Tone generator problem

Thread Starter

woozycactus

Joined Jan 4, 2021
84
So I tried to build a 555 tone generator. Simple right? I got it to work but it's extremely distorted. If I use an led, the only thing I get is if I accidentally and very briefly short the positive and negative rail, the led turns on for a few seconds and then turns off. When I adjust the pot, it turns off faster. Anyone else ever run into this issue? I'll post schematic soon.Untitled.jpg
 
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MrChips

Joined Oct 2, 2009
24,134
Depends on what you mean by distorted.
Are you expecting to hear a nice clean tone like the note from a flute?
You are not going to get that from a square wave signal from the output at pin-3 of a 555-timer IC.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
84
Depends on what you mean by distorted.
Are you expecting to hear a nice clean tone like the note from a flute?
You are not going to get that from a square wave signal from the output at pin-3 of a 555-timer IC.
Well the YouTube video was very clean. Just solid tones but either way it's not working correctly
 

Papabravo

Joined Feb 24, 2006
16,772
I don't know how much time you spend listening to square waves, but they sound really awful and....harsh is the best word I can think of.
An LED is a pretty heavy load for the output -- you might need to add a current limiting resistor. Putting a low impedance speaker from pin 3 to ground is guaranteed to sound awful if you get any sound at all. It is like shorting a power supply to ground -- not too useful.

One more thing your "schematic", such as it is does not show any kind of "sound" transducer. You might want to clean up that minor detail so we can see what is really happening.
 

Papabravo

Joined Feb 24, 2006
16,772
I expect it to work and not sound like popcorn more than a tone
And it looks like your expectations have diverged from reality. Never fear there is a solution, but we don't know what it is yet.
Do you have a datasheet for the part you are using and do you know how to calculate the expected frequency given the values of the R's and C's in your circuit?
If you don't have one we can help you find one.
 
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Thread Starter

woozycactus

Joined Jan 4, 2021
84
And it looks like your expectations have diverged from reality. Never fear there is a solution, but we don't know what it is yet.
Do you have a datasheet for the part you are using and do you know how to calculate the expected frequency give the values of the R's and C's in your circuit?
If you don't have one we can help you find one.
I mean I am using an 8 ohm speaker. This design is off of a YouTube video and it sounded very clean. I am making this as part of a bigger project but need to get this working first. The goal here is to produce a variable tone generator that can get up to 15k hertz. believe me, I know this design will not get that high but its a start on learning these circuits. Note I already burned up 3 555 chips with a different design but it was very clean tones. This design does not fry my chips but sounds like crap on my end.
 

BobTPH

Joined Jun 5, 2013
3,648
Popcorn?

Are you getting something that sounds sort of like a small gas engine running on slow: bup bup bup bup…

That is what a sub-audio frequency, around 5-10 Hz would sound like.

Bob
 

AnalogKid

Joined Aug 1, 2013
9,351
Besides that whole sine save vs. square wave thing, the design you posted has a couple of problems.

1. It can not drive an 8 ohm speaker directly. At a minimum you need a coupling capacitor between the 555 output and the speaker. Separate from that is the amplitude of the peak current through the speaker, and whether or not it exceeds the value on the 555 datasheet.

2. It can not drive an LED directly. While some LEDs and LED strips have current limiting built-in, most do not. For a standard LED, you must add a series resistor to limit the current through the device. The LED datasheet will give a safe maximum value.

3. Back to the tones ... There is a variation of this circuit that uses 1 fewer part and produced a 50/50 square wave. This is the cleanest sounding waveform a 555 output can produce without a more complex circuit, external filtering, taking the capacitor voltage waveform as the output through a buffer of some kind, etc.

Since we have no idea of what you started with, please post a link to the YouTube video. Also, it would help if we could see a schematic of the "different design".

ak
 

Papabravo

Joined Feb 24, 2006
16,772
I mean I am using an 8 ohm speaker. This design is off of a YouTube video and it sounded very clean. I am making this as part of a bigger project but need to get this working first. The goal here is to produce a variable tone generator that can get up to 15k hertz. believe me, I know this design will not get that high but its a start on learning these circuits. Note I already burned up 3 555 chips with a different design but it was very clean tones. This design does not fry my chips but sounds like crap on my end.
The results speak for themselves. A step backward and a cleaned up well thought out design schematic with verification are what is required. I don't see how you can succeed on your present course, and you didn't bother to answer any of my questions, so I'm almost ready to pass the baton to another with more patience and forbearance.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
84
The results speak for themselves. A step backward and a cleaned up well thought out design schematic with verification are what is required. I don't see how you can succeed on your present course, and you didn't bother to answer any of my questions, so I'm almost ready to pass the baton to another with more patience and forbearance.
Not trying to skip around question it was 2 in the morning when I replied last. I don't have data sheets with me at the moment, but can get them after work, no I don't know what frequencies I should be hearing. It's a learning project to start with.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
84
Besides that whole sine save vs. square wave thing, the design you posted has a couple of problems.

