Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

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1500 questions
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3 answers

Why is earth used for ground? Literally earth?

I never considered earth to be particularly conductive. It's just dirt, after all. However, I've seen "earth ground" conductive stakes driven into the ground in order for electricity to be grounded, because it will find its way down there. However,…
user3916009
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3 answers

Are UV LEDs really dangerous?

I just bought some UV LEDs I bought them for testing banknotes and identity papers. I read the documentation and saw some warnings about UV light in which the vendor advises not to look directly at the light and not to expose skin to the light. Can…
Superdrac
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26
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ATMega8: why do VCC and AVCC have to be connected?

I often read that it is good practice to connect VCC with AVCC. Even in the ATMega8 datasheet it says so: AVCC is the supply voltage pin for the A/D Converter, Port C (3..0), and ADC (7..6). It should be externally connected to VCC, even if the …
Peter
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26
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3 answers

Why are high impedance circuits more sensitive to noise?

Why are high impedance circuits being more sensitive to the noise? They have less current flowing through them, but how is that related to noise, since external noise becomes voltage on the wires, and then current proportional to resistance?
1p2r3k4t
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26
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4 answers

Is an omnidirectional antenna a must for a cell phone?

I have read somewhere (but unfortunately I am not able to remember where) that cell phones do need an omnidirectional antenna. If it is so, what are the reasons for that? Why a normal directional loop antenna could not be (efficiently) used ?
Standard Sandun
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26
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2 answers

Single transistor level up shifter

I need a simple, single directionnal level shifter for 3.3V -> 5V conversion. There are many options on the internet, some using a logic ic and some using 2 NPN transistors (converter and inverter), but I never found an option using only a single…
Nicolas D
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5 answers

What could cause a microcontroller to unexpectedly reset?

One particularly irritating variety of bug in a microprocessor-controlled system is for the microprocessor to unexpectedly reset. An important tool for debugging this kind of problem is a list of possible causes. What could cause a microcontroller…
Stephen Collings
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Is a bleeder resistor on a small circuit mandatory at the decoupling capacitors?

I have this basic circuit with an MSP430 (The outputs go to LEDs) I have noticed a strange (to me, not saying much though) circumstance. In this circuit, I always have to wait around 20 seconds or manually short out the capacitor (when it's off) to…
Dan
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4 answers

How to place decoupling capacitor in four-layer PCB?

I searched a technology document about placement of decoupling capacitors and the main idea is shown in the following picture: I think it is reasonable but do I have to put the decoupling capacitor and MCU in the same layer? it is not convenient…
oilpig
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26
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MOSFET as a voltage controlled resistor

This question might be too localized, but I try. Is it possible to replace a variable resistor by a MOSFET, under conditions shown in the following schematic? If yes, can someone propose a MOSFET type or the required MOSFET parameters. simulate…
sergej
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What PCB fabrication methods for *prototypes* are used by professional engineering departments today?

Ten years ago, I worked at a small engineering department within Philips Semiconductors that prototyped all designs before getting them professionally fabricated outside. The method was pretty standard: Print artwork using a cheap laser printer…
Larry Harson
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5 answers

What does dBm mean?

When working with radios, I've seen the term "dBm". What does this mean? The wikipedia page gives a table showing the equivalent power in Watts. Is the dBm output just the power level of a transmitter? How does this differ from signal strength…
Toby Jaffey
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Criteria behind selecting pwm frequency for speed control of a dc motor?

I'm working on a speed control circuit for a brushed dc motor (24v, 500rpm, 2A, 4kgcm). The main components that I plan to use are PIC16f873, 4n25 optocoupler, IRFZ44N MOSFET, BY 500 - 800 diode(for free wheeling). What is the criteria behind…
raforanz
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Can Arduino be used in commercial products?

Is it legal for me to sell a product that's built with an Arduino? I know that it's open source, but does that mean I can sell my product for profit, or only for use in prototyping?
nathangiesbrecht
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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 as a slave. How would I increase the number of…
Manishearth
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