54 votes
Accepted

What's special about 14.31818 MHz?

It is exactly 4× the NTSC color-burst frequency of 3.579545 MHz. Since it is (well, used to be) used in huge quantities in commercial color TV sets, it is both commonly available, and ...
Dave Tweed's user avatar
  • 173k
39 votes

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

You have clearly built a circuit that is fully analog in nature and produces a frequency in each oscillator that is dependent upon various factors such as: Changes to the voltage level of the power ...
Michael Karas's user avatar
34 votes
Accepted

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

What I can't figure out is why the circuit appears to get spontaneously detuned, i.e. one or more of the individual circuits end up with frequencies that are different from what they were tuned to (...
Todd Wilcox's user avatar
33 votes

Why are two 555 timers in separate sub-circuits cross-talking? (Poltergeist in the Breadboard)

Why did you leave out C3? From Charles Platt's Make: Electronics (1st edition): There is a reason for everything in an electronic circuit (and Platt did explain why it is needed). You have learned ...
StainlessSteelRat's user avatar
32 votes

How can you achieve decent clock accuracy in microcontrollers (e.g., max 1 second drift in a year)? How do digital watch manufacturers accomplish it?

Have you tried comparing with what accuracy you actually get from a digital watch? I don't remember them delivering "1 second per year" accuracy. The crystal you linked was 50ppm. The ones ...
pjc50's user avatar
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31 votes
Accepted

Why not put a crystal oscillator inside the microcontroller?

A crystal is very different in physical construction from an MCU, and most crystals are annoyingly large to integrate into a chip package. It's possible, however, to integrate other types of (smaller) ...
nanofarad's user avatar
  • 20k
29 votes
Accepted

What is meant by 'local' in local oscillator?

You got that wrong: The "local" in oscillator doesn't describe the kind of oscillator used. It could just be an LC-tank, it could be a crystal-derived oscillator, it could be something synthesized ...
Marcus Müller's user avatar
29 votes

How can I see if my oscillator works without using an oscilloscope?

Often if you can't see an oscillator output you can hear it. Years ago an headphone was a detector of choice for many interesting behaviours. Of course it depends on the level and the frequency but ...
Lorenzo Marcantonio's user avatar
26 votes

Why is there no sine wave oscillator chip?

The main problem with sine wave generation is that it takes two resonant elements to tango in producing a 180° phase shift -- classically, an inductor and a capacitor. At RF, this isn't a problem ...
ThreePhaseEel's user avatar
26 votes
Accepted

Ceramic resonator changes and maintains frequency when touched

As said in the other answers, ceramic resonator oscillator circuits are extremely sensitive as they have high input impedance and huge gain. The bias resistance in the circuit is about 1 megaohm and ...
Justme's user avatar
  • 149k
25 votes

Are there any microcontrollers that do not require an external clock source?

Many (most?) MCU's have an internal oscillator that can be used as the clock. Typically there will be a configuration that is held in non-volatile memory to set the clocking mode. The actual method ...
Kevin White's user avatar
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23 votes
Accepted

Crystal oscillator load capacitance, again

Is there a one true answer to the question? It all seems very frustrating to me. Why doesn't an oscillator start? A crystal oscillator will fail to start when the crystal and the capacitors ...
Andy aka's user avatar
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23 votes
Accepted

How do processors control their clock speed?

This is done using a device called a phase-locked loop, or PLL. Here is a block diagram of a basic PLL: simulate this circuit – Schematic created using CircuitLab The oscillator on the ...
alex.forencich's user avatar
23 votes

Why not put a crystal oscillator inside the microcontroller?

A crystal is fabricated on a completely different process and from a completely different material than a microcontroller is. You can't integrate them both into a single chip, so you would have to ...
Hearth's user avatar
  • 32.6k
23 votes

Simplest practically buildable oscillator

Pearson-Anson oscillator Neon bulb, resistor, capacitor, voltage supply high enough to light bulb. The capacitor charges through the resistor, when the voltage across it reaches the neon bulb's ...
GodJihyo's user avatar
  • 23.4k
23 votes

Ethernet port as a signal generator

Is it technically possible? No. Highly specialized hardware, relatively specific coupling, and a very limited set of amplitudes actually imposable on the line make that infeasible. Don't get me wrong:...
Marcus Müller's user avatar
21 votes

Why the prevelance of mechanical oscillators in electronic circuits?

