Variable tone sound circuit based on 555 chip

The 555 timer has low cost and reliable performance. It only needs several external resistors and capacitors to realize pulse generation and conversion circuits such as multivibrator, monostable trigger and Schmitt trigger. It is also widely used as a timer in instrumentation, household appliances, electronic measurement and automatic control. The internal circuit block diagram and external pinout diagram of the 555 timer are shown in Figure 2.9.1 and Figure 2.9.2, respectively. It consists of two voltage comparators, three equivalent series resistors, an RS flip-flop, a discharge tube T and a power output stage. It provides two reference voltages, VCC /3 and 2VCC /3 555. The function of the timer is mainly determined by two comparators. The output voltages of the two comparators control the state of the RS flip-flops and discharge tubes. Apply voltage between the power supply and ground. When the 5 pin is left floating, the voltage at the non-inverting input of the voltage comparator C1 is 2VCC /3, and the voltage at the inverting input of C2 is VCC /3. If the voltage of the input terminal TR is triggered If it is less than VCC /3, the output of comparator C2 is 0, which can set the RS flip-flop to 1 to make the output terminal OUT=1. If the voltage of the threshold input terminal TH is greater than 2VCC/3, and the voltage of the TR terminal is greater than VCC /3, Then the output of C1 is 0, and the output of C2 is 1. The RS flip-flop can be set to 0 to make the output 0 level.

Variable tone audio circuit diagram