Ultrasonic burglar alarm & digital clock

I have acquired what appears to be a digital clock with twin ultrasonic transducers facing towards the front. When I power it up, it is quiet, but as soon as I move in front of it, it initiates a loud clicking noise, almost as though by ticking like a clock it won't warn off intruders, but would warn the owner that there had been an intrusion. There is... more » By invalid  - Nov 20 - 1 new of 1 message

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	Continuing: Preventing mosfet breakdown in boost regulator (LT1961)
	Hi, I have some problems with a boost-regulator using Linears LT1961 which has a built-in FET rated at 35 VDC absolute maximum ratings - it breaks on startup, leaving the FET in near short-circuit (3 ohms..). The configuration is standard step-up topology with a 10 uH inductor, low-Vf schottky diode, 12-20V input and 28V output. The circuit seems... more » By BW  - Nov 20 - 11 new of 11 messages

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Audio VCO design

As part of a larger system, I need to design and build an audio VCO which will produce tones ranging from around 50Hz to 4KHz or so when the applied DC input voltage changes from 0.5volts to 2.5volts. This will be used simply as a tuning aid for visually impaired users so the actual voltage/frequency relationship, and waveform produced, is... more » By David Chapman  - Nov 20 - 15 new of 15 messages