XO controlled 480Hz Oscillator

What is the simplest way to get 480Hz from a crystal controlled oscillator? Looks like most of the pre-packaged XO's and VCXO, seem to put out much higher frequencies. Would a series of dividers be the best way?

Thanks, Chris KQ6UP

Reply to
Chris
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Chris schrieb:

Hello,

there are also crystal controlled oszillators together with a pin programmable divider in one small case.

Bye

Reply to
Uwe Hercksen

Dunno if one would go down to 480Hz, but if it did it'd be the way to go.

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www.wescottdesign.com
Reply to
Tim Wescott

480Hz what? Forever constant frequency square wave? Yes.

If you want to vary the frequency you may want to use a programmable divider, and the easiest way to do _that_ may well be to use a small microprocessor, particularly one with a hardware timer.

If you want a sine wave you could either divide down to a 480Hz square wave and filter, at the cost of a fairly elaborate analog filter. Or you could use that microprocessor again to generate a 480Hz almost-sine wave to a DAC or PWM, in which case you can use a much less elaborate (and therefor easier to design and cheaper) analog filter.

If you can live with a healthy bit of output impedance, you could do this with PIC, a resistor, a cap, and either a crystal and it's capacitors or a crystal oscillator that'll be bigger than the PIC.

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Reply to
Tim Wescott

Clarification: I only need a digital (read square wave) output. Fairly high voltage swing (12V) into a high Z load.

Regards, Chris

Reply to
Chris

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No need to vary the frequency. Yes, square wave 480Hz 12V swing into a high Z load.

For this application the frequency is fixed, but it needs to be accurate. I don't think a xtal oven is called for, but I do need the rock.

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Square wave, sorry for not clarifying.

Thanks, Chris KQ6UP

Reply to
Chris

The simplest way is MCU with external crystal. For 480 Hz output, the crystal is likely to be a multiple of 3 MHz. The 12.0 MHz would be the most common.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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Reply to
Vladimir Vassilevsky

Is an MCU the same as a PIC?

Regards, Chris KQ6UP

Reply to
Chris

Crystal oscillator, divide by the appropriate (large) number.

Come to think of it, a PIC may still be the smallest way to go -- one 8- pin PIC is way smaller than all the 74whatever161's you'd need, or a PAL for that matter.

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www.wescottdesign.com
Reply to
Tim Wescott

All PICs are MCUs. Not all MCUs are PICs. The top contenders that I know of are the PIC and the AVR from Atmel. There are probably low pin- count 8051 derivatives out there, not to mention the '430 from TI.

Intersil ought to revive the 1802 core, in a 16-pin package surrounded by all the usual peripherals.

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www.wescottdesign.com
Reply to
Tim Wescott

Would a CD4060B + 7.86432 MHz crystal + 1 resistor (maybe 2) + 2 caps running at 12 volts work for you? Output (rail-to-rail square wave) from Q14.

-- Silvar Beitel

Reply to
Silvar Beitel

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That sounds pretty easy divide by 2^14. Would that be a custom crystal, or a standard freq?

I will be trying to repair a 480Hz standard tuning fork. It is actually a 960Hz fork that had it's divide by 2 flip flop die. It is from a 70's vintage piece of equipment. The fork is hermetically sealed with solder in a can. I try to get in there tonight, and if the dead part is some obsolete IC or something, I will probably replace with a crystal and divider to get my 480Hz. A crystal would be more quiet and stable I believe.

Thanks, Chris KQ6UP

Reply to
Chris

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I'm old school, so I would build two divider chains out of logic gates. The first divider gets you to 960Hz, but it probably won't be a square wave. You use a binary counter and some gates to do the division. Follow up with a divide by two to get a square wave at

480Hz. You need a level shifter to get the larger 12V signal.

You should investigate if the uP scheme causes jitter in the signal. In the dark ages when I played with uP, they always had peripheral timer chips that the uP could control so that the division would be jitter free. Maybe modern uP have these built in.

Reply to
miso

Guessing: not standard. But check crystal suppliers / distributors and see. How close to 480 Hz do you need the output to be? If not particularly close (i.e. stability is your main requirement), perhaps a catalog part will work. Good luck.

-- Silvar Beitel

Reply to
Silvar Beitel

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This looks like exactly what I need. Would this have this have a jitter problem?

Chris

Reply to
Chris

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All electronics has jitter. A logic gate is an analog circuit after all. But a uP could have issues if not programmed correctly, especially if interrupts are used. [Interrupts have to be serviced in a timely manner.] There is some skill in doing real time programming, though the divider task doesn't sound complicated.

Assuming you could find that part, it would be part of the first half of the circuit. A ripple counter needs to be clocked on one cycle, then read on the next. [I'm thinking of ripple counters I've done in silicon, not off the shelf, so you need to read the datasheet.] You clock it, let the dividers ripple down the chain, then "sample" the result on the other half of the cycle. That is, you do the comparison with logic gates after the flip flops have settled. This will yield a short pulse when the countdown condition has been met. You then follow up with a divide by two to square it up.

I think in terms of gates, but I rarely build PCB products. You may want to investigate the uP, or even some programabe logic chip. What you do on a PCB is different than custom IC design.

Reply to
miso

The 4060 has a nice square output.

--
www.wescottdesign.com
Reply to
Tim Wescott

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The chip that I posted the link to does not look like a programmable chip. It just looks like 14 cascaded binary dividers.

Regards, Chris

Reply to
Chris

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Farnell doesn't stock it, so it probably isn't a standard frequency, but getting a custom frequency in that range is no big deal.

Probably. Look at the 74HC401013 from NCXP or TI if you want to use a standard crystal - it gives you a programmable 8-bit divider in a single package, and you can cascade them if you want more bits

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You will have to buffer the output to get a 12V swing, or use the slower HEF401013BEY from ST Microelectronics.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

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I found a source of dirt cheap CD4060B's. There are no example circuits in the data sheet. Would just use a very generic xtal oscillator?

Thanks, Chris KQ6UP

Reply to
Chris

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