Oscillator using NE555

Thread Starter

Trailer

Joined Jan 22, 2023
57
I've built a standard variable frequency oscillator circuit using NE555. The supply voltage is 14.8 volts, output is around 12.6 volts which is acceptable for my application the only drawback was the out frequency was too low (just few Hz).
I replaced the 47 micro electrolytic capacitor connected to pin 6 with 0.1 micro and the variable resistor between pins 7 and 8 from 5k to 1M and I got the required frequency range (70 to 1200 Hz) but the output voltage dropped to 4.7 volts!!
I need to maintain the frequency range and an output voltage no less than 10 or 11 volts (or higher if possible).. any suggestions?
 

dl324

Joined Mar 30, 2015
17,009
Welcome to AAC!
the output voltage dropped to 4.7 volts!!
I have the pinout for 555 timers committed to memory but, for the benefit of those who don't, a schematic would be appreciated.

What is connected to the output? Is the supply voltage still 14.8V when that happens?

I replaced the 47 micro electrolytic capacitor connected to pin 6 with 0.1 micro and the variable resistor between pins 7 and 8 from 5k to 1M and I got the required frequency range (70 to 1200 Hz)
What is the other resistor value?
 

WBahn

Joined Mar 31, 2012
30,250
I've built a standard variable frequency oscillator circuit using NE555. The supply voltage is 14.8 volts, output is around 12.6 volts which is acceptable for my application the only drawback was the out frequency was too low (just few Hz).
I replaced the 47 micro electrolytic capacitor connected to pin 6 with 0.1 micro and the variable resistor between pins 7 and 8 from 5k to 1M and I got the required frequency range (70 to 1200 Hz) but the output voltage dropped to 4.7 volts!!
I need to maintain the frequency range and an output voltage no less than 10 or 11 volts (or higher if possible).. any suggestions?
Schematics are the language of electronics -- please speak the language. Even a sketch will do.

What are you powering the circuit with? How much current can it supply?

What is your output load?

Do you have proper bypass capacitors in place?

Is there a resistor connected between the power supply and the discharge pin? Again, a schematic is the way to present your circuit.

How are you measuring the output voltage? With a scope? Or with a multimeter? If you are measuring it with a multimeter, are you using AC or DC ranges? What is the frequency bandwidth of your meter?
 

Thread Starter

Trailer

Joined Jan 22, 2023
57
Welcome to AAC!
I have the pinout for 555 timers committed to memory but, for the benefit of those who don't, a schematic would be appreciated.

What is connected to the output? Is the supply voltage still 14.8V when that happens?


What is the other resistor value?
Yes supply remains at 14.8
No load connected
I'm posting the schematic in few moments
 

LowQCab

Joined Nov 6, 2012
4,217
A Digital-Multimeter will not accurately measure the "on" Voltage of a square-wave,
You will either need a "Sample & Hold" Circuit, or preferably, an Oscilloscope.
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Thread Starter

Trailer

Joined Jan 22, 2023
57
A Digital-Multimeter will not accurately measure the "on" Voltage of a square-wave,
You will either need a "Sample & Hold" Circuit, or preferably, an Oscilloscope.
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Thanks.. I know it's not very accurate but still it's giving an adequate reading with the original setup (13.7v) which is expected.. I also use a software oscilloscope (on PC) which is only reliable for frequency but still gives clear indication of the big difference in voltage drop between both settings
 

Thread Starter

Trailer

Joined Jan 22, 2023
57
Schematics are the language of electronics -- please speak the language. Even a sketch will do.

What are you powering the circuit with? How much current can it supply?

What is your output load?

Do you have proper bypass capacitors in place?

Is there a resistor connected between the power supply and the discharge pin? Again, a schematic is the way to present your circuit.

How are you measuring the output voltage? With a scope? Or with a multimeter? If you are measuring it with a multimeter, are you using AC or DC ranges? What is the frequency bandwidth of your meter?
Circuit fed by 15V voltage regulator connected from transformer
All other queries are replied on the schematic.. I hope I covered all of them20230123_053103.jpg
 

dl324

Joined Mar 30, 2015
17,009
Schematic attached
I calculate the frequency with R2=5k and C1=0.01uF to be 13kHz with capacitor tolerance being the biggest factor if it's ceramic. Duty cycle is 45%, so I'd expect the output voltage to be around 5.8-7.4V using VDC on your meter.
\( f = \frac{1}{T} = \frac{1.44}{(R_1+2R_2)C} = \frac{1.44}{(1k\Omega+10k\Omega)0.01uF}=13kHz\)
 
Last edited:

LowQCab

Joined Nov 6, 2012
4,217
1)
What is the eventual use of this Square-Wave- Oscillator ?

