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Tester or Measurement (Instrument) Circuits

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


Last Updated: October 24, 2017 02:55 PM
Circuits Designed by Dave Johnson, P.E. :

Lithium Battery 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 . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2012

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 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

Locate a Plastic Pipe -  I used this circuit once to track down the location of a plastic pipe, buried underground.  it transmits a weak RF signal, which can be picked up by a portable AM radio from about 6 feet away . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2004

Low Power Amp Monitors Light -  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. . . Circuit by Dave Johnson P.E.-August, 2010

Low Value Capacitance Meter -  This circuit was originally designed to measure the volume of fluid inside a medical syringe.  As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. . . Circuit by David A. Johnson P.E.-December, 2004

Low Voltage 120vAC Power Line Alarm -  This circuit will turn on a beeper when the line voltage drops below 100 volt AC.. . . Circuit by David Johnson P.E.-July, 2006

Low Voltage Indicator for Lead-Acid Battery -  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 . . . Hobby Circuit designed 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:

Logic probe with integral pulser function -  This project is a combination Logic Probe and Logic Pulser.  it is capable of testing all sorts of digital and microcomputer projects.  You will find it extremely handy when designing a project as the golden rule is to test everything in steps and stages during the design-and-construction process.   __ Designed by Collin Mitchell

Logic Probe with Sound -  This logic probe can be selected to operate on TTL or CMOS logic levels, depending on switch S1.  A string of resistors associated with switch S1 sets the threshold levels for a window comparator comprising IC 1a and IC 1b.  Depending on whether the level applied to the probe is high or low, the window comparator turns on LED1 (high) or LED2 (low).  The 1.2M and 680k resistors set the probe signal to a midrange value when the probe is open-circuit, thereby preventing either LED from being lit.__ Learning Electronics

Logic Probe1 with pulse TTL/CMOS -  One of the most frustrating problems with experimenting is not be able to check the logic state of TTL or CMOS ic's without the use of a triggered oscilloscope. The schematic diagram above shows a simple and inexpensive way of building a 'Logic Probe' yourself. it will provide you with three visible indicators; "Logic 1" (+, red led) , "Logic 0" (-, green led) , and "Pulse" (yellow led)  __ Designed by Tony van Roon  VA3AVR

Logic Probe2  with pulse TTL/CMOS -  This circuit uses the four 2 input NOR gates contained within the 4001 CMOS IC , and is primarily intended for testing CMOS circuits.  The probe derives its power from the supply of the circuit being tested.  The first gate, N1, has its inputs tied together so that it operates as an inverter, and it is biased by R1 so that roughly half the supply potential appears at its output __ Designed by Tony van Roon  VA3AVR

Logic Probe3 Audible TTL/CMOS -  A logic tester with an audible indicator can be handy when troubleshooting or testing a crowded circuit board.  it allows you to keep your eyes on the circuit, rather than on a LED on the tester.  The project described in this article is just such a tester.  it provides an audible indication of the logic level of the signal presented to its input __ Designed by Tony van Roon  VA3AVR

Logic PSU with OverVoltage Protection -  A simple 5 Volt regulated PSU featuring overvoltage protection. __ Designed by Andy Collison

Logic Pulser -  Has DiP switch for setting output waveform characteristics.   __ Contact Collin Mitchell

Loop Sensor -  Many security systems use a closed loop of wires and switches arranged so that whenever a door or window is opened, the loop will be broken and the alarm will sound.  An obvious problem is that someone can tamper with the system, short out the loop, and later on, come back and burglarize the premises__ 

LOPIC Logic Probe with Pulser -  This project is a combinationLogic Probe and Logic Pulser.  it is capable of testing all sorts of digital and microcomputer projects.  You will find it extremely handy when designing a project as the golden rule is totest everything in steps and stages during the design-and-construction process.  if you are not sure how a Logic Probe or Pulser works__ 

Low battery cut-off for a car or truck -  Also acts as a Master On / Off Switch.  NOW, Also a New P-Mos Version.  Supplies Positive voltage to grounded devices.   __ Designed by G.L. Chemelec

Low Battery Indicator -  File contains several designs, please scroll to find this circuit.  Here is a low battery indicator that flashes a lamp when the battery voltage falls below about 5 volts.  The circuit draws about 25 microamps when not flashing so battery life is not significantly shortened by the circuit.  The two 1 megohm resistors set the switching point at V/2 (plus a little due to the emitter-base diode drop) and when this voltage is above the zener voltage the circuit cannot turn on.  When the battery voltage drops below 5 volts, the base voltage drops to 2.5 volts and the emitter can reach a voltage sufficient to turn on the PNP (2N4403 or similar).  When the PNP conducts, the NPN also conducts dropping the voltage across the circuit even more and the circuit snaps on.  When the 4.7 uF capacitor has discharged, the circuit turns off and the capacitor begins charging again.   __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Low Battery Indicator Ii -  This circuit indicates the remaining battery life bAy varying the duty cycle and flash rate of an LED as the battery voltage decreases.  in fact, the circuit actually indicates five battery conditions: (1) a steady glow assures indicates that the battery is healthy; (2) a 2Hz flicker (briefly off) indicates that the battery is starting__ 

