how can double the frequency

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abc

 

not very easy to do unless you know before hand what the freq is you want to double.

Say you have a 1hz signal and you want to double it to 2hz your problem is that by the time you even know it is 1hz you are going to be half a second to late to change it to 2hz. You cannot use the incoming freq to clock the new freq.

Your best bet is use a PIC to determine the input freq and then output a value that is double to and oscillator.

It is very easy to halve a freq but not the other way round. What is your application maybe there is another way that achieves the same result.

 

There are several ways to do it but if you expect an answer
you should try to better specify the problem (signal shape,
frequency range, level,...)

 

i am making a ultra sonic frequency generator, if i get around 20khz i want to double it to around 30khz, very high i guess

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abc

 

Well 30KHz isn't double 20KHz

You could do it with a PLL (Phase Locked Loop), you use a divide by two circuit from the output of the PLL and compare it to the input frequency, once locked the PLL oscillator is running at twice the frequency of the input frequency - it's a standard PLL technique.

Perhaps you should mention exactly what you are trying to do, for a start why not simply generate the frequency you want?.

 

If you want to double the frequency and obtain a square wave, you can do it simply using an XOR gate. If you feed your 20KHz square wave directly into one input and via a resistor/capacitor integrator (to delay it) to the other input you will get a pulse out every time the input waveform changes polarity, ie. at twice the input frequency.

You need a delay of 12.5uS to equal mark/space at 40KHz, so feed through a resistor of 18K0 to the second gate and then a 1nF from gate to ground.

 

Hi Pebe,
This sounds to easy to be true! Would you mind sharing the circuit diagram with us? (pretty please???) :shock:

 

Frequency multiplication (integral) is common in radios. Look in references for RF (radio frequency) - or seach diode frequency multiplication. Note that in a power supply the output of a full wave bridge rectifier is double the input - it's not a pure sine wave but it's a start.

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stevez

 

A freehand circuit is attached. I hope it comes out OK ‘cos I’ve not tried printing it this way before – (still not come to grips with a decent drawing prog). If you want a description, then here goes:

You probably know that if you feed similar inputs (high or low) to each gate input of an EXOR gate (one section of a 4070) then the output is low. If you feed one input with a high and the other with a low then the output will go high - it does not matter which gate input is which. You get a similar result with an EXNOR (part of a 4077) but the output polarity is reversed.

Looking at the circuit, when the input waveform is low, both inputs will be low and the output will be low. When the input goes high, input1 will go high but the C1 will hold input2 low for a short time, so the output will go high. C1 starts to charge via R1 until the voltage on C1 reaches the gate threshold (about 50% of Vdd), when both inputs will be high and the output will go low. With R1=18K and C1=1nF that will take about 12.5microsecs. So when the input goes high there is a positive pulse of 12.5microsec duration at the output.

With an input at 20KHz, the input will be high for 25uSec before going low again. When it goes low, input1 goes low straight away but input2 is delayed again by 12.5uSec giving another 12uSec pulse at the output. The result is that for every cycle at 20KHz there are 2 pulses each of 12.5uSec at the output. So the output alternates between high and low every 12.5uSec. That is a square wave at 40KHz.

Attached Images

xor_doubler.gif (2.8 KB, 607 views)

 

I think what you are looking for is a mixer circuit. If you mix two frequencies in a non-linear device, the output contains the sum and difference frequencies, so to get 30 kHz from 20 kHz, mix 10 kHz with the 20 kHz and filter the output to reject the difference and 20 kHz and pass the 30 kHz. Do a Google search for mixer circuit.

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see my website: www.geocities.com/russlk

 

What are you builbing?A electonic dog wistle?

Moust of us dont hear 20 000 Hz (soem kids hear this)

PS:
I hear max 18 500 Hz (I tested this on my compter)

 

yeah ultra sonic dog whistle i want to generate 30 to 40 khz but i am only getting 20 khz. which i checled from osscilscope

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abc

 

So why not just increase the frequency of the oscillator?. It seems like hard work adding loads more circuitry to remedy a fault in the original design.

 

yes,your right!why dont you just set the oscilator to a higher freq!

 

I found this:

Frequency doubler with 4069
http://users.otenet.gr/~athsam/frequ..._with_4069.htm

Frequency Doubler with 4011
http://users.otenet.gr/~athsam/frequ..._with_4011.htm

Frequency Multiplier X100 with Noise Rejection for low frequency (you may modify it to make ti x2)
http://users.otenet.gr/~athsam/frequency_multiplier.htm