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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. :

Fluid Level Monitor -  This circuit was originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid.  Two custom insulated metal tubes form a capacitor plate.  The capacitance between the two tubes increases as the level of the liquid rises. . . Circuit by David A. Johnson P.E.-June, 2000

Footstep Alarm for Human Traffic -  This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps.  At has an adjustable sensitivity . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Freezing Temperature Alarm -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by Dave Johnson P.E.-November, 2014

Front End + Power Supply Circuits of the Electric Filed Disturbance Monitor -  This schematic is the power supply and front-end sections of my field monitor, "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

Full Wave Rectifier -  This is a classic circuit that can accurately convert an AC signal to DC.  At 40KHz the input signal can be as low as 0.05 volts peak to peak.. . . 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:

Fixed Frequency "Tuner Dipper" -  After building the "clothesline reel" 1/2 wave end feed antenna, with integral "L" tuner and resistive SWR bridge, I found it difficult to find a good match using the built-in bridge.  I also found it difficult to key the transmitter and make the adjustments at the same time.  One really needs three hands for the operation, as the tuner will not sit still by it's self. __ Designed by Steven Weber, KD1JV

Fixed Voltage Power Supply -  The fixed voltage power supply is useful in applications where an adjustable output is not required.  This supply is simple, but very flexable as the voltage it outputs is dependant only on the regulator and transformer you choose.  The maximum output current is 1.5A __ Designed by Aaron Cake

Fixture Determines Leakage of Capacitors & Semiconductor Switches -  06/06/07 EDN Design Ideas:  The low input-bias current of a voltage-follower op amp allows this simple fixture to measure the leakage current of capacitors and reverse-biased active devices.   __ Circuit Design by Marián Štofka, Slovak University of Technology, Bratislava, Slovakia

Fixture Statically Tests Programmable-Gain Amplifiers -  06/26/08  EDN Design Ideas:  Using a simple fixture having a common ground point, you can statically test digital gain-programmable amplifiers __ Circuit Design by Marian Stofka

Flame Failure Monitor -  A minimum amount of hardware is needed to build a simple flame or fire failure monitor that enables you to monitor the status of the flame in a chamber/furnace.  Owing to its integrated alarm generator, the interface can be easily adapted for use with a wide range of light/heat sensors.  Here a readily available photo transistor __ Designed by T.K. Hareendran

Flat Battery Indicator -  This small circuit was developed to monitor the battery in a model hovercraft.  The lift in the model is produced by an electric motor driving a fan.  To avoid the possibility of discharging the rechargeable battery pack too deeply, the design lights a conspicuous LED mounted on the model when a preset threshold voltage is__ 

Fleapower Detects shorts -  07/02/98 EDN Design Ideas:  (FILE
has several circuits, please scroll to find this one) Sometimes, the need arises for a short-circuit tester that supplies a low current to the device under test (DUT) and also uses voltages lower than 100 mV to prevent conduction of semiconductors.  The circuit in Figure 1 meets these requirements.  R1 limits the current in the DUT to 0.9 mA.  The voltage on the DUT can not exceed the value set by the ratio R2/ (R1+R2).  The NE5230 micropower op amp compares the voltage on RX (representing the DUT) with the voltage at the junction of R3 and R4.   __ Circuit Design by W Dijkstra, Waalre, The Netherlands

Flexible Fault Protection -  App Note 2765: IC __ Maxim Integrated

Floating Surge Stopper Provides Unlimited Overvoltage Protection -  Protecting sensitive electronic circuitry from voltage transients is an essential part of any system be it automotive, industrial, avionics or even battery-powered consumer applications.  offers a wide variety of solutions for these applications with its surge stopper family.  The LTC®4366 is the new exciting __ Linear Technology/Analog Devices App Note, Hamza Afzal Applications Engineer-Mixed Signal Products Nov 7th 2012

Fluid Depletion Sensor -  his circuit detects the absence, rather than the presence of a conductive fluid.  This requires the use of AC, rather than DC for sensing, in order to prevent an electrolytic process from corroding the electrodes.  The AC is produced by a sensor oscillator,  __ Designed by Andrew R. Morris