Low Battery Monitor Delays System Shutdown -  App Note #134__ Maxim Integrated

Low Capacitance Scope Probe Adapter -  An adapter to allow low capacitance probing of high frequency circuits.   __ Designed by Dick Cappels

Low Cost Benchtop Power Meter -  09/11/98 EDN Design Ideas:  NOTE:    FILE
has several circuits, please scroll to find this one.  With a few inexpensive ICs  and passive components, you can easily make a multirange power meter suitable for use on your benchtop.  The circuit in Figure 1 measures currents from microamps to amps and voltages as high as 100V.  The voltage at VOUT, which you can monitor with a DVM, indicates the load's power. __ Circuit Design by Jim Todsen, Burr-Brown Corp, Tucson, AZ

Low Cost Dual Channel Active AC Analog Probe -  introduction When we are experimenting with AM receivers for LW, MW and SW we are in need of high impedance analog probe with low input capacitance, e.g.  well below 20pF. The required input...__ Electronics Projects for You

Low cost video Motion Detection -  This device uses a PIC 16F819 and an LM339 to detect motion on a video signal.  The incoming video is 'clamped' using one section of the LM339, the sync tips are detected with another section, and a 3rd section can detect VBI or other data.   __ Designed by Luhan Monat-Mesa Arizona

Low Cost, 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

Low frequency / audio frequency DB output meter -  Schematic only, no circuit description __ Designed by Guy Roels ON6MU

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

Low Noise Amplifier for Phase Noise Measurements -  The phase noise of low noise oscillators and signal sources is usually determined by measuring the audio noise voltage at the output of the phase comparator in a phase-locked loop.  The phase comparator is typically a low noise doubly-balanced mixer with a phase slope from a few tenths of a volt per radian to a few volts per radian.  The low __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

LOW OHM Digital Meter -  They Measure from: 0.001 to 1.999 Ohms, or from: 0.01 to 19.99 Ohms.   __ Designed by G.L. Chemelec

Low Ohms Adaptor For Dmms Based On An LM317 Regulator -  This adaptor circuit is essentially a 100mA constant current source.  it is applied across a low-value resistor of unknown value (ie, the resistance to be measured) and the resulting voltage drop can then be measured by a digital multimeter (DMM).  Setting your DMM to the 200mV range will enable it to measure up to 2O__ 

Low Ohms Meter -  This project was published in the September 2012 issue of the Australian magazine "Amateur Radio", and has been designed using parts which are very readily available (see the circuit and parts list).  There is little point in supplying a kit of parts to amateurs who have been around a while - most will be in your junk box.  However, the printed circuit board (1.6 mm thick FR4 fibreglass, 35 micron copper, easyflow lead- tin solder coated, plated through holes, solder masks, component silk screen) is another matte __ Designed by VK5JST / VK5TR

Low Power Amp Monitors Light -  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. . . Circuit by Dave Johnson P.E.-August, 2010

Low Power Antenna Analyzer & ATU Tuning Aid -  Using just a few mw of output power, this circuit is used to find the 50 ohm resonance frequency of antennas or can be used to adjust an Antenna Tuning Unit for 50 ohm match, without generating QRM.  The unit is powered by a 9 volt battery and a Frequency counter is required to know where the oscillator is tune to. __ Designed by Steven Weber, KD1JV

Low Power EKG & Heart Rate Monitor using the MSP430FG439 -  This design details how to build a digital heart-rate monitor using a MSP430FG439 microcontroller (MCU). The heartbeat rate per minute is displayed on an LCD and generates a digital data stream via an RS232 serial port to allow EKG waveform display on a PC. The entire application runs using a CR2032 3-V lithium battery.__ Texas Instruments

Low Power LED Voltmeter -  This is a low power voltmeter circuit that can be used with alternative energy systems that run on 12 and 24 volt batteries.  The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries and over the 22 to 32 volt __ Designed by G. Forrest Cook

Low Power Pulse Oximeter & EKG Reference Design -  This reference design details non-invasive optical plethysmography – pulsoximetry – using the MSP430FG437 microcontroller (MCU). The pulsoximeter consists of a peripheral probe combined with the MCU displaying the oxygen saturation and pulse rate on a LCD glass. The same sensor is used for both heart-rate detection and pulsoximetering in this application. A custom LabViEW GUI has been developed for this application to display the heart signal, heart rate and % SaO2 number. All the necessary files and steps to get this GUI up and running have been provided along with this report.__ Texas Instruments

Low power voltage-to-frequency converter makes a wireless probe for testing an inductive power supply -  26-May-05 EDN Design Ideas:  inductive pickup measures low-power circuit's supply __ Circuit Design by Francis Rodes, Eliane Garnier, and Salma Alozade, ENSEIRB Talence, France

