Questions tagged [switches]

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

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Why does this microswitch datasheet specify a minimum load current? [duplicate]

The Omron VX series datasheet mentions on page 6 that "Using a model for ordinary loads to open or close the contact of a micro load circuit may result in faulty contact.", and shows that their micro ...
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2answers
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How do these modern power buttons on devices work

In the older days and still now we have buttons where one way is off and the other way is on, its mechanically built to connect or disconnect an electric path physically. On modern devices like ...
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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 ...
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Why is my NPN base so slow to turn off?

The circuit below is about as simple as it gets, yet it's not behaving like I expect. V3 is a 3.3Vpp square wave going into the base of the transistor, so I would expect to see V_Out be high when V3 ...
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2answers
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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 ...
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3answers
899 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 ...
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4answers
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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 ...
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4answers
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Can I achieve a one shot button without a 555?

I have a complex circuit, but my problem only relates to one small part. I have a relay, which is energised by pulling the low side low using an NPN. I would like a pushbutton to operate the ...
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4answers
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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 ...
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4answers
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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 ...
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4answers
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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 ...
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7answers
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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 ...
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Using transistor as switch, why is load always on the collector

I find in reference circuits that when BJT is used as switch when it will be used in saturation mode, the load is always at the collector. For NPN the emitter is connected to the ground, for PNP the ...
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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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3answers
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Switching 12V with an active low 5V signal

I’m trying to switch 12V (max 30mA) with a signal from a MCU that I’d prefer to be active low (so the output voltage is 12V when the control signal is 0V, and 0V when the control signal is 5V). Since ...
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Why is it safer to place a switch on the positive side of a voltage source?

According to the research I've done, it is safer to place a switch on the positive side of a voltage source: http://www.allaboutcircuits.com/textbook/direct-current/chpt-3/safe-practices/ This only ...
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2answers
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Autonomously-powered (battery-less) wireless pushbutton

What would be a feasible approach/circuit-design to make a self-powered wireless pushbutton, assuming it is even realistic? This is what I mean by each of the three terms: Self-powered: Power ...
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2answers
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Is it ok to leave analog switch inputs floating?

Will I run into problems if I leave a few of the analog pins on a CMOS switch (such as the DG409) floating? I know that CMOS digital inputs should never be left floating due to the fact that the ...
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2answers
639 views

Trying to understand how a guitar pickup switch works

At the risk of being off topic, I need to ask a guitar electrical question. I am trying to replace an old guitar's pickups (including the pickup switch). The idea is to put two active humbuckers. ...
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554 views

Why do some of my IE converter circuits have a large offset voltage?

The following circuit is an active current to voltage converter with switchable gain. Schematic Not shown: The inverting input is held low through a 10K resistor when the circuit is powered on but ...
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3answers
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Why is this reed switch / solenoid circuit not working?

The (normally open) reed switch should close by waving a magnet across it, completing the circuit. The 6v solenoid lock should pull inwards allowing the door to be opened. When the magnet is removed ...
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6answers
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How can I convert the output from a momentary switch to a pulse on push and a pulse on release?

The title pretty much says it all. I have an idea to try out involving a op-amp differentiator circuit and a diode bridge, but I am flying blind. Also I am trying to accomplish this without a micro-...
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Can multiple Schmitt triggers in series fully debounce a switch?

After dealing with software debouncing for a while, I find it takes a huge toll on the system, so I thought of initially making a hardware debouncer with one Schmitt trigger (74HC14), a capacitor, ...
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4answers
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Switch for DC application

I have two solar panels in series totaling a maximum of 80 VDC and 500 Watts. I believe that would be a maximum of 6.25 Amps. Could a 20A 120/277V AC switch handle that since 6.25 Amps is a ...
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860 views

Pull Switches - why so expensive

I would like to use a pull switch as a trigger for an alarm that I'm building. When the switch is triggered it will turn on a siren and potentially a strobe light. I've found plenty of options out ...
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5answers
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Transistor as a one-time switch

I'm trying to develop some sort of a one-time switch. Let's say when a criminal opens a switch - transistor opens and alarm sets on. I want it to continue working once switch is closed again. I ...
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3answers
1k views

Ten millions cycles on arduino

I am trying to build a suitable pull-switch for my invention. Inside the switch, there is a tiny metal plate. When the user pulls the switch, this metal plate gets close to and makes contact with two ...
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2answers
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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-...
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4answers
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Difference between Multiplexer/Demultiplexer and Analog Switch

What (if any) difference is there between mux/demux IC's and analog switch IC's? I'm comparing this in the context of chips with the same IO lines (for example a 1:2 or 2:1 mux/demux vs. a SPDT ...
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4answers
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Does a switch need to be debounced when opened?