2)
Does the Duty-Cycle need to always be stable at ~50% ?

3)
Do You want to be able to adjust the Duty-Cycle ?

4)
What is the needed Range of Frequencies ?

5)
Do You want a Frequency-Range-Selector-Switch to cover a very broad range of Frequencies ?

6)
What is your expected maximum-Output-Current ?

7)
Is this project supposed to be a "Bench-Top" piece of "Test-Equipment" ?
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Thread Starter

Trailer

Joined Jan 22, 2023
57
I calculate the frequency with R2=5k and C1=0.01uF to be 13kHz with capacitor tolerance being the biggest factor if it's ceramic. Duty cycle is 45%, so I'd expect the output voltage to be around 5.8-7.4V using VDC on your meter.
\( f - \frac{1}{T} = \frac{1.44}{(R_1+2R_2)C} = \frac{1.44}{(1k\Omega+10k\Omega)0.01uF}=13kHz\)
I just tried your proposed setting and you're within the readings I'm getting.. with R2 = 5k the frequency range 11k to 15k and out volt around 6.8. But the 555 is not very stable.. besides I'm only looking for a frequency range of 100Hz to 1.5 or 2kHz max.. and still the out voltage is too low
 

dl324

Joined Mar 30, 2015
17,009
But the 555 is not very stable
What does not stable mean?
besides I'm only looking for a frequency range of 100Hz to 1.5 or 2kHz max.. and still the out voltage is too low
You can't get a realistic measure of output voltage swing with the DCV setting. Even with AC, you won't get an accurate reading. DVM's usually have limited frequency range and are expecting to measure RMS voltage.
 

MrChips

Joined Oct 2, 2009
30,980
What does not stable mean?
You can't get a realistic measure of output voltage swing with the DCV setting. Even with AC, you won't get an accurate reading. DVM's usually have limited frequency range and are expecting to measure RMS voltage.
Oh! That never crossed my mind.
I was assuming that you were examining the output on an oscilloscope.
You cannot measure the output voltage correctly with a DMM.
 

Thread Starter

Trailer

Joined Jan 22, 2023
57
1)
What is the eventual use of this Square-Wave- Oscillator ?

2)
Does the Duty-Cycle need to always be stable at ~50% ?

3)
Do You want to be able to adjust the Duty-Cycle ?

4)
What is the needed Range of Frequencies ?

5)
Do You want a Frequency-Range-Selector-Switch to cover a very broad range of Frequencies ?

6)
What is your expected maximum-Output-Current ?

7)
Is this project supposed to be a "Bench-Top" piece of "Test-Equipment" ?
.
.
.
1) What is the eventual use of this Square Wave Oscillator ?
- it's a bench top piece but not a reference test equipment.. therefore very high accuracy is not vital

2) Does the Duty-Cycle need to always be stable at ~50% ?
- Not necessarily.. minor deviation is ok

3) Do You want to be able to adjust the Duty-Cycle ?
- No

4) What is the needed Range of Frequencies ?
- from around 50 Hz up to 1500 or 2000 Hz max which I'm already getting now but with big voltage drop

5) Do You want a Frequency Range Selector Switch to cover a very broad range of Frequencies ?
- No.. I'm using the R2 potentiometer as the frequency selector for the narrow band of frequencies (see no. 4)

6) What is your expected maximum Output Current ?
- No more than 200mA

7) Is this project supposed to be a "Bench-Top" piece of "Test-Equipment"
- see first query
 

Thread Starter

Trailer

Joined Jan 22, 2023
57
Oh! That never crossed my mind.
I was assuming that you were examining the output on an oscilloscope.
You cannot measure the output voltage correctly with a DMM.
I'm also using a software oscilloscope.. voltage reading is not very trusted but in comparison between both my settings it still indicates a big difference in voltage drops
 
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