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Circuits of the Week - June to January 2007
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

06/24/07

Bi-Directional Charge Coupled Powers MOSFET Relay

 

The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line… [Hobby Circuit designed by David A. Johnson P.E., 1999]

06/10/07

1us LED Pulse Driver + Voltage to Frequency Converter

 

This circuit receives the signal from the above amplifier and launches powerful 1uS infrared light pulses from a low cost LED that are frequency modulated by the audio information. The 10KHz center frequency of the pulse stream is low enough so a standard… [Hobby Circuit designed by Dave Johnson P.E., 3/22/99]

06/03/07

50/60Hz Sync Generator-Fully Isolated

 

This circuit will produce a single pulse at the zero voltage cross points of the power line voltage. An opto-coupler provides a very safe 5KV isolation… [Circuit designed by David A. Johnson P.E., 4/2005]

05/27/07

One Amp Current Injector

 

I designed and built this thing many years ago. I published the hobby circuit in the now defunct Radio Elecronics magazine back in 1992. The electronic circuit injects a precise 1 amp of current into any unknown resistor, up to about two ohms. Two alkalineal… [Hobby Circuit designed by Dave Johnson P.E., 1998]

05/20/07

40KHz Light Detector with Sunlight Immunity

 

This hobby circuit below was designed to turn on an external 12v relay, whenever it detects light from a nearby LED light source, modulated at 40KHz to 50KHz. This circuit was originally designed to operate from a fast moving vehicle… [Hobby Circuit designed by David A. Johnson P.E., 1/14/07]

05/13/07

Medium Power 125khz Oscillator

 

This circuit adds even more inverters in parallel to deliver yet more power. The values shown are for 125KHz… [Circuit designed by Dave Johnson P.E., 3/12/02]

05/06/07

Low Power Universal LED Flasher

 

This low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts. The 1.0Hz 10ms LED pulsed current is held to a constant 10ma… [Circuit designed by Dave Johnson P.E., 7/11/06]

04/29/07

Ultra Low Power Latching Relay Circuit

 

The circuit below takes advantage of some inexpensive small super capacitors. The circuit pumps 6 volt pulses into the separate 5 volt latching and unlatching relay coils. A short 25ms pulse is all that is needed to flip the relay states. A third super capacitor is used to supply a higher peak current than a small lithium cell might otherwise be able to supply… [Circuit Solution designed by Dave Johnson P.E., 4/29/07]

04/22/07

Miniature Lighthouse Light Simulator

 

The circuit I came up with is shown below. It uses two dual low power op amps. The first two devices form a classic oscillator circuit whose output is a triangle waveform signal. That signal is routed to a current regulator circuit, which converts the triangle voltage signal to a triangle current signal through the lighthouse LED. A third op amp generates pulses timed so they occur at the peak of the triangle waveform. The result is a LED, which gradually grows brighter, then flashes even brighter before dimming again. This should produce a light, which simulates a rotating lighthouse light… [Circuit Solution designed by Dave Johnson P.E., 5/7/06]

04/15/07

Electrical Device Harvests Earthworms

 

A 120vac or 240vac isolation transformer is used to force earthworms from the ground… [Circuit designed by Dave Johnson P.E., 4/2005]

04/08/07

Automotive Electrical Voltage Indicator

 

This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present… [Circuit designed by Dave Johnson P.E., 12/17/06]

04/01/07

Indicate Electrical Current with this Circuit

 

I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts. The circuit turns on a small LED, whenever it detects current flowing to a remote load… [Hobby Circuit designed by David A. Johnson P.E., 10/16/05]

03/25/07

Wave Power Generator Demo System

 

An inexpensive stepper motor is used as a voltage generator in this wave generator demo… [Circuit designed by David A. Johnson P.E., 3/25/07]

03/18/07

60 Watt Lamp With Auxiliary 14v LED Lamp

 

This circuit controls power to a standard 60 watt lamp plus generates an auxiliary 14v DC supply which can power an automotive style 12 LED array… [Circuit designed by David A. Johnson P.E., 5/1/05]

03/11/07

Simple Wire Security Loop Alarm

 

A wire loop is used to protect valuable objects in this simple alarm circuit. The electronic hobby circuit is powered by a 9v battery. The alarm beeper is activated if the wire loop is severed. The standby current is so low that the 9v battery should l… [Circuit designed by Dave Johnson P.E., 3/1/07]

03/04/07

Fake Car Alarm Light

 

Whenever the car’s ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system… [Circuit designed by David A. Johnson P.E., 10/16/05]

02/25/07

Motion Alarm Using Piezoelectric Device

 

An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm… [Circuit designed by Dave Johnson P.E., 2/25/07]

02/18/07

Hot AC Power Line Indicator

 

The circuit below is designed to detect when a power cable is active (hot) . When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow. It is powered by a 3v CR2032 lithium coin cell. I… [Hobby Circuit designed by David A. Johnson P.E., 5/1/05]

02/11/07

555 Timer Forms Simple PWM Motor Controller

 

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… [Circuit designed by Dave Johnson P.E., 2/1/07]

02/04/07

Low Voltage H-Bridge

 

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 designed by Dave Johnson P.E., 2/4/07]

01/28/07

Does Power Line have 120 VAC or 240 VAC?

 

Two LEDs indicate if a power line has 120vac or 240vac voltage on it… [Circuit designed by Dave Johnson P.E., 1/28/07]

01/14/07

18v AC to DC Power Supply

 

This is a classic linear power supply which produces a regulated 18v, rated at about 1 amp… [Circuit designed by David A. Johnson P.E., 7/9/06]

01/07/07

Laser Used As Vehicular Traffic Counter

 

This is an illustration how a laser could be used to count traffic and measure the speed of each car passing through the sensor area… [Circuit designed by David A. Johnson P.E., 1/7/07]


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