Questions tagged [switches]

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

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111 votes
9 answers
117k 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 ...
Spechal's user avatar
  • 1,213
22 votes
9 answers
67k 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 ...
endolith's user avatar
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14 votes
3 answers
111k 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?
user1406716's user avatar
28 votes
5 answers
25k 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 ...
Frank's user avatar
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8 votes
1 answer
23k 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 ...
Dorokun's user avatar
  • 81
8 votes
2 answers
22k 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-...
Pangolin's user avatar
  • 1,045
3 votes
3 answers
8k 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?
MrBit's user avatar
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19 votes
6 answers
26k 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 ...
LunchMarble's user avatar
12 votes
2 answers
29k 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 ...
Buzai Andras's user avatar
6 votes
3 answers
31k 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, ...
Dan's user avatar
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37 votes
2 answers
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-...
endolith's user avatar
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12 votes
3 answers
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 ...
0xakhil's user avatar
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7 votes
3 answers
9k 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 ...
Ageis's user avatar
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4 votes
1 answer
3k views

Two directional FET switch. Is it possible?

Is it possible to have a high side MOSFET switch that will allow any direction of current? I was trying to design one but without the success. Or should I use a relay?
0___________'s user avatar
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4 votes
3 answers
17k 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 ...
user7994's user avatar
  • 138
2 votes
2 answers
14k 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 ...
Amit Kumar's user avatar
1 vote
1 answer
4k views

Automatic Power Selection with MOSFET

I need a circuit which will automatically disconnect the battery from LOAD when ext. DC power is connected so that the battery won't get damaged. Theoretically a pair of diodes can solve this but ...
vSLY's user avatar
  • 48
1 vote
3 answers
11k 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 ...
joaocandre's user avatar
65 votes
5 answers
43k 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 ...
rajat's user avatar
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28 votes
4 answers
51k views

What is the purpose of "MOSFET driver" ICs

There are dedicated "MOSFET driver" ICs available (ICL7667, Max622/626, TD340, IXD*404.) Some also control IGBTs. What is the practical purpose of these? Is it all about maximizing the ...
18 votes
3 answers
34k 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 ...
zud's user avatar
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13 votes
6 answers
2k 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 ...
user16307's user avatar
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12 votes
6 answers
26k 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 ...
Cloud's user avatar
  • 820
11 votes
5 answers
2k views

Using a 2 A, 48 VDC rated switch in a 8 A, 12 VDC circuit

I have a push button make/break switch rated at 2 A, 48 VDC. I want to use it on my aircraft in an 8 A, 12 VDC circuit. Can I use this switch in this circuit or will the switch burn up?
litewave1 's user avatar
10 votes
8 answers
19k 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, ...
TRISAbits's user avatar
  • 1,368
6 votes
3 answers
3k 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 ...
CatalinM's user avatar
  • 387
5 votes
2 answers
5k 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 ...
nalzok's user avatar
  • 329
3 votes
2 answers
776 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 ...
efox29's user avatar
  • 12k
3 votes
2 answers
13k 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 ...
slippery's user avatar
  • 339
2 votes
2 answers
1k 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. ...
Mark Stevens's user avatar
1 vote
3 answers
790 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 ...
Andrius B.'s user avatar
1 vote
1 answer
3k 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: ...
Garet's user avatar
  • 111
-6 votes
3 answers
3k 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 ...
Marc Striebeck's user avatar
58 votes
5 answers
73k 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 ...
osvein's user avatar
  • 735
30 votes
3 answers
61k 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 ...
Anonymous Penguin's user avatar
11 votes
4 answers
30k 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 ...
Haravikk's user avatar
  • 285
10 votes
4 answers
79k 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 ...
Mark Harrison's user avatar
8 votes
3 answers
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 ...
James's user avatar
  • 322
7 votes
2 answers
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 ...
Michael Koval's user avatar
6 votes
1 answer
5k 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 ...
danpat's user avatar
  • 61
5 votes
2 answers
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 ...
Piotr Kula's user avatar
  • 2,144
5 votes
7 answers
11k 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 (...
Majenko's user avatar
  • 56.2k
4 votes
2 answers
305 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 ...
Chris's user avatar
  • 151
3 votes
2 answers
4k views

5v Electret microphone to PC mute switch pop help

I've got a PC microphone that fires off a loud pop when muted. Upon taking it apart it appears that its mute circuit is really simple and therein may lie the issue. I've combed this board for fixes ...
Bob Ablah's user avatar
3 votes
1 answer
2k 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 ...
user avatar
2 votes
3 answers
2k 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 ...
Glyn Davidson's user avatar
2 votes
4 answers
2k views

How do transistors and MOSFETs generate pulsating signals and can be used as oscillators? [closed]

I see many circuits in which transistors or MOSFETs are used as "automatic" on and off switching devices. This on and off switching creates an oscillating signal. Can somebody explain how a ...
abdussamed17's user avatar
2 votes
2 answers
8k 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 – ...
puppetworx's user avatar
2 votes
2 answers
4k 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 ...
M.Ferru's user avatar
  • 3,946
1 vote
3 answers
26k 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 ...
ANKIT JAIN's user avatar

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