Questions tagged [switches]

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

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22
votes
3answers
42k 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 ...
19
votes
3answers
10k 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 ...
14
votes
3answers
220k 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 ...
9
votes
4answers
8k 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 ...
13
votes
4answers
49k views

Difference between High- and Low- side switching of power?

Is there any real difference between high- and low-side switching? Assume: Switching is for on/off control of an object (My case RPi) Base/Gate can be driven to Vcc and GND
8
votes
1answer
13k views

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 ...
6
votes
3answers
20k views

A good circuit for a large number of push button inputs?

I'm planning to build a kid-friendly "universal remote" so the kids can turn on and off a myriad of IR-controlled devices with one or two easy presses... The remote is going to have maybe 20 big ...
7
votes
2answers
14k views

Switching a current with an NPN transistor and a P-MOSFET

Just learning about transistors and I'm trying to clearly understand how to apply them for basic switching, in terms of the two standard cases, i.e., Active HIGH behavior and Active LOW behavior. For ...
9
votes
3answers
20k views

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 ...
7
votes
4answers
2k views

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 ...
5
votes
3answers
9k views

Switch on computer with microcontroller

I'm making a simple microcontroller based circuit to turn on a computer when certain events are triggered. I am interfacing it using the PCs soft power switch pins on the front panel header: There ...
4
votes
3answers
9k views

Need a soft latching power on/off that starts OFF

I have spent a few days looking for a soft latching power on/off switch. I have breadboard-tested several designs, including at least these three: Design #1 Design #2 Design #3 Testing: I tested ...
4
votes
2answers
9k views

How to make my own atx power switch?

I'm assembling a new computer from components. It's something I've done quite a few times, but now I would like to skip the case. Except for some structural integrity and LEDs, the only technical ...
2
votes
4answers
5k views

How can I turn off a 3.3V circuit with a 3.3V microcontroller

I'm working with ATTiny85 that has low current (40 mA) GPIO. In the other side I have a power supply (battery with ~5V) connected to a LM317 and an ESP8266 that demands high current (more than the ...
11
votes
4answers
3k views

Is there a more efficient alternative to pull down resistors?

I am building a LED spinner circuit and I am at the point of optimizing it. The whole circuit itself only draws about 10-20mA max. I was today looking at this part of the circuit: Now as you can see, ...
10
votes
4answers
12k views

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 ...
10
votes
2answers
2k 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
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 ...
7
votes
4answers
11k views

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 ...
4
votes
1answer
19k views

Simulating SMPS with ideal switch in LTSpice?

Yes, this in a portion of a homework assignment (hence the idealized and slightly asinine problem statement). Aside from solving the circuit (which I have done), I am supposed to simulate the ...
3
votes
6answers
6k views

Parameters when choosing a relay

Is this a good circuit to use as a air condition switch with a help of microcontrollers 5V? What relay to use in this situation? What parameters should I take into consideration when choosing relay?
3
votes
7answers
3k views

Switching resistances in op-amp amplifier

I am building an inverting amplifier with an op-amp to attenuate a signal (ie: gain < 1) and I would like to be able to change the gain electronically by connecting multiple resistors to a switch ...
3
votes
3answers
69k 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 ...
3
votes
2answers
3k views

Best practice to switch +V or GND connection?

Consider LAMP1 and LAMP2 in the simple example circuit below: Which is the "better" practice, using the switching component (...
2
votes
1answer
331 views

Is the 50% loss of energy when charging a cap from a battery a set rule in stone? [duplicate]

This question is similar to A capacitor stores half the energy when charged from a battery each and every time? (And no it is not a duplicate it is different in that it has been made more clearer.) ...
2
votes
2answers
639 views

switch on a long wire end causing microcontroller to shutdown

i've a push button connected to micro-controller using a 100m 18ga wire that cause the micro-controller to shutdown after few times of working properly the circuit is fully functional with a short ...
2
votes
2answers
3k 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 ...
2
votes
2answers
542 views

Will cutting only the Power Lines damage the Data Lines or the Device?

A USB 2.0 Cable should have 4 cables. They are the Vcc, Data+, Data- and Ground. Will only disconnecting the Vcc OR Ground Wires damage the Connected Device or the Data Wires? I currently have a USB ...
0
votes
2answers
3k views

Is there a better way to plan a circuit to square a 3 bits binary number?

I need to plan a circuit that will square a 3 bit binary number: $$\{Y_2, Y_1, Y_0\} \rightarrow \{S_5,S_4,S_3,S_2,S_1,S_0\} $$ I thought of the common way we multiply numbers and used it to plan the ...
9
votes
3answers
39k views

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 ...
7
votes
4answers
5k views

Switch 5V with back voltage protection

I'm trying to develop a design which involves switching a 5V rail. The design goals are: As low cost as possible (i.e. Can't use a fancy integrated solution) Relatively low current handling ( ...
6
votes
1answer
2k views

How is this Pushbutton Debounce code?

