help with frequency tracker and generator

Anubisbot · 2008-09-06 18:27

Hi, i am working on a solid state tesla coil what should run at 4Mhz .

I want to use the propeller to generate the differential 4 Mhz pulse to drive 2 BC 546 to beaf it up to drive 2 bigger mosfets in push pull mode.
And i want it to be self tuned, so i need to track the resonance frequency of the secondary coil with a antenna..

Would be spin good to use , or is it to slow to change the PLL frequency on the fly?
And if i have to us e PASM, could some one help me with the code since i never wrote any PSAM [noparse]:([/noparse]

Any help or ideas are welcome and would help big times......

Post Edited (Anubisbot) : 9/6/2008 6:32:39 PM GMT

Mike Green · 2008-09-06 19:13

Spin should be fine for controlling the tuning. I assume you're using one of the cog counters to generate the 4MHz pulses. You don't have to change the frequency that quickly and you only have to load a new value into the FRQA/B register to adjust the frequency.

If you want to determine the resonant frequency of the secondary coil, you don't detect a frequency, you normally detect the power output (or output voltage) which goes up near resonance. Typically, you have a detector coil or nearby antenna followed by a diode and capacitor so you have a simple half-wave rectifier and you measure the voltage across the capacitor, then you tune for peak voltage.

The Propeller can measure voltages easily using one of the cog counters all in Spin. Read the Application Note (AN001) on the use of the cog counters. Download the ADC (analog to digital converter) object from the Object Exchange and read the comments and documentation.

Anubisbot · 2008-09-06 19:59

Hi Mike,
yes i want to use the NOC PWM for the pushpull of the 4MHz , and thank for the tip with the ADC and the voltage peak to mesure.

But what i still dont get is how to set the two pins for the differential output.

CON
        _clkmode        = xtal1 + pll16x
        _xinfreq        = 5_000_000

PUB NCO_PWM_single_ended_mode
'             mode  PLL        BPIN     APIN
  ctra    := %00100_000 << 23 + 1 << 9 + 0  'Establish mode and APIN (BPIN is ignored)
  frqa    := $8000_0000                     'Set FRQA so PHS[noparse][[/noparse]31] toggles every clock
  dira[noparse][[/noparse]0] := 1                              'Set APIN to output
  repeat                                    'infinite loop, so counter continues to run

I know i have to set mode bits to %00101 but i still dont get how to set the the 2 pins??
would this %00101_000_00000000_011111_000_100000 be the right ctra for differential mode with pin 15 and 16 ??

Best regards
Anubisbot

Mike Green · 2008-09-06 20:19

From page 205 in the Propeller Manual, I get: %0_00101_000_00000000_001111_000_010000

The BPIN and APIN fields contain the B and A pin numbers with values from %000000 to %011111 for I/O pins 0 to 31.

Beau Schwabe · 2008-09-06 20:30

Anubisbot,

Please post pictures of your final project or work in progress, I would love to see them.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Anubisbot · 2008-09-06 21:44

Beau Schwabe (Parallax) said...
Anubisbot,

Please post pictures of your final project or work in progress, I would love to see them.

I will post some pictures later, as soon i have my basic test circuit set up.

But i think i may use the mode %00011 PLL differential , but i still dont get how to calculate the frequency with the PLLDIV
?? Since i am still so new to the propeller i dont get it ??
Do u have a example on how to set the PLL differential mode to 4MHz on pin 15 and 16 ??
And may be a little more simple explanation on how to calculate and set the Frequency??

Best regards Anubisbot

Anubisbot · 2008-09-06 22:43

CON
        _clkmode        = xtal1 + pll16x
        _xinfreq        = 5_000_000

PUB NCO_PWM_single_ended_mode
'             mode  PLL        BPIN     APIN
  ctra    := %0_00101_000_00000000_001111_000_010000
  frqa    := 5400                     'Set FRQA so PHS[noparse][[/noparse]31] toggles every clock
  dira[noparse][[/noparse]16..15] := 1                              'Set APIN to output
  repeat

this should give me on pin 15 and 16 a 100.5Khz freq.

And it does it but only on pin 15 (or 16 when i swap 16 and 16 in the dira brackets )

What do i do wrong????

Update :

I found the problem , it was :=1 for the dira

CON
        _clkmode        = xtal1 + pll16x
        _xinfreq        = 5_000_000
            _PLA        = 5.375
PUB NCO_PWM_single_ended_mode
'               mode  PLL           BPIN       APIN
  ctra    := %0_00101_000_00000000_001111_000_010000
  frqa    := Round(_PLA*100000.0)                     'Set FRQA so PHS[noparse][[/noparse]31] toggles every clock
  dira[noparse][[/noparse]16..15] ~~                              'Set APIN to output
  repeat

So now i have the generator for my push pull frequency
Next i have to set up the ADC and them i will make a first test run with 12V input and then later with 32V.
I will update the post as soon i have some more news and pictures...

Post Edited (Anubisbot) : 9/6/2008 11:47:13 PM GMT

Anubisbot · 2008-09-07 14:20

CON _clkmode = xtal1 + pll16x
    _xinfreq = 5_000_000
 _PLA        = 537  
VAR long parameter

PUB go | x
x:=100
  cognew(@entry, @parameter)
   parameter :=  _PLA*x      
   repeat


DAT

        org

entry   mov dira, diraval              'set APIN to output
        mov ctra, ctraval              'establish counter A mode and APIN
        mov frqa, par                  'set counter to increment 1 each cycle



:loop   rdlong value, par              'get an up to date freq
        mov frqa, value                'set FRQA from value
        jmp #:loop                     'loop for next cycle

diraval long |< 16 + |< 15                                    'APIN=15 BPIN=16
ctraval long %0_00101_000_00000000_001111_000_010000          'NCO/PWM APIN=15 BPIN=16

value   res 1

After all night up, i have figured it out how it works in asm.
So far so good. No i have a stupid question, is it possible to start 2 new cogs with Pasm from the same spin file??? If so how does it work in the the dat section.

If it would be possible i could use the frequency tracker in easy to set the new freq to the parameter variable.???

Or is there another way to link 2 PASM Cogs with each other with a common variable ??

Like always all ideas are welcome, and do help...
Best regards
Anubisbot

potatohead · 2008-09-07 23:36

You can start 2 new cogs.

Just differentiate each assembly program with an org, and a label that you can use to pass the entry point to the cognew command.

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help with frequency tracker and generator

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