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Computer Simulation of a Clock
Oscillator using a 555 Timer Chip
In this exercise, you will use a 555 timer chip in a clock oscillator configuration.
In this application, the oscillating frequency is set by properly selecting values
of the capacitors and resistors that control its operation.
- Start the simulation by entering the circuit schematics into the PSPice
schematic editor as follows.
- From the Start icon, select EET applications, then Design Lab,
then Schematics.
- Hit <Ctrl-G> (hold down the Ctrl key and press G, lower case
or upper case) to obtain a component part. Enter the part name
555. Select "Place" and "Close" to place the part in the circuit.
- Hit <Ctrl-G> to get R ( resistor), C (capacitor), vdc (battery),
agnd (analog ground), and <Ctrl w> (wire) to compete the
circuit as shown below: The parameter values will be set following
the procedure:
- Save the file name by clicking on File, then Save As
- To geta file, click on File Menue, and select Open, then highlight
the file name, and hit <Enter>.
- Set up the transient parameters by clicking on the following:
Analysis
Setup
Transient
- Set T-Step 20us and T-Stop 20 ms.
- Click OK
- Click Close
- Hit <F11> to run the simulation or click Simulate on the Analysis Menu. The
following output probe will be displayed.
- Hit <F11> to simulate or from the Analysis Menu, click on Simulate. The
following output probe will be displayed. Calculate T high, T low, the Period,
and the oscillating frequency.
- Calculate T high, T low, the period of the waveform, and the oscillating frequency.
- Calculate the oscillating frequency from the resistance and capacitance values
and compare it with the simulation results.
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