Fluid Level Detector -  The above circuit uses an AC-sensing signal to eliminate electrolytic corrosion on the probes.  The AC signal is rectified and used to drive Transistor T1 that drives the relay.  The relay is a 12-V type of your choice.  Transistor T1 can also be a TUP.   __ Designed by Tony van Roon  VA3AVR

Fluid Level Monitor -  This circuit was originally designed to monitor the level of liquid natural gas in a tank but it can be used to also measure almost any liquid.  Two custom insulated metal tubes form a capacitor plate.  The capacitance between the two tubes increases as the level of the liquid rises. . . Circuit by David A. Johnson P.E.-June, 2000

Fluid Sensor & More -  it Can Detect Most Liquids and more.   __ Designed by G.L. Chemelec

Fluid-Level Detector -  The above circuit uses an AC-sensing signal to eliminate electrolytic corrosion on the probes.  The AC signal is rectified and used to drive Transistor T1 that drives the relay.  The relay is a 12-V type of your choice.  Transistor T1 can also be a TUP.   __ Designed by Tony van Roon  VA3AVR

FM telephone line bug transmitter (88MHz to 94MHz) -  Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio.  The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet.  it is extremely easy to build and is therefore a good, useful beginner project.  __ 

FodTrack  -  My world-famous realtime satellite tracking system!  __ Designed by Manfred Mornhinweg

Footstep Alarm for Human Traffic -  This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps.  At has an adjustable sensitivity . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

Fortune Finder -  Searching for buried treasure can be a rewarding experience - try out this metal locator next time you go prospecting or beachco__ SiliconChip

Four Temperatures 8 digit LED termometer, using PIC16 & LM50B -  Since I started my watercooling prejoect, I have been verry interested in how well it perform,
the only way is to measure all temperatures before and after,
The motherboard temperature sensors is useless unacurate, so i'm using LM50B.  By using this LM50B sensor I get 1 C of real accuracy I use a PIC 16F876 to drive a four two digits LED displays, the PIC 16 has 4 analog inputs with 10 bits resolution, now I can display 4 temperatures at the same time to monitor performance :-) I monitor CPU, Chipset, GFX card, Harddisks. __ Designed by Thomas Scherrer OZ2CPU

Fox & Hound Wire Tracer -  The "Fox" and "Hound, " made by Triplett Corporation (www.  triplett.  com) , are a transmitter and receiver for tracing telephone (and others) wires through walls.  You connect the transmitter to the wire, and the receiver helps you trace the wire from several inches distance away.  Triplett doesn't say much about how they work, but th Fox and Hound apparently use inductive coupling of a low-frequency signal, maybe around 50 to 100KHz __ Designed by Tony van Roon  VA3AVR

Frankenstein's Dosimeter -  Frankenstein's Dosimeter is so named because it's made from body parts removed from various dead radiation instruments.  With a little "spark" of life from a battery, these old components come alive, making a pretty decent radiation dose measurement device.  The circuit may be used with a homemade chamber, too; just leave out the three diodes and 2.2 megohm that drive the guard ring (unless your homemade chamber has one).   __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Free program Designs & analyzes passive & active filters -  7-Jul-05 EDN Design Ideas:  Filter design simplified with Matlab-focused program __ Circuit Design by James Squire, Virginia Military Institute, Lexington, VA

Freezing Temperature Alarm -  The circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).    A 9v battery powers the circuit.    The average 9ua current is so low that the battery should last for many years.. . . Circuit by Dave Johnson P.E.-November, 2014

Frequency comparator draws 8 mA -  03/03/97  EDN Design Ideas:  The circuit in Figure 1includes all the necessary components to build a simple, low-power frequency comparator.  The circuit centers around the operation of IC 1, which integrates an amplifier, a comparator, and a voltage reference. __ Circuit Design by Dalius Baranauskas, Semiconductor Physics Institute, Vilnius, Lithuania

Frequency comparator has status output -  12/26/02 EDN Design Ideas:  The original application for the circuit in Figure 1 was to check the number of revolutions of an engine with only one LED as an indicator.  The measurement of the number of revolutions usually involves sensors with a frequency output proportional to the number of revolutions.  The circuit compares the frequency output of such a sensor with a lower and upper limit and gives a visual result, usi __ Circuit Design by Susanne Nell, Breitenfurt, Austria

