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Circuits of the Week - December to May 2005
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

12/25/05

Peak to Peak 300v Signal Generator

  Merry
Christmas

This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times... [Hobby Circuit designed by Dave Johnson P.E., 6/03/2000]

12/18/05

Time to Dust Indicator

 

I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit completely but in concept it should work... [Circuit by David Johnson P.E., 6/06/2000]

12/11/05

Temperature Sensor With 4 to 20ma Current Loop

 

I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor... [Circuit by David A. Johnson P.E., 7/04/2000]

12/04/05

Protects from Battery Polarity Reversal

 

This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was... [Hobby Circuit designed by David Johnson P.E., 3/09/2002]

11/27/05

3mw Laser Test -20Mhz VCSEL

 

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 David Johnson P.E., 6/17/2000]

11/20/05

Digital noise generator

 

When you need to test an audio circuit with broadband noise, this circuit works great. It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly. I included a level control pot... [Hobby Circuit designed by Dave Johnson P.E., 7/04/2000]

11/13/05

Door Knob Alarm

 

Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms. A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected... [Circuit by David A. Johnson P.E., 5/29/2000]

11/06/05

Light Detectors With Ambient Light Compensation

 

These circuits were taken from a few application notes on infrared remote control devices. They use a current compensation method to separate the modulated light pulses from ambient light. They appear to have limited bandwidth and may only work at the 30K... [Circuit by Dave Johnson P.E., 7/05/2000]

10/30/05

Solid State Relay Requires Only 50ua Drive Current

 

This circuit demands a control current that is 100 times smaller than that needed by a typical optically isolated solid state relays. It is ideal for battery-powered systems. Using a combination of a high current TRIAC and a very sensitive low current SCR... [Circuit by David Johnson P.E., 6/03/2000]

10/23/05

Battery Powered Capacitance Switch

 

A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad.... [Hobby Circuit designed by David Johnson P.E., 10/16/2005]

10/16/05

AC/DC relay from Charge Coupled MOSFET

 

This circuit acts as an AC/DC relay with a rating up to 50 volts peak and up to 10 amps of current.  The differential oscillator supplies voltage to the gates of the two FETs with good isolation will drawing only 1.5ma of current... [Hobby Circuit designed by Dave Johnson P.E., 10/16/2005]

10/09/05

Gated Crystal Oscillator with Very Low Power

 

The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed. The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed... [Hobby Circuit designed by David Johnson P.E., 6/03/2000]

10/02/05

Optical Fiber Receiver-5Mhz Broad Band

 

This circuit is a simple broad band light detector that uses a very inexpensive IC and a PIN photodiode that is packaged for use with plastic optical fibers. It has a bandwidth from 1KHz to over 5MHz.  It is great for experimenting with various modulated... [Hobby Circuit designed by Dave Johnson P.E., 6/04/2000]

09/25/05

Detects Shadow Activated Motion

 

This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes... [Circuit by David Johnson P.E., 8/21/2005]

09/18/05

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…[Circuit by David Johnson P.E., 3/11/1999]

09/11/05

Two Pushbutton Motor Controller

 

Two small pushbutton switches, a few diodes and two relays form a method to control on/off power to a brush motor as well as the motor direction.  The circuit was originally designed for a motorized lifting platform... [Circuit by David A. Johnson P.E., 9/11/2005]

09/04/05

Shadow activated (or hand wave) motion detector

 

The circuit below works quite well in typical indoor room lighting.  I would not recommend its use in direct sunlight.  Two small PIN photodiodes positioned about one inch apart form a shadow detector.  With no shadow cast on the devices, both devices produce nearly identical current levels.… [Circuit Solution designed by David A. Johnson P.E., 5/1/06]... [Circuit Solution by Dave Johnson P.E., 8/21/2005]

08/28/05

Motor Speed Regulator

 

This circuit regulates the speed of a small drill motor I use for PC board work. It is much handier for delicate work than a larger AC powered tool. The tool I have came with a useless 9 volt AC adapter. The motor would whine at high RPMs unloaded, but would slow to a crawl when loaded. This circuit solves the problem.Designed by Andrew R. Morris  ... [Designed by Andy Morris, 8/28/2005]

08/21/05

1.5v LED Flasher Version A

 

