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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

Master Category List - Dave's Circuits

Text & Graphics Copyright David A. Johnson, PE - ALL Rights Reserved.
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 Discriminator Circuits

12v Cooling Fan Thermostat  -  This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level.  Both the high and low temperatures are both adjustable . . . [Circuit by David Johnson P.E.,  02/06/11]


1us Light Pulse Discriminator  -  This circuit is designed to detect the narrow 1uS pulses produced by the above Amplifier circuit. The clean logic type pulses produced by the discriminator are then sent to a frequency to voltage converter. The circuit is designed to process a pulse frequency . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/11/99]

40Khz Ultrasound Receiver  -  A X100 transistor Amplifier is followed by a zero cross detector circuit, using a voltage comparator.  The output is a TTL logic signal, corresponding to the received 40KHz signal . . . [Circuit by David Johnson P.E.,  01/29/06]


AC Peak Detector that is Precise  -  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 . . . [Hobby Circuit designed by David Johnson P.E.,  02/11/02]


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 . . . [Circuit by David Johnson P.E.,  02/09/02]


Battery Charge Current Indicator  -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current . . . [Circuit by David Johnson P.E.,  07/23/06]


Circuit indicates Battery Charging Current  -  Anyone who has ever had a shocking experience on an especially dry day is acutely aware of the kinds of high voltage that can be generated from a simple walk across a carpeted floor. Those same finger to metal sparks can destroy or disrupt sensitive elect . . . [Hobby Circuit designed by David A. Johnson P.E.,  01/23/11]


Cooling Fan Thermostat (12v)  -  This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level.  Both the high and low temperatures are both adjustable . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/06/11]


DC Current Indicator #4  -  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 . . . [Circuit by Dave Johnson P.E.,  10/16/05]


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 resist . . . [Circuit by David A. Johnson P.E.,  10/16/05]


Detect Short Xenon Lamp Flashes  -  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. . . . [Hobby Circuit designed by Dave Johnson P.E.,  02/15/02]


Detect the narrow 1uS pulses  -  This circuit is designed to detect the narrow 1uS pulses produced by the above Amplifier circuit. The clean logic type pulses produced by the discriminator are then sent to a frequency to voltage converter. The circuit is designed to process a pulse frequency . . . [Circuit by Dave Johnson P.E.,  03/11/99]


Flash Detector for Xenon Lamp  -  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 . . . [Circuit by David Johnson P.E.,  02/15/02]


Indicate DC Current Flow  -  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 resist . . . [Hobby Circuit designed by David A. Johnson P.E.,  10/16/05]


Indicates Battery Charge Current  -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/23/06]


Indicator for Acceptable Voltage  -  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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/09/02]


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 . . . [Circuit by Dave Johnson P.E.,  02/11/02]


Thermostat for 12v Cooling Fan  -  This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level.  Both the high and low temperatures are both adjustable . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/06/11]


Version 4 of a DC Current Indicator  -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  10/16/05]


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 150 . . . [Circuit by David A. Johnson P.E.,  02/18/06]


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 . . . [Circuit by David A. Johnson P.E.,  02/15/02]


Zero-Cross Detector-Wide Band  -  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 150 . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/18/06]


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