Suppose that an input on a microcontroller has a pullup resistor to 5V and a switch to ground (normally open) connected to it. I know that a switch should be debounced (in my case, in software) when ...
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3answers
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Should a mechanical power switch float or ground main power when the system is off?

Whenever I've put a mechanical switch on a design to allow a battery to be connected / disconnected, I've always just floated system power whenever the switch is open, like this: However, a colleague ...
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2answers
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Button debounce ringing

I have a circuit where I am using a tactile switch to pull 3.3v down to ground and investigating debouncing the button. My relevant part of the circuit is The 100nF cap does work here my signal has ...
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1answer
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Use the RESET PIN on Attiny85 as Input with voltage divider

Voltage divider & pull-up with analogRead The Attiny has 6 pins that you can use as I/O. While 5 of them are really easy to use the Pin 1, the Reset PIN , obviously Resets the Microcontroller if ...
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5answers
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How to have arduino only turn on when enough power has been collected?

There was recently an article in the Christian Science Monitor about the launch of a cracker-size satellite. The article says that the satellite has, "power storage in capacitors, and switching ...
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699 views

Blowing a Fuse to Permanently Disable Functionality

Certain electrical designs require permanently disabling hardware functionality on the fly. Sending an overcurrent to a weak fuse may be a method for accomplishing this, breaking the circuit in a ...
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5answers
877 views

How to build a timed audio switch?

I want to build a simple device with 2 inputs and 1 output, all TRS 1/8" audio jacks. The device picks one of the inputs to pass through to the output depending on the time of day (at night, it ...
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6answers
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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 ...
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8answers
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Can I use a 10A light switch with an appliance with a 13A fuse?

I have a vacuum cleaner, which I wish to add a switch to, so that I can leave it plugged in all the time and use the switch to turn it on and off. The vacuum cleaner has a fuse rated 13 Amps. I ...
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4answers
913 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: ...
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3answers
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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 ...
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4answers
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Control 5 V load with transistor 3.3 V - Raspberry Pi

I'm currently having this project where I put a Raspberry Pi, batteries and a touch screen inside a book that can fit my pocket. This screen is constantly on, and I want to be able to turn it on and ...
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What small IC could give switchable I2C pullups?

My goal is to replace a DPST on pullup resistors with something simple, cheap and very small that can be activated with the I2C bus voltage. I thought that this might be a common enough requirement ...
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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, ...
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857 views

Can the inductive kick be discharged without a freewheeling diode, in this example?

In literature we commonly see the use of a freewheel diode to protect the circuit against the inductive kick when the switch goes from closed to open (Fig 1). However, what would be the pros/cons of ...
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Latching switch ideas

I'm trying to build a latching switch connected to a door and would appreciate ideas. The switch is connected to a microcontroller input pin, and I'd like it to operate as follows: When a person ...
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1answer
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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 ...
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557 views

Ideal component to switch 84V DC?

I wanted to control a 84V LED strip using a ATtiny13a microcontroller with minimal power wasted. I just want to turn it on and off, don't need any PWM dimming. The strip uses 270mA current and is ...
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2answers
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Why would a “power switch” be designed this way?

This unit is an ARINC 429 bus analyzer, manufacturer "AIT" (Aircraft Interface Technologies), model "429A". Yes, it's confusing. Rated 115VAC/3A/60-440Hz. It has a 250W SMPS inside ...
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MOSFET load switch

I'm trying to create a load switch using a pair of MOSFETs However, I'm confused about MOSFET threshold voltages. I need to switch about 0.1A at 3.3V. GPIO2 is 1.8V logic. What do I need to read in ...
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1answer
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Rubber push-button

On lots of electronic devices, such as this Korg drummachine/sampler, there are some soft rubber push buttons. What are they called? (I'm looking for the most common name, so I'll can find them ...

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