# Tagged Questions

A resistor obeys Ohm's law (V=IR); the current through it is equal to the voltage across it divided by the resistance (equivalently $I=\frac{V}{R}$)

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### Replacing 75ohm heating coil with resistors?

I am trying to remove the Thermal Fuse, Thermostat, 75 Ohm, and 15O Ohm heating elements from this diagram: This is the schematic for a popcorn machine that has two heating coils and a DC fan to ...
41 views

### creating a basic voltage regulator [on hold]

How do I create a simple voltage regulator for a 120V input voltage. The voltage regulator basically need to send an output of 25%, 50% and 75% of the input. Can this be done by simply using a bunch ...
31 views

### how to transform an audio signal in square saw or sine wave? [on hold]

What is the basic schematic to change an input audio signal to different wave shapes (sawtooth, square, etc)... i'd like to learn the principles behind it... links, books or online guides are ...
85 views

### Would 2 100k Ohm resistors provide the same as a 200k ohm in series?

Practically what it says in the title. I would also like to know if it would emit more heat and would the tolerance be higher?.
37 views

### Force microphone on TRRS connector without a mic connected

I have a TRRS connector for my Android phone. I want to be able to enable/disable the mic on the cable using a button. So for this I have connected a 1.2 kOhm resistor to a button and when its 'on' ...
39 views

### Choosing the right diode for a 9v circuit with npn transistors? [on hold]

I'm super naive to this field, so pardon me if i sound stupid. i'm building a guitar stompbox and i want to use a diode to be sure the signal doesn't go backwards. how do i pick the right diode? are ...
108 views

### Voltage across a 2.2k resistor [on hold]

I've just begun learning about electronics, and have been performing a few experiments on measuring voltage,current with a multi-meter. If I have a single resistor having a resistance of 2.2k ...
5k views

### What is a “100R” resistor?

Sometimes I see references to "R" resistors. For example: Obviously the 100 refers to 100 Ohms. What does 100R mean?
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### Mathmatically analizing different voltages in a phase changing circuit

I am trying to understand a phase shift oscillator from a mathematical perspective, and to begin I simply took the phase-shifting part of the circuit and am now trying to analyze the voltages as a ...
190 views

### What should my resistor wattage be to run a LED on 240VAC?

I'm looking for a sanity check on my figures here because I'm concerned my resistor wattage is unrealistic. I would like to run a red LED on a 240 VAC line. I have found that the forward voltage for ...
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### I made a fluctuating circuit that controls an LED to be on or off, How does it work? [duplicate]

I have this circuit, The two ends represent the positive and negative terminals of the battery. Values R6-4.7K R1-470K R2-470K R3-4.7K C1-.1 uf C2-.1 uf All ...
105 views

### can a simple diode and resistor in series qualify as an inverter? [closed]

I'm working on a single-sided PCB and I find transistor pins are too close together for tracks to run through, so I'm wondering if I could roll off my own inverter by using the cathode of a diode as ...
82 views

### Resistor and voltage of a circuit

I'm a beginner in electronics and I was studying when I had a question, how to calculate the voltage after passing by a resistor. Ex: there is a circuit of 10mA with a 5V voltage, what is the voltage ...
77 views

### About calculus and resistors [closed]

how can you know the voltage of a circuit, after passing through a resistor? for example there is a 5 volt supply and a resistor of 120 ohms, what will be the voltage after passing through this ...
193 views

### Different voltage drop in serial and parallel circuit with resistor

I have a circuit powered by 9V battery, I'm using two 2V LEDs. If I connect the LEDs in series with 10k Ohm resistor, the voltage before resistor is 9V, after the resistor it's 3.3V and after the ...
49 views

### 4 (5) band 5% resistor with superfluous black end?

I need to replace a resistor (brown black black gold black - if I am reading it correctly) - the kind I need is shown in the images below, but I can't seem to find an exact match of the colour code. ...
33 views

### Reed switch wiring

I'm trying to connect a simple reed switch to my Raspberry to check if my door is open or not. I found plenty of tutorials online, but all of their schematics behave different, so I decided to create ...
305 views

When you have one resistor in a series circuit, the amount of voltage taken up by that resistor is 100%. Adding another resistor (same Ohms) makes that voltage drop 50%. Why, since only current should ...
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### Are resistors the only legal way to tie various power designations together?

