Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [switches]

Devices to interrupt or route a signal or power one of several ways.

91
votes
8answers
78k views

Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons ...
53
votes
3answers
7k views

Fan speed switch: why OFF :: HIGH :: MED :: LOW?

Many AC fans, including inexpensive floor models, have a rotary speed control which rotates from OFF to HIGH to MED to LOW. Since the switch does not rotate 360°, you have to rotate it backwards to ...
46
votes
5answers
10k views

Why do you need 2 resistors when hooking up a transistor as a switch

What is the point of R2 in the following diagram: I get that R1 controls the current to the Base, but what does R2 do?
45
votes
5answers
27k views

Why do some tactile switches have 4 terminals?

I am wondering why some tactile switches have 4 terminals instead of two? For example, take a look at these switches, like the image below: Tactile Switches http://www.pranelectronics.com/gifs/12t....
40
votes
5answers
49k views

When to use pull-down vs. pull-up resistors

After learning and experimenting with microcontrollers, I've understood the concept of pull-up- and pull-down resistors. I now understand when and how to use them, and how they work. I've mainly used ...
34
votes
2answers
3k views

What's the difference between field-effect transistors (FETs) marketed as switches vs. amplifiers?

For instance, the J108 JFET is listed as "N-Channel Switch", and the datasheet mentions the RDS on resistance, while the J201 JFET is listed as "N-Channel General Purpose Amplifier" (and the on-...
23
votes
5answers
19k views

How do I make the turn off and turn on time equal in a NPN transistor?

I have a simple NPN switch, see the diagram. I feed a 100KHz square wave (TTL) to the base of this transistor and it turns on very very fast (a few nSec) but it doesn't turn off as fast, it almost ...
21
votes
5answers
65k views

How do I fix an Omron d2fc-f-7n microswitch from unwanted clicks?

Omron d2fc-f-7n microswitches are used in computer mice all around, and they eventually start clicking several times per hit. AFAIK there is a flexible metal plate that wears out due to metal fatigue, ...
20
votes
4answers
33k views

What is the purpose of “MOSFET driver” IC's

There are dedicated "MOSFET driver" IC's available (ICL7667, Max622/626, TD340, IXD*404). Some also control IGBTs. What is the practical purpose of these? Is it all about maximizing the switching ...
19
votes
3answers
9k views

How can I design a circuit that will turn on when a wire is cut?

I'm trying to build my own cable lock alarm (for science!) and am having trouble figuring out a way to detect that a wire has been cut. The circuit has to Use no power at idle (or at least, very ...
18
votes
6answers
23k views

Pull Down Resistors

In my quest to understand electrical engineering, I have stumbled across this tutorial: http://www.ladyada.net/learn/arduino/lesson5.html I have understood the diagrams until I got to switches. I am ...
18
votes
1answer
29k views

Is it possible to use just a capacitor to debounce a button?

I have been wondering: why cannot you just hook up a capacitor to a button to debounce it? I have been figuring out how to reduce the work my microprocessor has to do, but I have very limited space on ...
17
votes
6answers
5k views

Choosing Configuration Jumpers - Solder bridges, 0-ohm resistors, DIP switches, pin jumpers

I'm working on a development board, and need to let users set some configurations. It will be used by students and engineers who are trying to build circuits on a breadboard; I'm not dealing with ...
14
votes
7answers
4k views

Relays vs. thyristors: What is best for swiching 230 V lights on and off rapidly (~ 5 Hz)?

I am building my own disco/party lights. 230 V/60 W bulbs, and ideally I would like to switch them on and off at 5 Hz. I was planning on a simple setup with an Arduino controlling the lights. My ...
14
votes
5answers
2k views

Why are reed switches made in glass tubes?

Why are reed switches made in glass tubes? Reed switches sense magnetic fields, and glass is not the only material not affected by a magnetic field. They can use plastic for example. Why are most of ...
14
votes
4answers
3k views

Why does electric arc in a switch prefer a curved path over a straight path?

Recently I found this video of a 500 kilovolts line being opened under load. When the switch contacts are pulled apart an electric arc predictably starts. While the contacts are close to each other ...
14
votes
1answer
737 views

How do I find a shutter-style (off-half-full press) momentary button?

