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Tester or Measurement (Instrument) Circuits

Test Equipment:  #'s - A        B - D        E - G
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Last Updated: January 01, 2018 04:02 AM
Circuits Designed by Dave Johnson, P.E. :

Laser Burst Light Detector -  This circuit was originally designed to detect weak flashed of laser light bounced off of a fabric video projection screen.  it was used as part of a firearm training system.  it generates a 100mS output pulse whenever it detects a 3ms to 5ms laser burst, modulated at 40KHz.  it is very sensitive and could be modified for long range laser communications. . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

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 by David A. Johnson P.E.-March, 1999

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 be. . . Circuit by David A. Johnson P.E.-July, 2000

Lead-Acid Battery Low Voltage Indicator -  Lead-acid batteries should not be discharged below a certain voltage.  Discharging a cell below about 1.8v and can often damage it, which will result in a lower amp-hour capacity.  Large battery banks are critical in off-grid energy storage systems.  One. . . Circuit by David A. Johnson P.E.-July, 2006

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
6 Models Available - Call 806-368-7747

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

LED Audio UV Monitor -  The circuit is completely conventional, and is based on the App Note  From National Semiconductor.  The circuit is shown in Figure 1 and as you can see it uses a single IC and a few discrete components.  The extra diode (D3) is included to ensure that the DC to the LEDs is almost unfiltered __ Designed by Rod Elliott  ESP

LED Bargraph Optical Tachometer -  For the electric R/C enthusiast, a tachometer can be a very useful piece of equipment.  When I first built this tach back in 1995, it was essential, as there were very few off-the-shelf electric R/C power systems that just worked.   __ Designed by Stefan Vorketter

LED based transistor teste -  Here is the circuit of a very simple transistor tester which used two LEDs for displaying the condition of a transistor.  Both PNP as well as NPN transistors can be tested using this circuit.  Quad 2 input CMOS NAND gate IC CD4011B is the heart of the circuit.  Out of the four NAND gates inside the IC , only three are used here and they are used as NOT gates by shorting their input terminals.  Gates U1a, U1b, resistor R1 and capacitor C1 forms a square wave oscillator.  __ 

LED Battery Condition Indicator -  in the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery.  A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider.  The LEDs __ Designed by Bill Bowden

LED Battery Meter -  will measure any low voltage battery on a 10 LED scale!  __ Contact P. Townshend - EduTek Ltd

LED battery voltage Monitor -  A fuel gage for your gel cell battery. __ Designed by Steven "Melt Solder" Weber  KD1JV

LED Binary Calculator -  You can't calculate binary values as is on most handheld calculators and using the windows one is just a pain, so I decided to make my very own (binary only) calculator.  This calculator supports all the basic functions like : NOT, OR, AND, XOR, __ 

LED Decibel Meter -  The circuit below responds to sound pressure levels from about 60 to 70 dB.  The sound is picked up by an 8 ohm speaker, amplified by a transistor stage and one LM324 op-amp section.  You can also use a dynamic microphone but I found the speaker was more sensitive.  The remaining 3 sections of the LM324 quad op-amp are used as __ Designed by Bill Bowden

LED dimmer uses only two lines -  03/21/02 EDN Design Ideas:  The circuit in Figure 1provide as 32 steps of brightness control-from 0 to 100%-for a backlight or instrument panel, using just two general-purpose-microprocessor signals.  in addition, the circuit requires little board space, because it uses only three SOT-23s and one µMax package __ Circuit Design by Jerry Wasinger, WallyWare Inc, Norcross, GA

LED display Digital Voltmeter -  This digital voltmeter is ideal to use for measuring the output voltage of your DC power supply.  it includes a 3.5-digit LED display with a negative voltage indicator.  it measures DC voltages from 0 to 199.9V with a resolution of 0.1V.  The voltmeter is based on single IC L7107 chip and may be fitted on a small 3cm x 7cm__ 

LED display digital Voltmeter -  This is an easy to build, but nevertheless very accurate and useful digital voltmeter.  it has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present.  The circuit employs the ADC (Analogue to Digital Converter) i.C.  CL7107 made by iNTERSiL. __ Designed by © Smart Kit Electronics

LED driver doubles as fault Monitor -  08/05/04  EDN Design Ideas:  LEDs find wide use as indicators and as light emitters in devices such as optocouplers.  in some applications, the LED or the emitter may be located remotely at some distance from the main unit.  Typical examples are dashboard-mounted automotive indicators and industrial optosensors.  in critical applications, you may require some means of monitoring the integrity of the LED __ Circuit Design by Anthony Smith, Scitech, Biddenham, Berdfordshire, England

