided with a single-chip microcomputer circuit, a decoder circuit, a key circuit, a display circuit and an alarm circuit, and the single-chip microcomputer circuit is respectively connected with the decoder circuit, the key circuit, the display circuit and the alarm circuit, and the decoder The circuit is also connected to the display circuit.

Preferably, the chip U1, the exclusion RP1, the resistor R1, the coupling capacitor C1, the capacitor C2, the capacitor C3 and the crystal oscillator Y1 provided with the above-mentioned single-chip microcomputer circuit, the 10 pins, 11 pins and 12 pins of the chip U1 are respectively connected to the button circuit, and the chip Pin 13 of U1 is connected to the alarm circuit, pin 9 of chip U1 is connected to the negative pole of coupling capacitor C1, the positive pole of coupling capacitor C1 is connected to the power input terminal VCC, pin 9 of chip U1 is also connected in series with resistor R1 to ground, pin 18 of chip U1 The pin series capacitor C2 is grounded, the 19-pin series capacitor C3 of the chip U1 is grounded, the two ends of the crystal oscillator Y1 are respectively connected to the 18-pin and 19-pin of the chip U1, the 20-pin of the chip U1 is grounded, and the 21-pin and 22-pin of the chip U1 , ..., 28 pins are respectively connected to the display circuit, the 31 pin of the chip U1 is connected to the power input terminal VCC, the 32 pin of the chip U1 is connected to the 9 pin of the resistance RP1, the 33 pin of the chip U1 is connected to the 8 pin of the resistance RP1 Connection, the 34 pins of the chip U1 are connected with the 7 pins of the exclusion RP1, the 35 pins of the chip U1 are connected with the 6 pins of the exclusion RP1, the 36 pins of the chip U1 are connected with the 5 pins of the exclusion RP1, the 37 pins of the chip U1 are connected with the The 4 pins of the exclusion RP1 are connected, the 38 pins of the chip U1 are connected with the 3 pins of the exclusion RP1, the 39 pins of the chip U1 are connected with the 2 pins of the exclusion RP1, the 40 pins of the chip U1 are connected with the 1 pin of the exclusion RP1, Pin 40 of the chip U1 is also connected to the power input terminal VCC, and pins 32, 33, . . . , 39 of the chip U1 are respectively connected to the display circuit.

Preferably, the above-mentioned decoder circuit is provided with a decoder U2, the 1 pin of the decoder U2 is connected to the power input terminal VCC, the 19 pin of the decoder U2 is grounded, and the 2 pin of the decoder U2 is connected to the 39 pin of the chip U1. pin connection, the 3 pins of the decoder U2 are connected with the 38 pins of the chip U1, the 4 pins of the decoder U2 are connected with the 37 pins of the chip U1, the 5 pins of the decoder U2 are connected with the 36 pins of the chip U1, and the decoding Pin 6 of U2 is connected to pin 35 of chip U1, pin 7 of decoder U2 is connected to pin 34 of chip U1, pin 8 of decoder U2 is connected to pin 33 of chip U1, pin 9 of decoder U2 It is connected with the 32-pin of the chip U1, and the 11-pin, 12-pin, ..., 18-pin of the decoder U2 are respectively connected with the display circuit.

Preferably, the key switch circuit is provided with a key switch K1, a key switch K2 and a key switch K3, pin 1 of the switch K1 is connected to pin 2 of the key switch K2, pin 2 of the key switch K1 is grounded, pin 3 of the key switch K1 is connected to the chip Pin 10 of U1 is connected, pin 1 of key switch K2 is connected with pin 2 of key switch K3, pin 3 of key switch K2 is connected with pin 11 of chip U1, pin 3 of key switch K2 is connected with pin 12 of chip U1.

