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Digital  / Logic Circuits 
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Last Updated on: Thursday, November 30, 2017 04:23 PM

Circuits Designed by Dave Johnson, P.E.

Audio Frequency Digital Noise GeneratorWhen you need to test an audio circuit with broadband noise, this circuit works great.  It uses just three inexpensive C-MOS ICs that generate a series of output pulses whose widths vary randomly.  I included a level control pot. . . Circuit by Dave Johnson P.E.-July, 2000

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

A 1000:1 EHT Probe -  Do you need to measure the EHT voltage in a CRT-based scope, computer monitor or TV receiver, or perhaps in a photocopier, laser printer or microwave oven? You'll need an EHT probe to suit your digital multimeter    (DMM) to do this and you'll find they are pretty pricey.  Not to worry though, because here's one you can build for less than $40.__ SiliconChip

A 12V Digital Timer using a 240v Timer Module -  240V timers are very cheap these days.12V timers are not so cheap.  So why not use the "innards" out of a 240V timer and make a very flexible 12V timer?__ SiliconChip

A 4-Digit Alarm Control KeypA - D -  Alarm Control Keypads:  This Keypad is suitable for the Modular Burglar Alarm.  However, it has other applications.  Pressing a single key will energize the relay.  Entering the Four-Digit code of your choice will de-energize it.  __ Designed by Ron J.

A 4-Digit Keypad Controlled Switch -  Universal Keypad-Controlled Switches:  This is a Universal version of the Four-Digit Alarm Control Keypad.  I have modified the design to free up the relay contacts.  This allows the circuit to operate as a general-purpose switch.  I've used a SPCO/SPDT relaybut you can use a multi-pole relay if you wish.  __ Designed by Ron J.

A 6-Decade Resistance Substitution Box -  Get a million resistance values with this __ SiliconChip

A 6-Digit Frequency Counter Module -  Low-cost unit measures frequencies up to 40MHz__ SiliconChip

A Balanced Output Board for the Stereo DA - C -  This project was inspired by requests from a number of readers.  Essentially they said that the GPS module was great for obtaining a precise time but could we produce a project that used its full capabilities for use in a vehicle?__ SiliconChip

A cheap UV EPROM eraser -  An "anti-bacterial" toothbrush holder, a single capacitor and a simple IC carrier are all you need for a fully-functioning EPROM eraser.__ SiliconChip

A Dead-Simple Circuit Masthead Amplifier -  Decided to take the plunge and get into digital TV? For most people, it's simplejust plug the new TV or set-top-box into your existing antenna.  But for many, the old TV antenna and cable just won't be up to it.  Here?s a new kit from Oatley Electronics which could solve your digital woes __ SiliconChip

A Digital Tachometer for Your Car -  Compact design features a 4-digit LED display and a bargraph.  It can also provide gearchange indication and drive a rev limiter.__ SiliconChip

A Digital Thermometer/Thermostat -  It covers the range from -55 C to 1200C and has an over or under temperature alarm and switched outputs for thermostatic control.__ SiliconChip

A Digital Timer for Less than $20 -  Just "nick" the timer from an old microwave oven and fit it into a case.  The resulting timer has lots of uses.__ SiliconChip

A Digital Voltmeter for Your Car -  A PIC microcontroller makes it a snack to build.__ SiliconChip

A Fourth Generation of LCD Backlight Technology -  Linear Technology AN65 __ Designed by Jim WilliamsNov 1st, 1995

A Hierarchical Priority Encoder -  Anormal priority encoder encodes only the highest-order data line.  But in many situations, not only the highest but the second-highest priority information is also needed.  The circuit presented here encodes both...__ Electronics Projects for You

A Knock Detector for the Programmable Ignition  -  The Programmable Ignition System would not be complete without the addition of engine knock sensing.  This Knock Detector is useful for adjusting ignition timing maps and can also automatically retard the ignition timing if engine knock is detected.__ SiliconChip

A Lap Counter for Swimming Pools -  Do you swim laps to keep in shape? This simple Picaxe-powered counter will keep track of the number of laps you've done__ SiliconChip

A Little More Serious Frequency Meter -  Maximum input frequency is specified to be 30 MHz in the multi-chip configuration, and in single-chip configuration, there are both 5 MHz and 10 Mhz versions operating with 10 and 20 MHz crystals, respectively.  All versions have 9 1/2 digit resolution.  I haveused __ Designed by Dick Cappels

