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Tester or Measurement (Instrument) Circuits

Test Equipment:  #'s - A        B - D        E - G
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Last Updated: October 24, 2017 02:55 PM
Circuits Designed by Dave Johnson, P.E. :

Alarm Discriminator + Battery Monitor of the Electric Field Disturbance Monitor -  This schematic is the alarm discriminator plus the batterry monitor of my "Electric Field Disturbance Monitor".  The system can detect human and animal motion by the electric fields they disturb . . . Hobby Circuit designed by David Johnson P.E.-March, 2002

Alarm sounds when Power Cord is Unplugged -  Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries.  However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries.  So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time . . . Hobby Circuit designed by David Johnson P.E.-July, 2000

Alarm sounds when Water is Detected -  This simple circuit sounds a beeper when its electrodes detect water.  it is powered by a single 1.5v N cell.  A small 1.5v button battery will also work. . . Circuit by David A. Johnson P.E.-June, 2000

Alternating CW & CCW 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. . . Circuit by David Johnson P.E.-September, 2010

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:

Accurate USB 2.0 temperature sensor needs only a handful of parts -  05/24/07  EDN Design Ideas:  A USB-to-serial converter forms the heart of an accurate USB temperature sensor __ Circuit Design by Silvio Lauckner, Ismaning, Germany

Accurately measure resistance with less-than-perfect components -  11-Nov-04 EDN Design Ideas:  For transducers, such as strain gauges or thermistors, you must accurately and inexpensively measure resistance using circuitry built with imperfect components and in which gain and offset errors can significantly limit the accuracy of ohmic measurements.  The right circuit topology makes it possible to eliminate most error terms while measuring ohms, leaving the accuracy to be determined by jus __ Circuit Design by Dave Van Ess, Cypress Semiconductor

Acoustic Thermometry Measures Temperature to 0.1 Degree -  Start Clock Launches Acoustic Pulse into Measurement Path, Sets Width Decode Flip-Flop High.  Acoustic Paths Return Pulse, Amplified by Receiver, Trips Trigger, Resetting Flip-Flop.  Resultant Q Width Output, Representing Path’s Temperature Dependent Transit Time, is Converted to Temperature Reading by Microprocessor.  __ Linear Technology/Analog Devices App Note, Apr 29th 2011

Active Load Draws Constant Battery Power -  04/13/00 EDN Design Ideas:  Unlike nickel-metal-hydride and lithium-ion rechargeable batteries, the discharge voltage of alkaline batteries is not constant and tends to vary from 1.5 to 0.8V per cell.  Alkaline-battery manufacturers specify the discharge life of their batteries under constant powerloads.  Because of the varying discharge voltage, you can't simply connect a load resistor to the cells to verify or measure power profiles without incurring a lot of error in your measurements.  The circuit in Figure 1draws a constant power from the battery pack.  Thus, as the battery voltage decreases, the load current increases.  A single potentiometer allows a user to set the desired wattage draw.  The circuit is simple and inexpensive to build.   __ Circuit Design by Doug Farra

Active Voltage Positioning Reduces Output Capacitors -  DN224 Design Notes__ Linear Technology/Analog Devices

Active-feedback IC serves as current-sensing instrumentation Amplifier -  24-Jul-03 EDN Design Ideas:  High-speed current sensing presents a designer with some significant challenges.  Most techniques for sensing current involve measuring the differential voltage the current produces as it flows through a sense element, such as a resistor or a Hall-effect device.  The differential voltage across the sense element is generally small and is often riding on a common-mode voltage that is considerably __ Circuit Design by Jonathan Pearson, Analog Devices, Wilmington, MA

Active-filter & oscilloscope inspect a Class D Amplifiers output -  12/01/06  EDN Design Ideas:  Ease debugging of bridge-output pulse-width-modulated audio amplifiers with this circuit __ Circuit Design by John Guy, Maxim Integrated Products Inc, Sunnyvale, CA

