How many times something happens per second, measured in Hz (Hertz).
27
votes
8answers
2k views
Why do utility companies supply at a frequency of either 50/60 Hz?
It just struck me that Utility Companies world-wide supply domestic users at either 50/60Hz. It could have been selected to be 10 Hz, or 100 Hz ... whatever
Was 50/60 chosen at random? Is there some ...
19
votes
6answers
3k views
How to convert AC to DC
I am designing a circuit that needs to output 5VDC @ 1A. I'm trying to use a wall transformer to step the voltage down to 12VAC. The next step is the diode bridge and ripple capacitor.
The ripple ...
19
votes
6answers
684 views
How precise is the frequency of the AC electricity network?
If I make a digital clock which first detects the AC frequency roughly (whether it is 50, 60, 100Hz, etc), then uses it as its clock pulse source, how precise would it be? Would it work world wide ...
18
votes
4answers
2k views
Why does a faster clock require more power?
If you overclock a microcontroller, it gets hot.
If you overclock a microcontroller, it needs more voltage.
In some abstract way it makes sense: it is doing more computation, so it needs more energy ...
16
votes
5answers
695 views
What are 12.000393 MHz crystals used for?
I found them on www.digikey.com, and they're apparently made by different manufacturers, so there must be some use for them. What are they used for?
edit
and why? The 2400 baud modem doesn't offer an ...
14
votes
3answers
825 views
Negative frequencies: what is that?
I know that when the frequency is 0, the voltage will be pure DC. But in DSP and Digital Communication, I have seen mentioning of negative frequencies which I dont quite understand. For example, like ...
11
votes
5answers
447 views
Frequency limitation for homebrew CPUs
While looking into some custom built CPUs I've noticed the frequencies at which they operate are relatively low compared to modern CPUs (in the order of several MHz). Is there an electronics ...
11
votes
2answers
549 views
Why is a lower switching frequency more efficient?
I'm designing a 10V to 3.3V step-down converter. Looking at the LT8610, the applications example shows two similar circuits that have different switching frequencies.
The Efficiency vs Frequency plot ...
10
votes
2answers
450 views
Frequency ranges that causes a hazard to humans
I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know ...
9
votes
8answers
10k views
Maximum sample rate of Arduino Duemilanove?
G'day all!
I have an Arduino Duemilanove hanging around spare at the moment and thought I might try a few audio interfacing projects. I'm just wondering what sort of sampling frequency I can achieve ...
8
votes
4answers
374 views
Is there a device that converts any AC frequency to 60 hz?
If I have something like a windmill generator that generates AC current, but at variable frequency, what device(s) would I need to convert that variable frequency into a constant 60hz frequency, so ...
8
votes
3answers
2k views
How critical are UART frequencies?
I'm going to be using an 8 MHz crystal to run my microcontroller at 16 MIPS (PLL 4x, 2 cycle instructions.) However, 8 MHz doesn't divide into any UART frequencies AFAIK... so how critical are these ...
7
votes
2answers
614 views
Is it true that the power line frequency is kept accurate by atomic clocks?
I've heard rumors that the power line frequency is kept stable and accurate by syncing it with atomic clocks. Is this true? What kind of accuracy does it have? Is this true everywhere?
7
votes
1answer
413 views
Characterization of bypass capacitors
I was reading through a few post including Decoupling caps as well as this app note Xilinx Power Distribution Network.
I have a question regarding capacitor values within a power distribution system. ...
6
votes
2answers
613 views
4 Hz Stable Frequency generator
Whats a good circuit/design that will generate a very stable 4Hz signal (to feed into a counter) that won't drift with temp / time.
It's not so important that its exactly any particular frequency, ...
6
votes
4answers
396 views
Why can an oscilloscope only find frequencies 1/10 of the sampling frequency, despite Nyquist?
The oscilloscope at my university states both its sampling frequency and the maximum frequency that it can detect. However, the maximum frequency is just 1/10 of the sampling frequency! Nyquist's ...
6
votes
4answers
3k views
What is Frequency in electronics?
