Questions tagged [switches]

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

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104
votes
9answers
100k 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 ...
19
votes
9answers
55k 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
107k 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?
27
votes
5answers
23k 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 ...
8
votes
2answers
20k 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-...
19
votes
6answers
25k 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 ...
12
votes
2answers
24k 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 ...
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
3answers
9k 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 ...
5
votes
3answers
18k views

Switching between two power sources

I am designing a circuit, which can use either 5V from USB, or some higher voltage (7-12V) from a battery. If both power sources are connected at the same time, I want some kind of electrical switch, ...
1
vote
3answers
4k views

Bjt base current calculation

In a bjt transistor that is used as a switch (maximum saturation, Vce minimum as possible), what is the minimum base current that is required for a corresponding desirable collector current?
7
votes
3answers
8k 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 ...
0
votes
3answers
8k 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 ...
26
votes
4answers
43k 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 ...
57
votes
5answers
36k 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: (source: pranelectronics.com) What is the use of the two ...
16
votes
3answers
26k 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 ...
12
votes
6answers
22k 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 ...
4
votes
3answers
15k 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 ...
6
votes
1answer
14k views

SPDT in LTspice

I'm currently new to using LTspice as a circuit simulation software. Right now I'm trying to check if the IC (BD6221F-E2) that I included in the program is working. The process of making this IC is ...
3
votes
2answers
9k 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 ...
2
votes
2answers
12k 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 ...
2
votes
2answers
749 views

I need a switch that not only detects open/close, but also sends a pulse to wake up an ESP8266 whenever the (debounced) state changes

My application is that I'm trying to create a very small, "button battery" powered device to sense the opening and closing of a switch and send state changes via WiFi to another device on the network. ...
3
votes
2answers
3k views

“A zener with series diode”?

So I'm still reading The Art of Electronics Third Edition. On P.39, when dealing with inductive "kick", I found this sentence: For the fastest decay with a given maximum voltage, a zener with ...
3
votes
2answers
534 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 ...
1
vote
3answers
467 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 ...
0
votes
3answers
187 views

How to automatically disconnect from battery when USB +5v is present

I'm creating a SMD PCB where space is extremely limited. Usually, the application is powered by a battery (Single cell 3.7v lipo). To charge the battery, I'm using a USB cable. What I'd like is for ...
0
votes
3answers
22k views

Make a Latching Relay using SPDT Relays

I want to make circuit which can working like a Latching Relay which Hold Current using SPDT Relays. So i can use this circuit to Pules ON/OFF switch. Using limit switch when pressed a pulse goes ...
-6
votes
3answers
2k 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 ...
49
votes
5answers
61k 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 ...
6
votes
3answers
4k 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 ...
10
votes
4answers
70k 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 ...
7
votes
5answers
15k 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 ...
7
votes
3answers
21k 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 ...
7
votes
2answers
11k views

Purchasing a Switch - AC vs DC Current Specifications?

I'm trying to purchase several switches for a DC system with moderately low current (a few amps at 12V). When browsing for switches in parts catalogs (e.g. Mouser and Digikey) there are always ...
5
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 ...
2
votes
4answers
459 views

How do transistors and MOSFETs generate pulsating signals? [closed]

I see many circuits in which transistors or MOSFETs are used as "automatic" on and off switching devices. Can somebody explain how a MOSFET manages to pulse its gate within a circuit up to many hertz ...
5
votes
7answers
9k 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 (...
3
votes
1answer
4k 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
1k 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 ...
2
votes
2answers
3k views

High side switch and Low side switch

I wonder what is the difference between high side switch and low side switch. Basically it work the same way (electrically speaking) but I don't know if one is better than the other. Is there any ...
2
votes
2answers
6k views

Can I convert a toggle switch to momentary switch using a transistor and capacitor?

After searching online for an answer to how to convert a toggle switch to a momentary switch I found the circuit below. I've simulated it and it works in CircuitLab. simulate this circuit – ...
1
vote
2answers
497 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'...
1
vote
1answer
1k views

Convert a toggle switch into a momentary response

I'm working on a project and I need to use a toggle switch to control a device that expects a momentary signal. What I want is send a momentary pulse when turning it on and off. Ie: swith off to on: ...
4
votes
2answers
283 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 ...
0
votes
2answers
112 views

Mosfet switch not turning off

I'm hvaing trouble with my circuit, it's suppose to be a load switch to turn on a wifi module. However it's not working as intended. The idea is to set WIFI_CTRL to high to turn on WIFI_ENABLE. The ...
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
4k 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 ...
49
votes
5answers
11k 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?
9
votes
1answer
895 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 ...

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