Chuck commented about the audio oscillator being a BFO, and it reminded me that I’ve got an old RCA BFO audio oscillator stuck away in the garage. It was a cheap way of getting an audio sine wave that covered the full audio band without any switching. Nowadays it’s all done in sine and other
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Watson’s Buzz Beeper I built this Buzz Beeper to find out if an audible tone could be used for sending simple commands, like turn on. Recently I built a microphone preamp with a bandpass filter that can detect my whistle. But it can be triggered by loud noise. So how about I generate a tone
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This circuit could be used for blind to sense light. It’s a similar circuit to the police siren. The two transistors have a current gain of 200 X 200 or 40,000 so even a very tiny Q1 base current – microamps – causes a very large Q2 collector current. So a very small amount of
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This is from Electronics Illustrated Projects 1968. It shows crystal sockets, but instead a RF coil may be used and its value will be about 220 microhenrys. And C1 and C2 will have to be changed to bring the frequency down to the AM band. The germanium transistors are no longer available so silicon transistors
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Also photo posted to FB group Building Transistor Radios. I got several of these Wien Bridge Oscillator kits from an eBay seller in China. They are built using the circuit from http://redcircuits.com/Page13.htm More information can be found on the wiki for this oscillator. The kits come with no instructions, so to assemble it, use this red circuits
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