Polarity Reversal Switch -  switch the absolute polarity (180° phase shift) of signals with this simple circuit. . .  [Rod Elliott (ESP)]

Pop Free Microphone On/Off Switch Circuit -  This circuit uses a simple technique to eliminate the usual “pop” sound when an electret type microphone is switched on or off. The circuit is completely passive and will work on dynamic and electret type microphones . . . [Circuit by David Johnson P.E.,  02/15/02]

Porch Light Slave Switch -  This circuit turns on the porch light when a passive IR security light is activated. . . .  [Designed by Andrew R. Morris]

Porch Light Switch -  This circuit will activate a relay when light falls to a preset level. Light level can be adjusted with VR1 and the relay contacts may be used to operate an external light or buzzer. . .  [Andy Collison]

Power Load Sensing Automatic Switch -  WARNING:  This circuit requires experience with mains wiring. Do not attempt construction unless experienced and capable. Death or serious injury may result from incorrect wiring. . . .  [Rod Elliott (ESP)]

Power Switch for Lights or Small Motors -  Circuit could be used to operate lights or small motors in either high or low mode. Circuit for model railroad trains. . . .  [from Rob Paisley's Model Train web site]

Power switch provides soft start -  03/30/00 EDN Design Idea   In the circuit in Figure 1, series-connected MOSFETs turn on the line voltage near the zero-crossing point and off when the 555-timer delay lapses. That delay ranges from 1 to 7 msec. The MOSFETs’ body diodes and the 1N4005 diode. . .  [by John Haase, Colorado State University, Fort Collins, CO]

Power-Off Time Delay Relay -  The two circuits above illustrate opening a relay contact a short time after the ignition or light switch is turned off. The capacitor is charged and the relay is closed when the voltage at the diode anode rises to +12 volts. The circuit on the left is a common collector or emitter follower and has the advantage of one less part since a resistor is not needed in series with the transistor base. However the voltage across the relay coil will be two diode drops less than the supply voltage, or about 11 volts for a 12.5volt input. The common emitter configuration on the right offers the. . . 

Power-On Time Delay Relay -  Here's a power-on time delay relay circuit that takes advantage of the emitter/base breakdown voltage of an ordinary bi-polar transistor. The reverse connected emitter/base junction of a 2N3904 transistor is used as an 8 volt zener diode which creates a higher turn-on voltage for the Darlington connected transistor pair. Most any bi-polar transistor may be used, but the zener voltage will vary from about 6 to 9 volts depending on the particular transistor used. Time delay is roughly 7 seconds using a 47K resistor and 100uF capacitor and can be reduced by reducing the R or C values. Longer. . . 

Printer port activates CMOS switches -  05/02/02  EDN Design Idea   The cost-effective design in Figure 1 provides control for CMOS switches without the need for an external power supply. Analog switches such as those in the MAX4663 are ideal for use in low-distortion applications. They are preferable. . .  [by J Jayapandian, IGCAR, Tamil Nadu, India]

Printer Sharing Switch -  I had two computers, a Mac Mini and a generic Windows computer. Both were on different networks, but in the same room, and I wanted to share a Lexmark USB laser printer between the two of them. I ended up making this switch to share the printer between the two computers. . .  [From Dick Cappels' project pages]

Protected Analog Switches -  Analog Devices-Analog Dialogue. . .  [by Ritmanich, Will]

Protection Schemes for BI-FET Amplifiers & Switches -  Application Note. . .  [National Semiconductor]

Protects from Battery Polarity Reversal -  This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity. The N-channel FET connects the electronic device to the battery only when the polarity is correct. The circuit shown was . . . [Hobby Circuit designed by Dave Johnson P.E.,  03/09/02]

Push Button Motor Control -  This circuit uses solid state switching (transistors) to control direction of a DC motor. You have precise control of the movement of the motor, and an indication of direction provided by LEDs. . .  [Andy Collison's website]

Push Button Switch Debouncer -  This circuit will remove the transient spikes and contact bounces from a non-latching push button switch. . . .  [Andy Collison's website]

Pushbutton Activates Service Request Beeper -  A single press of a pushbutton switch turns on a beeper for one second but can’t be activated again for 60 seconds.  . . . [Circuit by David Johnson P.E.,  09/25/05]

Pushbutton Control for Single-Phase Appliances -  This circuit lets you switch off and switch on a single-phase appliance using two separate push switches. . . .  [© EFY Enterprises Pvt. Ltd. All rights reserved]

Pushbutton Controlled Up/Down Ramping Light -  There are times when you want a lamp to gradually change from dark to light and from light to dark, with each push of a pushbutton switch. The circuit below performs this control function using a flip/flop and a classic pulse width modulation or PWM . . . [Circuit by David Johnson P.E.,  03/22/09]

Pushbutton Oneshot & Latch -  This circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal. It can operate from 3v to 18v . . . [Circuit by David A. Johnson P.E.,  03/26/02]

Pushbutton On-Off Latch Circuit -  Often you want to turn on and off power to a device with a single pushbutton switch. The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v. It uses two inverters within a 74C14 or a CD4069 hex inverter package. Each press of the button toggles between the two on/off logic states.  . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/09/10]

Pushbutton replaces rotary switch -  10/26/00  EDN Design Idea   The problem of setting any one of four modes of aµC-operated process has a straightforward solution.  Have the µC check the states of some 4 bits of aµC. . .  [by Abel Raynus, Armatron International Inc, Melrose, MA]

Pushbutton switch controls power supply and µC -  09/25/97 EDN Design Idea   A simple circuit and pushbutton switch control the shutdown of both the switching regulator (IC1) and the µC. switching handheld units on and off with a pushbutton switch is a desirable feature. Thus, switching-regulator/ controller ICs for battery-powered applications provide a logic input to switch the device to a shutdown mode. This type of shutdown pin can require additional components and logic gates to implement the pushbutton interface. However, a simple circuit can implement an on/off function with no external logic (Figure 1). The circuit is based on IC1's step-down controller, which provides the toggle on/off function internally with a SET/RESET latch. . .  [by Greg Dittmer, Linear Technology Corp, Milpitas, CA]

Pushbutton Switch works through Glass -  This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass. Pushing the button moves a magnet near the reed relay, closing the relay contacts . . . [Circuit by Dave Johnson P.E.,  02/10/02]

Pushbuttons and digital potentiometer control boost converter -  02/17/05  EDN Design Idea   Digitally controlled potentiometers are useful for generating analog control voltages under the control of a microcontroller. In some applications, manual pushbutton switches could replace a microcontroller and simplify product des. . .  [by Simon Bramble, Maxim Integrated Products Inc, Wokingham, UK]

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