LED Flasher Indicates Low Battery Condition -  01/02/97 EDN Design Ideas:  Many portable electronic devices could benefit from a visual indication when their battery requires replacement.  Typical low-battery indicators simply turn on an LED when the battery voltage drops below a certain value.  Such circuits actually accelerate the battery's extinction by drawing excessive current.  The circuit in Figure 1 draws a mere 1 m A in its standby mode and averages only 20 m A when activated.  The low current imposes a minimal burden on any battery circuit.  An off-the-shelf, undervoltage sensor IC (IC 1) monitors the battery voltage--  __ Circuit Design by David Johnson, DiscoverCircuits.com

LED Oscilloscope -  George Katz of Balgowlah Boys high in Sydney presented a solid state oscilloscope.  He says "probably the best advantage is its very small size and the fact that it can run off the power supply of the circuit being tested.  Although it has a low frequency range, it can still be used for most circuits.  its poor resolution will still allow for most waveforms to be visualized.  ".  __ 

LED Oscilloscope 1 -  Uses a matrix of 100 LED as a display __ Designed by shaunwilson19 @ yahoo.com

LED power meter -  Used for testing RF transmitters __ Contact Collin Mitchell

LED Test Signal Generator-40Khz -  This 40KHz crystal controlled oscillator circuit drives an infrared LED with powerful 40ma pulses.  The circuit can be used to test optical communications circuits, designed to receive 40KHz modulated light signals . . . Hobby Circuit designed by David Johnson P.E.-February, 2002

LED Tester -    NOTE: Must register on this site __ Designed by Published in Elecktor July/Aug, 2010

LED Tester -  Schematic + info + pictures __ Designed by Lennie Zink

LED Thermometer -  This LED thermometer is designed for in home use, to read temperatures between about 60 and 78 degrees Fahrenheit.  it is based around a precision temperature sensor IC , the LM34DZ.  This sensor require no calibration and can measure temperatures of between -50F and +300F.  While the circuit shown here does not use the full range of that sensor, it can be modified to do so by simply changing the voltage reference to U2 at the sacrifice of precision. __ Designed by Aaron Cake

LED Volt Meter -  Here is a Simple LED Volt meter to Monitor the charge level in Lead Acid Battery or Tubular battery.  The terminal voltage of the battery is indicated through a four level LED indicators.  The nominal terminal voltage of a Lead Acid battery is 13.8 volts and that of a Tubular battery is 14.8 volts when__ 

LED Voltmeter -  Measures voltages up to 199.9V with 0.1V resolution.  __ 

LED Voltmeters 20 & 30 LED's -  These are Basic Expanded Voltmeters based on the National LM3914 chip.  They can be Switched to either Bar or Dot Mode.  The 20 LED one has a Minimum 2.5 volt range for Full Scale and it can be adjusted to Much Higher voltage ranges with the input potentiometer. __ Designed by G.L. Chemelec

LED Wink Tester for 1.5 Volt Cells -  This page contains a collection of circuits that wink when the power switch is thrown to indicated whether the 1.5 volt (and other voltages near 1.5 volts) cell still has a significant charge left.  Choose the best one for your application.   __ Designed by Dick Cappels

Led Strobe 2 -  this version has been built and tested and is very simple indeed - based on alien project astable!  __ Contact P. Townshend - EduTek Ltd

LED/Laser 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 . . . Hobby Circuit designed by David Johnson P.E.-July, 2000

LED7 Solar Tracker -  Schematic only, no circuit description __ Contact Duane C. Johnson

LEDs Indicate Sound Level -  08/25/11  EDN Design Ideas:  Build a battery-operated portable meter to measure sound-pressure levels.   This Design idea describes a battery-operated, portable soundlevel meter (Figure 1).  its portability makes it useful for detecting the source of noise in automotive engines and power trains, factory machinery, and residential HVAC (heating/ventilation/air-conditioning) systems __ Circuit Design by Stephen Kamichik, Ile Bizard, PQ, Canada

LEDs Light LAN-Cable Tester -  12/02/10 EDN Design Ideas:  A series of LEDs indicate the health of an Ethernet cable.  [Design ideas by Noureddine Benabadji, University of Sciences and Technology, Oran, Algeria __ Circuit Design by Noureddine Benabadji, University of Sciences and Technology, Oran, Algeria

