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PC sound cards form a readily available Signal Generator for testing electronic circuits. The utility of these signal generators is limited because the outputs are AC coupled and limited to ±2V.

Taking advantage of the two channels provided by the sound card this Instructable shows a scheme which uses one channel to output the Sin/Square/Triangle waveform with a fixed gain, while setting up a 441 Hz PWM square wave on the second channel. This PWM waveform is converted to ±8V averaged and summed with the first channel to provide a DC offset controllable by the duty-cycle setting.

This PC sound-card interface implements a Signal-Generator with Sin/Square/Triangle output frequency variable from 50Hz to 10kHz, an amplitude variable from 0 to 5V and a variable DC offset of +/- 4V.

As a bonus the MAX232 , SMD/DIP, provides a 40kHz / 100kHz signal which can be used for step-response testing of analog circuits.

How I went about it:

1. Scribbled the Idea on to a piece of paper.
2. Selected the devices required and drew the prototype circuit.
3. Bread-Boarded the circuit and developed the PC GUI software.
4. Decided to do a professional job.
5. Obtained free samples from Texas Instruments. ( This is a great facility provided by TI)
6. Drew the Schematic and Designed the PCB using Eagle 5.10.0
7. Fabricated the double-sided SMD PCB using the toner-transfer method. ( It is possible to handle these fine pitch devices)
8. Populated the PCB and checked out the functioning.
9. Made minor changes in the GUI software to handle Channel-Interchange and Offset-Invert.
10. Put the circuit into a small-matchbox enclosure.
11. Wrote up the documentation for this system.
12. Archived all technical data in a .rar file

 

Step 1: The Idea

The idea has three parts:

1. A MAX232 TTL-RS232 interface chip can be used to generate +/- 10V DC from +5V
2. One channel of the PC sound card can be programmed to output a fixed frequency PWM waveform which when converted to +/-10V using the MAX232 and averaged would provide a variable DC voltage depending on the PWM setting.
3. This can be suitably summed with the second PC sound-card output which is programmed to generate SIN/SQ/TRI outputs to form the final output.

A GUI program on the PC can control the generation of the SIN/SQ/TRI amplitude and frequency and also the PWM to create a variable offset.

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The prototype was bread-boarded using the Max 232 and LF353 DIP components.

This scheme can be implemented in case one does not want to work with the SMD components presented further on.

The Oscilloscope display shows a 4V Triangular wave offset by +2V.

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The PC sound-card interface implements a Signal-Generator with Sin/Square/Triangle output frequency variable from 50Hz to 10kHz, an amplitude variable from  0 to 5V and a DC offset of  +/- 4V.

As a bonus the DIP MAX232 provides a 100kHz 5V/1V signal which can be used for step-response testing of analog circuits.
Great idea. Very useful when playing with electronics.

About This Instructable

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Bio: I am a retired Electronic Systems Engineer now pursuing my hobbies full time. I share what I do especially with the world wide student community.
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