I was wandering around the pages of the Modern Electronic Circuits Reference Manual, a 1200 page tome by Markus, when I happened to see this odd circuit for a signal generator (see the schematic). My curiosity got the best of me, and I knew I had to build one, since I have a whole lotta
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I built up this FM microphone from belza.cz. The circuit is super simple, uses only a single transistor. The output of the electret condenser microphone is coupled directly to the base of the RF oscillator, and causes the frequency modulation. However since the microphone has no amplification, it is not sensitive and the user must
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Remember Capt. Hook and the crocodile? This circuit is almost the same as a flasher, except instead of an LED it uses a speaker. The result is that it pulses the speaker with a very short pulse of current. The circuit uses a 9V battery, but today the 9V battery is too expensive, so I
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I watched LAaRT on PBS OC tonight and was introduced to this guy who custom crafts guitars. On the episode they showed him talking about a wafer switch that he said came from a telephone system. This switch is like a rotary switch turned on edge and a lever added to move the contacts to
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I built this circuit back in June 2010, but it wasn’t stable, and tended to motorboat (yeah, the output went putt-putt). I had to do some troubleshooting to find out what it needed to cure the problems. I finally got it running, and was I in for a surprise! This thing is super sensitive, it
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QS sent me a link to a Youtube video of a young lady who explained the use of a light bulb in a Wien Bridge Oscillator and who mentioned that HP long ago used a light bulb in its audio generator. The HP 200CD audio oscillator was a part of the workbench of a guy
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The schematic found here looks to me like it could be a good sound level meter with a few changes. One thing that it has going for it is the meter is inside of the feedback loop, so it will have a linear scale at low levels. Some meters don’t and the forward voltage of
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I unpacked my ol’ headphone amplifier and tried to find the wall wart AC adapter for it. The jack is labeled 12VDC, center negative, so I looked through some boxes for the adapter that matched up. I found one and plugged it in, turned on the amp, and heard Hum-Bub, Hum-Bub, Hum-Bub… The amp was
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I came across and article in an old electronics magazine on how to make a directional microphone with a cardboard horn. I decided to copy the horn part. The horn consists of four triangle shaped pieced of cardboard cut from boxes. Each of the four pieces is 1 inch (25.4mm) at the small end, 12
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I have a lot of these 600 ohm telephone hybrid transformers that came out of a PBX (see here for much more info). They’re sturdy and well built, and make great audio transformers. Last week someone posted a video to Youtube of some Joule Thiefs that used an audio transformer and the frequency of oscillation
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