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Circuits designed by David Johnson, P.E.
Last Updated on:
Thursday, March 22, 2012 04:18 AM
Master Category List -
Dave's Circuits
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Comparator Circuit |
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ACCEPTABLE VOLTAGE INDICTOR
I have used this circuit many times in custom test fixtures where a simple
go-no go indication was needed. The circuit can also be used to adjust a
particular voltage be within specific high or low limits. The three LEDs
will indicate if the voltage is high, low or OK. When connected to other
converters, such as a frequency to voltage converter, a current to voltage
converter or a power to voltage meter, it could provide a quick indication of
a proper level.
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DC CURRENT INDICATOR #4 December 15,
2008
The circuit below uses some common components to turn on an LED whenever DC current
above a certain level is detected. The circuit uses a very popular LM393 dual
voltage comparator from National Semiconductor and a common 1N4148 signal diode.
The diode acts as a crude 0.7v voltage reference. Only one of the comparators
inside the 8 pin package is used. A pair of resistors across the diode forms a
voltage divider, which produce a reference voltage of about 0.015v. ....
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DC Current Indicator 6
The circuit below is a simple way to indicate when DC current is flowing through a
wire. The circuit is designed so it will turn on a LED indicator light, whenever the
voltage drop across a shunt resistor exceeds about 0.1 volts. The value of the resistor
can be selected based on the desired current flow. Although I show a circuit for 12v
operation, the circuit can be used over a wide range from 3v to perhaps 24v....
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PRECISION AC PEAK DETECTOR
This unique circuit uses a very inexpensive voltage comparator to form a peak detector.
The DC voltage produced tracks the positive peak of the input signal. It works
from about ten millivolts to about 10 volts peak to peak. The maximum frequency is
about 150KHz.
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WIDE BAND ZERO CROSS DETECTOR
This circuit was designed to convert a low amplitude 40KHz signal into a clean square
wave signal. It will work with inputs as small as 5mv peak-to-peak or as large as
3 volts peak to peak. The input frequency can range from a few kilohertz to about
150KHz.
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XENON LAMP FLASH DETECTOR
This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil to
detect the short light flashes from a xenon lamp. The coil makes the circuit
immune to normal room lights. Its 10mv sensitivity can detect light flashes from a
range of over 100 feet. Reflections from a room’s walls and ceiling is usually
enough to trigger the circuit. The entire circuit draws only 3 Microamps from a 6
to 9 volt battery.
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Comparator Circuit
Master Category List - Dave's Circuits
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