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Circuits of the Week - January to December 2015
Last Updated on: 11/20/2015 01:24 PM

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

11/22/15

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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  05/07/06]

11/15/15

Doggie Water Dispenser Alarm -  I have two Beagle dogs.  They drink a lot of water; they go through about 3 gallons a week.  They have two water dispensers.  One is on the inside and second unit on the outside of my house.  Often, I forget to fill one of their two jugs and discover them completely empty.  I do worry that my dogs might get dehydrated if I ever forget to fill both of their containers . . . [Circuit by Dave Johnson P.E.,  06/04/12]

11/01/15

Flashing LED Advertising Badge #1 -  I have seen numerous flashing light badges at trade shows and conventions. They are often handed out as gifts to promote some business. The devices often use inefficient circuits, which cause the battery power source to be quickly depleted . . . [Hobby Circuit designed by David Johnson P.E.,  03/26/02]

10/25/15

Three-Volt Powered Super Bright LED Flasher -  I have posted several kinds of LED flashers over the years. This is yet one more flasher, designed to flash any high power LED of any color.  It hits the LED with a 25ms 250ma pulse once every 2 seconds. This works out to an average current about 3ma.  It . . . [Hobby Circuit designed by David Johnson P.E.,  04/22/09]

10/18/15

3-Minute Closet Light -  I have a coat closet by my front door.  The thing is very dark at night and really needs some kind of illumination inside.  I could hire an electrician to install a light in the closet ceiling and then wire it to a toggle switch outside the door but that would cost me quite a bit of money . . . [Circuit by David Johnson P.E.,  12/25/11]

10/11/15

RFID Test Circuit -  I designed this test the concept of using light techniques to send identification data instead of RF. A more detailed discussion on this scheme can be found in the Imagineered new products section . . . [Hobby Circuit designed by David Johnson P.E.,  02/11/02]

10/04/15

Xenon Flash Receiver-Air Transparancy Monitor -  I designed this receiver circuit many years ago to monitor the quality of a mile long column of air for future optical communications experiments. The transmitter system (circuit 72 below) uses a powerful xenon flash in conjunction with a large 12 inch . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/17/00]

09/27/15

Improve the quality of standard TV images -  I designed this circuit many years ago, based on the claims that the technique would improve the quality of standard TV images. The circuit adds information to the edges of the objects and was reported to bring out more detail. After building and testing . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/08/00]

09/13/15

RS232 Data Bus Status Monitor -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volt . . . [Circuit by David A. Johnson P.E.,  12/09/07]

09/06/15

0VAC to 280VAC Variable Isolated AC Voltage -  I designed and built this circuit about 25 years ago. It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC. It provides complete isolation from the power line. It uses two 1:1 isolation transformers that are wired in parallel . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/08/00]

08/30/15

4 to 20ma Current Loop Senses Temperature -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/04/00]

08/23/15

Slotted Opto-Sensor used in 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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/08/00]
08/16/15 Battery Amp-hour Capacity Tester -  I bought some lithium ion rechargeable batteries a while back. I was planning on using them to modify some solar powered LED spot lights.  What I like about these new batteries is that they are the same size as a standard 1.5v alkaline AA cell . . . [Circuit by Dave Johnson P.E.,  02/05/12]

08/09/15

3-Minute Closet Light #2 -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuit’s standby current is only a few microamps.  A set of fresh batteries should last at least 200 light applications.  The circuit uses a Schmitt trigger inverter and two transistors.  When the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged . . . [Circuit by David Johnson P.E.,  11/14/10]

08/02/15

Model Train Lighthouse Flasher -  HO train sets often have authentic looking scale model homes and buildings.  A while back someone asked me to design a flashing LED light, which he could mount inside a model lighthouse and have it operate so it would appear to rotate and flash.  I designed a working circuit but I was never pleased with the results.  I’m still not 100% pleased but the revised circuit below seems to operate a bit better than the older circuit.… [Hobby Circuit designed by Dave Johnson P.E., May 2012] . . . [Hobby Circuit designed by David Johnson P.E.,  12/20/12]

07/26/15

Octillator with Ultra Low Current -  Here is a challenge.  Design an astable oscillator which draws only a few nanoamps of current from a +3v supply.  I gave this some thought and came up with the circuit below.  I used some pretty standard parts except for three surface mounted 1000M resist . . . [Hobby Circuit designed by David A. Johnson P.E.,  03/08/09]

