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 ...
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12 votes

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

You can add a TCXO such as Maxim's DS32kHz to the board if you like. Glue the chip down, preferably on a ground pour (dead bug style- legs in the air). Remove R214 (0Ω resistor). There are four ...
12 votes

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

Since the clock is running fast, you could try increasing the capacitance on the crystal by using a "gimmick", which is a capacitor made by two insulated wires twisted together. Magnet wire ...
  • 2,161
10 votes

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

Watch crystals are rarely more accurate than the 20 ppm you say. So replacing the crystal likely makes little difference. It might tick at wrong rate too, in that circuit, because you don't know the ...
  • 97.2k
8 votes
Accepted

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

Here is an 5 ppm 32768 Hz crystal in stock at Digi-Key. Here are 20, 10 ppm 32768 kHz crystals in stock at Digi-Key. It is difficult to match the long-term accuracy of power line frequency. It is ...
  • 3,649
4 votes
Accepted

Transfer function of second-order Butterworth filter

An error in your result Heretic, your result near the bottom of your question is: $$G(s) = \frac{Y(s)}{U(s)} = \frac{ R_f + R_{in}}{C^2R^2R_fs^2 + (2CRR_f - CRR_{in})s + R_f}$$ But it really should ...
  • 72.9k
4 votes

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

If you really want it to be in time with a powerline clock, you could always tick off the powerline. Fortunately you have a transformer, so isolated zero-crossing detection is easy (clipping diodes ...
  • 403
3 votes
Accepted

Finding poles by inspection - R to ground

To determine the time constants of a circuit, you must reduce the excitation or the stimulus to zero: you turn the source off. Here, the stimulus is \$V_{in}\$ and when made 0 V, it can be replaced by ...
  • 15.7k
3 votes

Transfer function of second-order Butterworth filter

Well, let's solve and show this mathematically. We are trying to analyze the following circuit (assuming an ideal opamp): simulate this circuit – Schematic created using CircuitLab When we use ...
  • 5,485
3 votes

Transfer function of second-order Butterworth filter

I do it with equal-value RC's and a gain of 1.6 times or with the feedback capacitor with double the value and a gain of 1 time like this:
  • 2,581
2 votes

Transfer function of second-order Butterworth filter

Replace the capacitors with their Laplace equivalent, \$\frac{1}{sC}\$, and solve via nodal analysis. (a) At the \$\small V_B\$ node, \$\small V_B=V_A =V_2 =\large\frac{R_1}{R_1+R_f}\small V_{out}\$ (...
  • 7,467
2 votes

Transfer function of second-order Butterworth filter

simulate this circuit – Schematic created using CircuitLab Node a: KCL $$\left(\frac{1}{R_{1}}+\frac{1}{R_{2}}+C_{1}s \right)V_{a}(s)-\frac{1}{R_{1}}V_{in}(s)-\frac{1}{R_{2}}V_{b}(s)-C_{1}sV_{...
  • 3,649
2 votes

Self-resonance frequency of chip inductors

All components are ultimately transmission line (TL) components. Or, even more generally still, just a pile of materials shaping 3D fields. Appreciate that, the more advanced our level of modeling (i....
  • 6,606
2 votes

Finding poles by inspection - R to ground

The author is referring to the Thevenin resistance \$R_{Th}\$ seen by each capacitor connected to a particular node. To find \$R_{Th}\$, set all sources to zero. Each amplifier’s output is a voltage ...
  • 3,649
1 vote

Finding poles by inspection - R to ground

The impedance looking into node N (for instance) does not in one bit depend on the voltage produced by amplifier A1's output so, for convenience, we can set the output of A1 to be 0 volts. ...
  • 396k
1 vote

How do we use step-up transformers to get a very high voltage compared to the initial voltage?

Increasing the frequency allows you to use smaller inductors or transformers, typically. The way I look at it is that the amount of magnetic energy that can be stored in an iron core depends on the ...
  • 26.5k

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