LastspikemikeDCC digital signal still has to be a wave, with a rise and fall.
LastspikemikePWM creates the effect of reduced voltage but it is delivered at full voltage. If you examine the wave form required to achieve that you should see a similarity with a DCC "wave" form. I use the term "wave" loosely of course. DC isn't really a wave but then neither is DCC.
So, is DCC a wave or not? (It is.)
Lastspikemike DCC is always positive, har har.
Each rail is always positive (or zero) in reference to ground, but the voltage across the rails alternates.
John-NYBWAs I said in the OP, I know just enough about electronics to get by (barely). You guys are up in the stratosphere now.
I tried to help, and I posted helpful information.
Fortunately Spike showed up and pointed out I was wrong and then SPIKED your thread with nonsense, so you didn't get bogged down with helpful information from someone who spent years training technicians on proper usage of a digital multi-meter.
You are better off for his participation. I mean, I can't even get facts right.
I earned a living using a multi-meter, but what would I know?
Sorry, but this is what the forums become with Spike input. Helping the OP takes a backseat to insulting helpful people, blowing hot air around, chest thumping, and general bully tactics. And of course, lots of incorrect information presented as fact just to start arguments.
-Kevin
Living the dream.
I haven't been bothered by anybody's contributions to this thread. My last post was meant to be self depricating. The problem with online forums is the tone of remarks isn't always apparent.
It is normal for threads to digress away from the subject of the OP. I have no problem with that either. Even if the information being presented is beyond my level of understanding, it might be useful to others.
LastspikemikeI understand how PWM works also. PWM and DCC are similar ideas. DCC allows transmission of a lot more information concurrently with the power delivery. PWM creates the effect of reduced voltage but it is delivered at full voltage. If you examine the wave form required to achieve that you should see a similarity with a DCC "wave" form. I use the term "wave" loosely of course. DC isn't really a wave but then neither is DCC. The frequency variation in PWM controls speed. Polarity controls direction, as usual for DC. The pulses of full voltage interrupted by periods of no voltage are equivalent to a digital speed control signal. DCC has its zero line at the "bottom" of the wave form (in effect, the actual electronics are not so simple I'm led to believe). DCC is always positive, har har. You should see a digital effect in a PWM wave form in the displayed frequency of the power pulses. DCC should look similar albeit much more obviously digital looking. The PWM creates a power signal by altering the frequency and therefore total duration of the pulses. DCC uses a similar signal to transmit a lot more information and does not vary the power delivered by any material amount. Except if used to drive a DC motor directly. Then DCC mimics PWM and address zero, in effect, is a decoder in the DCC control unit rather than each individual locomotive. When address zero is broadcasting all DC motors directly connected to the rails will move in the same direction at roughly the same speed. All decoder equipped locomotives will operate as they usually do. The two systems are quite different but exploit similar ideas. The decoder delivers DC power to the motor and the lights, of course. The internal rectifier takes the DCC power and converts (rectifies) it into DC power for the motor and all the other functions. The decoder part interprets the digital signal also carried with the power. The signal is used to, among other things, vary the average voltage delivered to the motor as well as its polarity. Quite clever in fact. Those lights are dimmer because the decoder has built in resistors of correct to step down the voltage leaving the diode bridge. Dimming those lights further, for variable lighting, would require additional electronics to further vary the delivered voltage. LED don't dim in the same way as incandescent as you will discover when selecting household lighting for dimmer controlled circuits.
PWM and DCC are similar ideas. DCC allows transmission of a lot more information concurrently with the power delivery.
PWM creates the effect of reduced voltage but it is delivered at full voltage. If you examine the wave form required to achieve that you should see a similarity with a DCC "wave" form. I use the term "wave" loosely of course. DC isn't really a wave but then neither is DCC. The frequency variation in PWM controls speed. Polarity controls direction, as usual for DC. The pulses of full voltage interrupted by periods of no voltage are equivalent to a digital speed control signal.
DCC has its zero line at the "bottom" of the wave form (in effect, the actual electronics are not so simple I'm led to believe). DCC is always positive, har har. You should see a digital effect in a PWM wave form in the displayed frequency of the power pulses. DCC should look similar albeit much more obviously digital looking. The PWM creates a power signal by altering the frequency and therefore total duration of the pulses. DCC uses a similar signal to transmit a lot more information and does not vary the power delivered by any material amount. Except if used to drive a DC motor directly. Then DCC mimics PWM and address zero, in effect, is a decoder in the DCC control unit rather than each individual locomotive. When address zero is broadcasting all DC motors directly connected to the rails will move in the same direction at roughly the same speed. All decoder equipped locomotives will operate as they usually do.
