User Manual

46
 Pin 4 (RESET): outputting low level when supplied a low one
 Pin 5 (CONTROL VOLTAGE): changing the upper and lower level trigger values
 Pin 6 (THRESHOLD): the input of the upper comparator
 Pin 7 (DISCHARGE): having two states of suspension and ground connection also
decided by the input, and the output of the internal discharge tube
 Pin 8 (VCC): the power supply
The 555 timer can work under three modes. In this experiment, the astable mode is used to
generate square waves.
Under the astable mode, the frequency of output waveform of the 555 timer is determined
by R
1
, R
2
and
2
C
:
In the above circuit, R
1
= R
2
=10KΩ=
4
10
Ω;
2
C
=100nF=
7
1 0

F, so we can get the frequency:
After connecting the circuit according to the schematic diagram, use an oscilloscope to
observe the frequency of the output waveform. We can see it is consistent with the above
calculated result.