Adapt Signals for Visual Perception -  10/12/95 EDN Design Ideas:  First, the display would extend brief periods of change in logic states to a period long enough for the eye to perceive (Fig 1a).  For example, if a signal is at logic high and switches to logic low for a period of 100 nsec and then returns to a high state, the period of the low-state signal is too short for the eye to perceive.  The logic-low period should __ Circuit Design by Paul Johnson, Qualcomm Inc, Escondido, CA

ADC enables temperature-compensated weigh-scale measurements -  5-Jul-01 EDN Design Ideas:  You can provide temperature compensation in weigh-scale applications by simultaneously measuring both the temperature of the bridge and the primary output of the bridge transducer.  Traditionally, an integrated multiplexer connects multiple input variables to a single sigma-delta ADC.  Each time the multiplexer switches the input, the ADC must flush the digital filter of all data pertaining to t __ Circuit Design by Albert O'Grady, Analog Devices, Limerick, Ireland

ADC's Reference Improves RTD Measurements -  10/27/94 EDN Design Ideas:  Temperature measurements using RTDs (resistance-temperature detectors]generally employ bridge circuits with stable power supplies for signal conditioning.  Unfortunately, this scheme generally produces nonlinear outputs.  A linear b __ Circuit Design by Bharat Heavy Electricals Ltd, Tiruchirapalli, India

Add gain to an absolute-value Amplifier -  08/22/02 EDN Design Ideas:  The absolute-value amplifier is a basic building block in test-and-measurement and signal-processing applications.  The addition of a DPP (digitally programmable potentiometer] adds another dimension, G (gain], to this key circuit.  Because the gain is programmable, you can use the circuit as an absolute-value amplifier (G&1] or an absolute-value attenuator (G>1] __ Circuit Design by Chuck Wojslaw, Catalyst Semiconductor, Sunnyvale, CA

Add Programmability to Sensor Amplifier -  03/21/02  EDN Design Ideas:  The pressure-sensor amplifier circuit of Figure 1 offers a number of advantages over the traditional approach using the classic three-op-amp instrumentation amplifier.  The circuit can operate from a single supply and uses only two  __ Circuit Design by Chuck Wojslaw, Catalyst Semiconductor, Sunnyvale, CA

Add-On Current Limiter -  This circuit allows you to set a limit on the maximum output current available from your PSU.  it's very useful when you power-up a project for the first time - or carry out a soak-test.  By setting an upper limit on the current available from your PSU - you can protect both your power supply - and any device connected to it __ Designed by Ron J.

ADE7751: Single Phase Energy Metering IC with On-Chip Fault Detection -  The ADE7751, available in SSOP packages, is pin compatible with the AD7751.  it has the same functionalities as the AD7751.  __ Analog Devices Product Notes

Adjustable 0W to 10W Load Box with UVLO & Thermal Shutdown -  The LT2940 measures a high side current and a differential voltage, multiplies them and outputs a current proportional to instantaneous power.  Bidirectional high side currents and bipolar voltage differences are correctly handled by the four-quadrant multiplier and push-pull output stage, which allows the LT2940 to indicate__ Linear Technology/Analog Devices App Note, Apr 26th 2010

Adjustable Audio Notch Filter -  A variable notch filter with both high and low pass filters. __ Designed by Andy Collison

Adjustment Free Inclinometer operates on 27V -  4/24/97 EDN Design Ideas:  The circuit in Figure 1 is an inclinometer (tilt-measuring circuit] in which the sensor is filled with liquid electrolyte.  Acting like a potentiometer, this sensor produces a voltage proportional to the tilt on the center electrode.  Because the liquid is subject to electrolysis, the sensor must have an ac-forcing voltage with an average dc component of zero __ Circuit Design by John Wettroth, Maxim Integrated Products, Sunnyvale, CA

Advanced VHF Power Meter -  The DVM (Digital Volt Meter) also displays the correct polarity sign.  There’s neither rocket science nor smoke and mirrors here folks: it’s all done simply with op amps and resistors!  __ Designed by Prject Wes Hayward, W7ZOI and Bobarkin, K7PUA that appears in QST, June 2001