I'm working with a schematic in Eagle and I use IC's with different types of power pins. I connect VDD to VCC to +5V and I connect GND to VSS to zero volts. When I look at the ERC, I receive warnings ...
155 views

### led circuit - a challenge of designing a circuit with 192 LEDs in

I have been faced with a challenge of designing the circuitry for an LED light. This light will have 96 LEDs in Cyan with a max Vf of 3.7V and another 96 LEDs in red with a Vf of 2.6V. There is to ...
74 views

### What Resistor Should I Use? [closed]

I have an 18V battery and a 12V bulb and I want to reduce the voltage with resistors. I have already used a transistor (L7812CV) which works fine but now I want to know how to do it with a resistor so ...
310 views

### Why use “OMIT” components on a PCB?

I have some experience with highfrequency circuit analysys. However I am a newbie in PCB design. I am analysing this circuit: http://www.ti.com/lit/ug/spmu365b/spmu365b.pdf (starts on page 36) and ...
69 views

### Is there a component that increases current? [closed]

There is a component that increases resistance and therefore reduces current, the resistor. I was wondering if there is a component I can use to increase current in a circuit.
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### L200c power supply, pot won't go down to 0 ohms

So I'm trying to make a power supply using the L200 regulator. I'm using the circuit in Figure 1. Programmable Voltage Regulator with Current Limiting. I made the circuit after that design. Except ...
210 views

### Improve Rise Time on 1Hz Signal

I am using a MCP79410 real time clock to generate a 1Hz square wave signal (50% duty cycle) for a low power display (Sharp Memory LCD). Without this signal charge builds up and the pixels show burn-in....
36 views

### Tool, algorithm or method to know which resistors to use for an equivalent resistance $R_T$?

Say I have to get a resistance $R_{T}$ and I have a bunch of resistors, $R_1, R_2, \ldots, R_n$. Does there exist a tool, algorithm or method that gets the resistance value closest to $R_T$ ...
40 views

### 24 VDC source to 0-5 VDC or 4-20 mA manual input

I have a PLC which offers analog inputs of either 0-5 VDC (6 VDC max) or 4-20 mA (sink). The source will be 24 VDC and I want the input to be manually adjustable (assuming with a potentiometer). The ...
97 views

### Resistor for a LED with high limits

My first electronics project in over a decade involves a Raspberry Pi 3 and two illuminated buttons. I want to understand what resistor I need for the LEDs, if any. The illuminated buttons have ...
69 views

### chip resistor/capacitor size vs performance for analog circuits

I am designing one four layer ADS1298 (TI) based analog PCB. Signal frequency is about 1.5Hz to 3.79kHz. It is a four layer board with most of the components and traces on top layer and the ground ...
124 views

### Transistor D-latch does not latch

Hello I have built a d latch using 4 NAND gates and an inverter made from transistors. Here is the schematic. For some reason the latch does not remember its previous input like it is suppose to do....
917 views

### Do surface mount resistors have voltage ratings?

The assumption of the question is that in all cases the power requirements have been met. I'm working on some mains (120 Vrms) applications and was speccing out resistors. How small of a ...
27 views

### Determining the required value of shunt and circuit design [closed]

This is a personal project related question. Being less knowledge in electronics I need some help. Please do help if anyone can solve the problem. I want to build a circuit with power supply 12v 5A ...
36 views

### How to distibute power between MOSFETs and resistors in current limiter cirquit

I thinking about making some sort of not-very-big-power hi-side current+voltage limiter, using cheap china SOT-23 P-chenel MOSFET like IRF9310PBF, BSC030P03NS3G or AO4407. But in some user cases ...
83 views

