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DIY Function generator circuit using Quad Op-Amp

FG’s are quite expensive in nature and not many could afford one for their experimentation and learning. This circuit design might come in handy for those who want to build a efficient FG of their own. This DIY function generator is the deluxe version of Function generator Circuit published on our site few days ago. This Function generator circuit built around quad opamp MCP6024 comes with added features such as adjustable and selectable Sawtooth waveform generation, selectable frequency ranges, output waveform selector switch and frequency counter oscilloscope trigger output. The output of this FG ranges from 30 seconds to 350 Khz.

CIRCUIT DIAGRAM:

WORKING OF FUNCTION GENERATOR CIRCUIT:

The heart of the function generator is the integrator, formed by U1A( IC MCP6024), R1, R2, S1- 6, C1 – 6, and the comparator with hysteresis, formed by U1B, R7, R8, R9, and R10. They work together in the following way. U1B has it’s output low, when the input feeding U1Ain- is less than the reference voltage, the output of U1A ramps up.

The output of U1A goes through R9 to input U1Bin+. When the voltage at U1Bin+ is greater than the reference voltage at U1Bin-, (half of the supply voltage), the output of U1B goes high. This raises the voltage at U1Bin+ causing U1B to switch states. Since the output of U1B is higher than the reference voltage at U1Ain+, the output of U1A begins to ramp down. When the output of U1A through R9 pulls the input U1Bin+ lower than U1Bin- reference, U1B output switches low. This causes U1A to again begin ramping up until the output of U1A causes the input U1Bin+ to go higher than U1Bin-, and the process repeats in an oscillating manner.

The output of U1A is a triangle wave. The output of U1B is a square wave. To produce a pseudo-sine wave, the output of U1A is connected by R11 to input U1Cin-. The network of resistors R12 – R17 and diodes D1 – D10 clip or reduce the gain of U1C progressively, as the triangle amplitude increases. This reduces and rounds off the tip of the triangle wave to produce the pseudo-sine wave. Diodes D1 – D10 are 1N34 germanium diodes. They were chosen for their lower forward voltage drop, (.35 volts), compared with silicon, (.6 volts).

The outputs of U1A, U1B and U1C are connected through R18, R19, and R20 to the input U1Din-. R21, a 10K potentiometer, provides the appropriate feedback to control the output level of U1D, from 0 to Vmax. A selector switches S8-10 is used to select the desired output type of waveform. Switches S1-S6 , selects different values of capacitance C1 to C6, to change the frequency range of the function generator.

Switch, S7, connects integrator input U1Ain+ to either +V/2 at the junction of R7 and R8, or the wiper of R5 which can be adjusted to nearly +5V or ground to create a saw tooth wave at the output of the integrator U1A. R23 is used to protect the output of U1B while providing an output signal to an external frequency counter or oscilloscope trigger. R2 is used to make a fine frequency adjustment in the output which will be handy in several situations.

OUTPUT WAVEFORMS:

Output waveforms of the FG circuit

PCB DESIGN:

You can Download the Gerber files of the above Design below.

DIY FG Gerber Files

DIY-FG-gerber-Files.rar

Version: 1

DIY-FG-gerber-Files.rarVersion: 1

475 Downloads

Details 33.6 KB475 Downloads Gerber files of DIY function generator Languages: English Author: Ron Hoffman Platforms: Windows 8 Category: Circuit Design Files License: Freeware Date: February 6, 2016

You can get the Bill of materials BOM of this project below.

Bill Of Materials DIY FG

Bill of Materials DIY FG.pdf

Version: 1

Bill of Materials DIY FG.pdfVersion: 1

1428 Downloads

Details 49.4 KB1428 Downloads Languages: English Author: Ron Hoffman Category: Project/Circuit Files Date: September 27, 2015

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