# Questions tagged [input]

Something put into a system or expended in its operation to achieve output or a result

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### BJT Input AC Signal Amplitude

This question is referring to npn BJT CE: If we look at base voltage vs. collector current plot we can see that at approximately 0.7V on base to emitter junction, the BJT starts rapidly conducting. ...
• 2,310
9 votes
9 answers
6k views

### 12V input on microcontroller pin

I'm trying to count pulses/sec. on a microcontroller pin in the ~5 to 100Hz range. The µC can operate at 5V input, so I have to get the voltage level down safely. A simple resistor comes to mind, yet ...
• 621
8 votes
2 answers
2k views

### What is the use for non-inverting input resistance in a negative feedback opamp?

Here in the Figure R5=50K. This resistor value is not in the equations to obtain output voltage, and in many tutorials non-inverting input is directly grounded without a resistor. What might be the ...
• 11.3k
6 votes
7 answers
13k views

### Multiplexing Inputs on a microcontroller

I have a 4 way DIL switch that I use to provide input to a microcontroller, and I need to free up a port to use for something else. Is there a way to multiplex 4 inputs into 3 microcontroller ports? ...
• 5,758
12 votes
6 answers
19k views

### Input voltage range of opamps

I understand that, for an ideal opamp, Vo is bounded by Vee and Vcc (i.e.; Vee < Vo < Vcc). But, what about the input voltage range? What is the allowed input voltage range in which opamp works ...
• 13.5k
7 votes
3 answers
6k views

### PIC - How to skirt around low maximum ADC input impedance?

Reading a 9V battery on a PIC is nothing new. The most simple and straightforward way is with a voltage divider. I'd like to keep the divider resistances cranked up into the hundreds of kohms so I'm ...
• 2,276
0 votes
1 answer
4k views

### Controlling a single phase AC fan with a 0-10V DC input

I have a fan motor which is a permanent split phase single phase capacitor motor: http://uk.rs-online.com/web/p/axial-fans/2781543/ I currently control this fan's speed with the following controller:...
• 11.3k
0 votes
4 answers
660 views

### Understading negative feedback [duplicate]

There is a question here about something similar, but it's asking about the internals of an op-amp. I'm having trouble understanding the function and use despite several hours of YouTube tutorials. ...
• 705
2 votes
2 answers
1k views

### 5v output to 3.3v?

I have a microcontroller and a Raspberry Pi, both running off of the same 5v supply, in parallel. The microcontroller has 4 5v output pins and the other is a Raspberry Pi, that can only accept inputs ...
12 votes
4 answers
3k views

### Is this clamping voltage divider for a high-impedance input a good, robust design?

I have an AC input as follows: Can range from ±10V to at least ±500V continuously. Runs from roughly 1 Hz to 1 kHz. Needs > 100 kΩ of impedance on it, otherwise its amplitude changes. May ...
• 467
10 votes
1 answer
6k views

### How is this 5-24V input circuit working?

Since I require some kind of wide range input (going to a microcontroller) for a new project, I looked through some designs that are already in use (or were considered at some point) for other ...
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9 votes
1 answer
943 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 ...
• 317
9 votes
1 answer
1k views

### What's mean these microcontroller pin input/output modes?

I bought an stm32f103ret6. When I saw the reference manual, I saw that it has several I/O modes. For input: floating, pull-up, pull-down For output: analog, open-drain, push-pull I have already ...
• 381
6 votes
4 answers
28k views

### 3 input XNOR gate operation

For 3 input XOR gate and XNOR gate, by solving the equations I got the result as in the picture. So according to the solution the outputs of the 3 input XOR and XNOR gates are same. This solution ...
• 133
2 votes
3 answers
6k views

### Digital Input Clamp Circuit Protection

To be able to connect some peripheral to digital input, I'm designing the circuit protection to avoid any possible failure due to over/under-voltage issue. So, I will add a clamp protection circuit. ...
• 357
1 vote
5 answers
10k views

### Can an opto-isolated input be analog?

Title says it all: can an opto-isolated input be analog or are they intrinsically digital? Why: I am looking to purchase a relay control board and am deciding between a few options. Here is my ...
0 votes
1 answer
4k views

### MCU Input Protection

I am working on a simple protection circuit for an I/O pin on an MCU. The device will be 3v battery powered. The MCU's I/O pin has a voltage tolerance of (GND - .6V) to (Vdd + .6V). Pull-to-ground ...
• 159
2 votes
2 answers
296 views