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... [Hobby Circuit designed by David A. Johnson P.E., 6/03/2000]

08/14/05

CMOS Oscillator, Draws Only 0.5ua

 

If truly low power oscillators interest you, this circuit draws a mere 2 microwatts (500nA) from a 6v battery. It uses a very inexpensive C-MOS IC to produce a frequency of 2Hz. However, by changing the component values you can push it to 300Hz... [Hobby Circuit designed by Dave Johnson P.E., 6/03/2000]

08/07/05

SSR Requires Ultra Low Control Current

 

Most solid state relays require at least 5ma and often more input control current, to fully turn on the device.  But such current levels often force battery powered circuits to use excessively large batteries.  The relay hobby circuit shown below demands only 50uA of input current... [Hobby Circuit designed by David Johnson P.E., 6/03/2000]

07/31/05

Solid State Touch Activated Switch

 

It does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch... [Hobby Circuit designed by Dave Johnson P.E., 6/03/2000]

07/24/05

DC Motor Drive with Auto Brake

 

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... [Circuit by David A. Johnson P.E., 9/25/2004]

07/17/05

9v Powered Xenon Photoflash Controller

 

This 9v battery powered circuit is designed for remote control flash needs. A charge control circuit turns off the high voltage generator when the photoflash capacitor is fully charged. A neon lamp is included to indicate when the system is ready to flash... [Circuit by David Johnson P.E., 6/03/2000]

07/10/05

Star Trek Doorbell

 

In the Star Trek “Next Generation” TV series, the doorbell outside the private quarters of a crew member makes a particular “beep-boop” sound.  The 3v battery powered circuit below tries to simulate this sound. The circuit uses one 74HCT74 dual D flip/flop... [Circuit by David A. Johnson P.E., 10/12/2001]

07/03/05

9V Pulse Generator

 

It is hard to design a pulse generator that produces clean logic pulses while drawing very low current. This circuit is designed to produce short 2mS pulses at a rate of one per second while drawing only 1 microamp from a 9 volt battery... [Circuit by Dave Johnson P.E., 6/03/2000]

06/26/05

200Mhz-400Mhz Voltage Controlled Oscillator (VCO)

 

If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency... [Circuit by David Johnson P.E., 3/19/1999]

06/19/05

1.5V Touch Activated Switch

 

A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad.... [Circuit by Dave Johnson P.E., 1/18/2002]

06/12/05

Fluorescent Lamp Night Light Needs Only 1 Watt

 

If you are tired of replacing small night light lamps, try this circuit. The line powered circuit uses a long life cold cathode fluorescent lamp. A simple charge pump technique runs the lamp without any transformer... [Hobby Circuit designed by David Johnson P.E., 3/26/1999]

06/05/05

Low Power 100khz Light Receiver

 

By starving a high speed logic inverter for current, this circuit can produce a sensitive 100KHz light receiver circuit, which is immune to ambient light, but only drawing 100 micro amps from a 3 volt supply... [Circuit by David A. Johnson P.E., 4/17/2005]

05/29/05

Line Powered 60hz Clock Generator

 

This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The opto-isolator used provides 5000 volts of isolation between the power line and the logic side of the circuit... [Circuit by David Johnson P.E., 2/23/1999]

05/22/05

Constant Current LED Driver

 

Bob Pease from National Semiconductor came up with this circuit and I have used it many times.  It maintains a constant current through one or more LEDs.  A single resistor controls the desired current.... [Hobby Circuit designed by David A. Johnson P.E., 11/25/2004]

05/15/05

Power Loss Beeper

 

For some medical equipment it is important for an operator when power is lost to the machine. The beeper is powered from a 9v battery and requires the machine to have a power switch with a third set of contacts... [Circuit by Dave Johnson P.E., 3/26/1999]

05/08/05

Hour Meter triggered by Machine Vibration

 

This hobby circuit allows an off-the-shelf battery powered digital hour meter to be turned on and off, according to a machine's operation, without requiring a direct electrical connection to the machine... [Hobby Circuit designed by David Johnson P.E., 12/26/1998]

05/01/05

3 Volt Low Battery Voltage Flasher

 

This circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment... [Circuit by David A. Johnson P.E., 12/24/1998]

 


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


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