blog.makezine.c... Another clever trick from the world of electronics - Pulse Width Modulation is a simple method for controlling analog devices via a digital signal. It's also an efficient way to drive motors, lamps, LEDs & more.
Another fantastic tutorial from Colin. I love the way he explains all of these difficult concepts in a clear way with visible examples. I can't wait to see more from him!
Quick note/correction: The part explaining that 12V at 50% duty cycle is 6V is inaccurate. A 50% duty cycle would give you 50% the POWER of that at 12V (think of it like you're running it at 12V but for half the time). This does not mean half the VOLTAGE though (Imagine a simple resistor: P=V^2/R, so half the voltage amounts to 1/4 the power, not 50%)
nope. power depends on load, no load information, no power information. It's a VOLTAGE waveform so 50% pwm of 12V = 6V average (DC). If you had 12 Ohm @100% (12V) = 12W, @50% (6V) = 3W; 25% power BUT still 6V is 50% of 12V
Fantastic that you're into electronics at your age, you might invent useful things for the marketplace one day and make money from them. You should probably do an electrical engineering degree. And yes, this guy definitely needs his own TV show. He's great to watch.
@TheTranceMusicLover actually, PWM sends pulses, meanwhy an LM317 limitates the voltage that pases through it, so it makes less heat than a limitating resistor, but still generating heat, that means you still losing power. So in conclusion: is better the PWM than the Voltage Regulator or the Limitating Resistor. Hope that helps:)
I find it very confusing to use a variable input voltage as a variable to determine PWM duty cycle. I know how PWM works, but I wouldn't recommend this particular video to someone who's still learning it. Please use a circuit that uses a potentiometer (as a voltage divider) as part of a 555 astable multivibrator instead.
Colin? I dont know if you still read these but my name is Will and you inspired me to love electronics through your videos. you are my hero and I would really love to meet you. thank you for everything.
Not exactly. AC goes in both ways. In PWM it is called a Alternating DC. Basically a DC which changes it's voltage during time. AC changes both voltage and the direction.
The best part about this video is that you're using a bent conical tip Metcal. Everyone gives me such a rash of crap for using it all the time instead of the cultish following the chisel tip uses, but it's very comfortable and not all ham handed when you're trying to get into a tight spot.
so you controlling the speed of the motor with modulation, but your controlling the modulation with voltage? why not connect the variable voltage directly to the motor?
Next vid ETA? I realize they probably take a while to put together (I really love the flow of the program: Problem, solution, history of solution, example of solution). Make something on radio circuits? Please?
@ccrimsonfox There is no such thing as a perfect world. The best we can do is to maximize efficiency given our current technology. The heat sink is for the bypass transistor driven by the pwm that switches current to the load. This circuit is still far more efficient than using a resistor.
@FractalDistortion PWM works with something called TIMING... You time each pulse, but every pulse is the same strength as the time between each pulse increases the intensity of the LED or motor decreases... it's all in the physics of how analog devices work!
what is he point of the PWM if it is just proportional to the input voltage? I thought the whole idea was to control duty cycle in order to contrl (for example) the speed of a motor that is running on a 12 volt dc input. If I have to control the input voltage already, that begs the question how am I doing that?
i would like to see more examples of this - maybe with arduino? i actually had an idea a long time ago using special light bulbs that were designed to work at maybe 50hz instead of 60hz. if you are using the full amount of current, how does that apply to the brightness ratio? aren't you being more efficient, and thus, it would stay bright? when would you actually notice? if it flickers, cant you use a capacitor to smooth it out? or would just using a lower wattage bulb be better?
Output duty cycle = CONSTANT * DC Input Voltage. The constant is just a number which doesn't change, so when you increase or decrease the DC voltage, the duty cycle increases or decreases (they are proportional). How much it changes is dependant of the magnitude of the constant. A lower constant will give you a smaller change and therefore more sensitivity.
@htfkid2000: No. PWM doesn't work with timing. You can change the frequency to whatever you want, timing doesn't matter, but the output power will depend on the ratio of the on to off portions of the duty cycle, and that ratio can be continuously variable. Digital in binary, analog is continuously variable.
@carfansunited I think the point is that Kip Kay and Collin ACTUALLY make things and so it was nice to have a reliable project every week aka weekend projects. Now the makemagazine channel is only "look here is a random person who MADE something who JUST TALKS about random stuff". This channel now is more lookatthisrandompersonzine
it's not such a great solution. i'd rather use an atmega8, which is mutch cheaper an easier to assemble, plus you can generate more than one pwm simultaneos, and also you can programme a ramp mechanism so you don't have abrupt changes in the motor's speed which are pottencially harmful.
... wait... if you need to control the PWM by changing the Voltage, can't you just apply the current directly to the device? I mean, what is point of applying 20V to the PWM, when 9V can power the motor. The output of this device is just controlable by the input, isn't it?
Actually pot drops both current and voltage. But PWM is far more efficient and better. Although in some serious circuits like a power supply or a supply for some ICs you will need to smooth that square wave using filters using some RC filters.
I subbed for Kipkay what seems over a year or more ago, but I have learned to love Collin's lab because I learn a little every new video! I just wish they would slow up with the personal blogish type videos :/ Good with the bad I suppose.
Hi Colin , The maximum output of the pwm was 21v , that is fine . But the Amps can be 2 to 4 Amps or greater . Will it not fry the scope ? Also you had 3 probes and 1 Earth. Please explain. Thanks .
Because not everyone is going to hook a variable voltage supply up to every motor they will ever run. It is more convenient to hook up a straight voltage and use PWM to reach the desirable results.
I thought the main principle behind PWMs was varying a load input WITHOUT changing the circuit's voltage. RC cars for example use a PWM to control motor speed while that 9.6V doesn't change.
i just use a potentiometer, and it does basically the same thing as hes talking about, except, you can go from anywhere between 0% to 100% speed, and its a lot more simple -_-
@kekejojo1212 no im not stupid and ive used this stuff before ive even seen this video, i love his videos... i wasnt trying to insult him or you, and im sorry if i came off as rude
Hey Collin, could you post the schematics you redrew for the PWM? It's not on the Jameco site, and I can only get a fuzzy view of it from the video. Thanks!
I love Collin's videos, but I don't want to subscribe to makemagazine's channel because of all the other sewing crap that would pollute my youtube homepage...
it will heat up your wires slightly though, so be careful when using it with mains electricity otherwise you could have a fire on your hands (quite unlikely).
