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Last Updated: December 01, 2017 03:41 AM

Circuits Designed by Dave Johnson, P.E.

Line Powered High Intensity LED FlasherThere are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with . . . Hobby Circuit designed by David Johnson P.E.-December, 2008

Line Powered White LED ArrayThere has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed. . . Circuit by David A. Johnson P.E.-February, 2010

Line-Powered Xenon Flash TransmitterThis line powered xenon flash circuit drives a small camera type flash tube.  It has an optical isolator to allow the flash to be safely triggered from some remote device.  A flash rate of 2Hz is possible with the circuit. . . Circuit by David A. Johnson P.E.-June, 2000

Logic Controlled 12v DC Motor with Automatic BrakeThere are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  This circuit will bring a fast moving DC motor to a stop in seconds.  The braking action is automatically applied whenever DC power is removed. . . Circuit by Dave Johnson P.E.-February, 2010

Low Battery Voltage FlasherThis circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment. . . Circuit by David A. Johnson P.E.-January, 1998

Low Current Flashing LED Power Indicator This circuit flashes a power indicator LED to keep the average current low . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Low Power H Bridge Motor ControllerThis circuit uses a few logic gates & a 74AC240 to control power to a small gear motor. . . Circuit by David A. Johnson P.E.-July, 2005

Low Power LED FlasherJudging from the numerous references I have received, this electronic circuit, hobby circuit seems to be rather popular.  Many published circuits which flash LEDs need 3 or more volts.  This electronic circuit uses only a single inexpensive C-MOS IC and . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Low Power Sequential Flasher using 10 LEDsA while back I posted a flasher circuit which flashed 10 LEDs sequentially.  That circuit was powered by four AA alkaline cells.  The circuit below operates much the same way but has been modified to run from a single 3v CR2032 lithium coin cell . . . Hobby Circuit designed by David Johnson P.E.-April, 2011

Low Power Universal LED FlasherThis low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts.  The 1.0Hz 10ms LED pulsed current is held to a constant 10ma. . . Circuit by David Johnson P.E.-July, 2006

Low Voltage 120vAC Power Line AlarmThis 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 Latch CircuitA Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor.  The kicker was that he wanted to power the circuit and the motor from a single 1.2v NiMH
battery cell.  Texas Instruments comes to the rescue with their family of low voltage single gate ICs.  Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0.8v and lower.  When used with a good NPN transistor, the circuit below works quite nicely. . . Circuit by Dave Johnson P.E.-March, 2013




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

Line Input for Zoom H2 -  NOTE : Must register on this site __ Designed by Published in Elecktor July/Aug, 2010

Line Powered Flashers -  Scroll to find this one.  Here is an unusual flasher circuit for 120VAC loads.  The circuit is similar to the two-transistor flasher seen in several circuits in techlib.  com except that an SCR is used __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Line Powered High Intensity LED Flasher -  There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with . . . Hobby Circuit designed by David Johnson P.E.-December, 2008

Line Powered White LED Array -  There has been a lot of excitement lately in the lighting industry.  Some companies are beginning to manufacture general lighting fixtures, which replace incandescent and fluorescent lamps, using LED lights.  When proper heat management is designed. . . Circuit by David A. Johnson P.E.-February, 2010

Linear & Switcher LED Supplies Combine, Overcome Disadvantages of Each Topology -  01/08/2013   To control their brightness, LEDs need a constant current; this can be done with a resistor placed in series with the LED string.  Both the LED-string voltage and the supply voltage can vary, so a dedicated LED driver is a must to guarantee the current accuracy.  Two solutions—each with advantages and disadvantages—are widely used: a linear constant-current LED driver or a step-down switching converter.   __ Circuit Design by Fabien Franc, On Semiconductor, Phoenix

Linear-brightness controller for LEDs has 64 taps -  03/15/07  EDN-Design Ideas Digital potentiometer controls the brightness of LEDs __ Circuit Design by Ahmad Ayar, Maxim Integrated Products, Sunnyvale, CA

Line-Powered Xenon Flash Transmitter -  This line powered xenon flash circuit drives a small camera type flash tube.  It has an optical isolator to allow the flash to be safely triggered from some remote device.  A flash rate of 2Hz is possible with the circuit. . . Circuit by David A. Johnson P.E.-June, 2000

Linux FRS Radio Control -  Easily control a FRS/GMRS radio from a computer.  __ Green Bay Professional Packet Radio