AF generator -  The sinewave generator is based on 4 op-amps which are present in a single TL084 i.c. (see fig.1).  Op-amps A1 and A2 are connected to the frequency determining RC networks R5+P1a/C1 and R6+P1b/C2, respectively.  in my version of the generator, P1 is replaced by a stepped attenuator (dual rotary switch with 12 positions, see above).  Moreover, I have included two additional frequency ranges; thus, S1 is in my version a dual rotary switch with 5 rather than 3 positions.   __ Designed by W.Mieslinger

AirfLow Monitor Protects Components -  09/28/95 EDN Design Ideas:  Many electronic components, including fourth-generation µPs, require forced-air cooling.  However, the reliability of electromechanical components, such as cooling fans, lags behind that of electronic devices.  Even if a fan does not fail, blockage of the air-intake vents can reduce airflow.  The circuit in Fig 1  helps you protect against high-temperature-induced system failures by monitoring the performance of the cooling system __ Circuit Design by Wes Freeman, Analog Devices, Santa Clara, CA

Alarm Discriminator + Battery Monitor of the Electric Field Disturbance Monitor -  This schematic is the alarm discriminator plus the batterry monitor of my "Electric Field Disturbance Monitor".  The system can detect human and animal motion by the electric fields they disturb . . . Hobby Circuit designed by David Johnson P.E.-March, 2002

Alarm sounds when Power Cord is Unplugged -  Many medical devices, such a portable X-ray and ultrasound equipment, carry their own batteries.  However, the frantic pace of some hospital emergency rooms might cause the device to be shoved off into a corner without being plugged back into an AC power source to recharge their batteries.  So, I designed this circuit to emit an audible alarm whenever the device’s power cord was unplugged from the wall for a period of time . . . Hobby Circuit designed by David Johnson P.E.-July, 2000

Alarm sounds when Water is Detected -  This simple circuit sounds a beeper when its electrodes detect water.  it is powered by a single 1.5v N cell.  A small 1.5v button battery will also work. . . Circuit by David A. Johnson P.E.-June, 2000

Alarm to remind you to turn off your DMM (digital multimeter) -  As I worked at some project I made constant use of my Bench DMM which has LCD readout.  When finished I would turn off the master switch for the equipment in use but always forgot to turn off the DMM and realized several mornings that it had been on all night.  I resolved to do something about that.  I developed this little Alarm circuit that warns me every 30 mins that my DMM is on.   __ Designed by Laurier's Handy Dandy Little Circuits

Alcohol Level Tester -  Yogesh ShuklaA lot of accidents happen every day due to drunk driving.  This is a very useful circuit for testing whether a driver is drunk or not.  The circuit is easy...__ Electronics Projects for You

Aliasing Aids Signal Analysis -  09/15/94 EDN Design Ideas:  Common wisdom decrees that digital-oscilloscope users must always guard against aliasing by choosing a sampling rate that is several times  highest frequency component of  signal you are measuring.  But, if you are analyzing narrowband intermediate-frequency (iF]signals in radios, pagers, and wireless communicators, you can make aliasing work for you instead of against youFiGURE ONLY __ Circuit Design by Stan Sasaki, Lake Oswego, OR

Alternating CW & CCW 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. . . Circuit by David Johnson P.E.-September, 2010

Altimeter Project -  Making a altimeter using the Basic Stamp ii.  I finally got my Basic Stamp Pocket Altimeter done.  My first version of my altimeter used a linear equation , which I found is not really accurate at all.  So I got a PAK iI math coprocessor to calculate the altitude.  Although the PAK iI worked like a charm in my old bulky altimeter, I wanted to make one that was pocket size and the PAK iI was just too big.  in pocket altimeter I overcame the Stamp's lack of math capabilties by using a method known as linearization to do the calculations.   __ Designed by Shaun Wilson

Altimeter/Variometer for free flying -  A handheld instrument intended for the paraglider and hang glider pilot.  Displays altitude above sea level, altitude above take off, climb and fall rates, flight time, maximum altitude.  Software-calibrated, features a backlit LCD, internal rechargeable batteries and internal charge regulator.  Uses a Basic Stamp ii.   __ Designed by Manfred Mornhinweg