Because the mechanical devices are much more stable than their electric counterparts. Let's compare a crystal oscillator to an LC oscillator: Crystal: Has a very high Q. According to wikipedia, a ...
C_Elegans's user avatar
  • 2,901
20 votes
Accepted

Why do some microcontrollers have numerous oscillators (and what are their functions)?

32kHz ultra low power oscillator: Used for RTCs (Real-time-clock). These can run in the background and enable time-keeping, even when the controller core is sleeping. This enables to have a running ...
jusaca's user avatar
  • 9,609
18 votes
Accepted

Do crystal oscillators synchronize by themselves when coupled by supply voltage?

They can do. When you want oscillators to lock to others like this, it's called 'injection locking', and is a useful but little-known technique. You would apply a bit more signal for injection than ...
Neil_UK's user avatar
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17 votes
Accepted

Trying to get a 32.768 kHz crystal to oscillate

Rereading, I'm pretty sure I need 25pF caps instead as I misinterpreted how load capacitance worked. You need 25pF caps less any stray board and chip capacitance. You'll probably end up at around 18-...
TimWescott's user avatar
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16 votes
Accepted

Why is my loudspeaker not working? From Make: Electronics

The frequency of oscillation is determined by the 470 kΩ resistors and 3.3 μF capacitors and will be roughly \$ \frac 1 {RC} = \frac 1 {470k \times 3.3\mu} = 0.64 \ \text{Hz}\$. i.e., less than one ...
Transistor's user avatar
  • 176k
16 votes

Why are two 555 timers in separate sub-circuits cross-talking? (Poltergeist in the Breadboard)

When the oscillators operate and switch the LEDs on and off, they will be creating voltage ripples on the power supply as the current demand changes. These voltage ripples can then cause other devices ...
HandyHowie's user avatar
  • 4,050
16 votes

External oscillators for a microcontroller

Crystal A crystal is nothing more than a resonant piece of piezoelectric crystalline material, bonded to pins such that it has a resonant electrical behavior. It is a passive device which cannot ...
nanofarad's user avatar
  • 20k
16 votes

How can I calibrate a retail digital clock that uses a 32.768 kHz crystal?

First, refer to this post for details of (we hope) the underlying oscillator schematic. You'll probably just see the crystal and the caps, with traces going into a chip. Verify that you've found the ...
TimWescott's user avatar
  • 46.2k
16 votes

Why not put a crystal oscillator inside the microcontroller?

Here's a crystal oscillator (source): In order to work, a crystal must be suspended in free air (or inert gas) by the edges. It works like a tuning fork, it is a mechanical resonator with electrical ...
bobflux's user avatar
  • 77.5k
16 votes

Simplest practically buildable oscillator

This is the simplest I know. Frequency is independent of devices (CMOS with 1/3 2/3 level trigger points) and supply voltage. simulate this circuit – Schematic created using CircuitLab
MOSFET's user avatar
  • 3,060
16 votes

Simplest practically buildable oscillator

There's always the relay oscilator. If you want to make it have a specific frequency you can add resistors and capacitors, but it will oscillate just fine like this, and make quite a racket.
QuadmasterXLII's user avatar
15 votes
Accepted

Using CMOS Schmitt trigger inverters in quartz crystal oscillator circuit

A Schmitt trigger inverter is a bad idea for the first inverter which is driving the crystal directly. It may not even oscillate at all as shown, or oscillate at some undesired frequency. Note ...
Olin Lathrop's user avatar
15 votes

32 kHz crystal not operating as expected

There are two main things going on: You don't have enough load capacitance. You don't understand load capacitance. Imagine one side of a crystal being driven with a sine wave at the crystal ...
Olin Lathrop's user avatar
15 votes
Accepted

Why does this simple circuit oscillate? (Ekasi oscillator)

First, the circuit as you present it is a bit too simple -- the resistor in series with the battery as shown on this page is necessary, and must be about the right value. Second, the reason the ...
TimWescott's user avatar
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