Preferably, the above-mentioned display circuit is provided with display LED1 and display LED2, 1 pin of display LED1 is connected with 14 pins of decoder U2, 2 pins of display LED1 are connected with 15 pins of decoder U2, 3 pins of display LED1 are connected with The 11-pin connection of the decoder U2, the 4-pin connection of the display LED1 and the 16-pin connection of the decoder U2, the 5-pin connection of the display LED1 and the 12-pin connection of the decoder U2, the 6-pin connection of the display LED1 and the 25-pin chip U1 Connection, the 7 pins of the display LED1 are connected with the 28 pins of the chip U1, the 8 pins of the display LED1 are connected with the 18 pins of the decoder U2, the 9 pins of the display LED1 are connected with the 13 pins of the decoder U2, and the 10 pins of the display LED1 Connect with pin 27 of chip U1, connect pin 11 of display LED1 with pin 26 of chip U1, connect pin 12 of display LED1 with pin 17 of decoder U2, connect pin 1 of display LED2 with pin 14 of decoder U2 , the 2 pins of the display LED2 are connected with the 15 pins of the decoder U2, the 3 pins of the display LED2 are connected with the 11 pins of the decoder U2, the 4 pins of the display LED2 are connected with the 16 pins of the decoder U2, the 5 pins of the display LED2 Pin 12 of the decoder U2 is connected, pin 6 of the display LED2 is connected to pin 21 of the chip U1, pin 7 of the display LED2 is connected to pin 25 of the chip U1, pin 8 of the display LED2 is connected to pin 18 of the decoder U2 Connection, the 9 pins of the display LED2 are connected with the 13 pins of the decoder U2, the 10 pins of the display LED2 are connected with the 23 pins of the chip U1, the 11 pins of the display LED2 are connected with the 22 pins of the chip U1, the 12 pins of the display LED2 are connected with the translator The 17-pin connection of encoder U2.

Preferably, the above-mentioned alarm circuit is provided with a resistor R2, a transistor Q1 and a buzzer F1, one end of the resistor R2 is connected to pin 13 of the chip U1, the other end of the resistor R2 is connected to the base of the transistor Q1, and the emitter of the transistor Q1 is connected to the base of the transistor Q1. One end of the buzzer F1 is connected, the collector of the transistor Q1 is grounded, and the other end of the buzzer F1 is connected to the power input terminal VCC.

Preferably, the model of the above-mentioned chip U1 is AT89C51, the resistance values of the resistor R1 and the exclusion RP1 are both 10 kΩ, the capacitance value of the coupling capacitor C1 is 10 microfarads, and the capacitance values of the capacitor C2 and the capacitor C3 are both 30 farads. The crystal oscillator Y1 is 12 MHz, the model of the decoder U2 is 74HC245, the models of the display LED1 and the display LED2 are both 7LEDSMG, the resistance value of the resistor R2 is 2.2 kΩ, the model of the transistor Q1 is 9012, and the model of the buzzer F1 for FMQ.

A kind of timer based on single-chip microcomputer of the present utility model is provided with single-chip microcomputer circuit, decoder circuit, button circuit, display circuit and alarm circuit, and single-chip computer circuit is connected with decoder circuit, button circuit, display circuit and alarm circuit respectively, The decoder circuit is also connected with the display circuit. The microcontroller-based timer has the advantage of having a time prompt. At the same time, the timer based on the single-chip microcomputer uses a common chip U1, and the connection of each circuit and each circuit component is simple, so the timer has the advantages of simple circuit and low cost. At the same time, the timer based on the single-chip microcomputer has the advantage of high accuracy.

Description of drawings

Utilize accompanying drawing to further illustrate the utility model, but the content in the accompanying drawing does not constitute any limitation to the utility model.

Fig. 1 is a schematic diagram of a timer circuit based on a microcontroller.

Figure 2 is a schematic diagram of the microcontroller circuit.

FIG. 3 is a schematic diagram of a decoder circuit.

FIG. 4 is a schematic diagram of a button circuit.

Figure 5 is a schematic diagram of the display circuit.

Figure 6 is a schematic diagram of the alarm circuit.

Figures 1 to 6 include:

SCM circuit 1, decoder circuit 2, button circuit 3, display circuit 4 and alarm circuit 5.

Detailed ways

The utility model is further described in conjunction with the following examples.

Example 1.

A timer based on a single-chip microcomputer, as shown in Figure 1-6, is provided with a single-chip microcomputer circuit 1, a decoder circuit 2, a button circuit 3, a display circuit 4 and an alarm circuit 5, and the single-chip microcomputer circuit 1 is connected to the decoder circuit 2 respectively. , button circuit 3, display circuit 4 and alarm circuit 5 are connected, and decoder circuit 2 is also connected with display circuit 4.

