Use the 555 Timer Wizard to build astable and monostable oscillator circuits that use the 555 timer.

  • Astable operation—Produces a free-running oscillator that does not need any input signal.
  • Monostable operation—Produces a single output pulse in response to an input trigger pulse. When an input signal is applied, each input pulse produces one output pulse.

Complete the following steps to build an astable oscillator:

  1. Select Tools»Circuit wizards»555 timer wizard. The 555 Timer Wizard dialog box appears.
  2. Select Astable operation from the Type drop-down list. Default settings are initially displayed.
  3. Enter values based on the following:
    • Vs—Enter desired source voltage.
    • Frequency—Enter the frequency at which you wish the circuit to oscillate, to a maximum of 1 MHz.
    • Duty—Enter the duty cycle for the circuit. For example, 60% indicates that the circuit will be “on” for 60% of each cycle. Value must be greater than or equal to 50% and less than 100%.
    • C—This is the value of capacitor C and is initially set to 10 nF.
    • Cf—This is the value of capacitor Cf and is normally fixed to be 10 nF.
    • Rl—Enter desired load resistance.

      As values are entered, R1 and R2 are calculated automatically.

  4. If (R1+R2)>3.3 Mohm or R1<1 kohm or R2<1 kohm, a warning message displays in the 555 Timer Wizard dialog box, as shown below the schematic preview in the example below.

    If this happens, change the value of capacitor C and other parameters until the error message no longer displays.

  5. Check the values of R1 and R2. If they are unavailable or unsatisfactory, change the value of capacitor C.
  6. Repeat the above two steps until R1 and R2 are satisfactory and there is no error message in the 555 Timer Wizard dialog box.
  7. Click Build circuit. The circuit, with the calculated component values is placed on your workspace.

Complete the following steps to build a monostable (one-shot) oscillator:

  1. Select Tools»Circuit wizards»555 timer wizard. The 555 Timer Wizard dialog box appears.
  2. Select Monostable operation from the Type drop-down list.
  3. Enter values based on the following:
    • Vs—Enter desired source voltage.
    • Vini—Set equal to Vs.
    • Vpulse—Enter desired voltage of input pulse. This should be less than Vs/3.
    • Frequency—Enter the frequency of the input voltage.
    • Input pulse width—Enter desired input pulse width. Must be less than Output Pulse Width/5. If it is not, the value in the Output pulse width field is changed by the system.
    • Output pulse width—Enter desired output pulse width.
    • C—This is the value of capacitor C and is initially set to 1 uF.
    • Cf—This is the value of capacitor Cf and is normally fixed to be 1 nF.
    • Rl—Enter desired load resistance.

      As values are entered, R is calculated automatically.

  4. Check the value of R. If it is unavailable or unsatisfactory, change the value of capacitor C or other parameters until a satisfactory value is reached.
  5. Click the Build circuit button.
  6. The circuit, with the calculated component values is placed on your workspace.