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Control Circuits

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Last Updated: October 18, 2017 05:04 AM

Circuits Designed by Dave Johnson, P.E.

Audio Activated SwitchThis circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.    It could be used to turn on a relay, routing the signal to were it is needed.. . . Circuit by Dave Johnson P.E.-July, 2006

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 David Johnson P.E.-July, 2000

Automatic DC Motor BrakeIn many DC motor powered systems you would like the motor to quickly come to a full stop.   This circuit provides an automatic electronic braking action to any DC motor ranging from 6v to 24v up to 1 amp of current.  Some of the component values could be changed . . . Hobby Circuit designed by David Johnson P.E.-September, 2004

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

Audio Attenuator Features 0.001% TH -  07/18/96  EDN-Design Ideas A single-channel audio attenuator package maintains input-signal fidelity as it attenuates the signal level in 1-dB selectable steps over 0 to -62 dB.  National Semiconductor's LM1971, with 3-dB bandwidth of more than 200 kHz, is a digitally controlled device that also includes a >100-dB mute function.  Applications include communications systems, cellular phones and pagers, and audio-mixing systems.   __ Circuit Design by Submitted by EDN Staff

Audio Controlled Christmas Lights -  Here is a simple circuit to control 110VAC things such as Christmas Lights with low voltage audio.  Be careful, high voltage AC can kill you.    The basic Idea was to have Christmas lights flash with the music.  In my design I use an ordinary amplified computer speaker, a diode bridge, and a ‘CRYDOM’ SSR   (Solid State Relay).  In order to increase the time that the lights were on as well as protect the SSR I used a Diode Bridge to rectify the signal from the amplifier circuit.   __ Designed by Written by Alan Parekh

Audio Frequency Digital Noise Generator -  When 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 David Johnson P.E.-July, 2000

Audio Graphic Equaliser -  Audio graphic equalizers are very common as commercial products (for Hi-fi, car audio and stage use) but circuits for them are very rarely published.  I didn't design this one but it's really very simple.  The details shown are for a 7 band but the principle can be extended to almost any number of bandsif you can find accurate enough components. __ Designed by Richard Torrens

Audio Level Control Device -  Controlling the level of an audio signal by means of an applied voltage or current has always been problematical but often desirable, particularly when it is necessary to control a circuit from a computer.  This App Note deals with voltage or current controlled attenuators using optocouplers, primarily in relatively static situations   (as opposed to the dynamic control that occurs in compressors, limiters and noise gates  __ Designed by Solines, a Cassio Company

Audio Level Indicator -  Audio Amplifier output relay delay __ Designed by Tomi Engdahl

Audio Level Meter -  Audio levels can be monitored using a small panel meter with this circuit built from discrete components.  The circuit has a flat frequency response from about 20Hz to well over 50Khz.  Input sensitivity is 100mV for a full scale deflection on a 100uA meter.  Built on two common emitter amplifiers, the first stage has a preset resistor which may be adjusted for a FSD.  The last stage is biased to operate at roughly half the supply voltage for maximum ac voltage swing.  Audio frequencies are passed through the 10u dc blocking capacitor and the full wave bridge rectifier converts the signal to a varying dc voltage __ Designed by Andy Collison

Audio Signal Detecting Auto Power-On Unit -  The switch detector unit is shown in Figure 1, and uses an LM358 dual opamp, and a handful of other parts.  The relay switching device is a MOSFET, selected because of the almost infinite input resistance.  The 2N7000 shown is recommended because it has a threshold voltage of less than 3V and is fairly cheap, but virtually any MOSFET will work just as well, even if the gate threshold is a little higher.  An MTP3055 can also be used, as shown originally in this circuit.   __ Designed by Rod Elliott  ESP

Audio spectrum analyzer on PIC32 -  This simple audio spectrum analyzer is based on PIC32 proto board on PIC32MX360F512L with 320×240px colour LCD   (LVC75Z779 Eval Board).  The analyzer can be connected to unamplified audio source like PC’s sound card, MP3 player and so

Audio Tone Controls -  Many people at one time or other, regardless of their interest in electronics, have adjusted these controls to suit their preference.  Whether its to boost the bass of their favorite CD, cut the noise / static on a talk radio station or compensate for poor loud speaker response, they've reached for the treble and bass tone controls.  