The single chip microcomputer circuit 1 is provided with a chip U1, an exclusion RP1, a resistor R1, a coupling capacitor C1, a capacitor C2, a capacitor C3, and a crystal oscillator Y1. Pins 10, 11, and 12 of the chip U1 are respectively connected to the button circuit 3, and the pins of the chip U1 Pin 13 is connected to alarm circuit 5, pin 9 of chip U1 is connected to the negative pole of coupling capacitor C1, and the positive pole of coupling capacitor C1 is connected to power input terminal VCC. The series capacitor C2 is grounded, the 19-pin series capacitor C3 of the chip U1 is grounded, the two ends of the crystal oscillator Y1 are respectively connected to the 18-pin and 19-pin of the chip U1, the 20-pin of the chip U1 is grounded, the 21-pin, 22-pin, ..., 28 pins are respectively connected to the display circuit 4, the 31 pin of the chip U1 is connected to the power input terminal VCC, the 32 pin of the chip U1 is connected to the 9 pin of the resistance RP1, the 33 pin of the chip U1 is connected to the 8 pin of the resistance RP1 Connection, the 34 pins of the chip U1 are connected with the 7 pins of the exclusion RP1, the 35 pins of the chip U1 are connected with the 6 pins of the exclusion RP1, the 36 pins of the chip U1 are connected with the 5 pins of the exclusion RP1, the 37 pins of the chip U1 are connected with the The 4 pins of the exclusion RP1 are connected, the 38 pins of the chip U1 are connected with the 3 pins of the exclusion RP1, the 39 pins of the chip U1 are connected with the 2 pins of the exclusion RP1, the 40 pins of the chip U1 are connected with the 1 pin of the exclusion RP1, Pin 40 of the chip U1 is also connected to the power input terminal VCC, and pins 32, 33, . . . , 39 of the chip U1 are connected to the display circuit 4 respectively.

The decoder circuit 2 is provided with a decoder U2, the 1 pin of the decoder U2 is connected to the power input terminal VCC, the 19 pin of the decoder U2 is grounded, the 2 pin of the decoder U2 is connected to the 39 pin of the chip U1, Pin 3 of decoder U2 is connected to pin 38 of chip U1, pin 4 of decoder U2 is connected to pin 37 of chip U1, pin 5 of decoder U2 is connected to pin 36 of chip U1, and pin 4 of decoder U2 is connected to pin 36 of chip U1. Pin 6 is connected to pin 35 of the chip U1, pin 7 of the decoder U2 is connected to pin 34 of the chip U1, pin 8 of the decoder U2 is connected to pin 33 of the chip U1, pin 9 of the decoder U2 is connected to the chip U1 The 32 pins of the decoder U2 are connected, and the 11 pins, 12 pins, ..., 18 pins of the decoder U2 are respectively connected with the display circuit 4.

The key circuit 3 is provided with a key switch K1, a key switch K2 and a key switch K3, the 1 pin of the switch K1 is connected with the 2 pin of the key switch K2, the 2 pin of the key switch K1 is grounded, the 3 pin of the key switch K1 is connected with the 10 pin of the chip U1 Pin connection, pin 1 of key switch K2 is connected with pin 2 of key switch K3, pin 3 of key switch K2 is connected with pin 11 of chip U1, pin 3 of key switch K2 is connected with pin 12 of chip U1.

The display circuit 4 is provided with a display LED1 and a display LED2, the 1 pin of the display LED1 is connected with the 14 pin of the decoder U2, the 2 pins of the display LED1 are connected with the 15 pin of the decoder U2, and the 3 pins of the display LED1 are connected with the decoder U2 Connect pin 11 of U2, pin 4 of display LED1 connects pin 16 of decoder U2, pin 5 of display LED1 connects pin 12 of decoder U2, pin 6 of display LED1 connects pin 25 of chip U1, display Pin 7 of LED1 is connected to pin 28 of the chip U1, pin 8 of the display LED1 is connected to pin 18 of the decoder U2, pin 9 of the display LED1 is connected to pin 13 of the decoder U2, pin 10 of the display LED1 is connected to the chip U1 The 27-pin connection of the display LED1 is connected with the 26-pin of the chip U1, the 12-pin of the display LED1 is connected with the 17-pin of the decoder U2, the 1-pin of the display LED2 is connected with the 14-pin of the decoder U2, and the display LED2 Pin 2 of the display is connected to pin 15 of the decoder U2, pin 3 of the display LED2 is connected to pin 11 of the decoder U2, pin 4 of the display LED2 is connected to pin 16 of the decoder U2, pin 5 of the display LED2 is connected to the decoder U2 The 12-pin connection of the encoder U2, the 6-pin connection of the display LED2 and the 21-pin connection of the chip U1, the 7-pin connection of the display LED2 and the 25-pin connection of the chip U1, the 8-pin connection of the display LED2 and the 18-pin connection of the decoder U2, the display Pin 9 of LED2 is connected to pin 13 of decoder U2, pin 10 of display LED2 is connected to pin 23 of chip U1, pin 11 of display LED2 is connected to pin 22 of chip U1, pin 12 of display LED2 is connected to decoder U2 The 17-pin connection.

