Electronic Replaces Mechanical Push-Push Switch -  09/28/06 EDN-Design Ideas Mechanical pushpushbutton switches (also known as alternate-action or push-on/push-off switches) can be bulky and expensive.  As an alternative, an electronic version uses a cheaper, NO (normally open) , momentary-on switch (Figure 1) Design by Donald Schelle, Maxim Integrated Products Inc. Sunnyvale, CA

Flashing LED Advertising Badge #1 -  I have seen numerous flashing light badges at trade shows and conventions.  They are often handed out as gifts to promote some business.  The devices often use inefficient circuits, which cause the battery power source to be quickly depleted . . . Hobby Circuit designed by Dave Johnson P.E.-March, 2002

Follow the Debouncing flip-flops -  02/17/00 EDN-Design Ideas During a recent development effort, we could not find literature detailing how to debounce an spst momentary switch using only logic (no capacitors, Schmitt triggers, or other components).  Our application placed the spst switches several feet from the logic board, and both noisy switches and line transients caused false triggers. Design by Ray Scott

Form Positive Pulses from Negative Pulses -  07/14/11  EDN-Design Ideas Create positive pulses even when negative pulses vary in amplitude.  The circuit in this Design Idea converts negative pulses to positive pulses.  Although that task may seem simple, the negative pulses have amplitudes of −5 to −2V.  The positive pulses also need different pulse widths, depending on the application, and the negative pulses are trapezoidal.  The pulses must travel over a long-distance transmission line to a control device.  Several circuits solve the problem, depending on the amplitude and shape of the pulses. Design by Vladimir Rentyuk, Zaporozhye, Ukraine

FPGA Emulates 74X74 Flip-Flop -  10/12/95 EDN-Design Ideas The Xilinx 4000 Series FPGA library contains a D-type flip-flop with either asynchronous preset or clear, but not both.  The circuit in Fig 1 provIdeas both functions, thereby eliminating the need to use discrete 74X74 ICs.  The circuit consists of a set flip-flops, two reset flip-flops, a 4:1 multiplexer(of which you use only two channels], and a few logic gates.  If either PR Design by Keith Gomarac, AIL Systems, Lancaster, CA

FPGA implements X.50 Division 3 recommendation -  04/13/00 EDN-Design Ideas The scheme in Figure 1a uses five delay cells and an XOR gate to configure the data stream for the X.50 Division 3 recommendation of ITU-T.  The X.50 recommendation defines the fundamental parameters of a multiplexing scheme for interworking data Design by Andres Martinez, Alcatel, Ramirez de Prado, Spain

Gated Oscillator Emulates a Flip-Flop -  03/16/95 EDN-Design Ideas The gated oscillator in Fig 1 holds its existing state when disabled rather than being forced high or low-a singular property.  Further, you can generate an output at one-half the input frequency if you choose R1 and C so that the oscillator changes state just once when its input goes high.  This configuration eliminates a flip-flop. Design by Einar Abell, ADA Instruments, Three Rivers, CA

Generate Short Delayed Pulse -  This circuit generates a short 10ms pulse 15 minutes after a “start” pushbutton switch is activated . . . Hobby Circuit designed by David Johnson P.E.-October, 2005

Generating a Delayed Pulse with a dual 555 Timer -  The circuit below illustrates generating a single positive pulse which is delayed relative to the trigger input time.  The circuit is similar to the one above but employs two stages so that both the pulse width and delay can be controlled.  When the button is depressed, the output of the first (__ Designed by Bill Bowden

Generator features programmable duty cycle -  10/26/00 EDN-Design Ideas The simple pulse generator in Fig 1 allows you to program its output's duty cycle.  You apply your duty-cycle code to the B port of IC1, a 7485 magnitude comparator.  The clock increments the 74193 4-bit counter, IC2.  When the output of the counter is equal to or greater than your duty-cycle code, IC3 resets the output flip-flop, IC4, until the counter, IC2, overflows.  Thus, your input code determines the output's duty cycle. Design by Shwang-Shi Bai, Chung Shan Institute of Technology, Lung-Tan, Taiwan

Generator has independent pulse width, frequency -  11/11/99EDN-Design Ideas A common circuit in electronics is the square-wave, astable multivibrator (one-shot), which is useful for various purposes, such as timing circuits and audible alarms.  The most common way to generate the desired square wave is to use the inexpensive 555 timer.  The need sometimes arises for a square wave with fixed frequency but variable pulse width or vice versa. Design by Davinder Oberoi

High Current MOSFET  Flip Flop with Debounced Pushbutton -  This circuit was adapted from the "Toggle Switch Debounced Pushbutton" by John Lundgren.  It is useful where the load needs to be switched on from one location and switched off from another.  Any number of momentary (N/O) switches or push buttons can be connected in parallel.  The combination (10K, 10uF and diode) on the left side of the schematic insures the circuit powers up with the load turned off and the NPN transistor conducting.  These components can be omitted if the initial power-on condition is not an issue. __ Designed by Bill Bowden

