XO controlled 480Hz Oscillator

On Feb 2, 8:29=A0am, Chris wrote: > What is the simplest way to get 480Hz from a crystal controlled > oscillator? =A0Looks like most of the pre-packaged XO's and VCXO, seem > to put out much higher frequencies. =A0Would a series of dividers be the > best way? >

You in North America? PLL the 60Hz power supply up to 480 hz. It will be spot on for frequency.

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Function of pin #3 Fairchild Q14 NXP Q13 ON Q14 ST Q14 TI QN

Best regards, Spehro Pefhany

--
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Thanks, John. The pain in the butt is that different datasheets have different designations. The one from TI that Chris posted goes to Q14.

Your post is great, because it brought that to light. I didn't know that, :-( until I saw your post :-)

Ed

Yes, I am in North America. I need the deck to be portable, so working off of mains is not usually going to be an option. The capstan motor does run on 60Hz 120VAC, but I would only be able to shoot footage where I have mains. The crystal/fork is for the inverter as the tape transport is run by a sync motor with a sprocketed capstan (the tape is perforated).

Regards, Chris Maness

Digikey has 60 KHz crystals. Divide by 5 three times, then by 2 for your 480 Hz. Or just divide by 1000 and low pass filter it before amplfing it to drive the 60Hz motor.

--
Greed is the root of all eBay.

--
I suspect you're right.

I got my data from the Philips 1996 CMOS data book, but going back to
the RCA bible, it's listed as Q14.

Thanks for the reality check. :-)

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I ordered some CD4060B's (25 for $3 on ebay). I am going to order some 3.9Mhz crystals and divide by 2^13 on the 4060. Should be very easy.

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All you need to know is:

1-All transfers to registers must go through the D. 2-All math operations must use the "stack" 3-All loading and storing to/from RAM must use a register

To know that the code I gave was the best that can be done.

One of the guys in this thread sent me an Application Guide:

This is a very interesting read. However, the information here does not seem to agree with the design suggestion for the crystal network in the data sheet for the 6040B. Fig. 13 (

). Shows that Cxtal=C1+C2+Cstray. If I understand the application guide 1/Cxtal=1/C1+1/C2. If my crystal is rated 17pF, then by the data sheet I need 2 8.5pF caps. Rs is current limiting. However, I am using an off the shelf 3932160Hz crystal from Digi-Key, and there is no indication to what the current limitation (per Rs in Fig. 13) should be. Also, "Rc" is claimed to be to broaden the freq. response. However, there is no reference to this in the application guide.

Any guidance would be appreciated.

Thanks, Chris Maness KQ6UP

Yes, but input (and stray capacitance should also be taken into account).

The data sheet is incorrect on this point.

It's limited by the maximum crystal power dissipation and series resistance of the crystal, crystal frequency, load capacitance, supply voltage. HC-49 ~4MHz crystals are usually good for 1-2mW, some of the SMD parts or kHz tuning fork types, down in the microwatts.

Given a physically larger crystal that can take 1-2mW of drive, you can probably forget about Rs, use 22-27pF for the caps and 1M for the parallel resistor. More caution is called for at high supply voltage.

n

Should I use 25pF trimmers so that I can dial in the freq.

Thanks, Chris

Your application cares about the last 0.01%? You can't 'pull' a normal quartz crystal much.

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Yes, my application does depend on the freq. being spot on. A little off, and my film dialog will look like a bad kung foo flick.

You can't 'pull' a normal

I am getting a freq. counter in a couple of days. It is supposed to be good within .3Hz. I was thinking that with the trimmer, I could account for a unknown, stray capacitance.

Just a thought. What do you think?

Regards, Chris

It will always be a bit off, the engineering question is how much is acceptable.

0.3Hz at what frequency? Accuracy or resolution? The first divided output is divided by 16 (IIRC), so about 245kHz, so you ought to be able to see +/-1ppm. Perhaps the slowest gate time is 3 seconds and it's a conventional (rather than reciprocal) counter. But the counter timebase might not be that *accurate*. ~4MHz crystals are typically accurate to +/-30-100ppm. 100ppm is 50 msec error in about 8 minutes, just for comparison.

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You may be better off placing a 100pF trimmer in series with the crystal. The C1 / C2 ratio doesn't want to be too far from 1.0 since it controls the swing at both ends.

The DC feedback resistor doesn't matter much so long as it is large enough. The crystal drive resistor needs to be low enough to get the crystal to start beyond that, you don't really use it to set the power level. The capacitors do more to set that than the resistor.

If you find that the oscillator runs slow, you may want to replace or parallel the crystal drive resistor with a small capacitor. This is not often explained in the data sheets and app notes but if the delay through the inverter of the 4060 is too large, the oscillator will want to run at a lower frequency. You fix this by adding a phase lead with the capacitor.

100 pm might apply to some cheap microprocessor crystals, but for decades (before frequency synthesizers) , channel crystals were made for radio telephones to within a few ppm. A 100 ppm crystal would have caused the transmission on the wrong channel, a slightly smaller error would cause bad audio distortion, since the signal would be partially outside the receiver de modulator bandwidth.

When ordering a frequency for a specific frequency, specify also the load capacitance or specify the frequency slightly (a few dozen ppm) above the desired frequency and pull it down to the desired frequency with a parallel capacitor. Pulling upwards is harder with a series inductance.

Overtone crystals (typically above 20 MHz) have a more limited pulling range.