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PWM with 555

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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.
 
I'm not sure what you mean.

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

**broken link removed**
 
There are other ways than PWM to alter the brightness of LEDs.
 
This isn't a 555 circuit either (good luck on that one), but it's the best LED fading circuit.

**broken link removed**

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.
 
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.
 
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.
 
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"
 
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.
 
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 **broken link removed** schematic. If you are just using 1LED you will not need the FET and related hardware down that end....
 
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 **broken link removed** schematic. If you are just using 1LED you will not need the FET and related hardware down that end....

im not "set" on the 555 my friend made it and i wanted a schematic but my friend is getting his second round of chemo today so i cant talk to him
 
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.

for the pot you can just do that with a pot for R1 or R 2 put i am sure i can do something with that.
 
for the pot you can just do that with a pot for R1 or R 2 put i am sure i can do something with that.

Slight correction:

If you simply pot R1 or R2 you aren't causing PWM, you are merely varying the RC component, thus the frequency. Potting pin 5 actually varies the duty cycle, resulting in PWM. Granted, with the use of a couple of diodes and hit-or-miss RC, one can produce PWM off pins 6-7, but that just adds more components.


At any rate, none of the above will have any effect on the brightness of the LED. That is a function of the current you place through the LED. Remember I=E/R.
 
yeah.......math
i need some new 9 volt batterys because all of my circuits are dim and quite

Why don't you order out a 12 volt Wall Wart, an LM7809 regulator, a couple of 1000 uF electrolytics and a 3.5 mm power receptacle, and build a 9-volt power supply for your experiments.

You could also get an LM7805 with caps, and put it on a seperate board for your TTL digital projects.

Or, forget the five volts for TTL and use only CMOS 4000 series ICs with your 9 volt supply.

You'll windup saving money versus the cost of batteries.
 
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