High-Speed Pulse Generator Has Programmable Levels -  12/31/69 EDN-Design Ideas Lilliputian dimensions associated with the submicron geometries of most digital and many analog processes result in much faster circuit operation.  As ICs speed up, the rise and fall times of most pulse and function generators, which are typically 5 nsec, become inadequate for measuring time intervals lower than 20 nsec.  You can overcome this limitation with analog comparators or advanced CMOS logic gates, which create faster digital edges. Design by John Guy, Maxim Integrated Products, Sunnyvale, CA

High-Speed Pulse Modulator Retains Signal Envelope -  06-Aug-09 EDN-Design Ideas Modulated signals have the ac components they need to pass through transformers. The circuit in Figure 1 enables you to convert an arbitrary, relatively slowly varying voltage waveform to a new waveform in which the instantaneous values of the original waveform alternate with positive and negative signs.  The new waveform retains information about the original waveform, . Design by MariĆ”n Stofka, Slovak University of Technology, Bratislava, Slovakia

High-Voltage DC Generator -  Voltage, by definition, is the electrical pressure that causes current to flow through a conductor.  When that pressure is sufficiently high, a high voltage is produced.  But how do we define high-voltage? Is 100, 1000, or 10, 000 volts considered high voltage? When compared to 10 volts, they all can be considered high voltage __ Designed by Tony van Roon  VA3AVR

Honeybee Counter -  I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive.  The low power circuit uses a slotted opto-sensor to detect the passing bees.  The circuit advances an electronic counting. . . Circuit by David A. Johnson P.E.-July, 2000

Indicates when it is Time to Dust -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per secondCircuit Solution by David Johnson P.E.-May, 2006

Indicates when it is Time to Dust -  I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough.  I have not yet built and tested this circuit completely but in concept it should work. . . Circuit by David Johnson P.E.-June, 2000

It's Time to Dust Indicator -  I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough.  I have not yet built and tested this circuit completely but in concept it should work . . . Hobby Circuit designed by David Johnson P.E.-June, 2000

LED Flashing Badge #1 -  I have seen numerous flashing light badges at trade shows and conventions.  They are often handed out as gifts to promote some business.  The devices often use inefficient circuits, which cause the battery power source to be quickly depleted. . . Circuit by David Johnson P.E.-March, 2002

LED Flashing Badge #2 -  This circuit uses a CD4013 dual D Flip/Flop IC.  A single lithium battery will provide months of continuous LED flashing.  It also has a tiny push-button switch to turn on and off the light flashing. . . Circuit by David A. Johnson P.E.-March, 2002

LM324 Pulse Width Modulator -  Schematic only, no circuits description. __ Designed by Tony van Roon  VA3AVR

Load Pulser Tests Supply's Transient Response -  04/11/96 EDN-Design Ideas  Modern µPs place severe demands on the transient response of the power source.  For example, Intel's P6 specification stipulates an output-current capability of at least 30A/µsec while maintaining output-voltage regulation within specified limits Design by Chester Simpson, National SemiConductor, Santa Clara, CA

Miniature Pushbutton On/Off Switch -  In many battery powered devices, you would like to turn the circuit on and off by pressing a small pushbutton switch.  One press turns the device on and second press turns it back off.  The flip/flop circuit below uses a minimum number of parts to perform . . . Hobby Circuit designed by David Johnson P.E.-October, 2005

Minimize the Short-Circuit Current Pulse in a Hot-Swap Controller -  27-May-04 EDN-Design Ideas Because of internal circuit-breaker delay and limited MOS-gate pulldown current, many hot-swap controllers do not limit current during the first 10 to 50 µsec following a shorted output.  The result can be a brief flow of several hundred amperes.  A simple external circuit can counter this problem by minimizing the initial current spike and terminating the short circuit within 200 to 500 nsec Design by Jim Sherwin and Thong Huynh, Maxim Integrated Products, Sunnyvale, CA

Momentary Touch Activated Switch -  A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad. . . . Hobby Circuit designed by Dave Johnson P.E.-January, 2002

Monostable 555 -  When the circuit is turned on, the output is LOW and a brief negative pulse on pin 2 will make the output go HIGH for a period of time determined by the value of R and C.  If pin 2 is low for longer than this period, the output will remain HIGH while pin 2 is LOW and immediately go LOW when pin 2 goes HIGH __ 555-Timer

Monostable Flip Flops (One Shot) -  The two circuits below illustrate using the 555 timer to close a relay for a predetermined amount of time by pressing a momentary N/O push button.  The circuit on the left can be used for long time periods where the push button can be pressed and released before the end of the timing period.  For shorter periods __ Designed by Bill Bowden

Multiple Pulse Generator -  I used this circuit to ring my doorbell rapidly three times when a car pulled into my driveway.  R2 and C2 set the output frequency.  Use a diode and resistor to change the duty cycle, if desired.  R1 and C1 set the cycle time which sets the number of pulse __ Designed by Andrew R. Morris

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