LEE Test Fixture Instructions -  App Note  AN-60-022__ MiniCircuits.com

Lego Mindstorms Double Rotation Sensor -  I usually use one motor for the left wheel and one for the right wheel.  The problem is that the motors are never perfectly matched and my RCX ends up going in circles.  I thought of buying two rotation sensors to keep track of the rotation of both wheel axles.  However this would use up two sensor ports, leaving only one for my other sensors __ Designed by Lloyd Gordon

Let You Isolate & Measure Current -  09/23/10 EDN Design Ideas:  isolation lets you measure current with an oscilloscope or other grounded probe.   __ Circuit Design by Anton Mayer, Murr, Germany

Level Shifted Low Side Current Monitor for Negative High Voltage Rails  -  A 2.5 V reference is chosen to provide sufficient headroom.  , Circuit Description, The input voltage to the AD7171 ADC is converted into an offset binary code at the output of the ADC.  The code is processed in the PC by using the SDP hardware board and LabViEW software.  A comparison is made between the code seen at the output of the ADC, recorded by LabViEW, and an ideal code calculated based on a perfect system.  , in order to calculate this ideal code, there are several assumptions which must be made about the performance of the system.  __ Analog Devices from the Lab

LF dB Output meter -  Ham Radio - Other __ Designed by Guy Roels ON6MU

LF Oscillator -  A low frequency test oscillator for testing tone controls and experimenting __ Designed by Andy Collison

Lie Detector -  Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth.  it is not as sophisticated as the ones the professionals use, but it works.  it works by measuring skin resistance, which goes down when you lie __ Designed by Aaron Cake

Lie Detector -  The circuit diagram of the Lie Detector is shown above.   it consists of three transistors (TR1 to TR3) , a capacitor (C1) , two lights or LEDs (L1 & L2) , five resistors (R1 to R5) , and a variable resistor (VR1).  This circuit is based on the fact that a person's skin resistance changes when they sweat (sweating because they're lying).  Dry skin has a resistance of about 1 million ohms, whereas the resistance of moist skin is reduced by a factor of ten or more. __ Designed by  © Hack Canada

Light Detector -  This circuit uses a unique cascode amplifier circuit to convert the current from a PIN photo diode to a current without any feedback network.  it is very stable and very sensitive.  This hobby circuit shown has the potential for a conversion factor of 10 volts per microwatt at 900nm.  I included a simple JFET post-amplifier with a gain of about 20. . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

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 . . . Hobby Circuit designed by Dave Johnson P.E.-April, 2005

Light Monitor Circuit -  The circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode . . . Hobby Circuit designed by David Johnson P.E.-August, 2010

Light Pollution Meter -  LED brightness control circuit and a millimeter to compare light levels to LED level __ Designed by Avery Davis

Light Receiver Works from 1Khz to Over 70Mhz -  This circuit uses one tiny C-MOS inverter IC to form a modulated light receiver with a very fast response.  it is designed around a PIN photo diode that is packaged for use with plastic optical fibers.  it can be used as an optical fiber receiver.  By using the open end of the optical fiber it can "sniff" out any modulated light signals. . . Circuit by David Johnson P.E.-June, 2000

Light Sensor Adapter for Oscilloscope -  This circuit is a simple visible light or IR detector for testing any equipment which outputs light. The circuit can be also used for measuring ambient light levels.  This circuit is based on one photodiode which is used in photocell mode so that the photodiode generates a voltage and current signal when it get light.   __ Designed by Tomi Engdahl

Lightening Detector -  A VLF receiver tuned to 300 kHz designed to detect the crackle of approaching lightning.  A bright lamp flashes in synchrony with the lightning bolts indicating the proximity and intensity of the storm.  it has a superior RF section with a single resonance near 300kHz and plenty of sensitivity.  The antenna is a telescopic antenna that extends to two or three feet __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Lighting Storm Monitor -  Schematic only __ Designed by va3iul

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Got Designs?
Please eMail
if you want me to link to and/or post your original design Thanks.

Test Equipment:  #'s - A        B - D        E - G
H - L        M - O        P - S        T - Z

HOME Schematics Index Hobby Corner Dave's Circuits Electronic Resources Contact Info
Imagineering Ezine    Discover Solar Energy Dave Johnson & Associates Faraday Touch Switches

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