Design and Implementation of a Relaxation Oscillator Circuit using an Operational Amplifier

Relaxation Oscillator
Circuit Description
The relaxation operational amplifier circuit is very easy to make only with a few components required
for it. It is possible to generate an output signal with no visibly applied input signal. In such conditions
feedback plays a vital role in order to achieve this. To be particular with positive feedback the oscillator
as well as other circuits can be build that can create an output signal in the absence of external input
signal. Operational amplifier circuits can be used to produce non-sinusoidal signals such as square
waveform, rectangular waveform triangular waveform, ramp waveform etc. To design a relaxation
oscillator it is most to know its working first. As we are using an operational amplifier for this design
purpose so it works in such a way that the oscillator produce a changing voltage at the particular
frequency by the charging and discharging of capacitor through resistors. The main part of this design is
to find the value of these capacitors and resistors which we are going to attach in the circuit of
relaxation oscillator. Now in order to understand how the circuit works add a resistor and capacitor with
operational amplifier instead of external signal and lets the capacitor charge and observe its behavior
when it gets discharged.
In order to find the values for capacitor and resistor we can use this formula:
f = 1
2.2∗R∗C
As we are provided with the value of frequency, the capacitor value is chosen according to market
availability and putting values in the formula the required resistor value is obtained which is to be
inserted in the circuit. The operational amplifier used is uA741. After having the hand calculated values
for all components they can be verified by the software.
Simulation
After finalizing the circuit the next important task is to implement it on some software. We are using ISIS
for checking our circuit. The circuit as such is drawn on software and al resistors and capacitors are
placed according to the design and they are provided with the values calculated for them. The PCB
layout of the circuit on ISIS comes out to be as:

Figure 1: Schematic Layout
From this schematic it is obvious that in our design of relaxation oscillator we are using 4 resistors, 2
capacitors and 2 connectors with operational amplifier uA741. When this circuit with our desired values
of resistor and capacitor is simulated it gives us the proper waveform which shows that our circuit is
right.
This is the simulation result:
Figure 2: Simulated Result
PCB Layout from ARES

The circuit above discussed is transferred to ARES for making the PCB layout. The front side of the PCB
comes out to be as shown below and the size of this generated layout is all according to the
measurements mention in assignment.
Figure 3: Front Side of PCB Layout
Similarly the back side of this layout looks like this:
Figure 4: Back Side of PCB Layout
The pins showing on this layout is the legs of components like resistors and capacitors. The dimensions
of this PCB board is such that it is no greater than 60mm by 60mm as it was mentioned in the
requirements.
Hardware Checking of Circuit
After compiling the circuit on software the next condition is to check the same circuit on hardware also
because many times it happens that the circuit does not behave exactly the same as on the software, as