Audio-Controlled Running Light -  This mains-operated audio-controlled running light can be used in discotheques.  The lamps glow in running sequence as per the sound of music.  Of the ten AC lamps, only one lamp permanently...__ Electronics Projects for You

Auto Heat Limiter for Soldering Iron -  Usually a soldering iron takes a couple of minutes to get adequately heated up to melt the solder, after which the heat generated is much above the requirement and is wasted.  Moreover, excessive heat decreases the life of the bit and the element, causing serious damage to the components.   __ Contact: IQ Technologies

Auto Power Off -  We are surrounded by battery operated equipment of all kinds, and this array is growing still.  Manufacturers and designers lean over backwards to make sure that their equipment draws a small current and can thus be operated by a battery.  This has its flip side, too.  because even if the equipment in question draws only

Auto Reset Over/ Under Voltage Cut- Out -  This over/under voltage cut-out will save your costly electrical and electronic appliances from the adverse effects of very high and very low mains voltages.  The circuit features auto reset and utilises easily...__ Electronics Projects for You

Auto-Fan, temperature control -  This circuit was designed to automatically activate a set of three or four small DC fans to cool a large cool-rib for a 10 Amp powersupply.  Can be used in a variety of other applications as well __ Designed by Tony van Roon  VA3AVR

Automate Switch-Over Between Battery & Source -  12/18/97 EDN-Design Ideas The use of a logic supply or an ac wall adapter can extend battery life in a small portable system by offloading the battery.  However, managing the switch-over between battery and external power can be messy.  For high-cell-count b __ Circuit Design by Len Sherman, Maxim Integrated Products, Sunnyvale, CA

Automatic 12 Volt Lamp Fader -  This circuit is similar to the "Fading Red Eyes" circuit   (in the LED section) used to fade a pair of red LEDs.  In this version, the lamps are faded by varying the duty cycle so that higher power incandescent lamps can be used without much power loss.  The switching waveform is generated by comparing two linear ramps  __ Designed by Bill Bowden

Automatic control starts loads softly -  10/13/94EDN-Design Ideas Applying ac power to the circuit in Fig 1 causes it to gradually increase the power to the ac load, effecting a "soft start.   "  The components connected to 555 timer IC1's pin 2 provide a trigger synchronized with the ac input's zero crossing.  In conventional 555 fashion, R1, R2, and C determine IC1's period.   __ Circuit Design by Liu Ning, Institute of Quantum Electronics, South China Normal University, Guangzhou, China

Automatic Curtain Closer -  This circuit uses a mixture of transistors, an IC and a relay and is used to automatically open and close a pair of curtains.  Using switch S3 also allows manual control, allowing curtains to be left only partially open or closed.  The circuit controls a motor that is attached to a simple pulley mechanism, to move the curtains__ 555-Timer

Automatic DC Motor Brake -  In many DC motor powered systems you would like the motor to quickly come to a full stop.   This circuit provides an automatic electronic braking action to any DC motor ranging from 6v to 24v up to 1 amp of current.  Some of the component values could be changed . . . Hobby Circuit designed by David Johnson P.E.-September, 2004

Automatic Emergency Light -  This emergency light has the following two advantages: 1.  It turns on automatically when the mains power fails, so you need not search it in the dark.2.  Its battery starts charging as...__ Electronics Projects for You

Automatic Emergency Light -  This circuit implements the concept of emergency light through relays.  The circuit lights up LEDs in case of power failure and charges the batteries otherwise.   __ Contact: IQ Technologies

Automatic emergency torch -  Just don’t think that this is yet  another addition to other emergency light circuits published in EFY earlier.  This circuit is a hit different. __ Designed by bhgya parma

Automatic Evening Lamp -  Presented here is a solution for switching off outdoor lamps even when you are not at home.  The lamp turns on in the evening and turns off in the morning so...__ Electronics Projects for You

Automatic fading lights -  Suitable for 230V incandescent bulbs; Ideal for Christmas decorations __ Contact: Flavio Dellepiane, fladello @ tin.it