The alarm circuit 5 is provided with a resistor R2, a transistor Q1 and a buzzer F1, one end of the resistor R2 is connected to pin 13 of the chip U1, the other end of the resistor R2 is connected to the base of the transistor Q1, and the emitter of the transistor Q1 is connected to the buzzer. One end of F1 is connected, the collector of transistor Q1 is grounded, and the other end of buzzer F1 is connected to power input terminal VCC.

The sounding principle of the buzzer F1 of the utility model is that the current passes through the electromagnetic coil, and when the electromagnetic coil generates a magnetic field, the vibrating membrane can be driven to sound, so the buzzer F1 needs to be driven by current, and the output of the IO port pin of the chip U1 The current is relatively small, and the normal TTL level output by the chip U1 is not enough to drive the buzzer, so the utility model adds a current amplifying circuit, specifically through a triode Q1 to amplify and drive the buzzer. The base of the transistor Q1 is controlled by the P3.7 pin of the chip U1 after passing through the current limiting resistor R12. It will make a sound; when P3.7 is connected to a high level, the current is cut off at this time, that is, there is no current flowing through the coil, and the buzzer will not make a sound at this time. Therefore, this can make the buzzer sound on and off by controlling the level of P3.7.

The 74HC245 decoder of the utility model is high-performance storage decoding, and can also be used as a data transmission system with short delay, and its decoding performance is high. When the high-speed memory enables the circuit quickly, the delay time and enabling time are generally less than the memory access time, so some system times can be ignored.

The display circuit 4 is made up of several light-emitting diodes. The number "8" is composed of seven segments of LEDs, and the decimal point is displayed through a light-emitting diode. Each segment of LED leads to an electrode respectively, and the names of the electrodes are a, b, c, d, e, f, g, dp, where dp is the electrode led out of the decimal point segment, and the corresponding one will light up when the diode is turned on. The display circuit 4 of the present utility model is a digital tube. Among them, the digital tube has two connection methods, common anode connection and common cathode connection. The cathodes of the diodes connected together are called common cathodes. At this time, when the cathodes are connected to a low level, the diode will light up. The anodes in the diodes are connected together to be called a common anode. LED display digital tubes are usually driven by hardware 7-segment decoding integrated circuits to complete the decoding from numbers to display codes. The utility model connects P0.0-P0.7 of the chip U1 of the model STC89C52 with the a-g and dp of the four common anode code tubes respectively, and when the digital tubes of low level are darkened, the digital tubes of high potential are connected. When the tube becomes bright, the control of the display circuit 4 is realized.

The three key switches of the key circuit 3 are all independent keys. There is no restrictive relationship between them, and the single key circuit 3 formed by I/O lines can only be connected to one key.

The working principle of the present utility model is as follows: the power supply module provides power for the timer based on the single-chip microcomputer, the user carries out timing setting to the single-chip microcomputer circuit 1 through the button circuit 3, the single-chip microcomputer circuit 1 starts timing, and the single-chip microcomputer circuit 1 is displayed on the display circuit 4 through the decoder. The real-time remaining time is displayed in , and when the set time arrives, the single-chip microcomputer circuit 1 sends a prompt signal through the alarm circuit 5 .

The timing function of the timer of the present utility model is realized by the single-chip microcomputer circuit 1, because the single-chip microcomputer circuit 1 has a 12MHz crystal oscillator, and this crystal oscillator promptly passes through the time of 1 machine cycle, then the counting frequency is 1MHz, thus just can calculate out of time.

It has been verified by multiple simulation experiments that the timing error rate of the timer based on the single-chip microcomputer of the utility model is smaller than that of the prior art. And the utility model is only provided with 5 circuits and the total number of electronic components of each circuit is less, so the timer of the utility model spends less time when welding, so the timer based on the single-chip microcomputer of the utility model also has The advantages of simple circuit connection and low cost.

The timer based on the single-chip microcomputer is provided with a single-chip microcomputer circuit 1, a decoder circuit 2, a key circuit 3, a display circuit 4 and an alarm circuit 5, and the single-chip microcomputer circuit 1 is respectively connected with the decoder circuit 2, the key circuit 3, the display circuit 4 and the The alarm circuit 5 is connected, and the decoder circuit 2 is also connected with the display circuit 4 . The microcontroller-based timer has the advantage of having a time prompt. At the same time, the timer based on the single-chip microcomputer uses a common chip U1, and the connection of each circuit and each circuit component is simple, so the timer has the advantages of simple circuit and low cost. At the same time, the timer based on the single-chip microcomputer has the advantage of high accuracy.

