We mentioned Pulse Width Modulation (PWM) when talking about [sprite_tm]’s marquee control. It’s a method of power control. While [sprite_tm] did it in software, [Afroman] sent along a very straight forward introduction to PWM using just a 555. Check out his video for coverage of this fundamental electrical design technique.
personally i have used this for quite some time now. it is quite reliable for some applications but is not to accurate if your controlling the pwm with anything but a resistor (or a pot) also i have been told its easier just to adjust pin 5
the diode part is awesome!
But now, the most of the pots out there are not precise enought for these use, maybe adding a resistor at each end could be very neat for cheapass servo control.
afroman does it again!!
huzzah. afrotech slowly consumes the internet.
A less common technique is pulse frequency modulation, which can be found in very efficient and low power switching power supplies. It lowers the switching losses in certain situations.
How timely. I was just digging through my box of junk and found a LED product demo that has 3 faders and a pic controller to mix RGB on 3-color LEDs. I hooked the leads up to the Heath Kit (1962) Oscilloscope I just nabbed off craigslist last week (for $20) and low and behold, it uses PWM to dim each colored LED.
I like this. So many projects use microcontrollers as overkill when a 555 timer will do the job.
is there a way to add another pot to control frequency also ?
@therian:
In this circuit the frequency is controlled by the capacitor connected to pin 2, I think. I don’t think you can change the frequency by changing resistance in this case.
@Sol & @therian:
the 100k gives you the fill sweep to change the frequency the best way is the cap at pin 2 102 makes it switch faster and 104 switches slower
changing cap is good enough, thanks
@bob: pulse-frequency modulation (pfm) is really only good for low current applications, where switching losses are significant; typically, conduction (and other) losses dominant at higher currents.
additionally, pfm can make emi more difficult to mitigate (at undetermined or over a wide frequency range); at higher currents the emi peaks are even higher, again a reason to (often) avoid pfm at higher currents.