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Circuits of the Week - July - December 2014
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

12/28/14

120 VAC Touch Switch

 

This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load… [Circuit designed by David A. Johnson P.E., 5/25/06]

12/21/14

Twelve-Volt Light/Dark Switch

 

At night, this circuit will route current to a 12v lamp, turning it on… [Circuit designed by David A. Johnson P.E., 7/9/06]

12/14/14

Battery (12v) Load Cutout Circuit

 

Lead-acid batteries should not be discharged below a certain point if they are to last.  Also, you don’t want certain 12v powered devices, which might be plugged into a car’s cigarette lighter outlet, to drain the car battery down to a point where the car… [Hobby Circuit designed by David A. Johnson P.E., 7/30/06]

12/07/14

LED Array powered by 24 VAC

 

24v DC is a very popular voltage used in industrial settings.  This hobby circuit below was designed to accept four different 24v DC alarm input signals, which are then used to drive a single low power beeper… [Hobby Circuit designed by David A. Johnson P.E., 5/1/10]

11/30/14

10Mhz To 20Mhz Light Receiver

 

Light power to volts conversion = APPROX. 15mV per microwatt at 850nM … [Circuit designed by David A. Johnson P.E., 4/2005]

11/23/14

Garage Door Closer

 

This circuit automatically closes the garage door after it is left open for some period of time. A magnet plus reed relay combination could be used to detect the open condition of the garage door.… [Circuit designed by Dave Johnson P.E. for DC Magazine, 4/26/11]

11/16/14

Micro Power 40Khz Burst Laser Diode Driver

 

Some laser tag or simulated combat games can use this circuit to send short bursts of modulated laser light at the opponent's vest, equipped with a matching light receiver. The circuit operates from three 1.5v cells (4.5v) that should provide enough energy… [Circuit designed by Dave Johnson P.E., 5/1/11]

11/09/14

Piezo Tap Relay - Circuit

 

This circuit uses a flat piezoelectric wafer, glued inside a plastic box, as a finger tap sensor. With each tap of a finger to the box holding the wafer, the circuit turns on and off AC or DC power to an external device. The circuit is powered by a 9v b… [Hobby Circuit designed by David A. Johnson P.E., 11/7/07]

11/02/14

Active Low Pass Filter Designs

 

This is a collection of inverting and non-inverting active low pass filter circuits.  I included one, two three, four and six pole filter circuits.  You can change the component value ratios shown to achive any frequency cut-off you may need… [Circuit designed by David A. Johnson P.E., 12/10/00]

10/26/14 3v Sweeping Siren Alarm
  A while back I was challenged by a visitor to the website.  He needed a very loud sweeping siren type audio sound generator powered by 3v.  He tried some of the commercial sirens but they were not very loud when powered by 3v.  He also said that those… [Circuit designed by Dave Johnson P.E., 6/29/08]

10/19/14

12kv High Voltage Generator

 

The hobby circuit below uses an unusual method to generate about 12,000 volts with about 5uA of current. Two SCRs form two pulse generator circuits. The two SCRs discharge a 0.047uF a 400v capacitor through a xenon lamp trigger coil at 120 times a secon… [Hobby Circuit designed by Dave Johnson P.E., 2012]

10/12/14

2uS Light Pulse Receiver

 

Although the LF357 is an obsolete part, this circuit gives you an idea how to build a sensitive modulated light detector with high ambient light immunity. The first section uses a 100mH inductor as an efficient photodiode current to voltage conversion ci… [Circuit designed by David A. Johnson P.E., 2012]

09/28/14

Laser/LED Light Output Intensity Meter

 

This circuit uses a large 1cm X 1cm silicon PIN photo diode and a transimpedance amplifier to measure the light power output of infrared and visible LEDs and laser diodes. It can be modified to produce almost any milliwatts to volts scale factor. It can b… [Circuit designed by Dave Johnson P.E., 10/16/05]

09/14/14

High Power Touch Switch Exciter Circuit

 

If you have hundreds of touch switches that need an excitation signal, then this circuit is what you need. Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power… [Circuit designed by David A. Johnson P.E., 4/2005]

08/31/14

Isolated AC Current Monitor Circuit

 

The hobby circuit below shows how a small current transformer from Magnetek can be used to monitor AC current to a load. The AC voltage developed at the secondary of the transformer can be scaled so it can be read by any digital multimeter. The transformer… [Hobby Circuit designed by Dave Johnson P.E., May 2012]

08/24/14

LED Flasher Universal 3v

 

The electronic circuit below will flash any LED color with fixed current pulses powered by a 3v battery. It uses a charge pump approach, which routes a constant current pulse through the LED, regardless of the LED voltage requirement. Using this approach… [Hobby Circuit designed by David A. Johnson P.E., May 2012]

08/17/14

1 Watt Fluorescent Lamp Night Light

 

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

08/10/14

Freeze Alarm

 

I chose an accurate thermistor from Keystone as the temperature sensor for this circuit. This device has a very specific resistance at a particular temperature. According to the data sheet for the thermistor, the device will have a resistance of 361K at zero degrees C, which is the freezing point of water. The thermistor is wired into a simple bridge circuit, which uses 1% resistors. The bridge is connected to a very low power voltage comparator. The circuit forms a switch circuit, which changes state, when the resistance of the thermistor reaches a certain value. At zero degrees C the voltage at the non-inverting input of the comparator exceeds… [Circuit Solution designed by David A. Johnson P.E., 5/7/06]

08/05/14

Light Intensity Monitor

 

For an on-going consulting project, I had to determine the light output decay time of different fluorescent lamps. I wanted to know how fast the light from a lamp dropped to a low level, after current was interrupted in the lamp. I used a high voltage tra… [Hobby Circuit designed by Dave Johnson P.E., 4/2005]

07/27/14

Solar Insulation Monitor

 

Owners of photovoltaic solar panels often like to monitor how bright the sunshine is. They can use this information to gage how well their solar panels are doing. On a typical clear day, the sun energy at sea level is about 1000 watts per square meter… [Hobby Circuit designed by David A. Johnson P.E., May 2012]

07/20/14

50Mhz Broad Band Optical Fiber Receiver Version A

 

If the above circuit it still too slow, you can try this circuit. What it lacks in sensitivity it makes up for in speed. The circuit attaches a plastic fiber optic PIN photodiode assembly to a small box containing a small 3v battery and a standard… [Circuit designed by David A. Johnson P.E., 1998]

07/13/14

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

07/06/14

Cheap Close-Up Camera Lens

 

I often use my digital camera to take photos of some electronic projects. At times, I need to get in close to capture some details. But, without some additional optics, my camera just could not maintain focus, as I received closer to an object. Being a cheap p… [Hobby Circuit designed by David A. Johnson P.E., 4/2005]


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