07/19/15

Very Loud 3v Powered Beeper -  Getting a high sound intensity from a piezoelectric type beeper is not easy when the available DC supply is only 3v.  The circuit below is not only efficient but produces a very intense sound.  The circuit combines a voltage boost section with a resonant  . . . [Circuit by Dave Johnson P.E.,  02/18/09]

07/12/15

One-Watt 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 slightly . . . [Hobby Circuit designed by David A. Johnson P.E.,  11/06/08]

07/05/15

125Khz Ultra Pure Sine Wave Signal Source -  For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed.  The circuit shown on this page produces a 10-volt peak-to-peak signal into a 50-ohm load, with a distortion of only 0.01% . . . [Hobby Circuit designed by David Johnson P.E.,  02/11/02]

06/28/15

Transistor-Switch detects Audio Signal -  For some audio systems it is desirable to have an automatic switch circuit turn on other devices, such as an Amplifier, if an audio signal is detected on one line.  The hobby circuit below will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.   The switch could be used to turn on a relay, routing the signal to where it is needed.  A single 3v lithium cell will power the electronic circuit for about 5 years . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/09/06]

06/21/15

Detector/Switch for Audio Signal -  For some audio systems it is desirable to have an automatic switch circuit turn on other devices, such as an Amplifier, if an audio signal is detected on one line.  The hobby circuit below will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.   The switch could be used to turn on a relay, routing the signal to where it is needed.  A single 3v lithium cell will power the electronic circuit for about 5 years . . . [Hobby Circuit designed by David Johnson P.E.,  07/09/06]

06/14/15

A Current Transformer used to Harvest Energy -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/17/10]

06/07/15

Short Range Reflective Object Sensor -  Drawing only 30uA from a 3v supply, this circuit will detect a human finger with a range of about 1 inch.  The sensor uses an inexpensive infrared LED and a matching photo diode . . . [Circuit by Dave Johnson P.E.,  07/09/06]

05/31/15

Homemade Corner Cube Reflector -  Corner cubes are optical devices which have a unique property.  Light sent into the front face will be sent back to the source in a parallel path.  As long as light can strike the reflective surfaces the it will always be sent back to the source.  Tiny co . . . [Hobby Circuit designed by Dave Johnson P.E.,  10/18/06]

05/24/15

Laptop Power Supply -  Concept Only.  I have a big screen HP laptop computer.  The large brick size AC to DC power supply is rated at 19.2v and 9.5 Amps, which is about 180 watts. I’d like to be able to use the thing in my car.  I looked into a 12v car adapter for it but never really found one that I liked. . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/26/09]

05/17/15

Demo of a Wave Power Generator System -  An inexpensive stepper motor is used as a voltage generator in this wave generator demo. . . . [Hobby Circuit designed by Dave Johnson P.E.,  03/26/07]

05/10/15

Switch activated by Piezo Vibration -  An inexpensive piezo wafer is used to detect vibration and when the vibration is sufficient a switch is activated . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/09/06]

05/03/15

0.5v Negative Supply -  Although not very efficient, this simple circuit, consisting of two LEDs and a photo diode, generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op Amp circuits, . . . [Circuit by Dave Johnson P.E.,  07/13/06]

04/26/15

Ultrasound Receiver-40Khz -  A X100 transistor Amplifier is followed by a zero cross detector circuit, using a voltage comparator.  The output is a TTL logic signal, corresponding to the received 40KHz signal . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/29/06]

04/19/15

Wire Loop Security Alarm -  A wire is looped through various objects which are to be monitored.  The loop wire is typically an aircraft cable but could also be any insulated stranded wire.  The loop is attached to a table or desk.  Should the loop be cut, the alarm is sounded . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/15/04]

04/12/15

Ocean Wave Power Generator Demo Unit -  A while back, a Discover Circuits visitor wanted a simply way to demonstrate how electricity could be generated from the up and down movement of ocean waves. The system was to be part of a science fair project, showing different renewable energy sources . . . [Hobby Circuit designed by David Johnson P.E.,  01/01/12]

