Help, Please. Generate multi phase sine wave.
bteddy
Posts: 65
in Propeller 1
Hello,
Right out the box, I'm a newbie to Propeller.
I need to generate five PWM sine waves each 72 degrees out of phase with each other.
Is this possible?
Thank you
Right out the box, I'm a newbie to Propeller.
I need to generate five PWM sine waves each 72 degrees out of phase with each other.
Is this possible?
Thank you
Comments
There are several ways to do this either in Spin or, if you need high frequencies, PASM. You can generate the output as PWM using the cog counter-timers, but you will need three cogs to generate five signals. There is a sine table in the ROM which is handy for this sort of thing, but it covers 0-90 degrees so you will have to scan it backward-forward and invert it to get the other quadrants.
Mike
The question is about PWM approximations to sine waves, the 5-phase motor's inductance does all the low
pass filtering needed.
Firstly is this is a 5 or 10 wire stepper?
My propeller is running at 100Mhz.
The frequency needed is 1mhz max but mostly 40khz.
My stepper is a Pentagon 5-wire motor.
I read somewhere that the counters are slower due to init., startup and stopping.
The article said DAC's would be faster and more accurate.
The Propeller does not have an internal DAC but the internal video should be better than the counters, right?
What frequency needs to be 1mhz (or 1MHz?) - do you really have a motor that can swallow 1MHz sine waves
A link to the actual Motor would help, along with what step rate you need, and drive scheme.
The range is 1/1 to 1/256 microsteps.
The rpm is 2400 max.
The motor is not the question.
The wave form is. How do I generate it?
You do need to provide better information, if you expect help. Readers here are not clairvoyant (tho some come close
The Motor is very much the question, as google suggests there are no motors "1MHZ at fuff step" - but I can find 40KHz pulse rate motors.
Google also suggests you need 10 independent drivers (5 HI side, 5 LO side), so it seems you seek 10 DACs, with ability to update all 10, at 1us intervals.
Very few MCUs can manage that, the Prop2 could do that, but is it not yet in full release.
How many of these do you expect to make ?
Sorry, the motor is not the question.
I did not not ask for help with the motor.
You put to much faith in Google.
Google is wrong some times.
That's why I am here asking.
"Google also suggests you need 10 independent drivers (4 HI side, 5 LO side), so it seems you seek 10 DACs, with ability to update all 10, at 1us intervals."
It is only five, "Five wave forms"(what i am asking about), "five" hi/lo drivers, "five" half bridges, that connect ti the five motor wires.
If you don't know please don't respond dragging this unto an unrelated topic.
To all others, sorry about any confusion.
This is what I would like to do. Right now I don't care about wave specs. I just need to know how to get 5 wave forms 72 degrees out of phase each.
Thank you
-Phil
Now, how would I do that, please?
Thanks
-Phil
-Phil
Is 8 bit to large?
I was shooting for 12 bit resolution.
While researching this I saw something that said 32 bit was way to much, 16 bit was slightly out of some MCU's reach
but 12 bit was a good compromise.
Create a sine table of 256 samples
12 bit resolution from mcu.
3.3v output swing
72 degree separation.
I'm just trying to learn how to create the wave forms.
Larger/smaller, faster/slower I can work out later.
With the wave forms I can experiment if the signal is too small I can run them thru a amplifier to get what i need.
This is just the first step.
Thank You
How many full steps per rev does your motor have? How many micro-steps per step do you really need? What's the desired maximum RPM?
-Phil
What do you mean analog again?
A pulsed wave can be amplified to increase amplitude or divided to increase frequency.
Forget about the use, please.
How do i create the multi wave?
Oriental Motor, who actually make 5-phase motors, have PDFs that show the excitation I mention.
Now you can perhaps see why the motor matters ?
The image you link, is for a Motor+Driver package, so you appear to be wanting to replace an existing Motor driver, with your own design ?
As already mentioned, you need (at least) 5 DACs to do that, plus the power drivers to turn those sine-waves into motor levels.
The Prop 1 does not have DACs, but Prop 2 does.
Prop1 can do Pulse Density modulation in HW, (2 per COG) but you will doubtless already know why that is less than ideal for motor drive. PWM needs SW assist.
The Prop 1 can generate NCO type step control, so it can nicely manage Step/Direction to a smarter DAC motor driver.