Example 2.

A timer based on a single-chip microcomputer, other features are the same as in Embodiment 1, the difference is that the model of the chip U1 is AT89C51, the resistance value of the resistor R1 and the resistance RP1 are both 10 kilohms, and the capacitance value of the coupling capacitor C1 is 10 microfarads, the capacitance value of capacitor C2 and capacitor C3 is 30 farads, the crystal oscillator Y1 is 12 MHz, the model of decoder U2 is 74HC245, the model of display LED1 and display LED2 are both 7LEDSMG, and the resistance value of resistor R2 is 2.2 kohms, the model of transistor Q1 is 9012, and the model of buzzer F1 is FMQ.

The utility model uses a 74HC245 decoder that can accept 3-bit binary weighting to input addresses, and when power is supplied, the decoder provides eight mutually exclusive low outputs (Y0 to Y7). The 74HC245 decoder has three unique input terminals: two valid input terminals for the bottom of the feet and one effective input terminal for the high feet. Take full advantage of his composite enabling features, which can be easily completed and extended.

The timer based on the single-chip microcomputer is provided with a single-chip microcomputer circuit 1, a decoder circuit 2, a key circuit 3, a display circuit 4 and an alarm circuit 5, and the single-chip microcomputer circuit 1 is respectively connected with the decoder circuit 2, the key circuit 3, the display circuit 4 and the The alarm circuit 5 is connected, and the decoder circuit 2 is also connected with the display circuit 4 . The microcontroller-based timer has the advantages of simple circuit and low cost.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present utility model rather than limiting the protection scope of the present utility model. Although the utility model has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should It is understood that the technical solution of the utility model can be modified or equivalently replaced without departing from the essence and scope of the technical solution of the utility model.

Claims (6)