Amateur weather station to APRS interface ALWXI-01 -  Before putting the WS APRS interface into operation the network parameters should be set.  This can be done using a PC connected to the ALWXi-01 through a serial interface.  Any terminal emulating SW supporting TTY, VT52 or VT100 mode (HyperTerminal, WTT, etc.) will do the job just fine.  Connect the interface to the PC using a three wire cross-connected serial cable (RXD<-->TXD, TXD<-->RXD, GND<-->GND)  __ Designed by Aleksander Stare

AN 1404: the Truth About the Fidelity of High Bandwidth Voltage Probes 5988-6515EN -  Application Note__ Aligent

An Alarm Power Supply with Battery Back-up -  Power Supply Circuits:  This Power Supply is suitable for the Modular Burglar Alarm.  However, it has other applications.  it is designed to provide an output of 12-volts, with a current of up to 1-amp.  in the event of mains failure, the back-up battery takes over automatically.  When the mains is restored, the battery recharges.  __ Designed by Ron J.

An Audio-Video Test Generator -  Use it for testing VCR's, video monitors and the continuity of video cables.__ SiliconChip

An Autoranging True RMS Converter -  DN339 Design Notes__ Linear Technology/Analog Devices

An Electric Stethoscope -  Need to do a bit of self-diagnosis? Make sure your heart is still beating or check other body sounds? Maybe you would like to sort out some unusual rattles or other noises in your car's engine or other machinery? This electronic stethoscope will do the job ? and you can listen via headphones or a loudspeaker.  it has switchable frequency shaping in four bands so you can hone in on sounds which might otherwise be masked out.__ SiliconChip

An ESR Meter for Electrolytic Capacitors -  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

An Even Better LC Meter Based on Atmel AVR  ATTINY861 -  An improvement over "A Pretty Good LC Meter.  "  Enhanced capacitance self calibration, accurate operation without precision components, and only one micro controller.   __ Designed by Dick Cappels

An Experimenter's 1-Wire Barometer -  This article describes details for constructing a 1-Wire Barometer which will work on a Dallas Semiconductor Corporation 1-Wire network.   The reason for this second version is that the transistor level-changer of the original design was found to be temperature sensitive.  if you have constructed the original version (V1.0) you can modify it according to the diagram shown below.  This involves removing the transistor and 5 resistors, then rewiring it with 6 new resistors. __ Designed by David W. Bray

An inexpensive x-ray machine -  Has several x-ray circuits.  Scroll to find this one.  __ 

An introduction to acoustic thermometry -  04/21/11  EDN Technical Article: Use an ultrasonic transducer to measure air temperature in an olive jar.   __ Circuit Design by Jim Williams, EDN's most revered contributor, passed away in June 2011 after a stroke.  He was 63.

An Isolated Variable AC Mains Transformer  -  This is a means of testing AC mains operated circuits at variable AC voltages, and it also provides isolation to allow safe measurements of that circuit.   __ Designed by Dick Cappels

An RF Field Strength Meter using a Biased Schottky Deterctor and  a Moving Coil Meter -  A temperature compensated Schottky diode is used in an amplified, untuned field strength indicator that is powered by two AA cells idicates the relative field strength of
RF fields from a few kHz into the microwave region. 
 __ Designed by Dick Cappels

An RF Voltmeter for Transceiver Servicing -  This project was published in the November 2010 issue of the Australian magazine "Amateur Radio", and has been designed using parts which are very readily available __ Designed by VK5JST / VK5TR

An RIAA Preamplifier for Magnetic Cartridges -  Many modern amplifiers lack phono inputs.  This preamplifier solves that problem.__ SiliconChip

AN10 - Methods for Measuring Op Amp Settling Time -  Linear Technology AN10 __ Designed by Jim Williams - Jul 1st, 1985

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Test Equipment:  #'s - A        B - D        E - G
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