The two systems are quite different but exploit similar ideas.
The decoder delivers DC power to the motor and the lights, of course. The internal rectifier takes the DCC power and converts (rectifies) it into DC power for the motor and all the other functions. The decoder part interprets the digital signal also carried with the power. The signal is used to, among other things, vary the average voltage delivered to the motor as well as its polarity. Quite clever in fact.
Those lights are dimmer because the decoder has built in resistors of correct to step down the voltage leaving the diode bridge. Dimming those lights further, for variable lighting, would require additional electronics to further vary the delivered voltage. LED don't dim in the same way as incandescent as you will discover when selecting household lighting for dimmer controlled circuits.
Your copy and paste rebuttal is good until the last two paragraphs, where you appear to freelance ....
The motor and the function outputs do not use DC. That statement alone shows you aren't grasping PWM completely. BEMF would not exist if the decoder was supplying a linear variable DC voltage to the motor. Same for the function outputs, they are receiving PWM voltage. If you dim an LED way down using the CV adjustment, you can clearly see the pulsing. At full brightness, the pulsing is still there, but it is so fast, the human eye cannot detect it .... well, 99% of people can't.
The voltage supplied is either positive or negative in relation to the zero base as you can see in the DCC sine wave, not true DC voltage. The frequency of this wave is high enough that most humans cannot hear it. Some older decoders (like the old Atlas 340 and 341) used a lower frequency that would produce a very annoying buzzing sound. Again, DC voltage would not do that.
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
I just try to help with what I know.
Brent
"All of the world's problems are the result of the difference between how we think and how the world works."
Mark R.BEMF would not exist if the decoder was supplying a linear variable DC voltage to the motor.
BEMF is determined by motor RPM reagardless of what causes that motion.
LastspikemikeDCC has its zero line at the "bottom" of the wave form (in effect, the actual electronics are not so simple I'm led to believe). DCC is always positive, har har. You should see a digital effect in a PWM wave form in the displayed frequency of the power pulses. DCC should look similar albeit much more obviously digital looking. The PWM creates a power signal by altering the frequency and therefore total duration of the pulses. DCC uses a similar signal to transmit a lot more information and does not vary the power delivered by any material amount. Except if used to drive a DC motor directly. Then DCC mimics PWM and address zero, in effect, is a decoder in the DCC control unit rather than each individual locomotive. When address zero is broadcasting all DC motors directly connected to the rails will move in the same direction at roughly the same speed. All decoder equipped locomotives will operate as they usually do.
not sure the above says anything coherent ...
in addition to a DC component, DCC zero stretching includes an AC component that results in heat without any motion. PWM does not include an AC component resulting in useless heat.
greg - Philadelphia & Reading / Reading
So much unnecessary confusion in a thread about multimeters.
PWM is not FM; it doesn't use any sort of a sine wave, far less AC reversal. It chops a reference DC voltage into on-off pulses, full voltage alternating with zero voltage.
Most of the motors in model railroad equipment are voltage-controlled, meaning their speed control is a function of input voltage. PCM yields a percentage of reference voltage as the average of high-frequency 'on' and 'off' times; it does not send some digital code to a BLDC motor controller or whatever. The 'flicker' comes when the frequency of PWM is relatively low and hence the 'off' time is a large proportion of the duty cycle; you won't see any such flicker from higher frequencies.
Part of the DCC 'decoder' is a PWM synthesizer, for motor control. It has nothing to do with the DCC waveform or logic-pulse structure other than seeing a rectified DC input and being controlled by speed-step control data interpreted by the decoder.
DCC modulation is not a 'sine wave' -- it is a square wave, in the same way as PWM. That it is not a perfect square wave (physics limits it) is of comparative unimportance, as the decoder responds to pulse and gap durations far longer than the transition, and is not affected by the 'ringing' overshoot, etc.
The DCC voltage swings twice the reference voltage (28V rail-to-rail for 14V nominal) but only 14V is ever seen by connected equipment; the periodic reversal keeps DC charge transfer from accumulating (much as modem coding did in the dark ages before broadband Internet).
Is there a multimeter-related question still unanswered, or new multimeter-related questions to be asked? That is what needs to happen to bring this thread down from the space academy.
Ok, I'm out. This thread has exceeded my willingness to type any further rebuttals ....
Were is Steven Otte when we need him?Mel My Model Railroad http://melvineperry.blogspot.com/ Bakersfield, California Turned 84 in July, aging is definitely not for wimps.
Yet another thread brutalized by misinformation from one resident expert and sent to the gallows much too soon. Sorry to have to cut this one short, John, but it's best to end it on a less positive note before it gets even worse...
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.