### Is there a way to measure the Phase Shift between the input and the output voltages related by the equation: $V_o = V_i(a+jb).$? [closed]

Say $V_i$ is an input voltage, and the output voltage is given by $V_o = V_i(a+jb).$ Is there a way to measure the Phase Shift between these input and output voltages?
2 votes
1 answer
2k views

### Vbe vs Ic characteristics of NPN transistor at different Vce in active region

Below is an NPN transistor characteristics for Vbe versus Ic at different Vcb or Vce: It seems like in the active region, Vbe vs Ic curves gets steeper with an increasing Vce. The following ...
• 3,420
1 vote
3 answers
2k views

### What are the mechanisms at work in a pull-up or pull-down resistor circuits with a push-buttons and a GPIO?

I have a question regarding the GPIO (from a Arduino board for example). How does it work exactly when you use it as an input pin? What are the mechanisms at work when you use it in a pull-up and pull-...
• 11
26 votes
3 answers
36k views

### How do I extend the number of analog (input) pins available to me?

I already know how to extend the number of digital pins on an Arduino using a multiplexer. I want to increase the number of analog input channels that I have. One solution is to add another Arduino ...
• 2,832
38 votes
8 answers
3k views

### Add a passive hardware token using a 3.5mm jack

I have a box that I made for my niece, which allows her to exchange voice messages with me. It is powered by a Raspberry Pi and features two buttons, a LED, a microphone and a speaker. Now, for ...
• 603
7 votes
3 answers
15k views

### What kind of diode to use with ADC inputs

I am looking for diodes to protect my ADC from over voltage conditions. From what I have researched so far, I know that I need schottky diodes hooked up from the input to the ground and the input to ...
• 1,970
12 votes
3 answers
3k views

### Can unconnected inputs make an IC get warm?

I am using an ATF16V8 PLD for some simple glue logic. While testing it on a prototyping board, I noticed that it gets warm to the touch almost immediately. I checked that no outputs were short ...
• 399
6 votes
6 answers
4k views

### Simplest possible I/O for Homebrew 8-bit CPU

I am working on designing an 8 bit cpu as a personal project for no real reason. I am using mostly 74HC series chips and am generally focusing on ease of programming over performance. I am using ...
• 2,044
15 votes
5 answers
17k views

### Considerations when using internal pull-up/down resistors

I am working with STM32 micro-controllers. These micro-controllers have the option to set the input pin as pull up or pull down: Earlier I used to give external pull up or pull down resistor wherever ...
• 7,532
12 votes
3 answers
3k views

### 12 V input on 3.3 V GPIO, TVS pulled down or Schottky pull up?

I am building my own PLC that has to accept permanent inputs of up to 30 V DC into a STM32F with 3.3 V inputs. The switched input will have to work with 8-30 V, but 90% of the time the ...
• 836
11 votes
4 answers
3k views

### Where Does VDD+0.3V Input Limit Come From on IC chips?

There are a variety of integrated circuits that specify that their input voltage can span a fairly wide (absolute maximum) range, e.g. -0.3V to 6.0V (ref, pdf page 4), and then have a "Input Voltage ...
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7 votes
2 answers
6k views

### How to trigger a transistor from iphone's audio output jack?

I want to trigger a transistor using iPhone's audio output jack. My goal is to turn off an LED(which is fed by an external +5V battery) by sending an audio signal from iphone's output jack. At the ...
• 11.3k
1 vote
1 answer
1k views

### Wide voltage range input regulation (24V - 3.3V)

TL; DR: I need a circuit capable of handling input voltages from 24V to 3.3V (with a 10mA/5mA maximum current) and delivering 3.3V to the microcontroller (ESP32) input. Recently, I've been working ...
• 103
8 votes
3 answers
8k views

### Arduino Analog Input example clarification

First of all I'm total nub in electronics. Recently I got an Arduino Nano. Now I'm trying to understand why there is no potentiometer nominal at http://arduino.cc/en/Tutorial/ReadAnalogVoltage ...
• 183
3 votes
3 answers
9k views

### How to make clamping circuit to clamp exactly at 3.3 volts

I am building a circuit that attenuates the signal and sends it to 3.3V ADC, so I need to limit max voltage to 3.3V. After testing out some circuits for clamping the voltage(various schottky or zener ...
• 1,176
2 votes
1 answer
715 views

