Originally Posted by 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....

Originally Posted by AllVol

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.

Originally Posted by davidbball13

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.

Originally Posted by davidbball13

yeah.......math
i need some new 9 volt batterys because all of my circuits are dim and quite

Originally Posted by AllVol

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.

Originally Posted by Hero999

If you want your batteries to last longer then don't use a 555 timer, use the CMOS 7555.

Here's the circuit I was describing a couple of posts ago. U1 is a quad op-amp like the LM324 you could use a comparator like the LM339 but don't forget the pull-up resistors on the output.

U1A forms a Schmitt trigger oscillator oscillates at around 5 seconds per cycle; the fading rate is determined by R7 and C1.

U1B is exactly the same oscillator configuration as U1A but oscillates at around 250Hz which is the PWM frequency.

U1C acts as a comparator and compares the voltage on C1 and C2 and lights D1 if the voltage on C2 is greater than C1.

Notice how I've used fairly large resistor values? This helps reduce the current consumption and save battery life.