### SMD LED power supply [closed]

I bought some SMD LEDs like the ones in the picture, supplied by a 12 V adapter. I wanted to supply them individually for a project so i cut them and soldered to a 18 ohm resistor. I calculated its ...
63 views

### How to maximize the voltage range using an operational amplifier (differential amplifier)?

I'm trying to maximize the voltage range using voltage dividers and operational (differential) amplifiers, but am not able to do it. I do not have an electrical engineering background, but my project ...
145 views

### Detect AC current in series with load

I have a challenge at work to build a device to monitor the health of ceramic cartridge heaters, similar to this. It operates with an AC transformer and there are 5 heaters I'd like to monitor ...
45 views

### ATMega32u4 output power to input without external resistor?

I am new to electronics and have a SparkFun Pro Micro clone with an ATMEGA microcontroller. I wanted to know if I could set one pin to be an output that sends power to another pin that I have set as ...
67 views

### How resistors really works? [duplicate]

From what I've readed, a resistor is a component which limit the current in a circuit. Supposing that I've a load that is rated for 12v 500mA, if I put a resistor to limit the current to, for example, ...
5k views

### Why did my LED resistor burn while lighting four LEDs in series?

I have tried to create a circuit to switch a large 7-segment LED display (LDS-CD16RI) using a pair of MOSFETs, as follows: simulate this circuit – Schematic created using CircuitLab Here ...
28 views

### RC network in 12v 50watt halogen desklamp

I'm trying to repair a halogen desklamp that has a transformer based on this circuit: R is a 0.5 ohm 1watt resistor for the main RC network that was blown, I've got some replacements ordered on the ...
49 views

### Circuit Partial Failure

We are working on a circuit which appears to be failing during operation due to heat (putting a fan over it keeps it running). We have narrowed the possible parts down to a power resistor and a zener ...
236 views

### Weird 240 ohm resistor on zq line to DDR

I've been looking at schematics that interface ddr ram and noticed a weird notation for their zq pull down resistor. What is with the dot at the top as well as the 1%? Haven't seen this before.
3k views

### Is there such a thing as rubber band resistor?

I'm doing a project with some tight requirements, in which I need to measure the distance between two points, which might not be in direct view of each other, and on parts that are too small to mount ...
58 views

### High frequency rf resistors

I need non reactive resistors for use at LF thru HF (100KHz thru 30MHz) for use with radio receiving antennas as terminations. Carbon comp and carbon film work but have their shortcomings in stability ...
110 views

### Mosfet keep circuit closed (vape mod)

Hello i made circuit with IRLB3034 mosfet for using vape mod with low current rated button, but i have problem - mosfet is firing itself when i plug battery in and its overheating (coil is 0.5ohm). I ...
94 views

### Voltage Divider producing unexpected voltage

I am attempting to create a voltage divider that create 4.5 volts from a 9v battery. Using the voltage divider equation 4.7k / (4.7k + 4.7k) ) * 9v = 4.5v, I ...
130 views

### Why is the voltage across the capacitor constant?

I've connected a 6V DC voltage source via a 1Ω resistor to a 1F capacitor. I was expecting the simulation to reveal a less constant t-vs-v graph: it would start at 0 and after a while stabilize ...
61 views

### Termination resistor creating communication problem in RS485 MODBUS/TCP

In RS485 communication, what is the role of termination resisotor. Is it mandatory? I have been working on a project with MODBUS/TCP over RS485 where upto 32 slaves are there in some links, out of ...
80 views

### Motherboard RGB diode control and resistance?

I've recently acquired a new motherboard for my PC which features RGB strip control. That's well and good but I have particular need to control a single RGB diode with that same header. The issue I'...
207 views

### Will electricity flow in a perfectly conductive medium

I was just wondering that since resistance is required for a potential difference to build up, what happens when we have a perfectly conducting wire, 0 resistance, will current still flow through the ...