### Can you use a stepper motor as input?

I'm not too versed in EE so I apologize for my duncitude - My thought is that you can precisely control a stepper motor, but can you inversely get precise readings out of a stepper motor? For ...
2 votes
2 answers
11k views

### Recommended voltage/current for dry contact input?

What would be a reasonable value for voltage and max current to used in conjunction with a remote dry contact output so that it can return to my MCU (through isolator)? I plan on using this input for ...
• 811
1 vote
2 answers
693 views

### Several Questions About Analog Input

I am new in the automation industry, and now I am focusing on learning how to wire correctly analog inputs in detail, since last time I tried I damaged the module input because of wrong wiring. Here ...
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0 votes
2 answers
89 views

### Keyboard USB transform

I want to press a key on my keyboard, for example "a" and a device should take the scan code of the button I pressed and transform it to something else: e.g. "b" or the scan code ...
0 votes
3 answers
652 views

### Help to build a circuit to trigger event only after input signal changes from "1" to "0"

I'd like to build a kind of logic as shown in the picture ,but I can't do it and I really appreciate if someone can help on that. Basically what I'd like to achieve is that when the input signal ...
9 votes
4 answers
3k views

### Does there exist an IC that allows on-the-fly routing of signals?

Do there exist ICs with N input pins and N output pins which, either via EEPROM setting or via on-the-fly control by a microcontroller, allow one to route each of the N inputs to ANY of the N outputs? ...
• 4,812
5 votes
3 answers
1k views

### Measuring input current of opamp

I want to measure the current that goes into a noninverting opamp input. I've setup my experiment as follows: I can't measure the voltage drop across the 10M (R1) resistor directly since my DMM has ...
• 5,443
4 votes
4 answers
3k views

### Input impedance of an op Amp

I noticed that the input impedance of an op Amp is extremely high. Why is that so?
• 11.3k
3 votes
1 answer
1k views

### Op Amp input protection

I was looking for an Op Amp input protection circuit and the most common I found looks like this. When the voltage at Input Signal goes above/below Op-Amp's supply ...
• 1,900
2 votes
3 answers
2k views

### Bipolar Op Amp w/ Near Zero Offset?

My understanding is that if source resistance is low, a bipolar op amp has 10dB less noise than a JFET. I prefer the JFET op amps because the input offset is so low that you can eliminate coupling ...
• 1,410
1 vote
1 answer
41 views

### Input range for TPA311x

I'm reading through the datasheet of the TPA311x family. I'm looking for the input range for pins INPR and INPL but I cannot find this information. I see the absolute maximum ratings, but it's not ...
• 875
1 vote
1 answer
317 views

### Is 3.5VDC going to damage an stm32 analog input?

I have a pressure transmitter sensor that is supplied with 5VDC and provides 0.5-3.5VDC analog value within a pressure range of 0-4bar. The system that I'll be using the sensor within, will almost ...
• 181
1 vote
2 answers
3k views

### How can I interface with these 24 V signals?

I have a few 24V inputs to my micro controller from Limit switches. I have conditioned the signals as shown. Pulled down, de-bounced and level converted. I have some signals that are again 24V but ...
1 vote
1 answer
908 views

### Sallen Key topology input and output impedance

Ideal Operational amplifier Zi=(R1+R2)||Zc2 Zo=0 741 Operational amplifier Zi=(R1+R2)||Zc2 Zo=0 (at DC) For the input impedance when using a 741 I am not sure if I should consider the Fairchild ...
• 53
1 vote
1 answer
482 views

### DC Op-Amp Output at an unexpected voltage?

For some reason Op-Amps are impossible for me. I'm experimenting with them a little bit. I have the following circuit... simulate this circuit – Schematic created using CircuitLab This is the ...
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1 vote
2 answers
304 views

### dsPIC 30F6012A will not read RD9, appears to be software problem

I'm using a dsPIC 30F6012A. I have two PCBs with this chip, both displaying the same symptoms, implying it's not one-off damage. RD9 is definitely being driven to five volts, confirmed with a ...
1 vote
2 answers
1k views

### Detect 220Vac signal on Microcontroller

I'm developing a module and the control switch may be at long distances. Considering I have the 127 or 220Vac input, I want to use that for switch signal. I believe is better, instead of making a ...
• 117
1 vote
1 answer
575 views

### How not to waste power with digital inputs?

I am trying to make simple gates with n-MOSFETS, yet I'm not sure how to actually do physical gate inputs correctly. At first, I tried this (a single-pole, single-throw switch from +5V to gate). ...
• 287