A Low Cost AT Keyboard Translator -  This Low-cost project takes the complex scan codes from a PC keyboard and spits out standard ACCII codes.  It's just the shot for use with the BASIC stamp and PIC series of microcontrollers but has lots of other uses as well.__ SiliconChip

A Low Cost Audio/Video Distribution Amplifier -  Easy-to-build unit can distribute six channels of composite video    (& stereo audio) or three channels of S-video.__ SiliconChip

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

A Low-Cost 50MHz Frequency Meter -  It features an LCD readout, auto-ranging and two resolution modes.  And it can be run from a plugpack or battery operated.__ SiliconChip

A Low-Cost PC-to-I2C Interface for Debugging -  Tracking down problems in circuits which are programmed via an I2C bus can be tricky and time-consuming, unless you take advantage of a debugging program running on a PC.  Here's a low-cost, easy-to-build printer port to I2C interface designed to work with the Philips/NXP debugging program URD312.exe.__ SiliconChip

A Milliohm Adaptor for Digital Multimeters -  Do you occasionally need to measure very low resistances accurately but don't have access to an expensive benchtop Milliohm Meter or DMM? This low-cost adaptor will let you use almost any DMM to make accurate low-resistance measurements.__ SiliconChip

A Morse Clock-Look Mum, No Hands! -  If you want to know the time, you've got to learn Morse code.__ SiliconChip

A Moving Message Display -  It's easy to build, easy to program, easy on the pocket and easy on the eye.__ SiliconChip

A Multi-Function GPS Car Computer, Pt2 -  Last month, we introduced our new GPS Car Computer and provided full constructional details.  But there's a lot more that we haven't covered yet __ SiliconChip

A new PIC-based Flexitimer Mk.4 -  Here's a new and enhanced version of a very popular project: an easily-programmed low-cost electronic timer module.  It's compact, easy to build and offers a choice of either a single on period or continuous on/off cycling with independently programmable periods.__ SiliconChip

A PC to Die For: Part 2-You Can Build It Yourself -  Partitioning and formatting the hard disk drive, installing the operating system and sqashing the bugs__ SiliconChip

A PC-Controlled Burglar Alarm SystE - M -  Fancy a full-featured alarm control panel with dialler capabilities? This one is PC-programmed and controlled and can handle up to eight zones.  The PC only needs to be powered up for arming and disarming, or you can use an optional keypad.__ SiliconChip

A PIC-Based Musical Tuning Aid -  This compact device will help you tune almost any musical instrumentacoustic or electronic.  It can produce any note on the tempered musical scale    (standard pitch) in any of the eight most commonly used octaves, with an accuracy of better than ?0.08% or 1.3 musical cents.  The selected note is compared with that from the instrument either by ear or visually by using an eight-LED stroboscopic beat indicator.__ SiliconChip

A PID Temperature Controller -  What's a PID controller? PID stands for "proportional integral differential" and relates to a process which seeks to continuously correct the error between a measured variable and a desired setting by calculating an appropriate correction process.  In practice, it can largely avoid the large overshoots and undershoots that occur in simple temerature control systems.__ SiliconChip

A Poor Man's Q Meter -  Simple circuit mates with an RF signal generator and multimeter for quick-and-easy "Q" and inductance measurements.__ SiliconChip

A Portable Lightning Detector -  This little device could save your life...__ SiliconChip

A Precision Wideband Current Probe for LCD Backlight Measurement -  DN101 Design Notes__ Linear Technology/Analog Devices

A Programmable Continuity Tester -  Our go/no-go continuity tester giving you the ability to set minimum continuity.__ SiliconChip

A Programmable PIC-Powered Timer -  This PIC-based timer can be set for any period from one second up to 680 days and even    (theoretically) up to nearly 60 years.__ SiliconChip

A Programmable-Continuity-Tester -  Easy-to-build unit lets you set the continuity "pass" threshold to anywhere between 1Ω and 100Ω.  It makes an Ideal go/no-go tester.__ SiliconChip

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Digital or Logic Circuits:  #'s - C       D - G       H - M       N - R       S - T       U - Z

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