Frequency Halver

[stevieboy01]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

Steve

 

[Roger Hamlett]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

Steve

Accurate 'halving', not really. This is easiest to do digitally. Simple
counter, gives you any division wanted. For a sinusoidal output, you could
use a PLL, for a given range of frequencies. For a single frequency, you
can use a mixer, but this will only give 'half' for one input value.

Best Wishes

 

[Andrew Holme]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

Steve

Sine or square wave?

For square waves, you could use a synchronised multivibrator. This
technique was widely used before the advent of TTL. Make a 10 KHz
multivibrator and feed-in a small amount of the 20 KHz signal. This
works by "pushing" it over the threshold at exactly the right moment.

For sine waves, there's no "simple" circuit.

 

[John Woodgate]

I read in sci.electronics.design that Andrew Holme <[email protected]>

For square waves, you could use a synchronised multivibrator. This
technique was widely used before the advent of TTL. Make a 10 KHz
multivibrator and feed-in a small amount of the 20 KHz signal. This
works by "pushing" it over the threshold at exactly the right moment.

For sine waves, there's no "simple" circuit.

Half-wave rectify without a filter cap. Use the unidirectional pulses to
trigger the multi or, better, a triangle wave generator. Low-pass filter
the resulting waveform.

 

[[email protected]]

Sorry John, but I think you have just described a frequency doubler,
rather than a frequency halver.

For what it is worth, I'm pretty sure that there is no analog technique
that will halve the frequency of a sine wave. It is easy enough to use
a largely digital circuit to produce a sine wave which follows half the
average frequency of of an analogue sine wave, and if you got really
cute, you could track the phase of the input sine wave and produce an
output whose phase varied at half the rate - though since the maxima
and minima of a sine wave don't tell you much about the instantaneous
phase, this isn't going to be prefect either.

 

[John Larkin]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

Steve

Injection-locked oscillator, maybe, but not all that simple.

John

 

[Jim Thompson]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

Steve

I've done this for boom-box designs:

Square signal

Divide by 2 (digitally)

Filter to get back a sine wave

Use ENVELOPE of original signal as envelope for Div2

Actually sounds good even on classical music ;-)

...Jim Thompson

 

[Genome]

Sorry John, but I think you have just described a frequency doubler,
rather than a frequency halver.

Sorry Bill but John just described a frequency keep the samer. He used half
wave rectification.

How's the beer industry?

DNA

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

Sorry John, but I think you have just described a frequency doubler,
rather than a frequency halver.

If you mean me, the HW rectifier produces one pulse every 200 us for 20
kHz input. Triggering the multi or TWG in the correct way to get one
cycle per pulse is no different from what the sync circuit of a scope
does.

 

[[email protected]]

Sorry Bill but John just described a frequency keep the samer. He used half
wave rectification.

How's the beer industry?

Not making enough money to hire me again. I did get a phone call from
one of my ex-employer's sub-contractors earlier this week, but it turns
out that the work Haffmans wanted done wasn't the sort of work I can
prove I've done already.

 

[[email protected]]

A 20kHz sine wave repeats every 50usec. A half-wave rectifier without a
filter capacitor produces a series of half-sine pulses repeating every
50usec, whose Fourier transform contains quite a lot of second
harmonic, and nothing at 5kHz (that is, with a period of 200usec).

A suitable monostable can be used to ignore an arbitrary period after
an active pulse, which, for a limited range of input requencies, can
give you a half rate output. Going from there to a half frequency sine
wave is a bit more of a stretch.

 

[John Larkin]

Injection-locked oscillator, maybe, but not all that simple.

John

Or a parametric oscillator: one L, one C, one varicap.

John

 

[Genome]

Not making enough money to hire me again. I did get a phone call from
one of my ex-employer's sub-contractors earlier this week, but it turns
out that the work Haffmans wanted done wasn't the sort of work I can
prove I've done already.

Well, I suppose that's my fault... I drink cider these days.

Shit, those people at Haffmans look like they've been given a serious
beating with the ugly stick. Perhaps they've been snorting their own
product.

Mr. Michel Brueren looks like Vinny Jones.

Hey, sorry if I fucked the job up for you. If I wanted someone to give me
the same old crap that I had before then I wouldn't be looking for someone
to give me the same old crap because I already have the same old crap.

If I wanted a different perspective on things then I might do something...
different.

Love and kisses to the wife.

