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Circuits of the Week - June to January 2010
Last Updated on: 08/23/2015 07:05 AM

2015:  Jan-June   July-Dec     2014:  Jan-June    July-Dec     2013:  Jan-June    July - Dec   
2012:  Jan-June    July-Dec      2011:  Jan-June    July-Dec     2010:  Jan-June     July-Dec      
2009:  Jan-June    July-Dec      2008: Jan-June    July-Dec      2007:  Jan-June     July-Dec       
 2006:  Jan-June     July-Dec         2005:  May-Dec


AC Line Powered LED Pilot Light


This simple circuit can be used to light a LED indicator lamp, powered from the 120vac line.  I have included component values for 240vac lines as well... [Hobby Circuit designed by David Johnson P.E., 7/09/2006]


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 A. Johnson P.E., 2/11/2002]


Lighthouse LED Flasher


This was originally designed for a model in a HO train set.  It simulates the behavior of the light from a lighthouse.  The LED intensity gradually increases, then flashes with a bright light and finally decreases slowly in intensity... [Hobby Circuit designed by Dave Johnson P.E., 7/11/2006]


Indicates Battery Charge Current


This circuit turns on a LED whenever it detects at least 25ma of battery charge current... [Circuit by Dave Johnson P.E., 7/23/2006]


20Mhz VCSEL 3mw Laser Test Circuit


This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC... [Hobby Circuit designed by Dave Johnson P.E., 6/17/2000]


Version B of 1.5v LED Flasher


To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5 volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage... [Circuit by Dave Johnson P.E., 6/03/2000]


Control both Power & Direction of a DC Motor


TTL type Q and inverted Q inputs control a classic H-bridge circuit, rated at 50 volts and about 10 amps.  The circuit can control power and direction of a DC motor... [Circuit by Dave Johnson P.E., 2/04/2007]


Tap Switch uses a Piezo Wafer


Two different switch circuits are shown.  One sources current and the second sinks current.  Both switches are connected to a piezo wafer.  When the wafer is tapped, the switches are activated... [Circuit by David Johnson P.E., 2/11/2002]


Divide By 1.5 Counter


Two inexpensive ICs divide a TTL clock signal by 1.5. By following the circuit with another flip/flop, you could also generate a divide by three function…[Hobby Circuit designed by Dave Johnson P.E., 7/06/2000]


Unplugged Appliance Alarm


I received a call from an administrator at a large prison.  He told me that he was having problems with inmates who keep unplugging refrigerators, vending machines and microwave ovens in a commons area.  He wanted a battery-powered device, which could be mount... [Hobby Circuit designed by Dave Johnson P.E., 4/25/2010]


120 VAC / 240 VAC Indicator


Two LEDs indicate if a power line has 120vac or 240vac voltage on it... [Circuit by David A. Johnson P.E., 7/09/2006]


Non-Isolated Off-Line AC to DC Power Supply


This compact efficient circuit can provide up to 100ma of a regulated 5 volts from an AC power source ranging from 20vac to 120vac... [Circuit by David A. Johnson P.E., 7/13/2006]


UL Ground Resistance Tester


UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0.1 ohms.  This resistance must be tested with actual line current in excess or 10 amps.  The circuit shown uses a couple of LEDs to indicate if in fact the resistance is less than 0.1 ohms - modified on july 10, 2006... [Hobby Circuit designed by David A. Johnson P.E., 4/28/2001]


1uS Light Pulse Receiver + Post Amp


This circuit is designed to detect very weak light pulses lasting 1uS. It uses a tuned LC feedback network to provide high sensitivity while giving high ambient light immunity. A post voltage amplifier is included with a gain of about X20. The circuit is described in more detail in the receiver section of my Handbook of Optical Through the Air Communications.  Note: The LF357 op amp is no longer available, this circuit is for reference only.... [Circuit by David A. Johnson P.E., 3/11/1999]


PWM Motor Controller uses a 555 Timer


Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor... [Hobby Circuit designed by Dave Johnson P.E., 2/01/2007]


AC Power Line High/Low Voltage Tester


If you wish to test a line-powered device under both a 15% high and a 15% low voltage condition, you can use the circuit below.  The circuit uses an 18v transformer with a 3 amp rating.  A double pole, double throw toggle switch then switches in the... [Hobby Circuit designed by David Johnson P.E., 3/14/2010]


Xenon Flash Receiver-Pg2


This is Page 2 of the receiver circuit AIR TRANSPARENCY MONITOR, XENON FLASH RECEIVER... [Hobby Circuit designed by David A. Johnson P.E., 6/17/2000]


Line Powered White LED Array


There has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed... [Circuit by David A. Johnson P.E., 2/28/2010]


Logic Controlled 12v DC Motor With Automatic Brake


There are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  This circuit will bring a fast moving DC motor to a stop in seconds.  The braking action is automatically applied whenever DC power is removed... [Hobby Circuit designed by David Johnson P.E., 2/18/2010]


AC Current Controls Hour Meter


Many systems require routine maintenance based on machine operation time.  The circuit below is a simple way to turn on a hour meter whenever AC power is supplied to the machine.  An inexpensive snap-on current transformer from Magnetics Inc, is used to... [Circuit by Dave Johnson P.E., 2/13/2010]


+5v Powered Charge Pump Battery Charger


The circuit below will trickle charge a four cell pack of AA or AAA NiMH batteries.  The circuit draws current from the +5v available a USB connection and pumps about 70ma of current into the battery. This should be enough current to fully charge a pack of... [Circuit by David Johnson P.E., 2/07/2010]


Classic Linear 5v Supply Using 6.3vac Transformer


A classic method for producing a regulated +5v DC supply is shown below.  This circuit consists of an iron core transformer, a bridge rectifier, a filter capacitor and a voltage regulator.  Many people are tempted to use a very popular 6.3v transformer... [Circuit by David Johnson P.E., 2/14/2009]


Beeper indicats Check Engine


When driving down a busy road, you may not notice a “check engine” indicator light that suddenly turns on within the car’s instrument panel.  You could drive for many miles before noticing the light.  To provide an audible indication of trouble, the hobby... [Circuit by David A. Johnson P.E., 7/09/2006]


Energy Harvesting Using a Current Transformer


Energy harvesting is all the rage these days.  With some modern electronics, information from low power sensors can be sent to a distant data collection point using a low power RF transmitter.  To power these remote sensors, various energy sources can be... [Circuit by Dave Johnson P.E., 1/17/2010]


Broad Band 2Mhz Optical Fiber Receiver


If you need more sensitivity than the above circuit this circuit provides about ten times more gain. It too is designed around an inexpensive plastic optical fiber detector... [Hobby Circuit designed by David A. Johnson P.E., 6/09/2000]


Bidirectional Solid State Relay


The circuit below can switch up to 4 amps of current with a peak voltage up to 20v.  It is fully isolated using two inexpensive red LEDs. One LED forms a red light source, which illuminates a second red LED.  The circuit takes advantage of the 1.5v... [Circuit by David Johnson P.E., 5/01/2009]

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Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

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