Low resistance adapter for a DMM (digital multimeter) -  The power supply uses two 12.6 v 300 mA transformers because I had them on hand.  I would recommend a 24 VCT or 25.2 VCT 1A transformer.  if you can find a 200 mA unit by all means use it, it should be much smaller.  The bridge rectifier provides approximately plus and minus 18 volts.  The different sized filter capacitors are because the current demand from the +12 volt supply is approximately 25 mA while the demand from the -12 volt supply can be as high as 125 mA.  The two fixed voltage regulators provide the necessary 12 volt supplies. __ Designed by Max Robinson

Low Side Current Sense -  Sensing the amount of current through a load on the low side has the disadvantage of raising the return connection to the load from ground.  The advantage of such an approach is that it is very easy to implement using a basic non-inverting gain stage.  The LTC6081 operates linearly down to ground also in this single supply example.  __ Linear Technology/Analog Devices App Note, Mar 16th 2010

Low Speed AVR Oscilloscope -  A few months ago as I was surfing on the net, I saw an oscilloscope based on PIC 18F2550 microcontroller and a KS0108 controller based graphical LCD.  That was Steven Cholewiak's web site.  I had never seen before so amazing microcontroller, only oscilloscope.  That was realy impressive circuit, so I decided to design something like that but in C language instead.  __ 

Low Value Capacitance Meter -  This circuit was originally designed to measure the volume of fluid inside a medical syringe.  As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. . . Circuit by David A. Johnson P.E.-December, 2004

Low Voltage , High Current Time Delay -  in this circuit a LM339 quad voltage comparator is used to generate a time delay and control a high current output at low voltage.  Approximatey 5 amps of current can be obtained using a couple fresh alkaline D batteries.  Three of the comparators are wired in parallel to drive a medium power PNP transistor (2N2905 or similar) which in turn drives a high current NPN transistor (TiP35 or similar).  The 4th comparator is used to generate a time delay after the normally closed switch is opened __ Designed by Bill Bowden

Low Voltage 120vAC Power Line Alarm -  This circuit will turn on a beeper when the line voltage drops below 100 volt AC.. . . Circuit by David Johnson P.E.-July, 2006

Low Voltage Alarm -  NE555 Low Voltage Battery Disconnect Circuit __ Designed by Aaron Cake

Low Voltage Audio Amplifier -  This experimental (3) transistor class A audio power amplifier delivers 25mW into an 8Ω load, or 50mW into a 4Ω load using only a 1.5V power source.  At such low voltages, there are many issues to consider and much to learn.  To the best of my knowledge the following information is new to the world.  Background Months __ Designed by Jim Keith

Low Voltage Battery Disconnects -  Find out more about low voltage battery disconnect (LVD) circuits - used to protect batteries.   __ Designed by REUK-Renewable Energy UK website

Low Voltage Disconnect -  A simple automatic circuit that will disconnect a battery before it can be discharged too low and be in danger of cell damage.  Very useful for remote radio sites and to protect any battery used for emergency backup purposes.   __ Designed by Burton Lang

Low Voltage Indicator for Lead-Acid Battery -  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 . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Low-Battery Detector Preregulates Input Voltage -  08/15/96 EDN Design Ideas:  The circuit in Figure 1 uses the comparator and voltage reference of a low-battery detector to preregulate the input voltage.  The circuit provide as an additional regulated voltage output at VOUT1 and significantly reduces the linear regulator's (VOUT2's) power dissipation.  The two outputs (12V at 50 mA and 5V at 100 mA) are independent. __ Circuit Design by Khy Vijeh, Analog Devices Inc, Santa Clara, CA

Low-Battery Indicator has High-Efficiency -  05/03/01 EDN Design Ideas:  The usual method for implementing the low-battery warning featured in most battery-operated equipment is to illuminate an LED.  However, the LED exacerbates the low-battery condition.  You can greatly reduce the LEDs power consumption by operating it at a low frequency and a low duty cycle.   __ Circuit Design by Joe Neubauer

Low-Capacitance Adaptor for DMMs -  This neat little adaptor allows a standard digital multimeter to measure low values of capacitance - from less than one picofarad to over 10nF.  it will allow you to measure tiny capacitors or stray capacitances in switches, connectors and wiring.__ SiliconChip

Low-Component-Count Logic Probe Works with TTL & CMOS Logic -  04/07/11  EDN Design Ideas:  LEDs indicate logic levels.  The circuit in Figure 1 uses the LM358 dual op amp running as a comparator, plus a few other inexpensive components, to make a TTL (transistor-transistor-logic) /CMOS -logic probe.  The circuit gets its power from the circuit under test, which lets it work with TTL or CMOS logic.  The IC 1A and IC 1B op amps come in an LM358 package.  Switch S1 selects the TTL or the CMOS mode of operation.  The green LED shows logic low, and the red LED shows logic high.   __ Circuit Design by Aruna Rubasinghe

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

 


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