PWM with 555

AllVol said:

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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Hero999 said:

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.

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