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Questions tagged [switches]

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

92
votes
8answers
81k 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 ...
8
votes
2answers
18k views

Basic circuit to keep LED either on or off depending on night/day

How can I have a LED either on or off (not in between) depending on night or day with basic electronics? I have created the circuit below, but it only shines and in darkness it dims. The photo-...
15
votes
8answers
41k 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 ...
12
votes
3answers
98k 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?
23
votes
5answers
20k 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 ...
18
votes
6answers
24k 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 ...
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 ...
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-...
12
votes
2answers
20k 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 ...
7
votes
3answers
7k views

switch debouncing - would toggle switch still bounce

I'm having the classic debouncing headache with the Arduino. The switch is meant to turn an led on and off. So if I use a toggle button (SPDT) would it still bounce? Maybe it won't since it not a push ...
46
votes
5answers
28k 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....
9
votes
4answers
54k 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 ...
1
vote
3answers
235 views

Fast analog switch overshoot

The circuit purpose is to control square signal frequency from 100Hz to 1kHz (generated by MCU GPIO) and be able to control amplitude from 100mV to 2.3V. It is like a very simple signal generator. The ...
1
vote
2answers
8k views

NPN circuit to switch 12v 1A DC load by 3.3v 1A DC using PIR

I am trying to switch on a circuit using PIR motion detection. I have a PIR module which outputs 3.3v 1A DC when it detects a motion. I want to switch on a circuit rated at 12v 1A DC. I read some ...
-6
votes
3answers
1k views

A capacitor stores half the energy when charged from a battery each and every time? [closed]

I understand that when a battery is connected to a capacitor that half the energy is stored in the capacitor while the other half is lost to heat or whatever other losses are involved once the ...
41
votes
5answers
52k 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 ...
12
votes
3answers
19k 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 ...
6
votes
3answers
3k views

Implement MicroController Power Switch and re-use the button for other features

This is similar to other questions, but I feel it is different because of the reuse of the "power" button. I want a "latching" Momentary Power button. Behavior: User Pushes momentary button, holds ...
6
votes
5answers
11k views

Low Drain-Source MOSFET Leakage

I've been looking at the SM74611 Smart Bypass Diode from Texas Instruments and am very impressed with the reported reverse leakage current (0.3uA at 25C). Considering the device has a N-Channel FET, ...
5
votes
2answers
2k views

Smallest water detector / switch

I am looking for a small simple switch. But it has certain restrictions because I want to use it for salt water aquarium and copper exposure is lethal to some fauna, as well as some plastics. Looking ...
4
votes
3answers
14k views

Using a momentary push button as a latching on-off toggle switch

Please check the schematic here> Here is the circuit that I have developed. I am not very sure about the design. Here is what I want it to do. When the user presses the push button S2 the TPS_EN ...
7
votes
3answers
16k views

Using PWR_OK to Activate an ATX Power Supply Automatically

Okay so, I have an ATX PSU that isn't connected to a motherboard, and I'm currently using the simple paper-clip trick to ground PS_On in order to trick the PSU into ...
5
votes
7answers
8k views

Switching op-amp gain resistances - how?

Given the following circuit: What is the component / circuit I should be using to switch the signal between each of the gain resistors? (the ⊠s in the schematic) The inputs ID0 to ID2 are TTL (...
4
votes
2answers
2k views

What component to use for audio signal switching?

I'm looking to build a guitar pedal switcher based on a Raspberry Pi or Arduino (have not yet decided, but I have an unused Raspberry around and I lean towards that). Anyway, digital logic. Now, I ...
3
votes
2answers
7k views

What's a simpler way to switch between power sources?

I want to make a device that allows the user to switch between two different power sources (a wall mount and batteries). I could perform this circuit using two DPDT switches, but I would need to ...
3
votes
1answer
3k views

Resettable mechanical switch?

