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Circuits of the Week - December to July 2013
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

12/29/13

Machine Vibration Triggers Hour Meter

 

This 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. Machine vibrations are detected by an off-the-shelf piezo… [Circuit designed by Dave Johnson P.E., 1998]

12/22/13

Tester for Modulated Laser Diode

 

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… [Hobby Circuit designed by David A. Johnson P.E., 1998]

12/15/13 X100 Scope Probe
  Often a typical X10 oscilloscope probe will produce large measurement errors and will influence the circuit operation.  To reduce the effect such a probe has on the circuit, I reach for my X100 scope probe, with its 100M impedance.  This probe is a commercially made device but if you want to make one, it is not hard to do.… [Circuit designed by Dave Johnson P.E. for DC Magazine, 5/1/10]

12/08/13

LED Camping Lantern with Dimmer

 

A while back I received an email from a Discover Circuits visitor who wanted to build his own LED camping lantern. He wanted to use a single bright LED powered by 3 large alkaline D cells. He also wanted to be able to dim the light intensity down to a low night light level, to extend the battery life. The circuit below performs this task… [Hobby Circuit designed by Dave Johnson P.E., 12/8/13]

12/01/13

300v Peak to Peak Signal Generator

 

This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times… [Circuit designed by Dave Johnson P.E., 3/1/02]

11/24/13

Piezoelectric Device used for Motion Alarm

 

An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm… [Hobby Circuit designed by David A. Johnson P.E., 5/1/09]

11/17/13

125Khz Oscillator from CMOS Inverters

 

This circuit inverts the LC components so the inductor is grounded. Two inverters are needed to produce the needed oscillation. Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies… [Circuit designed by Dave Johnson P.E., 3/12/02]

11/10/13

AC Current Indicator Light

 

This circuit could be wired into a 120vac power line, which feeds power to any load, ranging from 40 watts to 250 watts. It will turn on a LED light whenever current is being drawn by a load. It is especially useful for remote lights, where you may not … [Hobby Circuit designed by David A. Johnson P.E., 2012]

11/03/13

Switch activated by Piezoelectric Vibration

 

An inexpensive piezoelectric wafer is used to detect vibration and when the vibration is sufficient a switch is activated… [Hobby Circuit designed by Dave Johnson P.E., 8/27/06]

10/27/13

Indicates when it is Time to Dust

 

I have used the circuit below for many different applications, which require ultra low power drain. It uses a single CA4013 flip/flop. One section forms a pulse generator. The generator produces 100uS pulses at a rate of about 1 per second… [Circuit Solution designed by Dave Johnson P.E., 5/7/06]

10/20/13

Battery Charging Current Indicator

 

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 Dave Johnson P.E., 6/1/05]

10/13/13

Detect Clear Fluid

 

This circuit detects when a clear fluid is inside a piece of clear plastic tubing. It can be used for fluid level control and monitoring… [Hobby Circuit designed by David A. Johnson P.E., May 2012]

10/06/13

Broken Solar Panels

 

As illustrated below, one way to salvage a large number of broken solar cells is to wire them in parallel, not in the more conventional series connection. Broken cells of various sizes and shapes are grouped together into panels of about one quarter to on… [Hobby Circuit designed by David A. Johnson P.E., 1/1/12]

09/29/13

Monitor Clear Fluids

 

This circuit detects when a clear fluid is inside a piece of clear plastic tubing. It can be used for fluid level control and monitoring… [Circuit designed by Dave Johnson P.E., May 2012]

09/22/13

1W White LED Night Light

 

This simple circuit is designed to plug into a standard AC electrical outlet. It uses four super bright white light emitting diodes (LED) in conjunction with a capacitor coupled full wave rectifier circuit. The LEDs are mounted in a box and are angled sli… [Hobby Circuit designed by David A. Johnson P.E., 11/06/08]

09/15/13

Signal Period to Voltage Converter

 

This circuit converts a square wave input signal into a voltage. But, the voltage produced is proportional to the time between edges (period) of the signal, not the frequency. The range is from 100uS to to 10mS, which produces a voltage from 100mV to 10 volts. Other scale factors are also possible. The circuit is powered from single 15v supply and uses inexpensive parts. It is great when a signal's period instead of its frequency needs to be monitored. Published in Electronic Design, Sept 27, 1990… [Hobby Circuit designed by David A. Johnson P.E., 5/1/10]

09/08/13

Alarm Sounds when Phone Line is Cut

 

Burglars, rapists and other criminals will often cut a phone line before they break into a home. The cut phone line will prevent many alarm systems from alerting the police. The battery powered circuit below will sound an alarm when the unit… [Hobby Circuit designed by Dave Johnson P.E., 10/16/05]

09/01/13

Modified Shake to Charge Flashlight

 

The complete schematic for this device is shown below. A few things should be pointed out. First, they use some very cheap 1N4001 diodes in the bridge rectifier circuit instead more efficient Schottky diodes. They also use a small 0.5 Farad cap with a … [Hobby Circuit designed by David A. Johnson P.E., 1/1/12]

08/25/13

100Khz Low Power 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 microamps from a 3 volt supply… [Hobby Circuit designed by David A. Johnson P.E., 12/17/06]

08/18/13

1.5v LED Flasher Version A

 

Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5 volt AA alkaline battery cell. The circuit uses a charge pump technique to provide… [Circuit designed by David A. Johnson P.E., 6/5/00]

08/11/13

Sound Triggered Night Light

 

A while back, I received a schematic from a guy by the name of Karl. He described a situation he and his wife found themselves in aboard a cruise ship in the Caribbean. They were staying in a room toward the inside of the ship, which did not have any port holes, windows or a balcony. At any time of the day, when the room lights were turned off, they found themselves in absolute total darkness. The complete lack of any light was a bit unnerving. They didn’t have a night light and could not find one for sale at the ship’s stores… [Circuit designed by Dave Johnson P.E., 8/4/13]

08/04/13

Clip-on AC Current Indicator Circuit

 

Several times over the last few years I have received calls from people looking for a simple circuit that would tell them when a sump pump or water well pump motor was running. These people told me that the electrical circuits that turn on and off the mo… [Hobby Circuit designed by Dave Johnson P.E., 1/1/12]

07/28/13

40Khz Precision Triangle Generator

 

This circuit generates a precision 40KHz triangle waveform… [Hobby Circuit designed by David A. Johnson P.E., 12/10/06]

07/21/13

Expanded Scale 12v Battery Voltage Monitor

 

The circuit below expands the battery voltage monitoring scale for a 12v battery so a more accurate voltage reading can be made. The numbers printed onto the face of a standard 0v to 5v meter are changed so the scale ranges from 10v to 15v. http://archil… [Circuit designed by Dave Johnson P.E., 10/16/05]

07/14/13

Generate Short Delayed Pulse

 

This circuit generates a short 10ms pulse 15 minutes after a “start” pushbutton switch is activated… [Hobby Circuit designed by David A. Johnson P.E., 10/16/05]

07/07/13

Machine 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… [Hobby Circuit designed by Dave Johnson P.E., 1998]


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