There are small MCUs that can manage the Table-DACs part, but that is an analog signal, so you need another modulation stage to turn into MOSFET-drive/current feedback.
It's not yet clear whether he needs analog output or PWM output. He seems to be going back and forth on this matter. On the one hand he mentions a 40kHz PWM rate and bridge drivers; on the other, an amplifier. So I'm perplexed.
OTOH, if he's using a driver that converts an analog input to PWM, I might recommend a different part, and let the Prop do the PWMing with the video driver. The PASM code would be harder to write, but it would use fewer than the three or four cogs necessary to produce five DUTY-mode outputs.
-Phil
The forum members are tying to be helpful but you still have not stated what you are trying to do other than experimentation.
What parts do you have and what are you trying to do with them?
I thing it's great your helping and haven't just said f it and disconnected.
Thank You.
I give short little questions for this reason, your reading to much into a simple question.
I have a Parallax Propeller.
I want to make 5 PWM waves 72 Degrees apart come out of it.
That is it. How do I do that.
All else is irrelevant.
How it's interfaced, irrelevant
What it is being interfaced to, irrelevant.
I never said analog, it was assumed.
All the other stuff came from your questions.
I said i'm a newbie at the propeller at the start.
To reiterate.
All I am asking on the parallax board is
"HOW TO MAKE THE PARALLAX PROPELLER SIMULTANEOUSLY PRODUCE 5 PWM WAVES 72 DEGREES APART"
The previous line is for bold only, I am not yelling at anyone, please don't take it that way.
Thank You for all you responses
one COG can do serial comms with simple serial, 7 COGs free to output a sine wave each. Each COG could use pins direct, timers or the Video circuit to output sine waves (or PWMs for them)
It is possible to start COGs apart from each other by providing a start CNT to wait for so separating the COGs by 72 degree should be possible
Using a P2 and TAQOZ might be way simpler, but that is not a option, yet
Anyways don't scare him away just because he is unsure where to ask what...
Enjoy!
Mike
-Phil
Could I run the PWMs continously if I used multiple sine lookup tables each table at a different phase?
Could phase 2 ,3, 4 be synced to phase 1 example phase 1 from cog0 video generator, then phase 2 from cog 1 delayed time period to equal 72 degrees etc.
How would I get the video generator to act as a pwm?
B
https://forums.parallax.com/discussion/104121
-Phil
Thank YOU!
jmg and Phil Pilgrim are two of the smartest people on the forum. Tread lightly if you want EXPERT help.
My guess is that you should work with the timer/counter of the P1. each COG has two of them and they run independent from your program in the COG. so your program can check parameter in a mailbox, and vary the settings of the counter outputting pwm.
You should write some PASM code to do that and then you have a very precise timing, basically you can count instructions, without interrupts the code of the P1 in PASM is taking the same sysclocks every time.
As of synchronization, usually instructions take 4 clocks, but waitcnt has a resolution of one sysclock. So basically you can set some start value when starting the COG to wait for a certain sysclock and then jump into the main routine.
Since you will use the same code for all sine COGs you can vary the distance between pwm pulses of different COGs (your 72 displacement) down to one sysclock by waiting a different amout of clocks after start of the pwm COG.
All of this might not be easy as a starter project, but not to complicated either. I would first write a small Spin program to run some tests, using serial for input output to the PC.
Then the PASM program in a COG talking over a 'mailbox' (a HUB ram location both COGs need to know and agree upon) and just start talking from Spin to my PASM COG. maybe just blinking some led on off, something simple to have the communication line fro user-terminal-spin-pasm running.
This is something most P1 program do and you will find examples of mailboxes everywhere where PASM is used by SPIN.
If you have that running, you might start doing pwm instead of blinking and start using the counters.
Programming the propeller is confusing at the beginning, because you have to rethink what you usually do since COGs are not threads, the run completely independent. But the programming model using one main COG and communicate with the other COGS over agreed HUB locations can lead to a very simple program separating the main code from the driver code.
You might need to read a lot about the timer/counter and hoe to talk to PASM cogs, but I promise to you that when done it will be some astonish short code.
Anyways, Enjoy!
Mike
I found a link to a template for multicore programming with Propeller.
https://www.parallax.com/sites/default/files/downloads/AN011-SimpleTemplate-v1.0.pdf
I don't know who to suggest this to but Parallax should do one for the video, the pwm, the counters, etc..
Thanks to all.