I'm looking for a mechanical on/off rocker or toggle switch that can be reset to a default state and position upon the removal of power. The application is in a vehicle where I want the switch to ...
3
votes
1answer
684 views

Switches needed in an n-location multiway switching system

Wikipedia shows us we can construct a two location multiway switching system with two 3-way switches: They also teach us how to perform three location multiway switching with two 3-way switches and ...
1
vote
2answers
398 views

Designing an ABBA circuit (3 input, 2 output) inputs: (GND, +V, Logic)

I'm working on a relatively simple Arduino project and want to reach an elegant solution for a circuit. I'm not sure if there is an existing IC for what I want to do, but here is a diagram for what I'...
4
votes
2answers
279 views

Need help installing a capacitor

Ok here's the problem. I have a power antenna in my car. The antenna goes up when a voltage is supplied to the voltage sensor in the antenna and goes down when the voltage is removed. I used this fact ...
4
votes
2answers
2k views

“A zener with series diode”?

So I'm still reading The Art of Electronics Third Edition. On P.39, when dealing with indicative "kick", I found this sentence: For the fastest decay with a given maximum voltage, a zener with ...
3
votes
2answers
394 views

Is a switches voltage and current rating a hard limit?

I have a need for a switch that can handle 28Vdc at about ~1A. The switches I would like to use have a rating of 24Vdc at 5A. I would think that the limit of switch is the power, so if we take a ...
0
votes
3answers
6k views

Switch current rating AC vs DC

I'm looking for a high current DC switch (able to switch something like 5V@30A) and I've encountered several DPDT that might do what I need, however they are only rated for AC applications (3A@250VAC ...
0
votes
0answers
70 views

How to convert light activated switch [duplicate]

Can anyone teach me how to convert a light activated switch into dark activated switch vice versa.
-1
votes
2answers
3k views

DC Motor reversing relays using a micro switch [closed]

I'm looking to use relays and 1 micro switch to reverse the polarity of the circuit. I will need a simple ON/OFF switch to have the motor turning in one direction and then when the micro switch is ...
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?
21
votes
4answers
34k 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 ...
10
votes
6answers
18k 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 ...
8
votes
1answer
833 views

How to implement a “rotary switch” like in audio equipment?

for my current project I'm planning to use an input "device" like this in the photo (don't know its real name): It is used in a lot of musical instruments and it is like a potentiometer that can be ...
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 ...
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 ...
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 ...
5
votes
6answers
22k views

MOSFETs or BJTs for using as switch for audio signals

I was wondering which component is better for using as voltage controlled switch for audio signals (e.g. music signal from mp3 player). Should I use MOSFETs or BJTs? The max rail voltage is ...
13
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 ...
5
votes
3answers
11k views

How to make a digitally controlled power switch?

I am new to electronics. I want to make a power switch controller by a digital pin as shown on the following figure. How to do this safely? Update: I forgot to let you know the bulb is just an ...
3
votes
2answers
2k views

Why do switches have a current and voltage limit?

I want to attach a switch to a 5 Volt battery pack to be able to turn it on and off. The batteries will power 4 DC motors. The current draw will be about 1 Amp. The switch I have is like the one here. ...
3
votes
5answers
3k views

Using MOSFET as switch

I am new here so I apologize in advance for any mistakes in the way I am going about this. I had a question regarding a project that I am working on. I am trying to use a MOSFET as a switch that I ...
3
votes
3answers
60k views

Change Direction of 12v DC Motor Rotation using Relay

I want to make a circuit to change 12 Volt DC Motor direction and move some thing between two points. Using Relay or some basic limit switches.Like this Image. I got a Circuit As i want... AUTOMATIC ...
8
votes
7answers
17k views

How can I turn on and off a switch every 20 minutes?

I want to make the above switch which will stay on for 20 minutes and then off for 20 minutes. This should be continuous. Actually, I want to place this switch for my air conditioner which I do not ...
7
votes
4answers
778 views

Does an Electron really travel thousands of Miles when I use a server in another Country?

When I press a key on my keyboard, it will alter the flow of electrons in a wire connecting to send data to my computer. Let's say it sends the bits: ...
6
votes
2answers
1k views

I need a circuit that allows current to flow in both directions through a load, and I came up with this. Is it good or is there a better way?

this is one of my first circuit "designs" (quotes on since it's simply switches). I need current to be able to flow in both directions through a certain load, and the direction of travel should be ...