generating a sine wave


Posted on Feb 7, 2014

After the recent pretty disappointing results with a transformer-based Component Tester, I`d like to try and generate a ± 10 V sine wave at approximately 50 Hz in some other way. Using as few components as possible. This is where we enter, eh, squarely into the analog electronics domain. Yes, we could generate it with an ATmega, but frankly that


generating a sine wave
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sounds like a bit of overkill, would require a fair amount of filtering to remove residual switching effects, and besides we`d still have to amplify it up to 10 Vpp. I`ve only just started exploring op-amps, really one superb resource on the web comes in the form of a free eBook from 2002 on the Texas Instruments site, titled Op Amps For Everyone , by Ron Mancini. It uses very few components. This one was dimensioned for about 1. 6 KHz, so I started with capacitors ten times as large, i. e. 0. 1 µF, to lower the oscillation frequency. Here`s the result, using a TLV2472 dual op-amp: Yeah, right. Clipping like crazy, i. e. overshooting into the limiting 0V and 5V power lines. The FFT shows it`s not anywhere near a pure sine wave, even though the shape vaguely resembles one: Hmm. Looks quite good here, just tried it with an LM358. With 10k resistors, 100nF capacitors and two 330R resistors for getting V/2 I get a clean sine wave of about 170Hz. Cosine looks also nice on my Rigol, X-Y shows a nice circle. After some minutes of measuring though, the amplitude of the signal slowly faded to zero, and now it doesn`t even start to oscillate at 5V. Raising the power suuply to 7V seems to fix that. Will have to have a look what could cause that




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