PWM with 555 - Electronic Circuits Projects Diagrams Free

davidbball13 · 29th May 2008, 05:41 PM

hey does anyone have a schematic for a 555 to pulse a LED meening to get brighter and then dimmer. i have looked around but i can find it.

**Krumlink** · 29th May 2008, 06:43 PM

You can just wire up a 555 timer and have a pot on it to change the frequency. It works fine and heres a good site:

Welcome to the Electronics Club

Hero999 · 29th May 2008, 07:46 PM

I'm not sure what you mean.

Do you want the LEDs to slowly fade on and off?

Check out this circuit.

davidbball13 · 29th May 2008, 09:11 PM

Quote:

Originally Posted by Hero999

I'm not sure what you mean.

Do you want the LEDs to slowly fade on and off?

Check out this circuit.

yeah thats what i want

davidbball13 · 29th May 2008, 09:13 PM

but the link has no PWM circuit

Hero999 · 29th May 2008, 09:26 PM

There are other ways than PWM to alter the brightness of LEDs.

HarveyH42 · 29th May 2008, 09:29 PM

This isn't a 555 circuit either (good luck on that one), but it's the best LED fading circuit.

http://ourworld.compuserve.com/homep...wden/page5.htm

Look for 'Fading-Red Eyes'. There is a lot of text with it, that can be useful for adapting the circuit to your needs/parts on hand. Nothing is critical, shouldn't be much of a problem. I did an RGB version of this a few years ago, still think it gives a better range of color then microcontroller versions I've done. The AVR version I use the most, simpler and just a few parts.

davidbball13 · 29th May 2008, 09:33 PM

LM1458 ?????? i have never herd of that. well i will look around more. i thik i am going to get an arduino or a bunch of PICs

Mikebits · 29th May 2008, 10:20 PM

The LM1458 is just a general purpose op amp that has been around since Moby Dick was a minnow. A PIC would be a bit of overkill, just to make a fading LED. I would go with Hero's solution.

Hero999 · 30th May 2008, 01:19 PM

Using PWM the easyiest way of doing this is to build two schmitt trigger oscillators, 200Hz and 0.5Hz. Schmitt trigger oscillators produce a triangle waveform on the capacitor, if you connect comparator's + input to one capacito and the - input to the other, at the output you'll have a PWM waveform oscillating between 0% and 100% duty cycle at 0.5Hz.

If you wanted to use a PIC then perhaps you would have got more help if you posted this in the microcontrollers section.

davidbball13 · 31st May 2008, 01:18 PM

Quote:

Originally Posted by Hero999

Using PWM the easyiest way of doing this is to build two schmitt trigger oscillators, 200Hz and 0.5Hz. Schmitt trigger oscillators produce a triangle waveform on the capacitor, if you connect comparator's + input to one capacito and the - input to the other, at the output you'll have a PWM waveform oscillating between 0% and 100% duty cycle at 0.5Hz.

If you wanted to use a PIC then perhaps you would have got more help if you posted this in the microcontrollers section.

the tital says "PWM with 555" not "PWM with a microcontroller"

AllVol · 31st May 2008, 02:20 PM

Quote:

Originally Posted by davidbball13

the tital says "PWM with 555" not "PWM with a microcontroller"

By its very nature, the 555 timer produces a pulse at its output, either astable or one-shot, depending on component structure. The voltage and current supply at the output is a function of the voltage used to power the device.

PMW (pulse width modulation) is the varying of the percent of on and off times of each pulse cycle. It has nothing to do with the original output values. Therefore, PMW in itself will have no effect on the brightness of a LED connected via current-limiting resistor to the output.

A quick way to see PMW in operation is to set up the 555 to produce a blinking LED with a frequency of some four or five flashes per second.

Then, connect the ends of a potentiometer to V+ and ground. Connect the wiper to pin 5 of the 555. You now have voltage controlled PMW. As you vary the pot, the LED will blink slower or faster, depending on the voltage supplied through the pot.

When the LED blinks slowly, it is because the high portion of the squarewave pulse is very narrow with respect to the off portion of the cycle. Conversely, the LED will blink faster when the on portion is greater (wider) than the off time.