Automatic fan controller -  This circuit use LM311, 2N3904 and some components

Automatic Fan Controller -  Th1, the 50K thermistor, is a standard type.  Mine was a bar or rectangular looking thingy.  Available from Tandy/Radio-Shack.  Almost any type will do.  I experimented with different models from 22K to 100K and all worked fine after replacing the trimmer pot.  The one used in the above circuit diagram was a 50K model.  This 50K was measured at exactly 25 °C and with 10% tolerance.  The resistance increases as the surrounding temperature decreases.  Tolerance for my application   (cooling a large powersupply coolrib) is 10%.   __ Designed by Izhar Fareed

Automatic Fan Controller for AIR-Conditioners -  Many central air-conditioning systems   (ACs) have the option for cooling and heating both.  These have a fan for blowing hot or cold air drawn from a central unit, often with no...__ Electronics Projects for You

Automatic Gain Control AGC -  This project is a digital Automatic Gain Control   (AGC) system using a PIC16F876 MCU.  The ability to set the gain level in a circuit and have it control itself is a very useful function.  This circuit is a building block of another project I am working on.  A 30W power amp for either the PCS, iDEN or CDMA frequency bands.  I will settle on one of those frequencies sometime soon.   __ Designed by steevn.geo @ yahoo.com

Automatic latch-off saves batteries -  01/04/07  EDN-Design Ideas Persistent latch prevents batteries from overdischarge __ Circuit Design by Kieran O'Malley, On Semiconductor, West Kingston, RI

Automatic Loudness Control -  Simple add-on module Switchable "Control-flat" option __ Contact: Flavio Dellepiane, fladello @ tin.it

Automatic Mains Disconnect -  Downloading and CD-burning programs usually provide the option of automatically shutting down the PC on completion of their tasks.  However, this energy-saving feature is of little benefit if even after the PC has been switched off, all of the peripheral equipment remains connected to the mains and happily consumes watt-hours.  The circuit shown here provides

Automatic Night-Light Feeds Directly From the AC Line -  EDN-Design Ideas 06/06/2012   Switch an ac load on and off with just four components.   There are many approaches to the problem of activating a light when it becomes dark, and a recent Design Ideas covers this topic   (Reference 1).  Some approaches require a dc power supply and an electromechanical relay, but a better approach involves feeding the device directly from the ac line, minimizing the number of components   (Figure 1).    __ Circuit Design by Abel Raynus, Armatron International Inc, Malden MA

Automatic Power Switch -  This circuit turns a slave device on when a master device is turned off or on depending on  state of S1.  The circuit is designed to be reliably and solidly on or off.  Some simpler slave switches can mistrigger or trigger partially,  __ Designed by Andrew R. Morris

Automatic Power-Off Saves Battery -  12/19/96 EDN-Design Ideas The Basic training program in Listing 1  helps visually handicapped people easily learn Braille dot code with the help of a trainer.  The trainer generates six-pin Braille code using six solenoids operating on an LPT1/2 either by directly connecting the low-power solenoids to the data bits of the parallel port or by driving solenoid pins  (pull-out type] using an UN2003 power driver  (Figure 1).  Push-in type solenoids require complemented  (0 for 1 and 1 for 0] Braille-code data bits or an extra inverter on the LPT1 port __ Circuit Design by Jose Carlos Cossio, Santander, Spain

Automatic Power-Resumption Alarm -  Most power-resumption alarm devices produce non-stop alarm when power resumes.  To overcome this problem, here is an automatic circuit that sounds an alarm for a few seconds only after power resumes....__ Electronics Projects for You

Automatic Pump Shut Off -  Put together an automatic system to switch off a pump when there is no more fluid left to pump.   __ Designed by REUK-Renewable Energy UK website

Automatic Range Hood -  Come to think about it, it’s a bit strange that range hoods in our kitchens don’t switch on and off automatically.  After all, a simple temperature sensor under the hood can detect whether a burner is on.  The circuit described here goes a step further and compares the temperature under the hood with the temperature just outside the hood.  At a certain   (adjustable) temperature difference, the hood will be switched on, possibly along with the lamp under the hood. __ Designed by Heino Peters © Elektor Electronics Magazine

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