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555 timer frequency changing

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ants

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I have a 555 timer circuit that I made up. It has a frequency of 100KHz. When I attach it to my amp through a potentiometer the frequency seems to drop to 80KHz. Is this right? I wasn't expecting that to happen.
 

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That may depend on the configuration ..
If the output pin [3] is somehow used to generate a square wave (e.g. 50% duty cycle) then obviously connecting "something" to this pin may vary the frequency .. see picture below ..
If this pin [3] is used only as the output - the frequency should be independent ..

IanP
:D
 

    ants

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It seems I've lost abut 1Khz because of that, i compared the 555 connected to the amp and then not.

But I've lost 14Khz taking R1 and R2 off a breadboard and putting them on the rest of the board. I made up the 555 and left those two off to adjust, then put them on last. How can switching the same components cause such a big change in frequency? Itys confusing. I will have to take them off the board again, then add a pot to R2 to give myself some leeway.
 

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The capacitance between any two adjacent tracks on any breadboard may easily rich 33-47pF, so be careful when you try to fine-tune circuit on a breadboard and then install them on a veroboard or the target PCB ..
In comparison, a pcb or Veroboard would have about 1-2-3pF ..

IanP
:D
 

    ants

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ants

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I have it working at target frequency, the duty cycle isn't as close to 50% as I'd like but its not worth worrying about. The capacitance value is 100pF but on the veroboard it is measured at 330pF. It is that which has been causing the problem. I put a potentiometer in place of R2 and adjusted till i found the right frequency and have now measured everything.

I'll bare in mind what a run around that is for future reference!
 

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I have it working at target frequency, the duty cycle isn't as close to 50% as I'd like but its not worth worrying about.
The way you can have exactly 50% duty cycle at all times would be to generate double the frequency and then divide it by two using a flip-flop ..
The capacitance value is 100pF but on the veroboard it is measured at 330pF
Hm … it looks like the veroboard must have been manufactured by Kuku-Maluku from Limpopo :D .. Funny as it sounds, the difference between 100pF cap and the measured value of 330pF is just to big .. Something else must have increased the capacitance, but what?

IanP
:D
 

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I've heard of frequency splitting and may come back to that. I have a 10uF cap on the output, this allows me to get a bipolar signal from the circuit, perhaps that is having some kind of effect. If I do the calcs for frequency and the measured R1, R2 then it implies C is 170pF, that is a bit closer. I think I would have to take components back off to find out exactly what is going on with that.

I have just more or less completed my project, a piezo driver, it has taken a couple of months, maybe 3. I built an audio amp with high GBP first off, then had to find the right transformer, then for test build a dual power supply, I will use batteries for the final portable version, then got the 555 working. Next thing is to make up a spare in case this one decides to wilt, and finally put it all in a nice box so it looks better.
 

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Sounds like an ambitious project ..
And don’t worry about some small discrepancies here and there ..

I wish you all the best ..
IanP
:D
 

    ants

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Was a bit ambitious, especially as it was my first and only project. I wish making the piezo was as quick, for that I have to rely on industrial companies, lead times can be 3 months and what they send may not work, so I have to start all over again. We'll see. Thanks.
 

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