Linux Infrared Remote Control LIRC -  This manual will guide you through the installation and configuration of LIRC.  Setting up LIRC currently is not an easy task.  So please take some time to read this documentation carefully.  If you don't understand a part of this manual or if you think there is something important missing you should complain __ Designed by Christoph Bartelmus

Liquid-Level Indicator -  The LTC2990 is used to monitor system temperatures, voltages and currents.  Through the I2C serial interface, the device can be configured to measure many combinations of internal temperature, remote temperature, remote voltage, remote current and internal VCC.  The internal 10ppm/°C reference minimizes the number of supporting __ Linear Technology/Analog Devices App Note, Mar 16th 2011

Little bike light using LEDs -  No circuit description, schematic only__ CdS Electronic

LM3909 LED flasher -  LED flasher with the LM3909 IC and runs from1.5-Volt battery.   __ Designed by Tony van Roon  VA3AVR

Load Detector controls power sources -  EDN-Design Ideas 11/11/1999    Emergency generators normally operate when the main power source fails.  Inverters run continuously (and expensively) even when no load-power demand exists.  Even unloaded, a medium-sized inverter consumes some tens of watts just to keep its fan running (and to make noise).  A generator running under no-load conditions just wastes fuel.    __ Circuit Design by Giovanni Romeo

Load Simulator Maintains Constant Power -  04/11/96 EDN-Design Ideas The circuits in Figures 1 and 2 show how you can emulate a constant-power load for cases when a simple load resistor is unacceptable.  For example, using a simple resistor as a load is unacceptable for applications that require you to accurately monitor generated or consumed power.  One such application is in battery-energy measurement.  You measure battery energy density (watts/hour) by measuring the total output power (W=VxI) over time.  This task is relatively simple if you use an automated system to take frequent and periodic measurements of the discharge current and battery voltage while keeping track of time.   __ Circuit Design by Khy Vijeh, Analog Devices, Santa Clara, CA

Load Switcher Draws Only 6 µA -  07/04/96 EDN-Design Ideas Although it draws only 6 µA, the circuit in Figure 1 enables a small ac signal as low as ±1 mV to switch relatively large load currents.  The circuit takes advantage of the IC's very low quiescent current, which, at 1.2 µA maximum per amplifier, is less than the self-discharge of a typical battery.  This current can flow through R1 without turning on Q1.  When you operate the circuit with a sensing coil (Figure 1) and stimulate it with a magnet, the circuit performs the function of a reed switch but with greater sensitivity.  Other applications include alarm systems, bipolar threshold sensing, and audio volume switching. __ Circuit Design by Douglas Dwyer, Frequency Precision Ltd, Okehampton, UK, and Nigel Brook, Maxim Integrated Products, Reading, UK

Logic Controlled 12v DC Motor with Automatic Brake -  There are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  This circuit will bring a fast moving DC motor to a stop in seconds.  The braking action is automatically applied whenever DC power is removed. . . Circuit by Dave Johnson P.E.-February, 2010

Logic-Level actuated gas solenoid for starting propane -  Despite exhaustive searching, every reasonably priced solenoid valve for controlling propane during pushbutton start required 12VDC, beyond the capabilities of a normal pump battery.  I know that there are methods to generate HV pulses which will actuate the solenoid, which will remain closed down to below 5V, but I went the more expensive and reliable route with a DC-DC converter, shown here, the Newport NMR101.  R2 is 10K, and R3 is 100K.  R1 is 39 ohms.  Vary R1 to acheive reliable closing of the valve and to keep current to ~90 mA through the solenoid.  The converter will draw 260 mA from the 5V source.  

Logic-Level actuated, adjustable glow-plug driver -  All of my turbine starts before the research on the ECU involved a very successful spark ignition.  I thought   (only briefly) of trying to add spark ignition to the ECU, but the mixture of delicate logic circuitry and perhaps 30, 000V simply don't mix.  My past experience with the hall sensor ignition for the radial engine bears this out in painful detail.  So I decided to go with a glow-plug driver.  

Long Range FM Transmitter -  This circuit is a circuit diagram fm transmitter.  This circuit is somewhat different from the previous fm transmitter circuit.  Transmitter circuit described here has the additional RF power amplifier stage, after the oscillator stage, to increase the power output of 200-250 milliwatts.  With a good matching 50-ohm ground plane antenna or multi-element yagi antenna, this transmitter can provide a good enough signal strength to a distance of about 2 kilometers.

