Electronics > Projects, Designs, and Technical Stuff
Dual-frequency (simultaneous dual resonance) analog sine wave gen with 1 op-amp?
Wolfgang:
Having fun and to learn something is the best of all reasons. >:D
Zero999:
Yes, an oscillator can output two frequencies. Often this is unintentional, such as a crystal oscillator exciting two modes or the crystal or an op-amp being unstable and generating a much higher frequency, as well as the intended oscillator frequency.
David Hess:
--- Quote from: Wolfgang on June 17, 2019, 12:08:16 am ---If you look for useful dual resonances there are SC cut crystal oscillators where the secondary (b Mode) resonance is tracked for exact crystal temperature measurement.
--- End quote ---
I remember those now. But didn't the other mode use a separate oscillator?
Wolfgang:
... normally yes. But it can also happen (unintentionally) in the same Colpitts type oscillator.
rfeecs:
--- Quote from: T3sl4co1l on June 16, 2019, 04:41:08 pm ---The history goes back to I think early Western Electric DTMF sets, which used a single transistor (they were expensive back then!) and a keypad matrixed selection of LC tanks, carefully tuned for the frequencies required.
--- End quote ---
That's a great example. Here's a schematic of the Western Electric 2500 Touch-tone phone:
http://www.repeater-builder.com/tech-info/dtmf/bell-dtmf.html
Only one transistor to generate two tones. Lots of DIACs, it looks like.
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