DNA

 

[John Fields]

I may be very stupid for asking this, but is there a simple analogue
circuit in which I can input a frequency (currently 20kHz) and output
half the frequency?

---
Not stupid at all, it's been the holy grail for pitch-shifters for
quite some time. I don't believe there's a simple analog solution and
even if you do it digitally in real time by sampling the input with
one clock, doing an A to D conversion on the slices and then doing a D
to A and outputting that analog signal at half the input sample clock
frequency implies sufficient storage to keep the buffer from
overloading.

Think about it like this: You've got a bathtub filling up at one
gallon per second and, at the same time, being drained at two quarts
per second, so eventually it'll overflow.

 

[John Woodgate]

I read in sci.electronics.design that John Fields <jfields@austininstrum

Think about it like this: You've got a bathtub filling up at one gallon
per second and, at the same time, being drained at two quarts per
second, so eventually it'll overflow.

Who the hell counts in base 4 these days? (;-)

 

[[email protected]]

Michel Brueren may look like Vinny Jones, but he's a perfectly
agreeable fellow.

The problem with the Dutch employment market is that they don't like
giving jobs to people over the age of about 45.

Of the 17,000 people over 57.5 who were drawing unemployment benefit
last year, about 250 succeeded in finding work - about 1.5%. We've all
got to apply for a job every week to hang onto our unemployment
benefit, which means that the employment agencies throw away 17,000 job
applications every week. Those of us who actually want to find a job
suspect that the agencies just scan the CVs for dates earlier than
1950, and throw anything including an earlier date.

They don't admit this - it would be against the (unenforced) law - so
they look for very specific experience, or invent specious reservations
if you bother going after them.

 

[Genome]

Michel Brueren may look like Vinny Jones, but he's a perfectly
agreeable fellow.

The problem with the Dutch employment market is that they don't like
giving jobs to people over the age of about 45.

Of the 17,000 people over 57.5 who were drawing unemployment benefit
last year, about 250 succeeded in finding work - about 1.5%. We've all
got to apply for a job every week to hang onto our unemployment
benefit, which means that the employment agencies throw away 17,000 job
applications every week. Those of us who actually want to find a job
suspect that the agencies just scan the CVs for dates earlier than
1950, and throw anything including an earlier date.

They don't admit this - it would be against the (unenforced) law - so
they look for very specific experience, or invent specious reservations
if you bother going after them.

My apologies to Michel.

BTW, I've done a nasty and forwarded this, and the last, post to other ugly
members of Haffmans. I hope their opinion of you is not affected in any way
by my general stupidity.

I am sure that they are very nice people and worth a cuddle.

DNA

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

or invent specious reservations
if you bother going after them.

You have to be Homo neanderthalis to qualify?

 

[Winfield Hill]

[email protected] wrote...

The problem with the Dutch employment market is that they don't like
giving jobs to people over the age of about 45.

Of the 17,000 people over 57.5 who were drawing unemployment benefit
last year, about 250 succeeded in finding work - about 1.5%. We've all
got to apply for a job every week to hang onto our unemployment
benefit, which means that the employment agencies throw away 17,000 job
applications every week. Those of us who actually want to find a job
suspect that the agencies just scan the CVs for dates earlier than
1950, and throw anything including an earlier date.

They don't admit this - it would be against the (unenforced) law - so
they look for very specific experience, or invent specious reservations
if you bother going after them.

That's a universal problem these days, where it's likely the person
making the hiring decisions is much younger and nervous or predudiced
about hiring someone his father's age.

I've said it here before, the answer is to start your own company
(and only hire older folks, starting with yourself, of course).
That'll solve the problem, and you might even have a good time.

 

[Roger Lascelles]

Sine or square wave?

For square waves, you could use a synchronised multivibrator. This
technique was widely used before the advent of TTL. Make a 10 KHz
multivibrator and feed-in a small amount of the 20 KHz signal. This
works by "pushing" it over the threshold at exactly the right moment.

For sine waves, there's no "simple" circuit.

You can sync a Wien Bridge oscillator - the HP204C sinewave oscillator had a
sync terminal which injected into the oscillator. Some of the sync signal
did appear on the output, depending on the size of the sync input. HP say
it will lock on harmonics of the sync input, but no mention of subharmonics.
However, a rectifier would divide by two and give you a guaranteed to lock
signal.

Roger Lascelles