I'm looking for a momentary button that has three positions, like a camera, so you can momentary-press halfway or momentary-press the full depth. I don't even know what to call it, so searching 41,...
14
votes
7answers
39k views

Make a momentary switch control a toggle

What are the simplest, cheapest, smallest ways to make a momentary switch produce a 2-state toggling output (latching momentary switch)? In other words, the output is continuously low, and when you ...
13
votes
3answers
1k views

Physics behind switch bounce when opening?

I was surprised to learn that a mechanical switch (SPST) bounces when it is opened. What causes the contact to temporarily return to touching? Does this phenomenon only happen with certain types of ...
13
votes
4answers
7k views

How to switch power of microcontroller by button?

I have a microcontroller device with battery power. Currently I toggle power by simple on/off switch. I want to toggle power by one pushbutton with minimal modification of the schematic (and ...
12
votes
4answers
9k views

How to best attach a wire to a switch without soldering?

I've got a switch like this one: Now my (quite novice) question is: How do I best attach a wire to the connector without soldering, e.g. for quickly trying something out? Right now I've folded the ...
12
votes
5answers
10k views

Why are some generic door alarm magnetic switches built using Normally Open reed switches instead of NC type?

Some generic, low-cost "door alarm" magnetic switch components are made of using "Normally Open (N/O)" type reed switches, ie, when the magnet is in proximity, the current stops flowing. If I were ...
12
votes
3answers
96k views

MOSFET as a switch?

In the picture shown, can "Output" be controlled to be 0V or 12V based on "Control"? Will be Drain and Source the way it is connected be a problem?
12
votes
1answer
1k views

Why do some toggle switches have terminals of different color?

I sometimes see three terminal rocker/toggle switches, and one terminal is a different color than the other two. Here is an example: (Image from ebay.com) What does the colored terminal indicate?
12
votes
3answers
7k views

How do 'hand clap' switches work?

I'd like to know how a 'hand clap' switch works. You know, the kind where you *clap-clap* and the light turns on, *clap-clap* again and the light turns off. How is the clapping sound detected? How ...
11
votes
3answers
2k views

Does this sort of “multi lane” switch exist? [duplicate]

Does a component exist that functions as a switch for multiple connections at once, 3 in my case. So power, ground, and data are coming in from the top. When the switch is in the left position (as ...
11
votes
6answers
1k views

Why would the transistor not switch?

I was reading an example from a text book. And for this circuit above the author claims when R3 is less than 100 ohm Q3 will not switch. I couldn't figure out the "reason" why. But I verified with ...
11
votes
3answers
152k views

Can you clarify what an 1NO1NC switch is?

I've come across multiple mentions of switches described as 1NO1NC. They often described as having 2 options: ON/(OFF) and (ON)/OFF and from what I gather they have 3 terminals for wires: a NO ...
11
votes
4answers
2k views

Rocket launcher circuit design

I'm building a model rocket launcher with my son. The circuit is very simple as you can see. We want to add a buzzer and a LED/bulb when it is turned on as a warning to stay clear of the rocket. How ...
11
votes
3answers
8k views

BJTs versus (MOS)FET to switch a load from a microcontroller

I would like to know what are the reasons for choosing bipolar junction transistor (BJT) versus a field-effect transistor (FET) (MOSFET or a JFET) to switch a load from a microcontroller. In our ...
11
votes
3answers
2k views

Explanation needed on using 2 transistors as a switch

I'm suggested to use following design to drive a load with a micro-controller. I would like to know that why is it needed to use 2 transistors (n-ch and p-ch) to act as a switch and not only one? I ...
11
votes
1answer
9k views

How do the lights on stairs work?

