![]() The prototype was bread-boarded using the Max 232 and LF353 DIP components. 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. 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. 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. A MAX232 TTL-RS232 interface chip can be used to generate +/- 10V DC from +5V 2. Wrote up the documentation for this system. Put the circuit into a small-matchbox enclosure. Made minor changes in the GUI software to handle Channel-Interchange and Offset-Invert. Populated the PCB and checked out the functioning. ( It is possible to handle these fine pitch devices) 8. Fabricated the double-sided SMD PCB using the toner-transfer method. Drew the Schematic and Designed the PCB using Eagle 5.10.0 7. ( This is a great facility provided by TI) 6. Obtained free samples from Texas Instruments. Bread-Boarded the circuit and developed the PC GUI software. Selected the devices required and drew the prototype circuit. Scribbled the Idea on to a piece of paper. As a bonus the MAX232, SMD/DIP, provides a 40kHz / 100kHz signal which can be used for step-response testing of analog circuits. 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. This PWM waveform is converted to ☘V averaged and summed with the first channel to provide a DC offset controllable by the duty-cycle setting. 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. The utility of these signal generators is limited because the outputs are AC coupled and limited to ☒V. PC sound cards form a readily available Signal Generator for testing electronic circuits. ![]()
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