NE555 timer help please?

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
I just finished building a tremolo for my guitar and it works really well after correcting my wiring errors lol

However, I have a clicking on the output caused by the output of the 555, I looked at the supply rail and there it is, a very tiny square wave
that rises and falls with pin 3 of the timer chip, I have placed a 100 uf Electrolytic across the supply pins as close as I can get to the chip which has helped a lot although the click is still faintly audible, how can I filter out this annoying artifact please?

Neil.
 

dl324

Joined Mar 30, 2015
12,786
Try putting a 0.1uF ceramic cap in parallel with the 100uF. The electrolytic is good for low frequency noise and the ceramic will be better at high frequency.
 

AnalogKid

Joined Aug 1, 2013
9,161
"My 555 is running at around 4Hz."

But the harmonic content of the vertical edges of the waveform are up into the tens of kilohertz range. That, combined with the extreme sensitivity range of human hearing make mixing square waves and audio a very difficult thing. This is why a sine wave or even a triangle wave would be better for your circuit. The clicking has two components, a) 4 Hz squarewave noise getting into the audio circuit power or ground and summing with the audio; b) you are amplitude modulating the audio with a 4 Hz square wave just like amplitude modulating an RF carrier for radio, and the human hearing system is demodulating it. If you can't change the oscillator, can you filter the square wave before it hits the attenuator so the audio doesn't change amplitude so rapidly?

The concept is called harmonic content. It falls out of the Fourier Analysis of a periodic waveform, and dates back to December 21, 1807, at 10:30 am., Paris time. Jean-Baptiste Joseph Fourier presented a paper detailing a new way to describe mathematically how heat spreads out into something when that something makes contact with a small hot spot. His mathematical technique now is called Fourier Analysis, based on the Fourier Integral, and is arguably the single greatest piece of engineering math between Isaac Newton and James Clerk Maxwell.

ak
 

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
That's what I'm wondering AK......can I filter it and how?.....

I don't have a clear enough circuit to post but in any case I would think this is a common problem with any audio circuit using this chip?

Neil.
 

GopherT

Joined Nov 23, 2012
8,012
That's what I'm wondering AK......can I filter it and how?.....

I don't have a clear enough circuit to post but in any case I would think this is a common problem with any audio circuit using this chip?

Neil.

Take a photo of it with your phone and post it, draw it by hand, take a photo, something.

the more communication, the more ideas flow.
 

crutschow

Joined Mar 14, 2008
26,973
Place a 100Ω or so resistor in series with the power to the 555.
Place a 470μF cap in parallel with a 0.1μF ceramic capacitor from the 555 power pin to ground.
 
Last edited:

davideather

Joined Dec 12, 2016
33
My 555 is running at around 4Hz.
It doesn't matter. The 555 puts an almost dead short across the power supply when it switches. That is the click you hear. The .1uF should help. Also as someone else suggested using the CMOS version 7555 will eliminate the problem, but if you don't want to do that you could try supplying the 555 via a 100 ohm resistor (use the 100uF cap on the power pins of the 555. This will further isolate the 555 spikes from the rest of the circuit
 

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
I placed a 90 ohm resistor in the supply and kept the 100 uf cap in place and it made no difference, I have sent off for some CMOS
555 timers and if that doesn't cure my clicking, then I will abandon the 555 idea altogether and find a circuit that will give me a variable sinewave
over the range 3 - 10 Hz.

what does the 10nf cap from pin 5 to ground do that I have seen in some circuits?

Neil.
 

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
Can anyone point me in the right direction for an oscillator schematic that will give me 1-10 Hz please?.....maybe op amp based?
 

GopherT

Joined Nov 23, 2012
8,012
Can anyone point me in the right direction for an oscillator schematic that will give me 1-10 Hz please?.....maybe op amp based?
Google Wein Bridge oscillator.
The basic circuits used for leaning purposes don't work, you need the circuit that is usually described later in the article that shows a feedback device to control oscillation.
feedback devices like a light bulb (incandescent) or a pair of back-to-back Zener diodes.

The incandescent bulbs you want are tiny - only a few milliamps and 6 to 8 volts. It shouldn't even emit light if done right - just heat a tiny bit.
 

GopherT

Joined Nov 23, 2012
8,012
Google Wein Bridge oscillator.
The basic circuits used for leaning purposes don't work, you need the circuit that is usually described later in the article that shows a feedback device to control oscillation.
feedback devices like a light bulb (incandescent) or a pair of back-to-back Zener diodes.

The incandescent bulbs you want are tiny - only a few milliamps and 6 to 8 volts. It shouldn't even emit light if done right - just heat a tiny bit.
There is also the famous bubba oscillator (works well enough if a square wave might have done the job. A member here wrote the Texas Instruments op amp oscillators white paper. @rmancini
 

Thread Starter

Fluxor1964

Joined Jun 11, 2015
182
What value zeners would I use?
Google Wein Bridge oscillator.
The basic circuits used for leaning purposes don't work, you need the circuit that is usually described later in the article that shows a feedback device to control oscillation.
feedback devices like a light bulb (incandescent) or a pair of back-to-back Zener diodes.

The incandescent bulbs you want are tiny - only a few milliamps and 6 to 8 volts. It shouldn't even emit light if done right - just heat a tiny bit.
 

AnalogKid

Joined Aug 1, 2013
9,161
To make a Wein bridge oscillator variable over a 10-to-1 range you need either a dual-gang pot or a dual-gang variable capacitor. For what you are doing, the pot is the way to go.

ak
 
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