I got this idea; instead of using a microphone and preamp at the end of a twisted pair, I would build a microphone, preamp and modulate a red laser with the audio and pick up the audio about ten yards away with a light detector. Notice that it runs on two 2V photovoltaic cells in
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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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Q: What was the first commercially successful semiconductor device? Hint: It wasn’t germanium. https://en.m.wikipedia.org/wiki/Henry_Harrison_Chase_Dunwoody
From FB group I take … Alejandro Cruz He said a diode is a diode but there are more than volts and current. The reverse recovery time is important. If it is rectifying 50 or 60 Hz AC then standard recovery time is good. If it’s rectifying high frequencies then it should be fast recovery
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I made one of these back in 1970 or so. It was inside of a coffee can using the lid for the speaker. This class A power LED driver works good for making a speaker from an audio output transformer and any sheet of steel, even a coffee can with a steel cover. Strip the
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A year or so ago I bought a few 1W mono amplifiers from a Chinese eBay seller for cheap – see the attached photos. The only marking on the PC board is YX-1667 but I’m not sure if that’s the potentiometer or the PC board itself. . I found that if I pushed the 3.5mm
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This is an adapter to connect a source such as a smartphone stereo headphone output to the input of an MP3 recorder. The view and diagram is looking at the back of the adapter where the plugs are inserted into the jacks. The switch handles are on the far side. The switch on the right
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Many years ago I saw electronic listening devices for receiving a block of ultrasonic frequencies that bats use and downconvert that block to frequencies that humans can hear. But no one to my knowledge has tried to convert human frequencies up to ultrasonic frequencies so that humans can try to establish a conversation with other
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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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