555 timer flashing LED, install speaker

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
I have the 555 timer setup ( 9 volts) with flashing LED, R LED of 335 ohms. I have a 2" diameter speaker, 8 ohms, 0.25W. Can I remove the LED and replace it with the speaker and get sound? I only have the one speaker so what are the current and voltage limitations? Please keep the replies simple as I am a beginner.555 timer flashing led.jpeg
 

Irving

Joined Jan 30, 2016
4,074
All you'll get from the speaker is a click when the LED would have come on and again when it goes off.... to make a sound the speaker has to be energised at the frequency of the sound.

You need a second 555 to provide that, or a buzzer rather than just a speaker.
 

crutschow

Joined Mar 14, 2008
34,847
Do you want the sound to be pulsed or continuous?
A pulsed sound can be done with two 555's as Irving stated.

You can connect speaker to the 555 output, but not sure now loud it will be.
The available power will not damage the speaker.

Connect a 220μF capacitor in series with the 555 output to the speaker (Cap + terminal to 555 output) to block the signal DC component through the speaker.
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
If I increase the frequency to more than 20HZ would I hear the speaker beeping or continuously on? Any limitations on current or voltage?
 

Irving

Joined Jan 30, 2016
4,074
Continuously on...

On A 9V supply with a capacitor as suggested reduce the 330ohm resistor to 60ohm, that will drive the speaker at its max allowed power.
 

Irving

Joined Jan 30, 2016
4,074
2 x 555 version. U1 generates pulses of 100mS every second, U2 generates a 440Hz tone (times & freq are approximate). U2 is held off by D1. Output is 400mW pulsed, 100mW average

1677527667058.png
 

Audioguru again

Joined Oct 21, 2019
6,785
An 8 ohms speaker driven directly or through a capacitor from a 555 that is powered from a little 9V battery draws very high current pulses of 940mA which might burn out the 555 and/or the speaker and kill the battery soon.
Use a piezo beeper (it uses a low current and is loud) that already has an oscillator in it that beeps when it gets DC from the 555.
 

Thread Starter

Jan Luthe

Joined Jan 10, 2015
89
Thank you everyone. I am making progress.
1. In laymen's terms, what does the suggested additional 220 u capacitor do? Presently all it does is slightly change the intensity of an LED in series with the speaker.
2. I have the original C1 down to about 0.5 n, frequency measured with a cheap DMM is over 1KHz (high pitched sound). The LED is quite bright. The current measured with the DMM is 0.4 milli amps. Is this correct?
 

djsfantasi

Joined Apr 11, 2010
9,188
Thank you everyone. I am making progress.
1. In laymen's terms, what does the suggested additional 220 u capacitor do? Presently all it does is slightly change the intensity of an LED in series with the speaker.
2. I have the original C1 down to about 0.5 n, frequency measured with a cheap DMM is over 1KHz (high pitched sound). The LED is quite bright. The current measured with the DMM is 0.4 milli amps. Is this correct?
A schematic is the language of electronics. Unless you provide one there are many unanswered questions about your circuit. Are you using Irving’s circuit? Or have you modified what you have? Because the capacitor in Irving’s circuit shouldn’t affect the LED.

EDIT: I missed that the LED in Irving’s circuit did not have a current limiting resistor which he mentions in his subsequent post.
 

Irving

Joined Jan 30, 2016
4,074
An 8 ohms speaker driven directly or through a capacitor from a 555 that is powered from a little 9V battery draws very high current pulses of 940mA which might burn out the 555 and/or the speaker and kill the battery soon.
Use a piezo beeper (it uses a low current and is loud) that already has an oscillator in it that beeps when it gets DC from the 555.
Agreed, a sounder would be more efficient. A 22ohm resistor in series with C5 will reduce the current to 200mA and 250mW peak, which is well within the 555's capability.

1. In laymen's terms, what does the suggested additional 220 u capacitor do? Presently all it does is slightly change the intensity of an LED in series with the speaker.
It removes the DC offset and allows the speaker coil to move in both directions (otherwise the drive is always in one direction, which can damage the speaker). Putting the LED in there actually overrides that, so take it out. If you want the LED as well put it, with its series resistor, directly from pin 3 to +9v as before.

2. I have the original C1 down to about 0.5 n, frequency measured with a cheap DMM is over 1KHz (high pitched sound). The LED is quite bright. The current measured with the DMM is 0.4 milli amps. Is this correct?
What value resistors? 0.5n is a bit small. You should reduce the resistor values proportionally,

The frequency is given by F = 1.4/(C. (R1 + 2 . R2))

440Hz is the A above middle C on a piano and a common frequency for a warning beeper. 1kHz is too high in my opinion.

A cheap DMM won't usually give a meaningful current reading on a pulsed current.
 
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Audioguru again

Joined Oct 21, 2019
6,785
A cheap DMM does not measure voltage, current or frequency accurately above 60Hz.
The calculated frequency is 583Hz and the current depends on how many parts are in the output and how much the battery voltage has dropped.
 

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Audioguru again

Joined Oct 21, 2019
6,785
The amps are low because a cheap meter cannot measure accurate current above 60Hz.
You do not have a schematic to show your circuit and where you measured current.
Measure the battery current that supplies DC to the main filter capacitor (33uF in post #14) when the circuit is driving the LED, the speaker and both.
The old 555 draws about 8mA from a 9V battery when oscillating with no load.
 

Audioguru again

Joined Oct 21, 2019
6,785
Where in the circuit did you measure low DC milliamps?
What load was used (speaker, LED or both) when measuring low DC milliamps?
Was the battery still 9.0V when measuring?

What is the part number on your 555? Is it an old fairly high power NE555 or LM555? Or is it a newer low power LMC555, TLC555 or ICM7555?
 
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