1. a timer based on single-chip microcomputer, it is characterized in that: be provided with single-chip microcomputer circuit, decoder circuit, button circuit, display circuit and alarm circuit, single-chip computer circuit is respectively connected with decoder circuit, button circuit, display circuit and alarm circuit connected, the decoder circuit is also connected with the display circuit; The chip U1, the exclusion RP1, the resistor R1, the coupling capacitor C1, the capacitor C2, the capacitor C3 and the crystal oscillator Y1 provided with the single-chip microcomputer circuit, the 10 pins, 11 pins and 12 pins of the chip U1 are respectively connected with the button circuit, and the chip U1 Pin 13 is connected to the alarm circuit, pin 9 of the chip U1 is connected to the negative pole of the coupling capacitor C1, the positive pole of the coupling capacitor C1 is connected to the power input terminal VCC, pin 9 of the chip U1 is also connected in series with a resistor R1 to ground, pin 18 of the chip U1 is connected in series The capacitor C2 is grounded, the 19-pin series capacitor C3 of the chip U1 is grounded, the two ends of the crystal oscillator Y1 are respectively connected to the 18-pin and 19-pin of the chip U1, the 20-pin of the chip U1 is grounded, and the 21-pin, 22-pin, ... ..., 28 pins are respectively connected to the display circuit, the 31 pin of the chip U1 is connected to the power input terminal VCC, the 32 pin of the chip U1 is connected to the 9 pin of the resistance RP1, the 33 pin of the chip U1 is connected to the 8 pin of the resistance RP1, Pin 34 of chip U1 is connected to pin 7 of RP1, pin 35 of chip U1 is connected to pin 6 of RP1, pin 36 of chip U1 is connected to pin 5 of RP1, pin 37 of chip U1 is connected to pin 6 of RP1 The 4 pins of RP1 are connected, the 38 pins of the chip U1 are connected with the 3 pins of the exclusion RP1, the 39 pins of the chip U1 are connected with the 2 pins of the exclusion RP1, the 40 pins of the chip U1 are connected with the 1 pins of the exclusion RP1, and the chip U1 Pin 40 of the chip U1 is also connected to the power input terminal VCC, and pins 32, 33, ..., 39 of the chip U1 are respectively connected to the display circuit. 2. A kind of timer based on single-chip microcomputer according to claim 1, it is characterized in that: described decoder circuit is provided with decoder U2, and 1 foot of decoder U2 is connected with power supply input terminal VCC, decoding Pin 19 of the decoder U2 is grounded, pin 2 of the decoder U2 is connected to pin 39 of the chip U1, pin 3 of the decoder U2 is connected to pin 38 of the chip U1, pin 4 of the decoder U2 is connected to pin 37 of the chip U1 Connection, the 5 pins of the decoder U2 are connected with the 36 pins of the chip U1, the 6 pins of the decoder U2 are connected with the 35 pins of the chip U1, the 7 pins of the decoder U2 are connected with the 34 pins of the chip U1, the decoder Pin 8 of U2 is connected to pin 33 of the chip U1, pin 9 of the decoder U2 is connected to pin 32 of the chip U1, pins 11, 12, ..., 18 of the decoder U2 are respectively connected to the display circuit. 3. A kind of timer based on single-chip microcomputer according to claim 2, it is characterized in that: described key circuit is provided with key switch K1, key switch K2 and key switch K3, 1 foot of switch K1 and 2 pins of key switch K2 Pin connection, pin 2 of key switch K1 is grounded, pin 3 of key switch K1 is connected to pin 10 of chip U1, pin 1 of key switch K2 is connected to pin 2 of key switch K3, pin 3 of key switch K2 is connected to pin 1 of chip U1 The 11 pins are connected, and the 3 pins of the key switch K2 are connected with the 12 pins of the chip U1. 4. A kind of timer based on single-chip microcomputer according to claim 3, it is characterized in that: described display circuit is provided with display LED1 and display LED2, and 1 pin of display LED1 is connected with 14 pins of decoder U2, and display LED1 Pin 2 of LED1 is connected to pin 15 of decoder U2, pin 3 of display LED1 is connected to pin 11 of decoder U2, pin 4 of display LED1 is connected to pin 16 of decoder U2, pin 5 of display LED1 is connected to pin 11 of decoder U2 The 12-pin connection of the encoder U2, the 6-pin connection of the display LED1 and the 25-pin connection of the chip U1, the 7-pin connection of the display LED1 and the 28-pin connection of the chip U1, the 8-pin connection of the display LED1 and the 18-pin connection of the decoder U2, the display The 9 pins of LED1 are connected with the 13 pins of the decoder U2, the 10 pins of the display LED1 are connected with the 27 pins of the chip U1, the 11 pins of the display LED1 are connected with the 26 pins of the chip U1, the 12 pins of the display LED1 are connected with the decoder U2 The 17-pin connection of the display LED2 is connected to the 14-pin of the decoder U2, the 2-pin of the display LED2 is connected to the 15-pin of the decoder U2, the 3-pin of the display LED2 is connected to the 11-pin of the decoder U2, Connect pin 4 of display LED2 to pin 16 of decoder U2, pin 5 of display LED2 to pin 12 of decoder U2, pin 6 of display LED2 to pin 21 of chip U1, pin 7 of display LED2 to chip The 25 pins of U1 are connected, the 8 pins of the display LED2 are connected with the 18 pins of the decoder U2, the 9 pins of the display LED2 are connected with the 13 pins of the decoder U2, the 10 pins of the display LED2 are connected with the 23 pins of the chip U1, and the display The 11 pins of LED2 are connected with the 22 pins of the chip U1, and the 12 pins of the display LED2 are connected with the 17 pins of the decoder U2. 5. a kind of timer based on single-chip microcomputer according to claim 4 is characterized in that: described alarm circuit is provided with resistance R2, triode Q1 and buzzer F1, and one end of resistance R2 is connected with 13 pins of chip U1, The other end of the resistor R2 is connected to the base of the transistor Q1, the emitter of the transistor Q1 is connected to one end of the buzzer F1, the collector of the transistor Q1 is grounded, and the other end of the buzzer F1 is connected to the power input terminal VCC. 6. A kind of timer based on single-chip microcomputer according to claim 5, it is characterized in that: the model of described chip U1 is AT89C51, and the resistance value of resistance R1 and exclusion resistance RP1 is all 10 kilohms, and the capacitance of coupling capacitor C1 The value is 10 microfarads, the capacitance value of capacitor C2 and capacitor C3 is 30 farads, the crystal oscillator Y1 is 12 MHz, the model of decoder U2 is 74HC245, the model of display LED1 and display LED2 are both 7LEDSMG, the resistance of resistor R2 The value is 2.2 kohms, the model of transistor Q1 is 9012, and the model of buzzer F1 is FMQ.