I will be designing an elapsed signal pulse timer.
it will count from 0.00000 to 9.99999 seconds.
so, I will nead a 100,000 hz generator.

The idea is to use a 6.4 meg Hz crystal and cmos 4060 to divide by Q6(64) to give me the 100,000 Hz.
then counting with 6 4026 seven segment counter/led driver ic's.



I bought a 6.4000 Meg Hz. Crystal.
Connected it to a cmos 4060 chip, and It seems to be working fine.

Instead of the 10pF and the 39pF Trimer cap, I use two 22pF caps as thats what I had handy.

It seemed to run fine.
the out put of the chip was devided by Q(cant remember) to give an audio frequency that mached the tone from a downloaded pc tone generator.
Test cunducted by ear.

I also noticed that if I removed the caps, the crystal still seemed to function the same.
Is it better to not use the caps?

Question:
is the 39pF trimmer cap used to increase the /decreace the frequency?

I don't want to increase/decrease the frequency.
I want it to run at exactly 6.4MHz.

How do I know that the frequency is exactly 6.4MhZ and not 6.4035Mhz?

I don't have a mutimeter with Frequency function, and I think all multimeters have an error percentage anyway.


I know nothing about this field.
But do you think the crystal is outputing the exact 6.4000 MHz?
I guess it should , since it has 6.4000 printed on the crystal.
thanks

Here's a part print screen of a 4060 data sheet

Attached Images

4060connections.gif (12.3 KB, 1402 views)

 

The capacitos are for the stability of the crystal.

Multimeters cant meshure that high freq. they mostly meshure up to about 100 kHz.Freqency counters do it or you can do that whith an osciloscope.

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Oh, Ok electro,

 

The capacitors are an essential part of the oscillator circuit, it 'may' work without them due to stray capacitance, but it's important to leave them in place!.

Yes, to trim the crystal to exactly the frequency you want.

You need to accurately measure it, a standard technique is to compare it to a reference frequency, most countries have some reference radio transmitters, very accurately set to a specific frequency. You can 'beat' the harmonics against each other, and adjust for zero beat (rather like tuning a guitar! - in fact, thinking on, EXACTLY like tuning a guitar!).

Using a tone generated from a PC is likely to less accurate than the unadjusted crystal :lol:

Unlikely!, you need to adjust the trimmer so it's exactly correct - but do you feel lucky?.

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Nigel saysYeah, I'll trim it and test it for a long time, to see if if goes out.

should I use the same capacitors as in the data sheet, even thou I'm useing a much higher crystal?

Thanks guys.

 

Even if you tune it to exactly 6.400MHz at a particular temperature, the frequency will change with different temperature.

You needs some means to keep the crystal oscillator at the same temperature if you want stable frequency output.

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L.Chung

 

Why not use the capacitor values (minus stray capacitance) that are spec'd by the crystal manufacturer?

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Uncle $crooge

 

Like everything, it depends on the accuracy you need - at one time "crystal ovens" were quite popular, these keep the crystal at a constant(ish) temperature to reduce frequency changes. They were generally quite crude devices, usually a big resistor switched by a mechanical thermostat.

However, reducing the crystals temperature range to 50-55 degrees C is much better than a range of -10 to +50 degrees C.

But it all depends what you need?.

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You can purchase crystals with a very low temperature coefficient. Probably a bigger problem at that frequency is trying to tune them accurately with the capacitors.

A possible way to ensure accuracy might be to take the one-second output from a digital watch and use it to synchronise your timer somehow.

 

He would be better off using a TCXO crystal oscillator module which is quite affortable and usually fulfil the frequency stability requirement of hobby purpose.

But I don't know whether they have TCXO of 6.4000MHz but they definitely have 1.0000MHz or 10.0000MHz.

Edit: you beat me, pebe.

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L.Chung

 

I once made an Xtal oscillator and was viewing the waveform on the CRO. The waveform actually registered a noticable change when I touched the crystal package. My guess was it was body heat. My friend thought it was mechanical pressure. I think he is right. The point I am trying to make is that it might not be very accurate.

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valtrex - http://www.######pills.com

[EDITED by mechie - adverts for pills are NOT WELCOME :evil: ]

 

A TCXO is really not enough more stable than an uncompensated crystal oscillator to justify the significantly higher price. As I recall, from an article written by a Hewlett-Packard engineer on the various types of frequency standards, a TXCO is only about 4 times more stable than an uncompensated xtal oscillator. An ovenized oscillator is much better, even more so if it uses a sophisticated proportional temperature control to eliminate the sharp on/off cycles of a mechanical thermostat.

I would guess that for your application, a trimmed but uncompensated crystal oscillator will be sufficient.

You can take the 100KHz output, connect it to a wire and turn a shortwave receiver to WWV at 5, 10, 15 or 20MHz, bringing the oscillator close enough to the receiver to set up a beat note. Then adjust the oscillator to zero beat the tone.

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

this might be helpfull

http://tf.nist.gov/timefreq/stations/radioclocks.htm

http://tf.nist.gov/timefreq/stations/wwvb.htm

 

Just how accurate do you want ?
A typical crystal will give something like 100ppm stability ?
That's 0.0001 % ?

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