04/05/15

24v NiMH Battery Charger Using a 12v Solar Panel  -  A while back I received an email from a guy in the UK.  He wanted to use a small solar panel, designed to charge 12v lead acid batteries, but use it to charge a 24v battery pack.  His 24v battery pack used 20 AA size NiMH cells.  He went on to explain that his 20 cell NiMH battery pack was used very infrequently . . . [Hobby Circuit designed by David Johnson P.E.,  10/12/11]

03/29/15

Monitor Water Seepage -  A while back I received a request from a company who needed a water seepage detector.  They wanted a device that ran on 24vac and detected water using a fully isolated circuit.  They wanted a circuit which switched off 24vac to a load when water was detected . . . [Hobby Circuit designed by David A. Johnson P.E.,  01/16/11]

03/22/15

10 LED Sequential Flasher using Low Powr -  A while back I posted a flasher circuit which flashed 10 LEDs sequentially.  That circuit was powered by four AA alkaline cells.  The circuit below operates much the same way but has been modified to run from a single 3v CR2032 lithium coin cell . . . [Circuit by Dave Johnson P.E.,  04/17/11]

03/15/15

Thermostat for 12v Cooling Fan -  This circuit will turn on a 12v DC powered cooling fan when the air temperature reaches a certain high temperature and will keep the fan turned on until the temperature drops below a second lower level.  Both the high and low temperatures are both adjustable . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/06/11]

03/08/15

Crystal Controlled 1KHz Signal Generator -  A while back I got an email from a Discover Circuits visitor.  He needed a way to calibrate a RPM display for a big diesel engine.  The engine had a tachometer output which produced 12 pulses per rotation with an Amplitude of about 5v RMS.  The full scale reading on the engine’s RPM speed display dial was 5,000 . . . [Circuit by David Johnson P.E.,  05/01/12]

03/01/15

CW & CCW Alternating Motor Driver -  A while back a company needed a motor controller for a custom door latching system.  The system used a small brush motor with a speed reduction gear to both latch and unlatch the door.  When pulsed for about 250ms in the clockwise direction, the motor would unlatch the door . . . [Hobby Circuit designed by Dave Johnson P.E.,  09/05/10]

02/22/15

36-Hour Watchdog Timer -  A watchdog timer is often used in computer systems to detect when a computer is hung up and is no longer running properly. If it does become locked up and is not able to supply a reset pulse to the circuit within a defined time frame the timer times out a . . . [Circuit by David Johnson P.E.,  04/11/10]

02/15/15

Lithium Ion Solar Battery Charger-#2 -  A single lithium ion battery cell needs 4.2v from a current source to insure it is fully charged.  A solar panel with just enough individual cells wired in series to produce the needed voltage would be more efficient than one with more cells for a given surface area.  If you divide 4.2 by eight you come up with a figure of 0.525 volts . . . [Hobby Circuit designed by Dave Johnson P.E.,  05/22/13]

02/08/15

Eight-Solar Cell Lithium Ion Battery Charger Version 3 -  A single lithium ion battery cell needs 4.2v from a current source to insure it is fully charged.  A solar panel with just enough individual cells wired in series to produce the needed voltage would be more efficient than one with more cells for a given surface area.  If you divide 4.2 by eight you come up with a figure of 0.525 volts . . . [Circuit by David A. Johnson P.E.,  05/21/13]

02/01/15

Momentary 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. . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/18/02]

01/25/15

Make a Geophone to Detect Foot Steps -  A home made geophone is made from a strong magnet, a coil of wire and a rubber band. The circuit is sensitive enough to detect the vibrations of a nearby foot stomp.  It could be used as an earthquake detector. . . . [Circuit by Dave Johnson P.E.,  06/02/06]

01/18/15

Press and Hold Latching Circuit -  A Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output . . . [Hobby Circuit designed by David Johnson P.E.,  06/30/13]

01/11/15

Water Pump controlled by Solar Power -  A Discover Circuits visitor had a problem.  He needed a simple on/off controller for his solar powered water pump.  His system used two 12v 50 watt solar panels wired in series.  The power from the solar panels drove a submerged water pump.  However, during . . . [Hobby Circuit designed by David Johnson P.E.,  10/03/10]

01/04/15

LED Array powered by 24 VAC -  24vac is a popular voltage.  It is often used in low voltage lighting systems and industrial controls.  It is much less dangerous than 120vac/240vac line voltages.  This hobby circuit below is one method to efficiently power a cluster of 7 white LEDs from 24vac. . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/19/09]

 

 


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