Long Range FM Transmitter -  The power output of many transmitter circuits are very low because no power amplifier stages are incorporated.  The transmitter circuit described here has an extra RF power amplifier stage, after the oscillator stage, to raise the power output to 200-250 milliwatts.  With a good matching 50-ohm ground plane antenna or multi-element Yagi antenna, this transmitter can provide reasonably good signal strength up to a distance of about 2 kilometres.  The circuit built around transistor T1 (BF494) is a basic low-power variable-frequency VHF oscillator.  A varicap diode circuit is included to change the frequency of the transmitter and to provide frequency modulation by audio signals.  The output of the oscillator is about 50 milliwatts.  Transistor T2 (2N3866) forms a VHF-class A power amplifier.  It boosts the oscillator signal power four to five times.  Thus, 200-250 milliwatts of power is generated at the collector of transistor T2.

Long-range 16-channel Remote Control SystE - M -  It's based on pre-built UHF modules, has a range of up to 1.5km and can be programmed just the way you want.__ SiliconChip

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 Voltage Flasher -  This circuit is designed to monitor two alkaline cells (3v) that form the battery often used in portable electronic equipment. . . Circuit by David A. Johnson P.E.-January, 1998

Low cost / Automatic Emergency Light -  The circuit comprises two sections: charger power supply and LED driver.The charger power supply section is built around 3-terminal adjustable regulator (IC1) LM317, while the LED driver section is built around transistor BD140(T2).  In the charger power supply section, input AC mains is stepped down by transformer to deliver 9V, 500mA to the bridge rectifier, which comprises diodes (IN4007x4). __ Contact: IQ Technologies

Low Cost Thermal Peak Detection Charger -  The electric model aircraft and car industries have produced a bewildering array of field chargers for NiCd motor battery packs.  These range from simple 6 or 7 cell chargers consisting of a resistor and mechanical timer, to more complex chargers with peak detection, cycling, and the ability to handle 36 cell packs __ Designed by Stefan Vorkoettert

Low Current Flashing LED Power Indicator -  This circuit flashes a power indicator LED to keep the average current low . . . Hobby Circuit designed by Dave Johnson P.E.-June, 2000

Low Power Blink LED -  Schematic only, no circuit description __ Designed by Rob Crockett

Low Power H Bridge Motor Controller -  This circuit uses a few logic gates & a 74AC240 to control power to a small gear motor. . . Circuit by David A. Johnson P.E.-July, 2005

Low Power LED Flasher -  Judging from the numerous references I have received, this electronic circuit, hobby circuit seems to be rather popular.  Many published circuits which flash LEDs need 3 or more volts.  This electronic circuit uses only a single inexpensive C-MOS IC and . . . Hobby Circuit designed by David A. Johnson P.E.-June, 2000

Low Power LED Flasher -  It doesn't get much simpler than this circuit.  Four components counting the battery! How can an LED be illuminated by a 1.5V circuit, when the forward voltage of an LED is about 2V? The LM3909 uses the 100uF capacitor as a charge reservoir, building up a voltage of about 2V before discharging the cap through the LED.   __ Designed by billd @ reprise.com

Low Power Sequential Flasher using 10 LEDs -  A while back I posted a flasher circuit which flashed 10 LEDs sequentially.  That circuit was powered by four AA alkaline cells.  The circuit below operates much the same way but has been modified to run from a single 3v CR2032 lithium coin cell . . . Hobby Circuit designed by David Johnson P.E.-April, 2011

Low Power Universal LED Flasher -  This low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts.  The 1.0Hz 10ms LED pulsed current is held to a constant 10ma. . . Circuit by David Johnson P.E.-July, 2006

Low side PWM Motor/Light Controller -  The diagrams are for 12V operation only and there are high side   (common ground) and low side   (common +12V) versions.  The low side version of the circuit uses an N Channel FET, the high side version of the circuit uses a P Channel FET.  N Channel devices tend to handle more current than P Channel devices, they are also less expensive.  The high side version of the circuit is useful when one side of the load has to be grounded __ Designed by G. Forrest Cook

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 Hot Swap Controller Ignores Backplane Noise & Surges -  DN319 Design Notes__ Linear Technology/Analog Devices

Low Voltage Latch Circuit -  A Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor.  The kicker was that he wanted to power the circuit and the motor from a single 1.2v NiMH
battery cell.  Texas Instruments comes to the rescue with their family of low voltage single gate ICs.  Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0.8v and lower.  When used with a good NPN transistor, the circuit below works quite nicely. . . Circuit by Dave Johnson P.E.-March, 2013

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Control Circuits:   #'s - A       B - C       D - G        H - L       M - P        Q - S        T - U        V - Z


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