1. It can not drive an 8 ohm speaker directly. At a minimum you need a coupling capacitor between the 555 output and the speaker. Separate from that is the amplitude of the peak current through the speaker, and whether or not it exceeds the value on the 555 datasheet.

2. It can not drive an LED directly. While some LEDs and LED strips have current limiting built-in, most do not. For a standard LED, you must add a series resistor to limit the current through the device. The LED datasheet will give a safe maximum value.

3. Back to the tones ... There is a variation of this circuit that uses 1 fewer part and produced a 50/50 square wave. This is the cleanest sounding waveform a 555 output can produce without a more complex circuit, external filtering, taking the capacitor voltage waveform as the output through a buffer of some kind, etc.

Since we have no idea of what you started with, please post a link to the YouTube video. Also, it would help if we could see a schematic of the "different design".

ak

Here is the video
 

MrChips

Joined Oct 2, 2009
24,134
Other members have given you sound advice so pay attention.
Yes, your circuit will produce sound that sounds like crap but we can fix that.

1) 555-timer cannot drive an LED properly when connected directly to pin-3. We can remedy that.
2) 555-timer cannot drive an 8Ω speaker directly.
3) Popcorn sound is called motor-boating when the power supply cannot supply enough current and the power supply is not properly filtered.
4) 555-timer astable circuit can output up to 1MHz square wave.

1) Put a resistor, 470-1000Ω, in series with the LED.

2) An 8Ω speaker is much too low for the poor 555 to handle. Use a driver transistor or an audio amplifier to drive the speaker. You can also use a piezoelectric transducer driven directly from the 555, pin-3.

3) Put a 100-1000μF aluminum electrolytic capacitor across the power supply lines.

4) 555-timer can generate the range of audible tones you desire. The range with one variable resistor is another matter.

555 pin-3 will output a square wave. A square wave contains the fundamental frequency plus the higher odd harmonics at decreasing amplitudes. A square wave sounds harsh to the ear. You can make the tone sound more "pleasant" to the ear by filtering out the harmonics. This helps to produce a signal that more closely resembles a sine wave, i.e. it is mainly the single fundamental frequency. You can do this for a given frequency. It becomes a challenge to do this over a wider range of frequencies.

In summary, we can fix what you have but you have to understand the limitations.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
84
Other members have given you sound advice so pay attention.
Yes, your circuit will produce sound that sounds like crap but we can fix that.

1) 555-timer cannot drive an LED properly when connected directly to pin-3. We can remedy that.
2) 555-timer cannot drive an 8Ω speaker directly.
3) Popcorn sound is called motor-boating when the power supply cannot supply enough current and the power supply is not properly filtered.
4) 555-timer astable circuit can output up to 1MHz square wave.

1) Put a resistor, 470-1000Ω, in series with the LED.

2) An 8Ω speaker is much too low for the poor 555 to handle. Use a driver transistor or an audio amplifier to drive the speaker. You can also use a piezoelectric transducer driven directly from the 555, pin-3.

3) Put a 100-1000μF aluminum electrolytic capacitor across the power supply lines.

4) 555-timer can generate the range of audible tones you desire. The range with one variable resistor is another matter.

555 pin-3 will output a square wave. A square wave contains the fundamental frequency plus the higher odd harmonics at decreasing amplitudes. A square wave sounds harsh to the ear. You can make the tone sound more "pleasant" to the ear by filtering out the harmonics. This helps to produce a signal that more closely resembles a sine wave, i.e. it is mainly the single fundamental frequency. You can do this for a given frequency. It becomes a challenge to do this over a wider range of frequencies.

In summary, we can fix what you have but you have to understand the limitations.
Look, I'm listening, I'm just replying to everyone while working, when I can. I have like 5 different types of amp chips, so I guess I need to find schematics for those. The point I am trying to make is the dude in the video I posted above is the exact same circuit and his works pretty clear tones. The power supply is a variable switching power supply but I get same results with 9 volt batteries. I will try the suggestions when I get home, just don't understand why I have a different outcome than the video. Also I tried a 4 ohm speaker and it's trivaly the same result
 
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