Keyboard Data-Acquisition System Is Cheap & Simple -  December 31, 1969   EDN-Design ideas   -     The most important criteria of a data-acquisition system for college science laboratories are simplicity and price rather than precision or speed.  The data-acquisition system in Figure 1 offers adequate precision of less than 0.5% and speed of 1 Hz to replace the outdated laboratory chart recorder in student laboratories.  You can install the system in 5 sec, operate it with a single toggle switch, and construct it for approximately $40.  The only additional equipment necessary is a computer running Excel and an ATbus (not Universal serial bus) , keyboard.    Design by Tom Lyons Fisher, Juniata College, Huntingdon, PA

KeyLock -  Press four keys in specific order, and relay will turn on for about to 5 seconds and that is it.  But first you must memorize your code following this way: press and hold button (button on pin 3) , so long until LED goes ON.  Now, when.   __ Designed by © Ivica Novakovic

Keypad Access -  Dual programmable keypad code lock.  Open electrical doors with your secret code only!  __ Designed by Michel Bavin

Keypad Circuit-with Parallel Code Entry -  Universal Keypad-Controlled Switches:  This is a universal four-digit keypad-operated switch - with a difference.  instead of entering the security code one number at a time - the four keypad buttons must be pressed simultaneously.  Split the code between two separately located keypads - and two people will have to be present in order to operate the switch.  Each person can have a different three-digit code. __ Designed by Ron J.

Keypad Combination Lock  -  A digital combination lock using a push button keypad.  The combination can be changed and the lock has an entry delay.   __ Designed by Andy Collison

Keypad Control for Multiple Appliances -  This circuit employs DTMF technique to switch on/off up to ten appliances.  it can be modified to operate up to 100 appliances using the same keypad.  The controller uses telephone-type keypad with__ Electronics Projects for You

Keypad Controlled Switch No.2 -  Universal Keypad-Controlled Switches:  This is a simplified version of the 4-Digit Keypad Controlled Switch.  I have modified the design to reduce the complexity of the circuit - and the number of components required.  As a result - the code is somewhat less secure.  However, there should be lots of situations where it will still be adequate.  __ Designed by Ron J.

Keypad Electronic Door Release -  The IC is a quad 2 input "AND" gate, a CMOS 4081.  These gates only produce a HiGH output, when BOTH the inputs are HiGH.  When the key wired to 'E' is pressed, current through R1 and D1 switchs Q5 on.  The relay energises; and Q5 is 'latched on' by R8.  Thus, the Alarm is set by pressing a single key, say one of the two non-numeric symbols __ Designed by Ron J.

Keypad Encoder ComMands Tape Transport -  09/02/96 EDN Design Ideas:  Sometimes, using a component in an application other than its intended application can yield savings in design time, component count, cost, and complexity.  The MM74C922N, originally designed to detect, debounce, and encode 16-key switch matrices, contains most of the elements needed for a full-function magnetic-tape-transport motion-control circuit (Figure 1).  The IC replaces more than nine packages of CD4000 flip-flops and random logic and provide as everything but a motion-sensing circuit.    Design by James Mears, National Semiconductor Corp, Tacoma, WA

Keypad engine immobiliser -  There's no need for a hidden "kill" switch.__ SiliconChip

Keypad Operated Switch No.2 -  I have modified the design to reduce the complexity of the circuit - and the number of components required.  As a result - the code is somewhat less secure.  However, there should be lots of situations where it will still be adequate.   __ Designed by Ron J

Keypad Project -  interfacing a 4X4 keypad to a BSiI using a 74922 encoder chip.  This is a great project for data entry, security keylocks, and much more.  Only uses 5 i/O pins on the Stamp.  __ 

Keypad sequence activates relay -  10/12/00 EDN Design Ideas:  Today, it seems that µPs assume even the easiest tasks, such as activating a relay (for an alarm or access control, for example]via a keyboard command.  However, a simpler and less expensive solution is available (Figure 1).  Moreover, the method does not entail programming and the concomitant, almost inevitable,  Design by JB Guiot, DCS AG, Allschwil, Switzerland

Latch Switch -  in this circuit a non-locking push switch is used to activate a load.  The load remains switched on until power is removed from the circuit.   __ Designed by Andy Collison

Latching power switch uses Momentary pushbutton -  01/20/2014  EDN-Design ideas   -      This could be the cheapest way yet to convert a momentary switch into an on-off power controller Design by Anthony Smith

Latching power switch uses Momentary-action pushbutton -  28-Oct-04 EDN Design Ideas:  Most inexpensive pushbutton switches, particularly pc-board-mounting and membrane types, have momentary action.  Latching types are often larger and relatively expensive, and they frequently are unavailable in the style you'd like to use.  You can thus have a problem if you need a small, inexpensive on/off switch for latching power to a load Design by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK

LCD 2x16 characters &  4x4 keypad assembly example -  Connect some 2x16 characters LCD display and 4x4 keypad with AVR microcontroller __ Designed by Jerry Meng

Light/Dark 12V Switch -  Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  it uses an inexpensive phototransistor as the light detector.   . . . Circuit by David Johnson P.E.-June, 2008

Light/Dark Activated Motion Detector -  This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes . . . Circuit by Dave Johnson P.E.-August, 2005

Logic offers Complementary Switch Control -  12/06/01 EDN Design Ideas:  The complementary-switch controller in Figure 1 uses a few inverter gates to provide drive signals for the complementary switches.  Complementary-switch configurations find wide spread use in synchronous-rectification circuits, charge pumps, full-bridge control circuits, and other circuits.  The circuit in Figure 1 provide as not only a complementary drive signal but also a deadtime delay Design by Yen-Hsu Chen, Analog Integrations Corp, Hsinchu, Taiwan

Low-cost switcher converts 5 to 24V -  02/16/98 EDN Design Ideas:  (File contains several circuits, scroll to find this one)  Design by Paul C Florian, Plano, TX

Low-Voltage Remote Mains Switch -  This circuit allows a 240V mains appliance to be controlled remotely via low-voltage cabling and a pushbutton switch.  The mains appliance (in this case, a light bulb) is switched with a suitably-rated relay.  All of the electronics is housed in an ABS box located in proximity to the appliance.  The pushbutton switch and plugpack are__ 

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