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Circuits of the Week - June to January 2006
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

06/25/06

6v NMH/NiCd Battery Tester

 

I designed this circuit to test rechargeable six volt battery packs under constant current conditions. As designed, the circuit applies a 10 amp load to the battery pack. A heat sink must be used on the main power transistor… [Circuit designed by David A. Johnson P.E., 12/12/04]

06/18/06

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 designed by Dave Johnson P.E., 12/1/02]

06/11/06

Exciter Circuit-12v Touch Switch

 

This circuit generates a 20KHz pseudo sine wave signal that can power approximately 50 remote touch activated switch circuits. This hobby circuit can support a cable length of approximately 2500 feet. A typical remote switch circuit is also shown as... [Hobby Circuit designed by Dave Johnson P.E., 4/2005]

05/28/06

Pushbutton Switch works through Glass

 

This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass. Pushing the button moves a magnet near the reed relay, closing the relay contacts… [Circuit designed by David A. Johnson P.E., 2001]

05/21/06

Pop Free Microphone On/Off Switch Circuit

 

This circuit uses a simple technique to eliminate the usual “pop” sound when an electret type microphone is switched on or off. The circuit is completely passive and will work on dynamic and electret type microphones … [Circuit designed by Dave Johnson P.E., 2/15/02]

05/14/06

Really Loud Output Beeper Circuit

 

I you need a real loud beeper, this circuit delivers about 110db (12 inches away) from a 9v battery using a single inexpensive C-MOS IC. An off-the-shelf piezoelectric beeping device is driven at resonance to insure maximum efficiency. By changing the control IC to a 74AC14, the same circuit can operate from 3v and 1.5v batteries... [Hobby Circuit designed by Dave Johnson P.E., Published in Electronic Design, Aug 5, 1993]

05/07/06

Honeybee Counter

 

I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees. The circuit advances an electronic counting… [Circuit designed by Dave Johnson P.E., 1998]

04/30/06

DC Motor Brake

 

When the power switch is closed, the gate voltage of Q1 turns Q1 on. The drain of Q1 swings low, turning off Q2. Current flows freely into the DC motor with only one diode drop from D2. When the power switch is open. The gate voltage of Q1 swings low, causing the drain of Q1 to swing high. This turns on the transistor Q2. With Q2 on, the resistor R3 is switched in parallel with the motor, producing a braking action. The value of R3 can be selected for the desired braking action. A zero ohm resistance will produce the fastest slow down of the motor. The circuit below is good for about 500ma of motor current. A Q2 transistor with a lower on resistance would be needed for bigger motors. Also, D2 would need to increase in size… [Circuit Solution designed by Dave Johnson P.E., 5/1/05]

04/16/06

Alarm Sounds At Freezing Temperatures

 

This electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F) . A 9v battery powers the hobby circuit. The average 9ua current is so low that the battery should last for many years… [Hobby Circuit designed by David A. Johnson P.E., 7/11/06]

04/09/06

Ultra Low Power Astable Multivibrator

 

Taking advantage of some new voltage comparators, this circuit can produce a nice square wave signal while drawing only 1.6 microamps. With the inclusion of a diode, the circuit can also produce short pulses instead of a square wave signal… [Circuit designed by Dave Johnson P.E., 4/2005]

03/26/06

Two Line Telephone Line Status Indicator

 

Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive… [Circuit designed by David A Johnson P.E., 1998]

03/19/06

Cascode Light Receiver Circuit

 

This page provides a detailed explanation of how the modified cascode light receiver circuit operates. The cascode technique in conjunction with an inductive load provides very high current to voltage conversion as well as very high speed… [Circuit designed by Dave Johnson P.E., 2/15/02]

03/12/06

Advertising Badge with Flashing LED-Version 2

 

This circuit uses a CD4013 dual D Flip/Flop IC. A single lithium battery will provide months of continuous LED flashing. It also has a tiny push-button switch to turn on and off the light flashing… [Circuit designed by Dave Johnson P.E., 3/26/02]

03/05/06

Tester for Brown Out Voltage

 

I used this circuit years ago to test AC line powered devices under 95vac line voltage conditions. It has a rating of 250 watts… [Circuit designed by Dave Johnson P.E., 7/12/06]

02/26/06

Piezoelectric Beeper that is Very Loud

 

This circuit generates a continuous tone instead of a pulsing one for your hobby project. As seen in the schematic, the hobby circuit delivers about 110db (12 inches away) from a 9v to 12v source using a single inexpensive C-MOS IC. An off-the-shelf piezo… [Hobby Circuit designed by Dave Johnson P.E., 6/3/00]

02/19/06

Fluid Level Monitor

 

This circuit was originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid. Two custom insulated metal tubes form a capacitor plate. The capacitance between the two tubes increases as the level of the liquid rises… [Circuit designed by David A. Johnson P.E., 6/13/00]

02/12/06

Xenon Lamp Flash Detector Amplifier

 

This circuit has a very low standby current requirement yet has very high sensitivity toward the light flashes from a xenon lamp. When connected to a flip/flop it can serve as an on on/off Controller … [Circuit designed by David A. Johnson P.E., 4/2005]

02/05/06

Low Value Capacitance Meter

 

This circuit was originally designed to measure the volume of fluid inside a medical syringe. As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads… [Circuit designed by David A. Johnson P.E., 2/6/06]

01/29/06

Modulated Laser Diode Tester

 

This circuit can either be used to test laser diodes or as a general purpose modulated light source. The circuit has an adjustable diode threshold current and an adjustable modulation frequency. The frequency can be adjusted from below 30KHz to above 50MH… [Circuit designed by David A. Johnson P.E., 1998]

01/22/06

Micropower 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. The circuit… [Circuit designed by David A Johnson P.E., 1998]

01/15/06

Human Traffic Footstep Detector Preamp

 

This circuit uses a surplus geophone to detect human footsteps from 100 feet away. It was designed for monitoring the Mexico/USA border. This preamp part of the system draws about 50 microamps from a 12 volt supply… [Circuit designed by David A. Johnson P.E., 4/2005]

01/08/06

Unplugged Power Cord Alarm

 

Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries. However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries. So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time… [Circuit designed by Dave Johnson P.E., 1998]

01/08/06

Optical Interrupter Draws Microamps

 

This circuit is great for battery-powered systems that use slotted type optical interrupters. It draws only 10uA from a 3v battery that should allow up to 5 years of operation from a lithium battery… [Hobby Circuit designed by Dave Johnson P.E., 6/4/00]

01/01/06

Caps Provide Voltage Boost to Series Regulator

 

This circuit adds some capacitors and diodes to a traditional transformer type series regulator circuit to extend the normal operating range. It can insure regulation during low line voltage conditions or it can squeeze a few more watts out of a plug-in-the-wall power adapter power supply… [Circuit designed by Dave Johnson P.E., 1998]


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