Hope this answers some of your questions.

AllVol · 31st May 2008, 02:21 PM

That acronym should be PWM, not PMW.

Hero999 · 31st May 2008, 02:30 PM

Quote:

Originally Posted by davidbball13

the tital says "PWM with 555" not "PWM with a microcontroller"

Only a 555 isn't the best way of doing this, comparators are.

erosennin · 31st May 2008, 02:47 PM

Sure they are if you want to sit there with a pot doing the adjustment manually, and end up with an inaccurate, inconsistent result.

davidbbal13... Take everyone's advice and either do it with an opamp or a 12series pic... This forum is full of people who are quite knowledgeable, I myself have not reached this level yet, but don't discount their advice just because you are set on a 555.
Is this some form of assignment? That you are forced to utilise a 555 timer.

If you are set in your ways, look at this schematic. If you are just using 1LED you will not need the FET and related hardware down that end....

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29th May 2008, 05:41 PM	(permalink)
davidbball13	PWM with 555 hey does anyone have a schematic for a 555 to pulse a LED meening to get brighter and then dimmer. i have looked around but i can find it.

29th May 2008, 06:43 PM	(permalink)
Krumlink	You can just wire up a 555 timer and have a pot on it to change the frequency. It works fine and heres a good site: Welcome to the Electronics Club __________________ MechTronics World of Warcraft is a disease

29th May 2008, 07:46 PM	(permalink)
Hero999	I'm not sure what you mean. Do you want the LEDs to slowly fade on and off? Check out this circuit. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

29th May 2008, 09:13 PM	(permalink)
davidbball13	but the link has no PWM circuit Last edited by davidbball13; 29th May 2008 at 09:13 PM.

29th May 2008, 09:26 PM	(permalink)
Hero999	There are other ways than PWM to alter the brightness of LEDs. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

29th May 2008, 09:29 PM	(permalink)
HarveyH42	This isn't a 555 circuit either (good luck on that one), but it's the best LED fading circuit. http://ourworld.compuserve.com/homep...wden/page5.htm Look for 'Fading-Red Eyes'. There is a lot of text with it, that can be useful for adapting the circuit to your needs/parts on hand. Nothing is critical, shouldn't be much of a problem. I did an RGB version of this a few years ago, still think it gives a better range of color then microcontroller versions I've done. The AVR version I use the most, simpler and just a few parts.

29th May 2008, 09:33 PM	(permalink)
davidbball13	LM1458 ?????? i have never herd of that. well i will look around more. i thik i am going to get an arduino or a bunch of PICs

29th May 2008, 10:20 PM	(permalink)
Mikebits	The LM1458 is just a general purpose op amp that has been around since Moby Dick was a minnow. A PIC would be a bit of overkill, just to make a fading LED. I would go with Hero's solution.

30th May 2008, 01:19 PM	(permalink)
Hero999	Using PWM the easyiest way of doing this is to build two schmitt trigger oscillators, 200Hz and 0.5Hz. Schmitt trigger oscillators produce a triangle waveform on the capacitor, if you connect comparator's + input to one capacito and the - input to the other, at the output you'll have a PWM waveform oscillating between 0% and 100% duty cycle at 0.5Hz. If you wanted to use a PIC then perhaps you would have got more help if you posted this in the microcontrollers section. __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez

31st May 2008, 02:21 PM	(permalink)
AllVol	That acronym should be PWM, not PMW. __________________ All those who believe in psycho kinesis, raise my hand.

31st May 2008, 02:47 PM	(permalink)
erosennin	Sure they are if you want to sit there with a pot doing the adjustment manually, and end up with an inaccurate, inconsistent result. davidbbal13... Take everyone's advice and either do it with an opamp or a 12series pic... This forum is full of people who are quite knowledgeable, I myself have not reached this level yet, but don't discount their advice just because you are set on a 555. Is this some form of assignment? That you are forced to utilise a 555 timer. If you are set in your ways, look at this schematic. If you are just using 1LED you will not need the FET and related hardware down that end.... __________________ What is a joule per second?