Frequency Comparer Produces Binary Result -  09/29/94 EDN Design Ideas:  instead of resorting to full-blown frequency counters, the simple circuit in Fig 1 uses four ICs  to rapidly compare the frequency of two pulse trains.  The circuit produces a binary 0 if f1 is greater than f2 and a binary 1 if f1 is less than f2.  The circuit exploits the fact that inevitably two consecutive leading edges of the higher frequency pulse train will follow each __ Circuit Design by Jay Kirschenbaum, Columbia University, New York, NY

Frequency Counter -  This is a circuit that uses IC NE555, five decade counters along with a 7-segment driver IC to form a 5 digit decimal counter.  The output of the decimal counter is used to drive the numerical display of frequency counter.   __ Designed by Electronics Projects for You

Frequency Counter -  This is the support page for the simple frequency counter project in Homebrew, RadCom October 2006.  The original design used a gate time of one second which gives a count resolution of 1Hz.  Maximum input frequency is about 50MHz.  A VHF/UHF prescaler for this counter is described in Homebrew, RadCom February 2008.  U2 is a PIC 16F628 (PIC 16F628-20 or PIC 16F628A).  The PIC  crystal frequency is 10.240MHz.  The firmware is easily modified so that a 10MHz crystal can be used instead.  Homebrew for March 2008 shows how this counter can be used with a GPS or Loran controlled gate. __ Designed by EI9GQ homebrew radio

Frequency counter -  This project explain a very powerful frequency counter which has many useful software functions.  The software can add or subtract 3 different iF frequencies (±455 kHz , ±10.7 MHz and ±21.4 MHz).  You have also two level of resolutions, 1kHz and 100Hz __ Contact maxit91 @ hotmail.com

Frequency Counter -  Frequency counter with output on 7-segment display __ Contact maxit91 @ hotmail.com

Frequency counter based on PIC16F628 & LCD display -  This is the support page for the simple frequency counter project in Homebrew, RadCom October 2006.  The original design used a gate time of one second which gives a count resolution of 1Hz.  Maximum input frequency is about 50MHz.  A VHF/UHF prescaler for this counter is described in Homebrew, RadCom February 2008.  U2 is a PIC 16F628 (PIC 16F628-20 or PIC 16F628A).  The PIC  crystal frequency is 10.240MHz.  The firmware is easily modified so that a 10MHz crystal can be used instead.  Homebrew for March 2008 shows how this counter can be used with a GPS or Loran controlled gate. __ Designed by EI9GQ homebrew radio

Frequency Division Battery Detector  -  This simple circuit uses an ultrasonic sensor (part # 255-400SR16) from Mouser electronics.  it amplifies the signal and then converts the ultrasonic frequency by digital division down to a human frequency.  The resulting sound at the headphones is a "buzz" when a bat calls nearby __ Contact archilochus57 @ yahoo.com

Frequency Emissions Detector -  The F.E.D. (Frequency Emissions Detector) will, of course, detect anyone's cell phone, so the detector really responds to just about anybody with more than two pennies to rub together.  Most phones occasionally transmit short bursts to the nearest cell tower, even when the phone isn't in use, so a typical 21st century loiterer will eventually set off the detector.  On the other hand, a deer can stare at it for an hour with no effect.  Let's face it, even most burglars emit digital signals these days.  So, in a sense, the F.  E.  D.  is a human detector.  With that in mind, consider using the output to activate a digital camera or video recorder to capture a record of the prowlers.  A recorded barking dog or, one of my favorites, a recording of police radio traffic will scare off most crooks.  Add some hidden flashing red and blue lights to the police chatter and the culprits will actually run away.   __  Contact:  Charles Wenzel of Wenzel Associates, Inc.