This has been floating in my mind for a while, everything has a frequency. Like a dc-dc converter, my scope is 100 MHz(i know that's a bandwidth but it has the unit of frequency). I understand that an ...
6
votes
4answers
550 views
MC34063A: Why am I overclocking this chip?
I've decided to get some experience with DC-DC converters and I've obtained an Onsemi MC34063A DC-DC converter. From documentation I've got the datasheet, the AN920 application note and the Excel ...
5
votes
5answers
431 views
Bandpass filter to isolate musical note “A2”
I would like to design a bandpass filter to isolate the musical note A2 ( 110Hz ) from its neighboring notes at a precision of a half-step. This means that ...
5
votes
1answer
218 views
What limits the modulation of digital signals?
I am trying to understand why there are different speed on different frequency bands. I see that e.g. ZigBee can do 250kb/s for both 2.4GHz and 868/915MHz, but ...
5
votes
2answers
304 views
How to Shift Carrier Frequency in QAM Signal?
If I wanted to apply a 100MHz frequency shift to a QAM signal with a 400MHz carrier frequency, I would
Demodulate it at the carrier frequency
Apply a frequency shift to the original signal
Modulate ...
5
votes
3answers
249 views
Can LEDs or optocouplers be used without a resistor if PWM is used?
LEDs are often connected through a resistor and the purpose of this seems to be to lower the voltage across the LED to around 1.8V. Can PWM be used to lower the voltage instead of a resistor? If so, ...
5
votes
1answer
262 views
Q factor for an LRC series circuit
Trying to prove to myself that the Q factor for an LRC series circuit is \$\sqrt{L/C}/R\$, but I am struggling with it...
My reasoning runs that the half power upper frequency limit is (ignoring the ...
5
votes
2answers
99 views
Rated frequencies and power requirements
(Here is a related, earlier question.)
Two microprocessors are identically manufactured. However, after testing the two processors, the manufacturer bins, rates and labels them to operate at ...
5
votes
2answers
601 views
Astable multivibrator with increasing frequency
I am wanting to design a circuit that uses an astable multivibrator as a clock source. However the difference being that over time the clock is gradually sped up until it reaches some multiple ...
5
votes
1answer
713 views
How to control Arduino frequency?
I'm porting a code from c in the Arduino platform (I'm using an Arduino Leonardo). I wanto to remote control a camera with an IR LED. The info about the remote control want to emulate here. The code, ...
5
votes
2answers
160 views
What is the meaning of the nominal frequency specified by manufacturers of crystals?
This answer led to the conclusion that it is unclear what the meaning of the frequency listed by crystal manufacturers actually means.
Given this graph on page 79 of this ECS Crystals Application ...
5
votes
4answers
316 views
Common Analog Signal Frequencies
I'm trying to scope out what frequencies different common analog signals are. The DPScope design specs provides a list of common lower (sub 1 MHz) frequencies (copied below).
audio (20 kHz)
...
5
votes
2answers
251 views
Injection locked frequency dividers
I am beginning to design a monolithic frequency synthesizer (around 2.4GHz) in which I need the maximum of spectral purity. I was looking at injection locked frequency dividers (ILFDs) for use as a ...
4
votes
3answers
1k views
Interview Question, what's limiting the output frequency for the FPGA circuit?
I recently received a question in an interview that partially stumped me. It went something like this:
You have an FPGA circuit that is supposed to be generating a signal with a frequency of 500MHz, ...
4
votes
2answers
532 views
Relation between Power consumed and MCPS (million cycles per second) consumed on a processor
I have been working on a ARM cortex A8 board on mp3 decoder.
While doing this I have a requirement saying the mp3 decoder solution I am doing should consume 50mW. This generated few questions in my ...
4
votes
3answers
3k views
3-phase Motor Speed Controller
Background
If you look at my profile description, you'll see that I'm involved in building and wiring up Carnival floats that are powered by an 800KVA, 415v, 3 phase Generator. Electrically, they ...
4
votes
2answers
221 views
Frequency response - finding transfer function
I have a this circuit:
I am asked to find |H(\$\omega\$)| in its simplest form.
I approached the problem by first recognizing that the first op am was a standard inverter. With that I basically ...
