# LFO+Lamp time constant

Discussion in 'General Electronics Chat' started by relicmarks, Apr 26, 2008.

1. ### relicmarks Thread Starter Active Member

Oct 13, 2006
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I have a Low frequency oscillator hooked up to a Lamp that sweeps the light of the Lamp

THe Lamp is controlling LDR light dependent resistors

I'm trying to make a RC time constant network to the LAMP so i can control the time constant's of the Lamp seperate from the LFO circuit

So the Lamp light will be throbbing more

Do you guys know what kind of function generator waveform would make a LAMP throb alot? Amplitude modulation NOT RF AM i mean i mean just modulating the Amplitude voltage up and down

I tried just turning the volume on my function generator up and down while it was sweeping the frequency and it made the LAMP throb more

But what else can make the LAMP throb more?

The 70's Strobbing light circuits is what im looking into

How can i make my LAMP strobb more that throbbing strobbing effect but at a low rate?

What circuit or network makes a LAMP strobb or throb effects?

2. ### mik3 Senior Member

Feb 4, 2008
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63
As i understood you want to control how bright is the lamp?

If you use PWM you can vary the duty cycle as to vary the average power delivered the lamp.

Or you can use a variable power supply to change the voltage across the lamp.

If i am wrong about what you want explain it better please.

3. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
LAMP light range
1.) Dark to bright range

I want to control the RC time constant of the Dark to Bright timing? like how long it takes for the lamp to go from DARK to bright

What circuit or network can do this?

4. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
What i thought about doing is using a squarewaveform to the LAMP but using a RC time constant inbetween the squarewaveform and the LAMP

So you get the GROUTH rise time and DECAY fall time that is exponential not linear

It will make the LAMP throb and strob more is what im looking for the strobbing effect

5. ### mik3 Senior Member

Feb 4, 2008
4,846
63
This is not called an RC time constant as far as i know. RC constant is the time a capacitor needs to charge up to almost 2/3 of its supply voltage. Anyway, if you want the lamp to increase its brightness linearly from dark to bright you can use a ramp generator circuit. By varying the slope of the ramp you will determine how much time the voltage across the lamp will need to go from zero volts (dark) to the rated voltage of the lamp (bright).
If you want to delay the lamp to turn on after say a switch is activated use a 555 timer IC.

6. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
How do you make the ramp Slope exponental>? so the slope has a time constant growth and decay ?

Rise time and fall time is linear

Growth time and decay time is exponental and looks like a "sharks fins"

By varying the slope of the ramp you will determine how much time the voltage across the lamp will need to go from zero volts (dark) to the rated voltage of the lamp (bright).

On the function generator what varys the SLOPE like this? on do you vary the TIMING of the slope? where this at on the function generator parameter?

7. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
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My function generator has a ramp waveform but its only linear not exponential how can i make it exponential ?

8. ### mik3 Senior Member

Feb 4, 2008
4,846
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On the function generator what varys the SLOPE like this? on do you vary the TIMING of the slope? where this at on the function generator parameter?

Its depends on the generator itself, maybe you can vary the timing of the slope or maybe you cant.

If you want to generate an exponentially rise and fall voltage you can build a voltage follower with an op-amp and put a capacitor on its input. Then charge the capacitor via a resistor. By using a switch you can charge and discharge the capacitor. The time will take for the voltage to rise from zero to 2/3 of full charging voltage across the capacitor is determined by the value of the capacitor and the resistor in series with the capacitor (if you charge it) or the resistor in parallel with the capacitor (if you discharge it). On the output of the op-amp you will take an exponential rise (charge the capacitor) and fall (discharge the capacitor) voltage. Also you can use variable resistors to vary the RC time constant.

9. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
Its depends on the generator itself, maybe you can vary the timing of the slope or maybe you cant.

What parameter on the generator will adjust the timing of the slope?

10. ### mik3 Senior Member

Feb 4, 2008
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The duty cycle .

11. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
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The duty cycle parameter of the ramp waveform?

12. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Emmm sorry, i got confused with the triangular wave. For a ramp if you vary its frequency you vary its rise time too.

13. ### SgtWookie Expert

Jul 17, 2007
22,183
1,728
I think a 555 timer will likely suit your needs.

Build your 555 circuit for a short ON time and a long OFF time.

14. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
By varying the slope of the ramp you will determine how much time the voltage across the lamp will need to go from zero volts (dark) to the rated voltage of the lamp (bright).

But how do u varying the SLOPE?

ramping from Zero to 5 volts to the LAMP

But how do u get that strobbing effect ? those older 1970's strobbing lights

15. ### mik3 Senior Member

Feb 4, 2008
4,846
63
If you want the voltage across the lamp to vary linearly search in google for ramp generators to see how they work.

If you want the voltage across the lamp to vary exponentially build the circuit i told you with the op-amp.

If you want the lamp just to turn on and off use a 555 timer IC as SgtWookie said. With the 555 you can vary the frequency of flashing and the how long the flashing stays on (duty cycle).

16. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
Whats the difference between slopes VS curves?

example: zero to +10 volts range

If i say the slope rises from zero to +10 volts it looks like a rise time

But i say the curve rises from zero to +10 volts it looks like what?

Where can i find different terms or names for curves please?

Some curves build or rise differential and others build/rise expontially i don't know how to describe this different curves is there a chart or terms please?

17. ### mik3 Senior Member

Feb 4, 2008
4,846
63
I think you know the graphs of e^x , cos (x) and so on in mathematics. if a voltage rises like the graph of e^x we say it rises exponentially, or if a voltage varies like the graph of the sine we say it a sinusoidal voltage. If you know the basic graphs in math then you will see why this voltage is called like taht and the other with another name.

18. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
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Potentiometer Tapers curves chart
1.) Antilog- looks like a build/rise exponential charging time
( looks like the curve is "Outward" compared to a linear slope)
2.) Linear- straight line
3.) Log- looks like a Decay time or discharge time curve
(Looks like the curve is "Inward" compared to a linear slope)
4.) "S" Curve

How to measures the curves deviation?
How to measure the curves Excursions?

I know how to measure the rise time or slope or a ramp
But with angular curves i don't know how to measure them or how to use the correct terms

All i could find is this potentiometer tapers chart

The Antilog curve looks just like a Growth exponential rise time what would you guys call this?

The Log curve looks just like a Decay exponential fall time what would you guys call this?

How would you guys measure this Angular curves? its Voltage + degrees?

19. ### mik3 Senior Member

Feb 4, 2008
4,846
63
If you really want to learn search the internet. Its a big topic. Search in google , you will fing thousands of info.

20. ### relicmarks Thread Starter Active Member

Oct 13, 2006
355
0
What should i type in google tho i don't know the names thats my problem

I can't find the correct names for these types of angular curves not linear