Frequency Measurements using Pc -  PROBiR GOYAL Here is a simple technique for measuring frequencies over quite a wide frequency range and with acceptable accuracy limits using a PC.  it follows the basic technique of measuring low...__ Electronics Projects for You

Frequency Meter & Pulse Generator -  Simplicity in circuitry was the design direction.  Zero mass (firmware only with no physical components) would the ultimate achievement.  This instrument doesn't have any front panel controls because the user interacts via an RS-232 terminal program at 9600 baud.  I needed a frequency meter for my experiments in Nondu, Thailand, where I really don't have room for a lot of instruments.  I wrote some straight forward code to read the 16 bit counter in the AT90S2313 after period of time, which was determined by running a timing loop.  By the way, I tried various approaches using interrupts from the 8 bit timer to set the counting interval, but found timing uncertainty resulted in intolerable jitter in the measurements, to as inelegant as it is, timing loops turned out the be give the best results.  The results of the counts are converted to acsiI and sent to the terminal.  After finishing the frequency meter, I realized that only half the Flash ROM was used and that I could fit a handy pulse generator program I found on the web into the same chip, but having two instruments in one.  The result is a combined counter and frequency meter.  The chip flips between the two programs, The only things common between the two programs is some initialization and some of the serial port i/O code.  The pulse generator firmware is pretty much as originally published, except that I modified it to drive a resistor network so as to allow the pulse output amplitude to be selectable.   __ Designed by Dick Cappels

Frequency multiplier improves line readings -  EDN Design Ideas:  March 26, 1998    [  NOTE:    FILE
has multiple design, scroll for this one.]  Because of the low frequencies involved, accurately measuring line-frequency variations is complicated. When you use an ordinary frequency counter with a 1-sec gate time, the reading would be 59, 60, or 61 Hz. To obtain 0.01-Hz accuracy, you must increase the gate time to 100 sec, a scale that most frequency counters do not offer. __ Circuit Design by Yongping Xia, Teldata Inc, Los Angeles, CA

Frequency source feeds entire lab -  01/23/03 EDN Design Ideas:  Plumbing a laboratory with a standard frequency makes a lot of sense if the lab uses multiple frequency counters, spectrum analyzers, and other frequency-dependent test equipment.  Rather than spending time keeping all of the instruments' oscillators in calibration or buying expensive, high-precision oscillators, you can use the circuit in Figure 1 to distribute a single calibrated frequency sou __ Circuit Design by Mitchell Lee, Linear Technology Corp, Milpitas, CA

Frequency Window Comparator has hysteresis -  11/07/96 EDN Design Ideas:  The frequency comparator in Figure 1 uses two VCOs.  C1, R1+R2, and the voltage at pin 9 determine the frequency of IC 1 (900 Hz].  C3, R5+R6, and the voltage at pin 9 determine the frequency of IC 2 (1580 Hz].  if fiN is lower than 900 Hz, then the output P2 of phase-comparator 2 in IC 1 is high and drives __ Circuit Design by W Dijkstra, Consultant, Waalre, The Netherlands

Frequency To Voltage Conversion -  Using the LM2917 for a few useful applications __ Contact P. Townshend - EduTek Ltd

Frequency-Activated Switch for Cars -  A cheap, adjustable design that lets you switch devices on and off according to speed.__ SiliconChip

Fridge Temperature & Humidity Indicator -  We can measure temperature and humidity inside the fridge using a normal temperature-humidity indicator but relative humidity (RH) could be inaccurate in that case.  The moment the fridge door is opened, ...__ Electronics Projects for You

Front End + Power Supply Circuits of the Electric Filed Disturbance Monitor -  This schematic is the power supply and front-end sections of my field monitor, "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

Frost Alarm -  The thermistor used has a resistance of 15k at 25 degrees and 45k at 0 degrees celsius.  A suitable bead type thermistor is found in the Maplin catalogue.  The 100k pot allows this circuit to trigger over a wide range of temperatures.  A slight amount of hysteresis is provided by inclusion of the 270k resistor.  This prevents relay chatter when temperature is near the switching threshold of this circuit __ Designed by Andy Collison

FSM Field Strength Meter -  This is a wide band signal strength meter circuit which responds to small changes in RF energy, designed to be used for the VHF spectrum and will respond to AM or FM modulation or just a plain carrier wave.   __ Designed by Andy Collison

Full Featured Transistor Tester -  Just the thing to check the transistors for any project __ Designed by Rod Elliott  ESP

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Got Designs?
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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

 


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