Simple Function Generator Circuit Diagram

This is a simple function generator circuit that can produce the following waveforms: square wave, triangular wave, and sine wave.

   

The circuit's main components are two 1458 IC's.  The 1458 is a dual op-amp IC, i.e., an IC that houses two op amps inside it.  The circuit uses four op amps, two from each 1458.

  

The bottom-most op amp in Figure 1 is configured as an astable multivibrator, which continuously generates a square wave.  Assume that C1 has no charge initially. The voltage at the inverting input is zero, while the voltage at the non-inverting input is very slightly positive (a ratio of the op amp's output offset voltage as determined by R1 and R2). This minute voltage difference at the inputs is enough to cause the op amp's output to swing to 'high'.

  

When the output becomes high, C1 starts charging up. The voltage at the inverting input soon exceeds that at the non-inverting input, forcing the output to swing to 'low', which discharges C1 again.  At a certain point, the voltage at the non-inverting input exceeds that at the inverting input again, and the output of the op amp goes high again.

   

This cycle wherein the first op amp's output swings between 'low' and 'high' goes on indefinitely, generating the square wave.

  

The two middle op-amps are both configured as integrators. The input to the second op amp is the square wave output of the first op amp.  Being configured as an integrator, this op amp outputs a triangular wave (the integral of a square wave), as shown in Figure 1. 

    

The triangular wave output of the second op amp is then fed into the third op amp, which is also configured as an integrator.  The output of the third op amp is a sine wave (the integral of a triangular wave).

   

The sine wave output of the third op amp is fed into the fourth op amp, which is configured as an inverting amplifier. The output of this last op amp is also a sine wave but opposite in phase as its input.

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PWM Generator Circuit Diagram

PWM waveforms are commonly used to control the speed of DC motors. The mark /space ratio of the digital wave-form can be defined either by using an adjustable analogue voltage level (in the case of a NE555 based PWM generator) or digitally using binary values. Digitally derived PWM waveforms are most often produced by the timer/counter modules in microcontrollers but if you do not want to include a microcontroller in your circuit it’s also quite simple to generate the signals using discrete logic components. An extension of the circuit shown can pro-duce two PWM waveforms from an 8-bit digital input word. Each signal has 15 val-ues. The 8-bit word can be produced for example from an expansion board fitted in a PC or from an 8-bit port of a processor which does not have built-in PWM capability or from a laptop’s printer port.

Discrete PWM Generator Circuit Diagram

The mark/space ratio is only programmable up to 15/16 rather than 16/16; a binary input of 0000 produces a continuous low on both outputs turning both motors off. Similar circuits often employ a dedicated ‘enable’ input to turn the motors off but it is not necessary in this design.

The diagram shows the circuitry required to produce just one waveform. For the full two channel circuit it is necessary to use an additional 74HC193. The clock signal produced by the HCF4060 generator can be used to drive both channels and the free flip flop in the 74HC74 package can be used for the second channel (the corresponding pin numbers are shown in brackets). Alto-gether the entire two channel circuit can be built using just four ICs.

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2MHz Square Wave Generator Circuit Diagram

2MHz Square Wave Generator Circuit Diagram. With the values shown the circuit generates a 2-MHz symmetrical square wave. Changing capacitors Cl and C2 to 0.01 µ¥ results in a frequency of 500 Hz. For the particular integrated circuits and power supply voltages (5.0 V), the reliable operating range of Rl = R2 is 2 k ohm to 4 k ohm.

2MHz Square Wave Generator Circuit Diagram

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