I am monitoring a pushbutton with a microcontroller where I am trying to take care of four things together: 50-msec debounce upon push-begin and 25-msec debounce upon push-release identify a short-...
6
votes
3answers
2k views

How should I use rotary switches and resistor networks to uniquely relate each possible combination of switch settings to an analog voltage?

I'm designing a switched-mode power supply. I need to give my users the ability to set a voltage setpoint, with a range of approximately 200-800V, and at least 4V of resolution. This needs to be a ...
6
votes
3answers
3k views

Ways of Switching between Two Sim Cards

I'm interested in building a circuit to switch between 2 sim cards, and found a design guide by GSM module manufacturer Telit. (New design guide link here, see pg. 16+) In particular, "Figure 6" of ...
4
votes
1answer
2k views

Switching a resistor by software

I want to communicate with a microcontroller over a CAN bus which needs (ideally) 120 ohm terminal resistors at the end of each bus. I want to integrate this resistor into the circuit and activate it ...
4
votes
3answers
1k views

How can I switch a high current with a low-rated switch?

I'm designing and building a breadboard power supply for myself, which draws power from an ATX-like SMPS (Mains in, single Molex plug out) via a 4-pin Molex connector. The design includes a switch to ...
4
votes
2answers
4k views

Digital Switching for Audio

I want to be able to digitally switch the input of a line-level preamplifier. I was considering using relays to physically connect or disconnect each source to the input of the amp, which would be ...
4
votes
1answer
683 views

Battery saving self-poweroff circuit

I'm designing a battery powered device, which must be turned on by an external 3.3V impulse from a comparator output (TLV3201), and for the sake of power efficiency I want the MCU to power itself off ...
4
votes
3answers
4k views

Is this a good way to debounce a switch?

There are plenty of debouncing circuits on the internet, but I couldn't really find one that fitted my needs / available parts, so I came up with my own, from what I had. There's nothing special about ...
3
votes
2answers
1k views

What good is an induction coil in a dimmer switch?

I asked about a dimmer switch, and was told one has an induction coil. What benefit is an induction coil in a dimmer switch? ZE-02S has induction coil built-in on the circuit board, so it is 5/8" ...
3
votes
3answers
5k views

Low Voltage DC Automatic Transfer Switch

I am new to circuits and have a very basic knowledge, and am currently interested in building a simple circuit that would take 2 DC inputs each of 12V 1.5A and output 1 x 12V 1.5A input even if 1 of ...
3
votes
1answer
335 views

Mosfet suggession for large drain current Sample Hold application

I'm using a MOSFET for a sample and hold circuit controlled by a microcontroller. I want to control the charging and discharging of a capacitor by a solar cell. For this I'd be using two MOSFETs. The ...
3
votes
1answer
508 views

Push button switch terminology

I'm looking for a push button switch that when you press it, it is open and then when you press it again, it is closed. I believe this is called an "alternate action" push button switch. Is this ...
3
votes
1answer
3k views

N-Channel MOSFET as on-off switch between battery and load

I'd like to use 3v microcontroller to activate a small fan after the microcontroller wakes from sleep. I'm not quite clear on the placement of the load (i.e. fan) and the LiPo battery in a MOSEFT ...
2
votes
4answers
1k views

Programmable point to point connections

I have an idea for a programmable breadboard, but I am not sure of the feasability of it. My thought is to connect each strip of a breadboard to some type of circuit that can make arbitrary ...
2
votes
3answers
2k views

Low side and High side switches

Why do we go for a Low side / High Side Switch ? Why do I find more of Low side switches than High Side in Automobile electronics ?
2
votes
2answers
4k views

Voltage rating for switch with high voltage but very low current

I'm building a small circuit for measuring high(ish) voltages with an oscilloscope. It's based on an isolation amplifier that measures the voltage across a measurement resistor (r3 below), attenuated ...
2
votes
1answer
3k views

PNP to NPN Transistor switch

I'm working on project that requires I switch a 12v power supply on the high side of a circuit, using a 3.3v micro controller. To make this work, I'm thinking a can connect a PNP transistor on the ...
2
votes
1answer
178 views

What might be inside my speaker switch?

I have a speaker switch which has been in continuous use since some time in the 1980s. It a QED SSU4. To my surprise, there are plenty of pictures on the net and even some for sale. Even more ...
1
vote
2answers
930 views

High side switching

I have designed a BJT based switch to enable and disable one or more loads with a microcontroller pin. The situation is the following: The controller pins work with 3.3V The devices require 12V to ...