Experiment and production of NE555 time base integrated circuit

1. Introduction to commonly used electronic components

(1) Names, circuit symbols, and letter symbols

(2) 555 time base integrated circuit

The 555 time base integrated circuit is a digital integrated circuit. It is a timer composed of 21 transistors, 4 diodes and 16 resistors. It has the functions of voltage divider, comparator, trigger and discharger. It has low cost, easy to use, wide adaptability, large driving current and certain load capacity. In electronic production, it can be made into a variety of practical small circuits after simple debugging, which is far superior to the transistor circuit.

There are many types of 555 time-base circuits at home and abroad, such as foreign products: NE555, LM555, A555 and CA555, etc.; domestic models include 5GI555, SL555 and FX555, etc. Their internal structure and pin numbers are the same, so they can be directly replaced with each other. But it should be noted that not all integrated blocks with 555 numbers are time-base integrated circuits, such as MMV555, AD555 and AHD555, etc. are not time-base integrated circuits.

The common 555 time base integrated circuit is a plastic dual in-line package (see Figure 5-36 ), with the word 555 printed on the front, pin ① in the lower left corner, and the pin numbers are arranged in a counterclockwise direction.

(Figure 5-36)

The functions of each pin of the 555 time base integrated circuit are as follows: Pin ① is the common ground terminal as the negative pole; Pin ② is the low trigger terminal TR, which is turned on when it is lower than 1/3 of the power supply voltage; Pin ③ is the output terminal V, and the current can reach 2000mA; Pin ④ is the forced reset terminal MR, which can be connected to the positive pole of the power supply or left floating when not in use; Pin ⑤ is used to adjust the reference voltage of the comparator, referred to as the control terminal VC, which can be left floating when not in use, or connected to ground through a 0.01μF capacitor; Pin ⑥ is the high trigger terminal TH, also known as the threshold terminal, which is cut off when it is higher than 2/3 of the power supply voltage; Pin ⑦ is the discharge terminal DIS; Pin ⑧ is the positive pole of the power supply VC.

The main parameters of the 555 time base integrated circuit are (taking NE555 as an example) power supply voltage 4.5~16V.

The output drive current is 200 mA.

When used as a timer, the timing accuracy is 1%.

When used for oscillation, the maximum frequency of the output pulse can reach 500 kHz.

When in use, if the driving current is greater than the above current, a circuit to expand the current should be added to the output end of pin ③, such as adding a transistor for amplification.

(3) Musical integrated circuit

It, like the integrated circuits that imitate animal calls and human language, are analog integrated circuits and use soft packaging, that is, the silicon chip is encapsulated with black epoxy resin on a small printed circuit board.

Since it is not suitable to manufacture components such as inductors, capacitors and adjustable resistors inside integrated circuits, some external components must be connected in order to make them function.

Note: The integrated circuit chip cannot be operated with power on during welding. Only after welding and inspection, can the power be turned on.

2.555 time base integrated circuit basic circuit experiment

In order to use fewer components and achieve basic mastery of the production and application of 555 timing integrated circuits, we have selected the following components for your experimental reference (the values ​​are no longer marked in the following circuit diagram 5-37).

R1 is a photoresistor, R2 ₌ 10K, R3 ₌ 2K, R4 ₌ 200Ω, R5 _{= 200Ω} , Rp is 150K, RT _is a thermistor, IC1 _is NE555, IC2 _is a music sheet with transistors and resistors soldered on it, there are one red and one green light-emitting tube VD1 _and VD2 _, SB is a push button switch, C1 ₌ 0.01μF, C2 ₌ 0.04μF, C3 ₌ 10μF, C4 ₌ 47μF, C5 ₌ 100μF (C3 _, C4 _and C5 _are electrolytic capacitors with a withstand voltage greater than 6V), GB = 6V, and the speaker is 8Ω.

(1) Touch circuit

This is a feature of the 555 time-base integrated circuit, which has a circuit flipping function, called a bistable working mode. Figure 5-38 is the most typical bistable circuit. In the figure, "open" and "close" are two metal sheets (iron or copper sheets). When the hand touches the "open" metal sheet, the pulse signal sensed by the human body is input to pin ②. At this time, pin ③ outputs a high potential and the light-emitting diode lights up. When the hand touches the "closed" metal sheet, the circuit flips, and pin ③ outputs a low potential, and the light-emitting diode turns off.

Figure 5-37

Note: The two pins of the LED have positive and negative poles, so make sure you don't make a mistake when welding (connecting). When the circuit is not connected to the metal sheet for testing, you should dip your hands in water or use a key to touch the pins to increase the inductance.