I remember that there's a very simple circuit diagram that explains how there can be 2 light switches for 1 light and that regardless of which switch you turn 'on/off' the light is toggled on/off. ...
11
votes
2answers
19k views

P-Channel MOSFET high side switch

I am trying to reduce the power dissipation of a P-Channel MOSFET high side switch. So my question is: is there any way in which this circuit can be modified so that the P-Channel MOSFET will ...
11
votes
3answers
8k views

Control 220V AC line using MCU

I want to switch ON and OFF an incandescent bulb using MCU. Please suggest an electric switch (like relay or something) for 220V 50Hz AC line which can be used here. I would prefer something very ...
11
votes
1answer
15k views

Need help to understand DigiKey/Mouser “Switch Function” terminology

I first read Switch Basics from Spark-Fun tutorial to help me better understand how to find what I am looking for using DigiKey/Mouser Advanced search terminology. I know I am looking for a ...
11
votes
3answers
18k views

Understanding Two MOSFET with sources connected

I am having problem understanding how this MOSFET configuration (used in battery charger) works? In this slide, what does it mean "blocking voltages in both directions while allowing ...
10
votes
11answers
4k views

Alternatives to a classic DIP switch

I'm looking for a part that enables a user to frequently change a configuration. Right now I'm utilizing a SMD DIP switch connected to an I2C I/O expander. What bothers me is the large footprint of ...
10
votes
6answers
17k views

Automatically switching from 9V battery to DC wall adapter on insertion

I have a simple circuit that runs off of a 9V battery. I'm re-designing it so that it can also run off of an external 12V DC source (ie: a wall adapter). I want to design the circuit so that if both ...
10
votes
5answers
41k views

What is the origin of on and off power switch symbol?

I know I (line) and O (circle) symbols are used to specify a switch that turn on and off the power supply. My question is What is its origin? Because I thought that it represent a power line that ...
10
votes
2answers
1k views

How to choose a switch?

There seem to be about 4 major flavors of transistors, and then there are NPN/PNP versions. There are also relays, SCRs, and TRIACs. When I need an microcontroller-controlled switch, what rules of ...
10
votes
2answers
1k views

What's the difference between small signal bipolar junction transistors (BJTs) marketed as switches vs. amplifiers?

For instance, the MMBT3904 and MMBT3906 BJTs are listed as NPN/PNP Switching Transistors, and the datasheets mention the switching times, while the BC846 and BC856 BJTs are listed as NPN/PNP general ...
10
votes
3answers
604 views

What causes this knee in my MOSFET drain voltage drop?

FINAL UPDATE: Understand a previously mysterious power MOSFET switching waveform wiggle! @Mario uncovered the root cause here below, distinctive to so-called VDMOS devices, typical of many power ...
10
votes
4answers
2k views

Protecting Microcontroller Input Pins from Soft Power Switch

I'm working on a soft power switch for a microcontroller where a momentary switch can turn the circuit on (including microcontroller), and then when the switch is pushed a second time, the ...
9
votes
4answers
2k views

Why use a “load switch” and not just one transistor as a switch

I am trying to understand the advantage of using a 'load switch" for switching applications. The load switch (like the one below), has two transistors to do the job. Why can't I just use one ...
9
votes
4answers
4k views

How can 16 buttons be connected with only 8 wires?

Here is the product. I understand the idea: these 16 buttons use a 4x4 matrix. 4 lines for rows, 4 lines for columns, and we have 8 cables. But: How can this work without any multiplexer ? Can this ...
9
votes
4answers
7k views

What is a push-up/pull-up resistor? [duplicate]

A.S. The question A question on pull up resistors answers only a part of my question as already mentioned in "EDIT" made shortly after this question was asked & answers here (below) are much ...
9
votes
4answers
14k views

How can I slow down the switch time of a MOSFET?

I have an NMOS that is switching too fast for my application. Into the gate I am sending a logic-level square wave (PWM). Unfortunately for me, as expected, the output is also a near square wave. How ...
9
votes
3answers
3k views

Using SPST switch as digital input?

I am new to "electrical engineering" and I am working on a little arduino project. I want to have a SPST switch be used as a digital input on the board. I have one of the switch leads connected to ...
9
votes
4answers
51k views

Calculating current load for a switch?

This SPST switch is labelled on the box as "Rated 10A at 125VAC or 6A at 250VAC". Is there a calculation as to the amperage it will handle at 12V DC? (update) As JYelton points out, a naive ...
9
votes
3answers
2k views

Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...