4
votes
3answers
212 views
How is microphone's frequency response determined
It seems this is the chicken and egg problem. To be able to determine the frequency response of a microphone one needs a speaker that has a known response. To be able to know the response of a speaker ...
4
votes
1answer
76 views
Least noisy pre-amplifier design
I am building a frequency generator circuit and need some advice. I am using the AD9833 DDS generator (programmed from a PIC16F876) to generate frequencies and I wish to be able to adjust the gain.
...
4
votes
2answers
247 views
Frequency multiply a digital signal using pure digital ciruitry (i.e. without PLL)?
Is it possible to multiply the frequency of a digital signal using digital components alone, and at the same time, preserve the duty cycle?
I could finally come across the circuit below: it doubles ...
4
votes
1answer
586 views
Frequency Reuse Patterns
In Multiple Access Protocol for cellular networks, there is this Frequency Reuse Patterns. And I am given a formula to one of the patterns that states: \$\text{Reuse factor }\mathbf{K} = i^2+j^2+ij\$
...
4
votes
2answers
421 views
Odd number frequency divider
Important note: You are not helping me do my homework. This is for a competition for engineering students, that encourages you to "use your network" ;)
I've got this pattern for a frequency divider ...
4
votes
3answers
947 views
Audio Frequency Shift Keying to Arduino
I am attempting to have an Arduino interpret an AFSK signal, this is very vague but can anyone just point me in the right direction for detecting the frequency of the AFSK signal with an arduino?
4
votes
2answers
153 views
Why are low frequency channels (10kHz - 200kHz) especially susceptible to interference?
I am working on a system which should communicate with a ~100kHz signal, and read that low frequency channels, e.g 10kHz to 200kHz, are especially susceptible to interference.
Why is that? Are they ...
4
votes
2answers
1k views
Problem with a Relaxation Oscillator (using Op Amp)
I'm studying a relaxation oscillator. This wikipedia circuit shows exactly my circuit with the only difference that I'm using different values for each resistor.
I called resistor R the one ...
4
votes
1answer
129 views
What frequency/band lends itself to interstellar communication? [closed]
Silly question perhaps... but I got to thinking after reading that the Voyager is now almost out of the heliosheath.
What frequency/band would be suitable to communicate across stellar systems; say, ...
4
votes
1answer
892 views
Required Bandwidth for ASK
In Amplitude Shift Keying, the bandwidth required is given by \$B=(1+d)S\$ where B is bandwidth, S is the signal rate, and d is a value of either \$0\$ or \$1\$.
But how could the required bandwidth ...
4
votes
2answers
302 views
Piezoelectric transducer drive circuit
I have a small (1/2"sq.) thin film piezoelectric transducer that I would like to use to test the frequency response of musical instruments. I want to be able to stick it on to any instrument , send a ...
4
votes
2answers
964 views
Low “Hum” Frequency Detector
How do I create a frequency detector that can detect low "hum" sound? (quite low frequency sound probably made by a air-con or similar type of machine)
Please feel free to ask me questions if my ...
3
votes
3answers
222 views
Reading frequencies without filters
Is it possible to read a set of frequencies with a PIC in such a way that for each frequency a different function is called?
The idea was to send multiple frequencies at different times (no ...
3
votes
4answers
624 views
Basic Frequency Control Circuit
How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why?
Here is the schematic which is ...
3
votes
5answers
611 views
How to deal with a DC adapter with irregular voltage output?
Background information:
I tried hard to get a Schmitt-trigger working, but it kept failing. By accident I figured out, that my AC-to-DC adapter produces a very irregular voltage output (I could hear ...
3
votes
3answers
642 views
Is Frequency for dc is zero?
We know the frequency of a direct current is zero. The reason is that there is no repetitive pattern.
But i was stumbled when i notice, why cant that straight line be cut into smaller pieces, and ...
3
votes
3answers
258 views
Very low frequency instrumentation amplifier
I'm trying to choose an instrumentation amplifier for very low frequency signals (seismic monitoring).
The trouble I'm finding is that on many of the data sheets, they only give response curves down ...