(2) Delay circuit

There are two types of delay circuits. One is the delayed off circuit, such as the corridor light; the other is the delayed on circuit, which is also called a timing circuit.

Figure 5-38 is a time-delayed closing circuit composed of a 555 timing integrated circuit. When the push-button switch SB is pressed (the hand is released after pressing), C4 _is discharged, the trigger pin ③ outputs a high potential, the LED lights up, and the timing starts. When C finishes discharging and is charged through R, the voltage rises from zero to 2/3 of the 555 power supply voltage, the pin ③ outputs a low potential, the LED automatically turns off, and the timing ends.

Figure 5-38

In the experiment, first turn the movable plate contact point of the adjustable resistor to the middle position (about 75K). Increasing or decreasing the resistance value during the experiment will find that the light-emitting diode will light up for a longer or shorter time. Remove C4 _and replace C3 _and C5 _. You will find that the larger the capacitance, the longer the light-emitting diode will light up. This means that the length of the delay is determined by the values ​​of RP and C. The larger the resistance value and the larger the capacitance value, the longer the delay time. In scientific and technological production, resistors and capacitors can be replaced as needed to achieve the purpose of delay.

(3) Flash circuit

The 555 time base integrated circuit in Figure 5-39 consists of input terminals _R3 , RP and C4 _to form an oscillating circuit. The level of the output of pin ③ keeps flipping high and low. When the output of pin ③ is low, VD1 _is turned on and emits light, and VD2 _is turned off; when the output of pin ③ is low, _VD1 is turned off and VD2 is turned on and emits light. In this way _, the red and green LEDs flash alternately.

Figure 5-39

During the experiment, first turn the contact point of the adjustable resistor to the middle position, and then increase or decrease the resistance value. At this time, the time for the LED to alternately emit light will also increase or decrease, but it is not very obvious. If C ₄ is replaced by C ₅ and C ₃ respectively , the length of the alternating light-emitting time will be very obvious. The oscillation frequency (i.e. the number of flashes of the LED per second) can be achieved by simply changing the resistance value of RP and the capacitance of C.

(4) Audio circuit

As long as the output end of the flash circuit is connected to a speaker (horn), as shown in Figure 5-40 , it becomes a sound device.

Figure 5-40

When experimenting, first turn the adjustable resistor to the middle position, then slowly increase or decrease the resistance value, and the tone will change accordingly. If you replace C _{1 with C 2,} you will find that the tone becomes lower. In electronic production, adjust the resistance value or replace the capacitor to achieve the tone you need.

(5) Light-controlled circuit

In Figure 5-41, the photoresistor and the resistor form a simple voltage divider, and pins ② and ⑥ are connected to the voltage divider point. When the light is strong, the photoresistor has a low resistance, so the potential of the voltage divider point is high. When the potential of pin ⑥ is above 2/3 of the power supply voltage, the upper comparator inside the 555 time base integrated circuit is in a reset state, the output pin ③ is low level, and no current passes. When there is no light or the light is weak, the photoresistor has a high resistance, and the voltage divider point is low potential. When the potential of pin ② is below 1/3 of the power supply, the lower comparator inside the 555 time base integrated circuit is in a set state (conduction), and pin ③ outputs a high level, making the light-emitting diode VD ₁ emit light.

Figure 5-41

During the experiment, first screw the movable plate contact point of the adjustable resistor to the middle position. After the circuit is connected, put a black plastic pen cap (do not use a metal pen cap) or other opaque objects on the photoresistor. At this time, the light-emitting diode will light up (if it is not bright, adjust the adjustable resistance value to make the light-emitting diode bright). If you want to make the light-emitting diode light up at a certain darkness (not completely black), you should slowly reduce the adjustable resistance value at the required darkness to make the light-emitting diode light up. When encountering a situation slightly brighter than this darkness, the light-emitting diode will not light up. This often requires repeated adjustments several times.

(6) Temperature control circuit

The circuit in Figure 5-42 uses a thermistor as a head, which is inserted into the object to be controlled. When the temperature rises, the resistance of the thermistor decreases. This feature is used to control the required temperature through the circuit.

Figure 5-42

After the circuit is connected, put the thermistor into hot water during the experiment, and slowly adjust the adjustable resistance value from large to small so that the LED just lights up. When the thermistor is taken out of the hot water, the LED goes out immediately, indicating that when the water temperature exceeds this temperature, the LED lights up as a prompt, and it will not light up if the temperature is lower than this.