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Circuits of the Week - December to July 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

12/31/06

Alarm Beeps when the “Check Engine” Light Turns On

 

When wired into a car’s indicator light panel, this circuit will turn on a loud beeper when the “check engine” light turns on… [Circuit designed by David A. Johnson P.E., 4/2005]

12/24/06

40KHz Limiting Amp

 

This circuit has a gain of X20 at 40KHz. The amplifier output level is limited to 2.5v peak to peak. Limiting action begins with a 50v peak to peak input… [Circuit designed by David A. Johnson P.E., 1/29/06]

12/17/06

Audio Activated Switch

 

This circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal. It could be used to turn on a relay, routing the signal to were it is needed… [Circuit designed by Dave Johnson P.E., 12/17/06]

12/10/06

Precision 40Khz Triangle Generator

 

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

12/03/06

Thermocouple Temperature Activates Relay

 

Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F… [Circuit designed by David A. Johnson P.E., 4/2005]

11/26/06

Medium Power 40Khz Ultrasound Transducer Driver

 

This crystal controlled circuit drives a 40KHz piezoelectric transducer with a 30v peak to peak signal… [Circuit designed by Dave Johnson P.E., 11/26/06]

11/19/06

Pump Motor Monitor

 

This circuit solves this problem in a novel way. It clips on the outside of the pump motor’s power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor. The circuit draws so little current that a small lithium cell will power the circuit for years… [Circuit Solution designed by David A. Johnson P.E., 5/7/06]

11/12/06

Modulated Light Monitor

 

This battery powered circuit will work from DC to 500KHz. It is designed to connect to an oscilloscope to monitor the light level changes and modulated signals… [Circuit designed by Dave Johnson P.E., 4/2005]

11/05/06

LED Pilot Light powered by AC Line

 

This simple circuit can be used to light a LED indicator lamp, powered from the 120vac line. I have included component values for 240vac lines as well… [Circuit designed by Dave Johnson P.E., 7/9/06]

10/29/06

Precision Fullwave Rectifier

 

I have used this handy circuit many times. It accurately converts an AC signal into pulsing DC, which can be filtered to provide an average of the input voltage. It works from millivolts to volts. The circuit shown requires a stable +5v reference if a … [Circuit designed by Dave Johnson P.E., 2001]

10/22/06

Illuminated 16vac Doorbell Lamp Replacement

 

A while back I noticed that the lamp inside the illuminated pushbutton switch for my doorbell burned out. I carefully removed the doorbell, opened the switch housing and then replaced the incandescent lamp inside with the circuit shown below. The circuit uses two small but very bright green LEDs from King Bright. The resistor sets the average LED current at about 3ma. The diode prevents reverse biasing the LEDs. The two lamps emit plenty of light and should last much longer than the incandescent lamp they replaced… [Hobby Circuit designed by Dave Johnson P.E., 10/22/06]

10/15/06

12v Lamp Current Indicator

 

This circuit turns on a LED indictor light whenever DC current flows into a 12v lamp… [Circuit designed by David A. Johnson P.E., 10/15/06]

10/08/06

Pushbutton Activates Service Request Beeper

 

A single press of a pushbutton switch turns on a beeper for one second but can’t be activated again for 60 seconds… [Circuit designed by Dave Johnson P.E., 9/25/05]

10/01/06

Solar PV Cell Test Fixture

 

This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions… [Circuit designed by David A. Johnson P.E., 10/1/06]

09/17/06

2.45ghz RF Signal Detector

 

This passive RF indicator is made from a few simple parts. A 100uA moving coil meter is used to display the relative intensity of the RF signal. This circuit can be used with some cell phones and many cordless telephones… [Circuit designed by Dave Johnson P.E., 4/2005]

08/27/06

Piezoelectric Vibration Sensor Activates Switch

 

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

08/20/06

Piezoelectric Triggered Switch

 

Two different switch circuits are shown. One sources current and the second sinks current. Both switches are connected to a piezoelectric wafer. When the wafer is tapped, the switches are activated… [Circuit designed by David A. Johnson P.E., 8/20/06]

08/13/06

Low Voltage Latching Relay Driver

 

Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source. By using a latching relay, power can be controlled to a load with a tiny battery… [Circuit designed by David A. Johnson P.E., 8/13/06]

08/06/06

6V TO 24V DC Day/Nigh Switch

 

Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down… [Circuit designed by Dave Johnson P.E., 4/2005]

07/30/06

Replace a Pushbutton Switch with this Intrared Safety Switch

 

Using a slotted optical sensor, this circuit can be used as a replacement for a large mushroom pushbutton safety switch… [Hobby Circuit designed by David A. Johnson P.E., 4/2005]

07/23/06

Battery Charge Current Indicator

 

This circuit turns on a LED whenever it detects at least 25ma of battery charge current… [Circuit designed by David A. Johnson P.E., 7/23/06]

07/16/06

40Khz Ultrasound Receiver

 

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… [Circuit designed by Dave Johnson P.E., 1/29/06]

07/09/06

9v Battery Voltage Monitor

 

This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.2 volts. It uses a LTC1440 comparator, which also contains a 1.18v reference diode. In standby mode, the circuit draws only 4uA… [Circuit designed by Dave Johnson P.E., 4/2005]

07/02/06

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 designed by David A. Johnson P.E., 05/20/06]


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


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